SPECIFICATION
TITLE OF INVENTION
CONTROL UNIT OF INDUCTION HEATING UNIT, INDUCTION HEATING
SYSTEM, AND METHOD OF CONTROLLING INDUCTION HEATING UNIT
Field of the Invention
[OOOl]
The present invention relates to a control unit of an induction heating unit, an
induction heating system, and a method of controlling the induction heating unit.
10 Particularly, the present invention is suitable for being used to make an alternating
magnetic field intersect a conductive sheet in a substantially orthogonal manner so as to
inductively heat the conductive sheet.
Priority is claimed on Japanese Patent Application No. 2009-283255, filed
December 14,2009, the content of which is incorporated herein by reference.
Description of Related Art
In the conventional techniques, for example, an induction heating unit has been
used when heating a conductive sheet such as a steel sheet that is conveyed through a
20 manufacturing line. The induction heating unit is provided with a heating coil, and
heats the conductive sheet using an eddy current induced by the heating coil. In this
induction heating unit, the eddy current is caused to the conductive sheet by an
alternating magnetic field (AC magnetic field) generated by the heating coil, Joule heat is
generated in the conductive sheet due to the eddy current. As an example of the
25 induction heating unit, a transverse type induction heating unit is disclosed. In the
transverse type induction heating unit, the alternating magnetic field is applied to the
2
conductive sheet in a manner that intersects a sheet surface of the conductive sheet,
which is an object to be heated, to be substantially orthogonal thereto.
As a method of controlling the transverse type induction heating unit, a
technique disclosed in Patent Citation 1 may be exemplified. In Patent Citation 1, a
capacitor is provided in parallel to the heating coil that makes up the induction heating
unit, the heating coil and the capacitor make up a parallel resonance circuit, and power is
supplied to the heating coil by a parallel resonance type inverter.
Patent Citation
10 [0003]
[Patent Citation 11 Japanese Unexamined Patent Application, First Publication
NO. 2002-3 13547
SUMMARY OF THE INVENTION
15 Problems to be Solved by the Invention
[0004]
However, when the heating coil of the induction heating unit is seen from a
power supply unit (power supply circuit) of the induction heating unit, the inductance
varies in response to the sheet conveyance speed of the conductive sheet that is an object
20 to be heated by the induction heating unit (in the following description, this inductance is
referred to as apparent inductance as necessary). Specifically, when the sheet
conveyance speed of the conductive sheet becomes fast (or slow), the apparent
inductance becomes small (or large).
However, in the technique disclosed in Patent Citation 1, the heating coil and the
25 capacitor make up the parallel resonance circuit. Therefore, when the apparent
inductance varies, the power fkequency, which is supplied to the heating coil, also varies.
3
For example, when the sheet conveyance speed of the conductive sheet becomes fast and
thereby the apparent inductance becomes small, the fkequency of the power supplied to
the heating coil increases. In this manner, when the frequency of the power supplied to
the heating coil increases, the temperature in the vicinity of an end portion (edge) of the
5 conductive sheet in the sheet width direction becomes higher than that in the vicinity of
the central portion of the conductive sheet in the sheet width direction. Therefore, there
is a concern in that a temperature distribution of the conductive sheet in the sheet width
direction may be non-uniform.
As described above, in the conventional techniques, in a case where the
10 conductive sheet is heated by using the transverse type induction heating unit, there is a
problem in that as the sheet conveyance speed of the conductive sheet varies, the
temperature distribution of the conductive sheet in the sheet width direction becomes
non-uniform.
The present invention has been made in consideration of this problem, and an
15 object of the present invention is to realize a temperature distribution that is more
uniform than that in the conventional techniques by preventing the temperature
distribution of the conductive sheet in the sheet width direction fiom being non-uniform
even when the sheet conveyance speed of the conductive sheet varies in a case where the
conductive sheet is heated using a transverse type induction heating unit.
20
Methods for Solving the Problem
[0005]
(1) A control unit of an induction heating unit according to an aspect of the
present invention controls AC power output to a heating coil of a transverse type
25 induction heating unit allowing an alternating magnetic field to intersect a sheet surface
of a conductive sheet that is being conveyed to inductively heat the conductive sheet.
4
The control unit includes: a magnetic energy recovery switch that outputs AC power to
the heating coil, a frequency setting unit that sets the output frequency in response to at
least one of the relative permeability, resistivity, and sheet thickness of the conductive
sheet; and a gate control unit that controls a switching operation of the magnetic energy
5 recovery switch on the basis of the output frequency set by the frequency setting unit.
(2) In the control unit of an induction heating unit according to (I), the
frequency setting unit may acquire attribute information that specifies the relative
permeability, resistivity, and sheet thickness of the conductive sheet, and may select a
frequency corresponding to the acquired attribute information as the output frequency
10 with reference to a table in which the relative permeability, resistivity, and sheet
thickness of the conductive sheet, and the frequency are correlated with each other and
are registered in advance.
(3) The control unit of an induction heating unit according to (1) or (2) may
further include: an output current setting unit that sets an output current value in response
15 to at least one of the relative permeability, resistivity, and sheet thickness of the
conductive sheet; a current measuring unit that measures an alternating current that flows
to the induction heating unit; and a power supply unit that supplies DC power to the
magnetic energy recovery switch and adjusts an alternating current that is measured by
the current measuring unit to the output current value that is set by the output current
20 setting unit, wherein the magnetic energy recovery switch may be supplied with the DC
power by the power supply unit and may output the AC power to the heating coil.
(4) In the control unit of an induction heating unit according to (3), the output
current setting unit may acquire attribute information that specifies the relative
permeability, resistivity, and sheet thickness of the conductive sheet, and may select a
25 current value corresponding to the acquired attribute information as the output current
value with reference to a table in which the relative permeability, resistivity, and sheet
5
thickness of the conductive sheet, and the current value are correlated with each other
and are registered in advance.
(5) The control unit ofan induction heating unit according to any one of (1) to
(4 ) may further include an output transformer that is disposed between the magnetic
5 energy recovery switch and the induction heating unit, lowers the AC voltage that is
output from the magnetic energy recovery switch, and outputs the lowered AC voltage to
the heating coil.
(6) In the control unit of an induction heating unit according to any one of (1) to
(5), the magnetic energy recovery switch may include first and second AC terminals that
10 are connected to one end and the other end of the heating coil, respectively, first and
second DC terminals that are connected to an output terminal of the power supply unit, a
first reverse conductivity type semiconductor switch that is connected between the first
AC terminal and the first DC terminal, a second reverse conductivity type semiconductor
switch that is connected between the first AC terminal and the second DC terminal, a
15 third reverse conductivity type semiconductor switch that is connected between the
second AC terminal and the second DC terminal, a fourth reverse conductivity type
semiconductor switch that is connected between the second AC terminal and the first DC
terminal, and a capacitor that is connected between the first and second DC terminals, the
first reverse conductivity type semiconductor switch and the fourth reverse conductivity
20 type semiconductor switch may be connected in series in such a manner that conduction
directions at the time of a switch-off become opposite to each other, the second reverse
conductivity type semiconductor switch and the third reverse conductivity type
semiconductor switch may be connected in series in such a manner that conduction
directions at the time of the switch-off become opposite to each other, the first reverse
25 conductivity type semiconductor switch and the third reverse conductivity type
semiconductor switch may have the same conduction direction at the time of the
6
switch-off as each other, the second reverse conductivity type semiconductor switch and
the fourth reverse conductivity type semiconductor switch may have the same conduction
direction at the time of the switch-off as each other, and the gate control unit may control
a switching operation time of the first and third reverse conductivity type semiconductor
5 switches and a switching operation time of the second and fourth reverse conductivity
type semiconductor switches on the basis of the output frequency that is set by the
frequency setting unit.
(7) An induction heating system according to another aspect of the present
invention allows an alternating magnetic field to intersect a sheet surface of a conductive
10 sheet that is being conveyed to inductively heat the conductive sheet. The induction
heating system includes: the control unit of an induction heating unit according to any
one of (1) to (6); a heating coil that is disposed to face the sheet surface of the conductive
sheet; a core around which the heating coil is wound; and a shielding plate which is
disposed to face a region including an edge of the conductive sheet in the width direction
15 and is formed from a conductor having a relative permeability of 1.
(8) In the induction heating system according to (7), the shielding plate may
have a depressed portion.
(9) In the induction heating system according to (8), the shielding plate may be
disposed in such a manner that a region, which is closer to the edge of the conductive
20 sheet than a region in which an eddy current flowing to the conductive sheet becomes the
maximum, and the depressed portion face each other.
[0006]
(10) A method of controlling an induction heating unit according to still another
aspect of the present invention controls AC power, which is output to a heating coil of a
25 transverse type induction heating unit allowing an alternating magnetic field to intersect a
sheet surface of a conductive sheet that is being conveyed to inductively heat the
7
conductive sheet. The method includes: outputting AC power to the heating coil by a
magnetic energy recovery switch; setting an output frequency in response to at least one
of a relative permeability, resistivity, and sheet thickness of the conductive sheet; and
controlling a switching operation of the magnetic energy recovery switch on the basis of
5 the output frequency that is set.
(1 1) In the method of controlling an induction heating unit according to (1 O), the
output frequency may be set by acquiring attribute information that specifies the relative
permeability, resistivity, and sheet thickness of the conductive sheet, and by selecting a
frequency corresponding to the acquired attribute information as the output frequency
10 with reference to a table in which the relative permeability, resistivity, and sheet
thickness of the conductive sheet, and the frequency are correlated with each other and
are registered in advance.
(12) The method of controlling an induction heating unit according to (10) or
(1 1) may fixher include: setting an output current value in response to at least one of the
15 relative permeability, resistivity, and sheet thickness of the conductive sheet; measuring
an alternating current that flows to the induction heating unit; and supplying DC power,
which is necessary for adjusting an alternating current that is measured to the output
current value that is set, to the magnetic energy recovery switch.
(13) In the method of controlling an induction heating unit according to (12), the
20 output current value may be set by acquiring attribute information that specifies the
relative permeability, resistivity, and sheet thickness of the conductive sheet, and by
selecting a current value corresponding to the acquired attribute information as the output
current value with reference to a table in which the relative permeability, resistivity, and
sheet thickness of the conductive sheet, and the current value are correlated with each
25 other and are registered in advance.
(14) In the method of controlling an induction heating unit according to any one
8 -
of (10) to (13), an AC voltage that is output from the magnetic energy recovery switch
may be lowered by an output transformer, and the lowered AC voltage may be output to
the heating coil.
(1 5) In the method of controlling an induction heating unit according to any one
5 of (10) to (14), the magnetic energy recovery switch may include first and second AC
terminals that are connected to one end and the other end of the heating coil, respectively,
first and second DC terminals that are connected to an output terminal of the power
supply unit, a first reverse conductivity type semiconductor switch that is connected
between the first AC terminal and the first DC terminal, a second reverse conductivity
10 type semiconductor switch that is connected between the first AC terminal and the
second DC terminal, a third reverse conductivity type semiconductor switch that is
connected between the second AC terminal and the second DC terminal, a fourth reverse
conductivity type semiconductor switch that is connected between the second AC
terminal and the first DC terminal, and a capacitor that is connected between the first and
15 second DC terminals, the first reverse conductivity type semiconductor switch and the
fourth reverse conductivity type semiconductor switch may be connected in series in
such a manner that conduction directions at the time of a switch-off become opposite to
each other, the second reverse conductivity type semiconductor switch and the third
reverse conductivity type semiconductor switch may be connected in series in such a
20 manner that conduction directions at the time of the switch-off become opposite to each
other, the first reverse conductivity type semiconductor switch and the third reverse
conductivity type semiconductor switch may have the same conduction direction at the
time of the switch-off as each other, the second reverse conductivity type semiconductor
switch and the fourth reverse conductivity type semiconductor switch may have the same
25 conduction direction at the time of the switch-off as each other, and the AC power may
be output to the heating coil by controlling a switching operation time of the first and
9
third reverse conductivity type semiconductor switches and a switching operation time of
the second and fourth reverse conductivity type semiconductor switches on the basis of
the output frequency that is set.
5 Effects of the Invention
[0007]
According to the control unit of an induction heating unit according to the aspect
of the present invention, the switching operation of the magnetic energy recovery switch
is controlled on the basis of the frequency in response to at least one of the relative
10 permeability, resistivity, and sheet thickness of the conductive sheet that is being
conveyed, and the AC power of this frequency is output fiom the magnetic energy
recovery switch. Therefore, the AC power of the frequency corresponding to the
attribute of the conductive sheet that is being conveyed can be applied to the heating coil
without being subjected to a restriction in regard to an operation with a resonant
15 frequency. Therefore, it is possible to prevent the temperature distribution of the
conductive sheet in the sheet width direction from being non-uniform even when a sheet
conveyance speed of the conductive sheet varies in a case where the conductive sheet is
heated using a transverse type induction heating unit. In addition, the AC power with
the frequency in response to the attribute of the conductive sheet that is being conveyed
20 can be supplied to the heating coil independently from operational conditions, such that
the induction heating control can be performed in a relatively simple and reliable manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[OOOS]
25 FIG 1 is a side view illustrating an example of a schematic configuration of a
continuous annealing line of a steel sheet according to a first embodiment of the present
10
invention.
FIG 2A is a longitudinal cross-sectional view illustrating an example of a
configuration of an induction heating unit according to the first embodiment of the
present invention.
5 FIG 2B is a longitudinal cross-sectional view illustrating an example of the
configuration of the induction heating unit according to the first embodiment of the
present invention.
FIG 2C is a partial perspective view illustrating an example of the configuration
of the induction heating unit according to the first embodiment of the present invention.
10 FIG 3 is a view illustrating an example of a configuration of an upper side
heating coil and a lower side heating coil according to the first embodiment of the
present invention.
FIG. 4 is a view illustrating an example of a configuration of a control unit of the
induction heating unit according to the first embodiment of the present invention.
15 FIG 5 is a view illustrating an example of a relationship between a voltage V, at
both ends of a capacitor of an MERS, a current IL that flows to the induction heating unit,
and an operation state of a semiconductor switch according to the first embodiment of the
present invention.
FIG 6A is a graph illustrating the relationship between frequency and
20 temperature ratio with respect to sheet conveyance speed, when power is supplied to the
induction heating unit using the control unit according to the first embodiment of the
present invention and a steel strip is heated.
FIG 6B is a graph illustrating the relationship between frequency and
temperature ratio with respect to sheet conveyance speed, when power is supplied to the
25 induction heating unit using a parallel resonance type inverter in a conventional
technique and the steel strip is heated.
FIG 7 is a view illustrating an example of a configuration of a control unit of an
induction heating unit according to a second embodiment of the present invention.
FIG 8A is a longitudinal cross-sectional view illustrating an example of a
configuration of an induction heating unit according to a third embodiment of the present
5 invention.
FIG 8B is a longitudinal cross-sectional view illustrating an example of the
configuration of the induction heating unit according to the third embodiment of the
present invention.
FIG. 8C is a partial perspective view illustrating an example of the configuration
10 of the induction heating unit according to the third embodiment of the present invention.
FIG 9A is a view illustrating an example of a configuration of a shielding plate
according to the third embodiment of the present invention.
FIG 9B is a schematic view illustrating an example of an eddy current that flows
through a steel strip and the shielding plate according to the third embodiment of the
15 present invention.
FIG 9C is a schematic view illustrating an example of a magnetic field that is
generated by the eddy current according to the third embodiment of the present
invention.
FIG. 10A is a view illustrating an example of a temperature distribution of a
20 conductive sheet, which is heated by the induction heating unit, in the sheet width
direction, in a case where the shielding plate according to the third embodiment of the
present invention is used.
FIG. 10B is a view illustrating an example of a temperature distribution of a
conductive sheet, which is heated by the induction heating unit, in the sheet width
25 direction, in a case where a shielding plate according to the first embodiment of the
present invention is used.
DETAILED DESCRIPTION OF THE INVENTION
[0009]
Hereinafter, embodiments of the present invention will be described with
5 reference to the attached drawings. In each of the following embodiments, a description
will be made with respect to an example in which a transverse type induction heating unit
and a control unit thereof are applied to a continuous annealing line of a steel sheet in a
manufacturing line. In addition, in the following description, "transverse type induction
heating unit" will be simply referred to as "induction heating unit7' as necessary. In
10 addition, unless particularly specified, in regard to attributes of the steel sheet (steel strip),
values at room temperature (for example, 25°C) will be used.
[OO lo]
(First Embodiment)
First, a first embodiment of the present invention will be described.
15
FIG 1 shows a side view illustrating an example of schematic configuration of a
continuous annealing line of a steel sheet.
In FIG 1, the continuous annealing line 1 includes a first container 11, a second
container 12, a third container 1 3, a first sealing roller assembly 14, a conveyance unit 1 5,
20 a second sealing roller assembly 16, a gas supply unit 1 7, rollers 19a to 1 9u, an induction
heating unit 20, and a control unit 100 of the induction heating unit. In addition, the
induction heating unit 20 and the control unit 100 of the induction heating unit make up
an induction heating system.
[OOl 11
25 The first sealing roller assembly 14 conveys (feeds) a steel strip 10 into the first
container 11 while shielding the first container 11 from external air. The steel strip 10
13
conveyed into the first container 11 by the first sealing roller assembly 14 is conveyed
into the second container 12 by the rollers 19a and 19b in the first container 11. The
steel strip 10 conveyed into the second container 12 is again conveyed into the first
container 11 by the rollers 19g and 19h while being heated by the induction heating unit
5 20 which is disposed at both an upper side and a lower side of a horizontal portion of the
second container 12 (of the steel strip 10 that is being conveyed). Here, the induction
heating unit 20 (heating coil thereof) is electrically connected to the control unit 100 of
the induction heating units, and AC power is supplied to the induction heating unit 20
fi-om the control unit 100 of the induction heating unit. An alternating magnetic field,
10 which intersects a sheet surface of the steel strip 10 in a substantially orthogonal manner,
is generated by the AC power, and thereby the steel strip 10 is inductively heated. In
addition, details of a configuration of the induction heating unit 20 will be described later.
In addition, in the following description, "electrical connection" will be simply referred
to as "connection" as necessary.
15 [00 121
The steel strip 10 that is returned into the first container 11 is conveyed to the
conveyance unit 15 by the rollers 19c to 19f after passing through a soaking and slow
cooling stage. The steel strip 10 conveyed to the conveyance unit 15 is conveyed to the
third container 13 by the rollers 19i and 19j. The steel strip 10 conveyed to the third
20 container 13 is conveyed while being made to move in a vertically up and down manner
by the rollers 19k to 19u and is rapidly cooled in the third container 13.
The second sealing roller assembly 16 forwards the steel strip 10, which is
rapidly cooled in this manner, to a subsequent process while shielding the third container
13 from external air.
25 To the "first container 1 1, the second container 12, the third container 13, and
the conveyance unit 15" that make up a "conveying path of the steel strip 10" described
14
above, non-oxidation gas is supplied by the gas supply unit 17. In addition, the first
container 1 1, the second container 12, the third container 13, and the conveyance unit 1 5
are maintained in a non-oxidation gas atmosphere by the "first sealing roller assembly 14
and the second sealing roller assembly 16" that shield the outside (external air) and the
5 inside (the inside of the continuous annealing line 1).
[00 131

FIGS. 2A to 2C show views illustrating an example of a configuration of an
induction heating unit.
10 Specifically, FIG2A shows a view illustrating an example of the induction
heating unit 20 according to this embodiment, which is seen from a lateral direction of a
line, and is a longitudinal cross-sectional view that is cut along the longitudinal direction
(the vertical direction in FIG 1) of the steel strip 10. In FIG 2A, the steel strip 10 is
conveyed toward the left direction (refer to an arrow facing from the right side to the left
15 side in FIG. 2A). In addition, FIG. 2B shows a longitudinal cross-sectional view
illustrating an example of the induction heating unit 20 according to this embodiment,
which is seen from an A-A' direction in FIG 1 (that is a view seen from a downstream in
the sheet conveyance direction). In FIG 2B, the steel strip 10 is conveyed from the
depth direction to the front direction. In addition, in FIGS. 2A and 2B, dimensions
20 [mm] are also illustrated. In addition, FIG 2C shows a partial perspective view
illustrating a part of an example of the induction heating unit 20 according to this
embodiment. In FIG. 2C, a lower-right region shown in FIG. 2B (region surrounded by
a broken line in FIG 2B) is overlooked from an upper side of the steel strip 10.
However, in FIG. 2C, the second container 12 is omitted for easy understanding of the
25 positional relationship between a shielding plate 3 1 and the steel strip 10.
[00 141
15
In FIGS. 2A to 2C, the induction heating unit 20 includes an upper side inductor
21 and a lower side inductor 22.
The upper side inductor 21 includes a core (magnetic core) 23, an upper side
heating coil 24, and shielding plates 3 la and 3 1c. The core 23 may be configured by
5 stacking a plurality of electrical steel sheets.
The upper side heating coil 24 is a conductor that is wound on the core 23
through a slot (here, a depressed portion of the core 23) of the core 23, and is a coil in
which the number of turns is "1" (so-called single turn). In addition, as shown in FIG
2A, the upper side heating coil 24 has a portion in which the shape of the longitudinal
10 cross-section thereof is a hollow rectangle. A water-cooling pipe is connected to an end
face of the hollow portion of the hollow rectangle. Cooling water supplied from the
water-cooling pipe flows to the hollow portion of the hollow rectangle (the inside of the
upper side heating coil 24) and thereby the upper side inductor 21 is cooled. In addition,
the shielding plates 3 1 a and 3 1 c are attached on the bottom surface (slot side) of the core
15 23.
[00 151
Similarly to the upper side inductor 21, the lower side inductor 22 is also
provided with a core (magnetic core) 27, a lower side heating coil 28, and shielding
plates 31b and 31d.
20 Similarly to the upper side heating coil 24, the lower side heating coil 28 is a
conductor that passes through a slot of the core 27 and is wound on the core 27, and is a
coil in which the number of turns is "1" (so-called single turn). Furthermore, similarly
to the upper side heating coil 24, the lower side heating coil 28 has a portion in which a
shape of a longitudinal cross-section thereof is a hollow rectangle. A water-cooling
25 pipe is connected to an end face of the hollow portion of the hollow rectangle, and
cooling water can be made to flow to the hollow portion of the hollow rectangle. In
16
addition, the shielding plates 3 1b and 3 1d are installed on the upper surface (slot side) of
the core 27.
[00 1 61
In addition, a coil face (face on which a loop is formed and through which a line
5 of magnetic force penetrates) of the upper side heating coil 24 of the upper side inductor
21, and a coil face of the lower side heating coil 28 of the lower side inductor 22 face
each other with the steel strip 10 interposed therebetween. Furthermore, sheet surfaces
of the shielding plates 3 la to 3 1d face end portions (edges) of the steel strip 10 in the
sheet width direction. To satisfl this positional relationship, the upper side inductor 21
10 is provided at an upper side (in the vicinity of the upper surface of a horizontal portion of
the second container 12) compared to the steel strip 10, and the lower side inductor 22 is
provided at a lower side (in the vicinity of the lower surface of the horizontal portion of
the second container 12) compared to the steel strip 10. In this embodiment, the
shielding plates 31a to 31d are copper plates that have a flat surface (refer to FIG 2C).
1 5 The shielding plates 3 1 a to 3 1 d weaken the degree of electromagnetic coupling between
the upper side heating coil 24 and the steel strip 10, and the degree of electromagnetic
coupling between the lower side heating coil 28 and the steel strip 10, thereby preventing
the vicinity of the edges of the steel strip 10 in the steel width direction from being
overheated.
20 In this manner, the upper side inductor 21 and the lower side inductor 22 are
different from each other in the position to be disposed, but have the same configuration
as each other. In addition, in this configuration, since an alternating magnetic field
generated from the heating coils intersects the conductive sheet 10 over the entire width
thereof, the entire width of the conductive sheet 10 may be heated.
25 [00 171
FIG 3 shows a view illustrating an example of a configuration of the upper side
17
heating coil 24 and the lower side heating coil 28. In addition, arrows shown in FIG 3
illustrate an example of a direction in which a current flows.
As shown in FIG 3, the upper side heating coil 24 includes copper pipes 41a and
41b, and a copper bus bar (connection plate) 42b that is connected to base-end sides of
5 the copper pipes 41a and 41b. In addition, the lower side heating coil 28 includes
copper pipes 4 1 c and 4 1 d, and a copper bus bar 42f that is connected to base-end sides of
the copper pipes 4 1 c and 4 1d.
[00 1 81
One output terminal of the control unit 100 of the induction heating unit is
10 connected to one end (front-end side of the copper pipe 41a) of the upper side heating
coil 24 through the copper bus bar 42a. On the other hand, one end (front-end side of
the copper pipe 41c) of the lower side heating coil 28 is connected to the other end
(front-end side of the copper pipe 41b) of the upper side heating coil 24 through the
copper bus bars 42c to 42e. In addition, the other output terminal of the control unit
15 100 of the induction heating unit is connected to the other end (front-end side of the
copper pipe 41d) of the lower side heating coil 28 through copper bus bars 42i, 42h, and
42g.
As described above, the upper side heating coil 24 and the lower side heating
coil 28 are connected in series to the control unit 100 of the induction heating unit by
20 combining the copper pipes 41a to 41d and the copper bus bars 42a to 42i, thereby
forming coils in which the number of turns is "1". Here, the direction (in FIG 3, a
clockwise rotation) of a loop of a current that flows through the upper side heating coil
24 is the same as the direction of a loop of a current that flows through the lower side
heating coil 28.
25 [00 191
In addition, as described later, the control unit 100 of the induction heating unit

19
connected to the other end of the rectifying circuit 11 0. The other end of the reactor 120
is connected to a DC terminal b of the MERS 130. The rectifying circuit 110 rectifies
AC power supplied fiom the AC power supply 160 and applies DC power to the MERS
130 through the reactor 120. The rectifying circuit 110 is configured by using, for
5 example, a thyristor. As described above, in this embodiment, for example, a power
supply unit is realized using the AC power supply 160 and the rectifying circuit 110.
This power supply unit is a unit that supplies DC power described later to the DC
terminals b and c of the MERS 130 in FIG. 4. Therefore, a DC power supply such as a
battery that has a current control function may be used as the power supply unit.
10 [002 11
[Configuration of MERS 1301
Hereinafter, an example of a configuration of the MERS 130 will be described.
The MERS 130 converts DC power, which is input fiom the rectifjing circuit
110 through the reactor 120, to AC power according to a method described later, and
15 outputs the AC power to the induction heating unit 20.
In FIG 4, the MERS 130 includes a bridge circuit that is configured using first
to fourth reverse conductivity type semiconductor switches 13 1 to 134, and a capacitor C
having a polarity. This capacitor C is connected between the DC terminals b and c of
the bridge circuit, and a positive electrode (+) of the capacitor C is connected to the DC
20 terminal b.
The other end of the reactor 120 is connected to the DC terminal b, and the other
end of the rectifying circuit 110 on the output side is connected to the DC terminal c. In
addition, one end (copper bus bar 42a) and the other end (copper bus bar 42g) of the
induction heating unit 20 are connected to the AC terminals a and d (refer to FIG 3),
25 respectively.
roo221
20
The bridge circuit of the MERS 130 includes a first path L1 reaching the AC
terminal d fiom the AC terminal a through the DC terminal b, and a second path L2
reaching the AC terminal d fiom the AC terminal a through the DC terminal c. The first
reverse conductivity type semiconductor switch 131 is connected between the AC
5 terminal d and the DC terminal b, and the fourth reverse conductivity type semiconductor
switch 134 is connected between the DC terminal b and the AC terminal a. In addition,
the second reverse conductivity type semiconductor switch 132 is connected between the
AC terminal d and the DC terminal c, and the third reverse conductivity type
semiconductor switch 133 is connected between the DC terminal c and the AC terminal a.
10 In this manner, the first and second reverse conductivity type semiconductor switches
13 1 and 132 are connected in parallel, and the third and fourth reverse conductivity type
semiconductor switches 133 and 134 are connected in parallel. In addition, the first and
fourth reverse conductivity type semiconductor switches 13 1 and 134 are connected in
series, and the second and third reverse conductivity type semiconductor switches 132
1 5 and 1 3 3 are connected in series.
[0023]
Each of the first to fourth reverse conductivity type semiconductor switches 13 1
to 134 allows a current to flow in one direction at the time of a switch-off in which an
on-signal is not input to a gate terminal thereof, and allows a current to flow in both
20 directions at the time of a switch-on in which the on-signal is input to the gate terminal.
That is, the reverse conductivity type semiconductor switches 13 1 to 134 allows a current
to flow only in one direction between a source terminal and a drain terminal at the time
of the switch-off, but allows a current to flow in both directions between the source
terminal and the drain terminal at the time of the switch-on. In addition, in the
25 following description, "a direction toward which each of the reverse conductivity type
semiconductor switches 13 1 to 134 allows a current to flow at the time of the switch-o£E"
is also referred to as "a switch forward direction" as necessary. In addition, "a direction
toward which each of the reverse conductivity type semiconductor switches 13 1 to 134
does not allow a current to flow at the time of the switch-off' is also referred to as "a
switch reverse direction" as necessary. Furthermore, in the following description, "a
5 connection direction with respect to the bridge circuit in the switch forward direction and
the switch reverse direction" is also referred to as "a switch polarity" as necessary.
[0024]
In addition, each of the reverse conductivity type semiconductor switches 13 1 to
134 is disposed to satisfj the switch polarity as described below. The first reverse
10 conductivity type semiconductor switch 13 1 and the second reverse conductivity type
semiconductor switch 132, which are connected in parallel, have switch polarities
opposite to each other. Similarly, the third reverse conductivity type semiconductor
switch 133 and the fourth reverse conductivity type semiconductor switch 134, which are
connected in parallel, have switch polarities opposite to each other. In addition, the first
15 reverse conductivity type semiconductor switch 13 1 and the fourth reverse conductivity
type semiconductor switch 134, which are connected in series, have switch polarities
opposite to each other. Similarly, the second reverse conductivity type semiconductor
switch 132 and the third reverse conductivity type semiconductor switch 133, which are
connected in series, have switch polarities opposite to each other. Therefore, the first
20 reverse conductivity type semiconductor switch 131 and the third reverse conductivity
type semiconductor switch 133 have the same switch polarity as each other. Similarly,
the second reverse conductivity type semiconductor switch 132 and the fourth reverse
conductivity type semiconductor switch 134 have the same switch polarity as each other.
In addition, the switch polarity of the first and third reverse conductivity type
25 semiconductor switches 13 1 and 133 is opposite to that of the second and fourth reverse
conductivity type semiconductor switches 132 and 134.
[0025]
In addition, in regard to the switch polarities shown in FIG 4, the switch polarity
of the first and third reverse conductivity type semiconductor switches 13 1 and 133, and
the switch polarity of the second and fourth reverse conductivity type semiconductor
5 switches 132 and 134 may be reversed to each other.
In addition, various configurations may be considered with respect to the first to
fourth reverse conductivity type semiconductor switches 131 to 134, but in this
embodiment, the first to fourth reverse conductivity type semiconductor switches 13 1 to
134 are configured by a parallel connection between semiconductor switches S1 to S4
10 and diodes Dl to D4, respectively. That is, each of the first to fourth reverse
conductivity type semiconductor switches 13 1 to 134 includes one diode (corresponding
one among diodes Dl to D4) and one semiconductor switch (corresponding one among
semiconductor switches S1 to S4) that is connected to the diode in parallel.
In addition, respective gate terminals GI to G4 of the semiconductor switches
15 S1 to S4 are connected to the gate control unit 140. An on-signal, which allows the
semiconductor switches S1 to S4 to be turned on, is input to the gate terminals G1 to G4
from the gate control unit 140 as a control signal to the MERS 130. In a case where the
on-signal is input, the semiconductor switches S1 to S4 enter an on-state, and may allow
a current to flow in a both direction. However, in a case where the on-signal is not input,
20 the semiconductor switches S1 to S4 enter an off-state, and can not allow a current to
flow in any direction. Therefore, when the semiconductor switches S1 to S4 are turned
off, a current can flow only in the conduction direction (forward direction) of the diodes
D 1 to D4 that are connected in parallel to the semiconductor switches S 1 to S4.
[0026]
25 In addition, the reverse conductivity type semiconductor switches included in
the MERS 130 are not limited to the first to fourth reverse conductivity type
semiconductor switches 13 1 to 134. That is, any reverse conductivity type
semiconductor switch is preferable as long as this switch has a configuration capable of
showing the above-described operation. For example, the reverse conductivity type
semiconductor switches may have a configuration using a switching element such as a
5 power MOSFET and a reverse conducting GTO thyristor, or may have a configuration in
which a semiconductor switch such as an IGBT and a diode are connected in parallel.
In addition, hereinafter, a description will be made by substituting the switch
polarity of the first to fourth reverse conductivity type semiconductor switches 131 to
134 with the polarity of the diodes Dl to D4. A switch forward direction (direction
10 toward which a current flows at the time of a switch-off) is a conduction direction
(forward direction) of each of the diodes Dl to D4, and a switch reverse direction
(direction toward which a current does not flow at the time of the switch-off) is a
non-conduction direction (reverse direction) of each of the diodes Dl to D4. In addition,
conduction directions between diodes (Dl and D2, or D3 and D4) connected in parallel
15 are opposite to each other, and conduction direction between diode (Dl and D4, or D2
and D3) connected in series are opposite to each other. In addition, conduction
directions of the diodes Dl and D3 are the same as each other. Similarly, conduction
directions of the diodes D2 and D4 are the same as each other. Therefore, the
conduction direction of the diode Dl and D3 and the conduction direction of the diodes
20 D2 and D4 are opposite to each other. In addition, the conduction directions of the
semiconductor switches S1 to S4 and the diodes Dl to D4 are set with a direction of a
current flowing to the induction heating unit 20 made as a reference.
[0027]
[Operation of MERS 1301
25 FIG 5 shows a view illustrating an example of a relationship between a voltage
V, at both ends of a capacitor C of the MERS 130, a current IL that flows to the induction
24
heating unit 20, and an operation state of the semiconductor switches S1 to S4.
In FIG 5, for a period in which a waveform rises on a side indicated as "Sl.S3
gate", the switches S1 and S3 are in an on-state, and the semiconductor switches S2 and
S4 are in an off-state. In addition, for a period in which a waveform rises on a side
5 indicated as "S2-S4 gate", the semiconductor switches S2 and S4 are in an on-state, and
the switches S1 and S3 are in an off-state. For a period in which a waveform does not
rise on either the "Sl-S3 gate" side or the "S2eS4 gate" side, all of the semiconductor
switches S1 to S4 are in an off-state. In this manner, when the semiconductor switch S1
is turned on (off), the semiconductor switch S3 is turned on (off), and therefore the
10 semiconductor switches S1 and S3 operate in conjunction with each other. Similarly,
when the semiconductor switch S2 is turned on (off), the semiconductor switch S4 is
turned on (off), and therefore the semiconductor switches S2 and S4 operate in
conjunction with each other. Hereinafter, an example of the operation of the MERS 130
will be described with reference to FIGS. 4 and 5.
15 [0028]
As shown in FIG 5, an initial stage of a period A is a dead time accompanying a
switch operation, and for this dead time, not only the semiconductor switches S1 and S3
but also the semiconductor switches S2 and S4 are turned off. For this dead time, a
current flows through the path of the diode D4 + the capacitor C + the diode D2, and
20 therefore charging of the capacitor C is initiated. As a result, the voltage V, at both
ends of the capacitor C is raised, and therefore the current IL (absolute value thereof)
flowing to the induction heating unit 20 decreases. When the semiconductor switches
S2 and S4 are turned on (while the semiconductor switches S1 and S3 are turned off)
before the charging of the capacitor C is completed, a current flows through a path of the
25 semiconductor switch S4 and the diode D4 + the capacitor C + the semiconductor
25
switch S2 and the diode D2, and therefore the capacitor C is charged (period A). That is,
in this period A, the voltage V, at both ends of the capacitor C is raised, and therefore the
current IL (absolute value thereof) flowing to the induction heating unit 20 decreases.
When the charging of the capacitor C is completed, the current IL flowing to the
5 induction heating unit 20 becomes zero. When the semiconductor switches S2 and S4
are turned on until the charging of the capacitor C is completed, and then the charging of
the capacitor C is completed, the energy (charge) charged in the capacitor C is output
(discharged) through the semiconductor switches S4 and S2. As a result, the current IL
flows through a path of the semiconductor switch S4 -+ the induction heating unit 20 -+
10 the semiconductor switch S2 (period B). That is, in this period B, the voltage V, at both
ends of the capacitor C is lowered, and therefore the current IL (absolute value thereof)
flowing to the induction heating unit 20 increases.
[0029]
When the discharging of the capacitor C is completed, the voltage V, at both
15 ends of the capacitor C becomes zero, and therefore a reverse voltage is not applied to the
diodes Dl and D3. Therefore, the diodes Dl and D3 enter a conduction state, and the
current IL flows through a path of the semiconductor switch S4 -+ the induction heating
unit 20 -+ the diode Dl and a path of the diode D3 -+ the induction heating unit 20 -+
the semiconductor switch S2 in parallel (period C). The current IL circulates between
20 the induction heating unit 20 and the MERS 130. Therefore, in the period C, the
absolute value of the current IL is attenuated in response to a time constant that is
determined by impedance of the upper side heating coil 24, the lower side heating coil 28,
and the steel strip 10 that is an object to be heated.
Then, in the dead time, not only the semiconductor switches S1 and S3, but also
25 the semiconductor switches S2 and S4 are turned off. For the dead time, a current flows
through a path of the diode Dl -+ the capacitor C -+ the diode D3, and therefore the
26
charging of the capacitor C is initiated (period D). As a result, the voltage V, at both
ends of the capacitor C is raised, and therefore the current IL (absolute value thereof)
flowing to the induction heating unit 20 decreases. When the semiconductor switches
S1 and S3 are turned on (while the semiconductor switches S2 and S4 are turned off)
5 before the charging of the capacitor C is completed, a current flows through the path of
the semiconductor switch S1 and the diode Dl + the capacitor C + the semiconductor
switch S3 and the diode D3, and therefore the capacitor C is charged (period D). That is,
in this period D, the voltage V, at both ends of the capacitor C is raised, and therefore the
current IL (absolute value thereof) flowing to the induction heating unit 20 decreases.
10 [0030]
When the charging of the capacitor C is completed, the current IL flowing to the
induction heating unit 20 becomes zero. When the semiconductor switches S1 and S3
are turned on until the charging of the capacitor C is completed, and then the charging of
the capacitor C is completed, the energy (charge) charged in the capacitor C is output
15 (discharged) through the semiconductor switches S 1 and S3. As a result, the current IL
flows through a path of the semiconductor switch S1 + the induction heating unit 20 +
the semiconductor switch S3 (period E). That is, in this period E, the voltage V, at both
ends of the capacitor C is lowered, and therefore the current IL (absolute value thereof)
flowing to the induction heating unit 20 increases.
20 When the discharging of the capacitor C is completed, the voltage V, at both
ends of the capacitor C becomes zero, and therefore a reverse voltage is not applied to the
diodes D2 and D4. Therefore, the diodes D2 and D4 enter a conduction state, and the
current IL flows through a path of the semiconductor switch S1 + the induction heating
unit 20 + the diode D4 and a path of the diode D2 + the induction heating unit 20 +
25 the semiconductor switch S3 in parallel (period F). The current IL circulates between
the induction heating unit 20 and the MERS 130. Therefore, in the period F, the
27
absolute value of the current IL is attenuated in response to a time constant that is
determined by impedance of the upper side heating coil 24, the lower side heating coil 28,
and the steel strip 10 that is an object to be heated. Then, it returns to the operation for
the period A, and the operations for the periods A to F are repetitively performed.
5 [003 11
As described above, when turn-on and turn-off (switching operation) timings
. (times) of the respective gate terminals G1 to G4 (GI and G3, and G2 and G4) of the
semiconductor switches S1 to S4 (S1 and S3, and S2 and S4) are adjusted, a current of a
desired frequency can be made to flow through the induction heating unit 20 (the upper
10 side heating coil 24 and the lower side heating coil 28), thereby realizing frequency
control type induction heating. That is, due to the gate control unit 140 that adjusts the
conduction timing of the semiconductor switches S1 to S4, a frequency of the current IL
that flows to the induction heating unit 20 that is a load can be controlled to an arbitrary
value. In addition, when capacitance Cp of the capacitor C is determined according to
15 Equation (1) described below, the period in which the voltage Vc at both ends of the
capacitor C is zero can be adjusted.
cp = ~/[(~xxxG)~-x--L (1])
Here, Cp represents capacitance (F) of the capacitor C, and L represents
inductance (H) of loads including the induction heating unit 20. In addition, ft
20 represents an apparent frequency (Hz) with respect to the capacitor C, which is expressed
by Equation (2) described below.
f, = lI(2xt + lff) --- (2)
Here, t represents a period (sec) in which the voltage Vc at both ends of the
capacitor C is zero, and f represents a frequency (Hz) of the voltage V, and the current IL
25 in a case where a period in which the voltage V, at both ends of the capacitor C is zero is
not present. When a capacitor C, which has capacitance Cp that is obtained by
28
substituting ft (that is, f) when t is zero in Equation (2) into Equation (I), is selected, a
period in which the voltage V, at both ends of the capacitor C is zero is not present.
[0032]
[Configuration of Frequency Setting Unit 1801
5 Returning to the description of FIG 4, an example of a configuration of the
frequency setting unit 180 will be described. The frequency setting unit 180 is a unit
that sets the frequency (output frequency) of AC power to be supplied to the induction
heating unit 20. To realize the function thereof, the frequency setting unit 180 includes
an object-to-be-heated information acquiring unit 18 1, a frequency setting table 182, and
1 0 a frequency selector 1 83.
The object-to-be-heated information acquiring unit 181 acquires attribute
information of the steel strip 10 that is an object to be heated. For example, the
object-to-be-heated information acquiring unit 181 acquires (receives) the attribute
information from an external computer that is an input unit through a network, or
15 acquires .(input) the attribute information on the basis of information that is input by a
user with respect to a user interface (one of input units) provided for the control unit 100.
Here, the attribute information of the steel strip 10 is information that is capable of
specifying a relative permeability, a resistance, and a sheet thickness of the steel strip 10.
For example, the relative permeability, the resistance, and the sheet thickness itself of the
20 steel strip 10 may be set as the attribute information, or in a case where the relative
permeability, the resistance, and the sheet thickness itself of the steel strip 10 are
determined according to specifications, a name (a trade name or the like) of the steel strip
10 having the specifications may be set as the attribute information.
[0033]
25 The frequency selector 183 uses the attribute information acquired by the
object-to-be-heated information acquiring unit 181 as a key and selects one fiequency
29
among frequencies registered in the frequency setting table 182. In the frequency
setting table 182, the attribute information and the frequency are correlated with each
other and are registered in advance.
Information of a frequency (output fiequency) selected by the frequency selector
5 183 is transmitted to the gate control unit 140. The gate control unit 140 determines
turn-on and turn-off (switching operation) timings of the respective gate terminals G1 to
G4 of the semiconductor switches S1 to S4 of the MERS 130 so that AC power of the
selected frequency is generated, and outputs an on-signal to a gate terminal of a
semiconductor switch to be turned on. In this manner, the MERS 130 outputs the AC
10 power of the frequency (the output frequency) that is set to the gate control unit 140 by
the frequency setting unit 180 to the induction heating unit 20 as described above.
[0034]
As described above, in this embodiment, the frequency (the output frequency) of
the AC power to be supplied to the induction heating unit 20 is automatically determined
15 in response to the relative permeability, the resistance, and the sheet thickness of the steel
strip 10. This is based on a finding obtained through various experiments performed by
the inventors, specifically, a finding that the temperature distribution (particularly, the
temperature in the vicinity of an edge) of the steel strip 10 is affected by the frequency of
the AC power supplied to the induction heating unit 20, the attribute information (the
20 relative permeability, the resistance, and the sheet thickness) of the steel strip 10 that is
an object to be heated, and a gap (distance between the upper side heating coil 24 and the
lower side heating coil 28).
Hereinafter, the reason why this phenomenon occurs will be described.
First, a description will be made with respect to a case where the temperature of
25 the steel strip 10 is equal to or higher than the Curie temperature.
When the steel strip 10 is at a temperature that is equal to or higher than the
3 0
Curie temperature, a main magnetic field that is generated from the induction heating
unit 20 penetrates through the steel strip 10, and an eddy current within the steel strip 10
(within a plane orthogonal to the sheet thickness) increases. This eddy current is
repelled from a main magnetic field and is apt to be biased to the vicinity of the edge of
5 the steel strip 10. Therefore, a high-temperature region is apt to occur in the vicinity of
the edge of the steel strip 10.
[003 51
Here, the eddy current within the steel strip 10 is proportional to a
cross-sectional area (cross-sectional area including a sheet thickness direction) of the
10 steel strip 10, such that in a case where the sheet thickness of the steel strip 10 is large,
the cross-sectional area of the steel strip 10 becomes large and therefore the eddy current
within the steel strip 10 increases.
In addition, the eddy current of the steel strip 10 is inversely proportional to a
resistance of the steel strip 10, such that in a case where the resistance of the steel strip
15 10 is small, the eddy current within the steel strip 10 increases.
In addition, a frequency of AC power supplied to the induction heating unit 20 is
proportional to an induced electromotive force that is generated within the steel strip 10
due to the main magnetic field generated from the induction heating unit 20. The eddy
current of the steel strip 10 is proportional to the induced electromotive force, such that
20 in a case where the frequency of the AC power supplied to the induction heating unit 20
is high, the eddy current within the steel strip 10 increases.
In addition, in a case where the gap is small, the main magnetic field generated
from the induction heating unit 20 becomes large, such that the induced electromotive
force generated within the steel strip 10 due to the main magnetic field becomes large
25 and therefore the eddy current within the steel strip 10 increases.
COO361
3 1
Next, a description will be made with respect to a case where the temperature of
the steel strip 10 is less than Curie temperature.
In a case where the temperature of the steel strip 10 is less than Curie
temperature, a relative permeability of the steel strip 10 is large, such that the main
5 magnetic field generated from the induction heating unit 20 is difficult to penetrate
through the steel strip 10 and therefore bypasses the edge portion of the steel strip 10.
As a result, in the vicinity of the edge of the steel strip 10 in the sheet width direction, the
current density of the eddy current becomes large, and therefore a high temperature
region occurs in the vicinity of the edge of the steel strip 10 in the sheet width direction.
10 As described above, factors (the frequency of the AC power supplied to the
induction heating unit 20, the relative permeability, resistance, and sheet thickness of the
steel strip 10 that is an object to be heated, and the gap), which have an effect on the
temperature of the steel strip 10, are independent from each other. Among these factors,
the relative permeability, resistance, and sheet thickness of the steel strip 10, and the gap
15 are determined by operational conditions (hardware restrictions on a material that is an
object to be heated and a facility). Therefore, in this embodiment, among these factors,
"the frequency (the output frequency) of the AC power supplied to the induction heating
unit 20" that can be controlled through on-line is changed using the frequency setting
unit 180 to adjust the temperature of the steel strip 10.
20 In addition, as is the case with this embodiment, when all of the relative
permeability, the resistance, and the sheet thickness of the steel strip 10, and the
frequency are correlated with each other and are registered in the frequency setting table
182, the temperature distribution of the steel strip 10 in the sheet width direction can be
adjusted in a relatively uniform manner. Therefore, it is preferable that all of the
25 relative permeability, resistance, and sheet thickness of the steel strip 10, and the
frequency be correlated with each other. However, it is not necessary to correlate all of
the relative permeability, resistance, and sheet thickness of the steel strip 10, and the
frequency, and at least one of the relative permeability, resistance, and sheet thickness of
the steel strip 10 may be correlated with the frequency in the frequency setting unit 180.
In addition, at least one of the relative permeability, resistance, and sheet thickness of the
5 steel strip 10, and the gap may be correlated with the frequency.
[003 71
[Configuration of Output Current Setting Unit 1 501
The output current setting unit 150 is a unit that sets a magnitude (output current
value) of the AC current IL supplied to the induction heating unit 20. To realize this
10 function, the output current setting unit 150 includes an object-to-be-heated information
acquiring unit 15 1, an output current setting table 152, and an output current selector
153.
The object-to-be-heated information acquiring unit 1 5 1 acquires attribute
information of the steel strip 10 that is an object to be heated, similarly to the
15 object-to-be-heated information acquiring unit 18 1.
The output current selector 153 uses the attribute information acquired by the
object-to-be-heated information acquiring unit 15 1 as a key and selects one current value
among current values registered in the output current setting table 152. In the output
current setting table 152, the attribute information and the current value are correlated
20 with each other and are registered in advance. In addition, a control angle of the
rectifying unit 11 0 is set in response to a difference between the current value (the output
current value) selected by the output current selector 153 and a current value measured
by the current transformer 170. In the case of adopting a thyristor rectifying device as
the rectifling unit 110, a gate firing angle of the thyristor is set. In this manner, the
25 value of the current flowing to the induction heating unit 20 is fed back and the control
angle (the gate firing angle) of the rectifling unit 11 0 is controlled, such that the value of
3 3
the current flowing to the induction heating unit 20 may be constantly controlled to be
the current value (output current value) selected by the output current selector 153. As
a result, the power supply unit (the AC power supply 160 and the rectifiing unit 110)
supplies DC power to the MERS 130, and therefore the alternating current measured by
5 the current transformer 170 can be adjusted to the current value (the output current value)
set by the output current setting unit.
As described above, in this embodiment, the current value (the output current
value) of the AC power supplied to the induction heating unit 20 is automatically
determined in response to the relative permeability, resistance, and sheet thickness of the
10 steel strip 10. This is because the current value corresponding to a target temperature
can be determined by the relative permeability, the resistance, and the sheet thickness of
the steel strip 10.
In addition, similarly to this embodiment, when all of the relative permeability,
resistance, and sheet thickness of the steel strip 10, and the current value are correlated
15 with each other and are registered in the output current setting table 152, a temperature
distribution and an average temperature of the steel strip 10 in the sheet width direction
may be set in a relatively appropriate manner. Therefore, it is preferable that all of the
relative permeability, the resistance, and the sheet thickness of the steel strip 10, and the
current value be correlated with each other. However, it is not necessary to correlate all
20 of the relative permeability, resistance, and sheet thickness of the steel strip 10 with the
current value, and at least one of the relative permeability, resistance, and sheet thickness
of the steel strip 10 and the current value may be correlated with each other in the output
current setting unit 150. In addition, at least one of the relative permeability, resistance,
and sheet thickness of the steel strip 10, and the gap may be correlated with the current
25 value.
[003 81

FIG 6A shows a graph illustrating the relationship between frequency and
temperature ratio with respect to sheet conveyance speed, when power is supplied to the
induction heating unit 20 using the control unit 100 according to the embodiment and a
5 steel strip 10 is heated. In addition, FIG 6B shows a graph illustrating the relationship
between frequency and temperature ratio with respect to a sheet conveyance speed, when
power is supplied to the induction heating unit 20 using a parallel resonance type inverter
in a conventional technique and the steel strip 10 is heated. Here, a temperature ratio
(temperature ratio of edgelcenter) is a value obtained by dividing a temperature in an end
10 portion (edge) of the steel strip 10 in the sheet width direction thereof by a temperature in
a central portion of the steel strip 10 in the sheet width direction thereof. The more the
value of the temperature ratio approaches 1, the more uniform the temperature
distribution of the steel strip 10 in the sheet width direction is. In addition, the
frequency is a frequency of a current applied to the induction heating unit 20. In
15 addition, specifications of the steel strip 10 are as follows.

- Material: Stainless steel sheet -Sheet Thickness: 0.3 rnm - Width: 500 rnrn
As shown in FIG 6A, when the control unit 100 according to this embodiment is
used, even in a case where the sheet conveyance speed varies, the frequency of the
20 current, which may be applied to the induction heating unit 20, may be held substantially
constant, and therefore the temperature ratio can be controlled to be substantially
constant.
On the other hand, when the sheet conveyance speed varies, the impedance of
the load varies, such that in a case where the parallel resonance type inverter in the
25 conventional technique is used, the inverter of the voltage source controls the output
frequency of the inverter in such a manner that a resonance condition of the load is
maintained. Therefore, as shown in FIG 6B, the output frequency of the inverter varies
in response to a variation of the impedance of the load. As a result thereof, the
temperature ratio varies significantly and therefore the temperature ratio can not be
controlled to be constant.
5 [0039]
As described above, according to this embodiment, the current IL of the
frequency (the output frequency) corresponding to the attribute (attribute information) of
the steel strip 10 is supplied to the induction heating unit 20 using the MERS 130.
Therefore, the control unit according to this embodiment is not subjected to a restriction
10 in regard to an operation with a resonant frequency like the conventional technique, such
that even when the sheet conveyance speed of the steel strip 10 varies, the frequency of
the current IL that is supplied to the induction heating unit 20 may be set to a desired
value in response to the attribute of the steel strip 10. Therefore, when the conductive
sheet is heated using the transverse type induction heating unit, even when the sheet
15 conveyance speed of the conductive sheet varies, it is possible to prevent the temperature
distribution of the conductive sheet in the sheet width direction from being nonuniform.
In addition, the current IL of a frequency, which is appropriate to the steel strip 10 that is
an object to be heated (particularly, which makes the temperature distribution in the sheet
width direction as uniform as possible), may be set to the induction heating unit 20.
20 In addition, in this embodiment, the control angle of the rectifying unit 110 is
changed in response to the attribute of the steel strip 10, and therefore the current IL
having a magnitude corresponding to the attribute of the steel strip 10 is supplied to the
induction heating unit 20. As a result, the current IL having a magnitude appropriate to
the steel strip 10 that is an object to be heated can flow through the induction heating unit
25 20. In addition, since the frequency is controlled to be constant, the temperature
distribution of the conductive sheet in the sheet width direction can be uniformly
3 6
controlled without actually measuring the variation in temperature with the passage of
time at various positions of the steel strip 10.
Furthermore, in regard to the induction heating system provided with the control
unit 100 and the induction heating unit 20 having the shielding plates 3 la to 3 Id, since
5 even when the sheet conveyance speed varies, the frequency of the AC power does not
vary, it is not necessary to consider a variation (variation with the passage of time) in the
eddy current generated at the edge portion of the steel strip 10. Therefore, when the
control unit 100 is used in the induction heating system, even when the operational
conditions vary, a heating amount in the vicinity of the edge can be appropriately
10 controlled by the shielding plates 3 1 a to 3 1 d.
[0040]
(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the
above-described first embodiment, the alternating current IL is made to flow to the
15 induction heating unit 20 directly from the MERS 130. Conversely, according to this
embodiment, the alternating current IL is made to flow to the induction heating unit 20
from the MERS 130 through a transformer. In this manner, in a ~ o ~ g u r a t i oofn t his
embodiment, the transformer is added to the above-described configuration of the first
embodiment. Therefore, in this embodiment, the same reference symbols as those
20 given in FIG. 1 to FIG 6B will be given to the same portions as the above-described first
embodiment, and a detailed description thereof will be omitted here.
[004 11
FIG. 7 shows a view illustrating an example of a configuration of a control unit
200 of an induction heating unit.
25 As shown in FIG 7, the control unit 200 according to this embodiment further
includes an output transformer 2 10 compared to the control unit 100 according to the first
3 7
embodiment shown in FIG 4.
A primary side (input side) terminal of the output transformer 210 is connected
to the AC terminals a and d of the MERS 130. A secondary side (output side) terminal
of the output transformer 210 is connected to the induction heating unit 20 (the copper
5 bus bars 42a and 42g). The transformation ratio (input : output) of the output
transformer 210 is N:l(N>l).
As described above, in this embodiment, since the output transformer 210
having the transformation ratio of N:l (N>1) is disposed between the MERS 130 and the
induction heating unit 20, substantially N times current of the current flowing through the
10 MERS 130 can be made to flow to the induction heating unit 20. Therefore, in this
embodiment, a large current can be made to flow to the induction heating unit 20 without
making a large current flow to the "semiconductor switches S 1 to S4 and the diodes Dl
to D4" that make up the MERS 130.
In addition, a plurality of taps may be provided on the primary side or the
15 secondary side of the output transformer 210 in such a manner that the transformation
ratio of the output transformer 210 can be changed, and the tap to be used may be
properly used in response to the steel strip 10 that is an object to be heated.
[0042]
(Third Embodiment)
20 Next, a third embodiment of the present invention will be described. In the
above-described first and second embodiments, a flat plate is used as the shielding plates
3 1 a to 3 1 d provided for the induction heating unit 20. Conversely, in this embodiment,
a depressed portion is formed in the shielding plates provided for the induction heating
unit 20. In this manner, this embodiment and the above-described first and second
25 embodiments are different in a part of a configuration of the shielding plates. Therefore,
in this embodiment, the same reference symbols as those given in FIG 1 to FIG. 7 will be
38
given to the same portions as the above-described first and second embodiments, and a
detailed description thereof will be omitted here.
[0043]
FIGS. 8A to 8C show views illustrating an example of a configuration of the
5 induction heating unit. FIG 8A, FIG. 8B, and FIG 8C correspond to FIG 2A, FIG 2B,
and FIG. 2C, respectively. Instead of the shielding plates 3 la to 3 Id shown in FIGS. 2A
to 2C, shielding plates 301a to 301d are used. In addition, the shielding plates 301a to
301d are disposed at positions shown in FIG 8B in such a manner that the depressed
portion described later faces (is opposite to) the steel strip 10 (in the second container 12).
10 In addition, the induction heating unit includes an upper side inductor 201 and a lower
side inductor 202. In addition, the upper side inductor 201 and the lower side inductor
202 are substantially the same as the upper side inductor 21 and the lower side inductor
22 shown in FIGS. 2A to 2C, respectively, except for the configuration of the shielding
plates.
15 100441
In addition, FIGS. 9A to 9C show views illustrating an example of a
configuration of the shielding plate 301 (shielding plates 301a to 301 d). Specifically,
FIG 9A shows a perspective view taken by overlooking the shielding plate 301 from an
upper side. In addition, FIG. 9B shows a view taken by overlooking a region of the
20 shielding plate 301d shown in FIG 8C from immediately above the steel strip 10. In
addition, FIG 9B shows only a portion that is necessary to explain a positional
relationship between the steel strip 10 and the shielding plate 301d. In addition, FIG.
9C shows a schematic view illustrating an example of a magnetic field that is generated
between the shielding plates 301a, 301b and the steel strip 10. However, in FIGS. 9B
25 and 9C, the second container 12 is omitted for easy understanding of an effect of the
shielding plates 30 1 a to 301d.
3 9
[0045]
As shown in FIG 9A, the shielding plate 301 includes a main shielding plate 50a
and a rear plate 50b.
The width and length of the main shielding plate 50a are the same as those of the
5 rear plate 50b. However, the rear plate 50b is formed of a copper plate in which a
longitudinal cross-section and a transverse cross-section are uniform, and conversely, the
main shielding plate 50a is formed of a copper plate in which two rhombic holes are
formed in the longitudinal direction thereof. The shielding plate 301 is formed by close
contact between the main shielding plate 50a and the rear plate 50b, and has two rhombic
10 depressed portions (non-penetration holes) 51 and 52 in the longitudinal direction. In
addition, in FIG 9A, dimensions [mm] related to the positions at which the depressed
portions 5 1 and 52 are disposed are also indicated.
[0046]
As shown in FIGS. 9B and 9C, the shielding plate 301 is installed on the bottom
15 surface (slot side) of the core 23 and the top surface (slot side) of the core 27 in such a
manner that a surface in which the depressed portions 51 and 52 are formed faces the
steel strip 10.
In this embodiment, as shown in FIG 9B, the depressed portions 51 and 52 of
the shielding plate 301 (301d) and a sheet surface of the steel strip 10 are opposite to
20 each other in the vicinity of an edge 10a of the steel strip 10 in the sheet width direction.
Specifically, a region that is located on the edge 10a side compared to the maximum
current passing region 56 faces the depressed portions 51 and 52 of the shielding plate
301. The region that is located on the edge 10a side includes a region between a
maximum current passing region 56 that is a region in which an eddy current flowing
25 through the steel strip 10 becomes maximum by operating the induction heating unit and
the edge 10a of the steel strip 10.
40
Particularly, in this embodiment, inner-side edges 5 la and 52a of the depressed
portions 51 and 52 of the shielding plate 301 (301d) are disposed on the edge 10a side
compared to the maximum current passing region 56, and outer-side edges 5 1b and 52b
of the depressed portions 5 1 and 52 are disposed on the edge side 10a compared to an
edge current passing region 57 that is a region through which an eddy current flowing to
the vicinity of the edge 10a of the steel strip 10 passes. Here, among edges of the
depressed portions 51 and 52, the inner-side edges 51a and 52a are edges that are closest
to a central portion in the width direction of the steel strip 10 and that are closer to the
corresponding depressed portions 52 and 51 (or the central portion of the shielding plate
10 301d in the sheet conveyance direction). In addition, among edges of the depressed
portions 51 and 52, outer-side edges 51b and 52b are edges that are farther from the
central portion of the steel strip 10 in the width direction and that are farthest from the
corresponding depressed portions 52 and 51 (or the central portion of the shielding plate
301d in the sheet conveyance direction).
15 [0047]
In this embodiment, due to the shielding plate 301 disposed as described above,
a decrease in the temperature of the steel strip 10 in the vicinity of the edge 10a is
suppressed. Hereinafter, a mechanism, which suppresses a decrease in temperature of
the steel strip 10 in the vicinity of the edge 10a due to the shielding plate 301, will be
20 described.
As shown in FIG 9C, when the induction heating unit is operated, main
magnetic fields 58a to 58c are generated, and therefore eddy currents 60a to 60e flow to
an edge side of the steel strip 10 in the sheet width direction. In addition, a magnetic
field 59i is generated by the eddy currents 60a to 60e. In addition, as shown in FIGS.
25 9A to 9C, eddy currents 53 to 55 flow through the shielding plate 301 (301a and 301 b).
The eddy current 53 is an eddy current flowing along a rhombic edge portion of the
4 1
shielding plate 301 (main shielding plate 50a). On the other hand, the eddy currents 54
and 55 are currents flowing along an edge portion of the depressed portions 5 1 and 52 of
the shielding plate 301. In this manner, in the shielding plate 301, the edge currents 53
to 55 flow to the rhombic edge portion of the shielding plate 301 and edge portion of the
5 depressed portions 51 and 52 of the shielding plate 301 in a concentrated manner.
Furthermore, magnetic fields 59a to 59h are generated by the eddy currents 53 to 55.
[0048]
As a result, as shown in FIG 9C, a repulsive force is generated between the eddy
currents 54 and 55 that flow through the shielding plate 301 (301a and 301 b) and the
10 eddy current 60 that flows through the steel strip 10. Due to this repulsive force, the
eddy current 60 (60a to 60e) flowing through the edge portion of the steel strip 10 moves
to an inner side (in an arrow direction shown under the steel strip 10 in FIG 9C) of the
steel strip 10 and a current density in a region in which a temperature decreases in the
conventional technique increases. Therefore, a decrease in temperature in the vicinity
15 of the edge (region slightly to the inside of the edge) of the steel strip 10 may be
suppressed, and therefore the shielding plate 301 can adjust the degree of electromagnetic
coupling between a region of the steel strip 10 on the edge side in the sheet width
direction and the heating coils 24 and 28. Here, the shielding plate 301 is made of
copper, and a necessary property is maintained even at a high temperature. Therefore,
20 even when the shielding plate 301 is exposed to high temperatures, a decrease in
temperature of the steel strip 10 in the vicinity of the edge thereof can be suppressed.
[0049]
Conversely, in a case the depressed portion is not present in the shielding plate
31 like the first embodiment, the eddy currents 53 and 54 do not flow through the
25 shielding plate 31 as shown in FIGS. 9A and 9C, and an eddy current flows to the
rhombic edge portion of the shielding plate 3 1 in a concentrated manner. Therefore, an
42
eddy current that flows to the vicinity of the edge of the steel strip 10 does not receive a
force biased to an inner side (central side) of the steel strip 10, and a current density of a
region (region slightly to the inside of the edge of the steel strip 10) in which a
temperature decreases does not increase. Therefore, a decrease in temperature in the
5 vicinity of the edge of the steel strip 10 may not be suppressed.
As described above, the inventors found that when the depressed portions 51
and 52 are formed in the shielding plate 301 made of copper, and the shielding plate 301
is disposed in such a manner that the depressed portions 51 and 52 are opposite to the
vicinity of the edge of the steel strip 10, a decrease in temperature in the vicinity of the
10 edge of the steel strip 10 can be suppressed. To confirm this fmding, the inventors
measured the temperature distribution in the sheet width direction of a conductive sheet
(corresponding to the steel strip 10) in a case where the shielding plate 301 according to
this embodiment is used and in a case where the shielding plate 3 1 according to the first
embodiment is used, respectively.
15 [0050]
FIGS. 10A and 10B show views illustrating an example of a temperature
distribution of a conductive sheet, which is heated by the induction heating unit, in the
sheet width direction.
Specifically, FIG 10A shows a graph with respect to the induction heating unit
20 (the induction heating unit according to this embodiment) using the shielding plate 301
according to this embodiment. On the other hand, FIG. 10B shows a graph with respect
to the induction heating unit (the induction heating unit according to the first
embodiment) using the shielding plate 31 according to the first embodiment. In
addition, the horizontal axis of graphs shown in FIGS. 10A and 10B indicates a position
25 in the sheet width direction of the conductive sheet, a position "0" in the horizontal axis
corresponds to an edge of the conductive sheet, and a position "250" corresponds to the
43
center of the conductive sheet. On the other hand, the vertical axis represents an
increase in temperature (temperature increase) of the conductive sheet due to heating.
Here, experimental conditions of graphs shown in FIGS. 10A and 10B are as follows.
Width of heating coil: 250 [mm] (length in a sheet conveyance direction)
5 Core: Ferrite core
Heating material: Non-magnetic SUS (stainless) sheet (a width of 500 [mm],
and a thickness of 0.3 [rnrn])
Sheet conveyance speed: 8 [mpm (rnlminute)]
Heating temperature: 30 to 130 [OC] (a temperature increase at a central portion
10 is set to 100 [OC])
Frequency of power source: 29 [kHz], 2 1 [Hz], and 10 [kHz]
Material of shielding plate: Copper
In addition, the closer the relative permeability of a material approaches 1, the
more easily the temperature in the vicinity of an edge decreases. In addition, when the
15 temperature of the conductive sheet (material to be heated) is equal to or higher than the
Curie temperature, the relative permeability of the conductive sheet becomes 1.
Therefore, the non-magnetic SUS (stainless) sheet was used as the heating material
having the relative permeability of 1.
[005 11
20 As shown in FIG 10A, in the induction heating unit using the shielding plate
301 according to this embodiment, it can be understood that when the frequency is
changed in the order of 29 [kHz] + 21 [kHz] + 10 [kHz], the temperature of the edge
decreases, and a decrease in temperature in the vicinity of the edge (here, at a position of
"50" to "100" in the horizontal axis) is suppressed (the temperature distribution in the
25 sheet width direction becomes uniform).
On the other hand, as shown in FIG 10B, in the induction heating unit using the
44
shielding plate 3 1 according to the first embodiment, it can be understood that when the
frequency is changed in the order of 29 [kHz] + 21 [kHz] + 10 m], the temperature
of the edge decreases, but the decrease in temperature in the vicinity of the edge (here, at
a position of "50" to "1 00" in the horizontal axis) becomes large.
5 In addition, in a case where the shielding plate is not provided, the temperature
in the vicinity of the edge (here, at a position of "50" to "100" in the horizontal axis)
does not decrease. However, since the temperature increase in the edge becomes
substantially 500 ["C], the edge was over-heated.
[0052]
10 As described above, according to this embodiment, the depressed portions 51
and 52 are formed in the shielding plate 301 made of copper, the shielding plate 301 is
disposed between the upper and lower side heating coils 24 and 28 and the steel strip 10
in such a manner that the depressed portions 5 1 and 52 face the vicinity of the edge of the
steel strip 10. Therefore, even when the steel strip 10 is exposed to high temperatures, a
15 decrease in temperature of the steel strip 10 in the vicinity of the edge thereof can be
suppressed.
Furthermore, in the induction heating system provided with the control unit 100
and the induction heating unit having the shielding plate 301, even when the sheet
conveyance speed varies, since the frequency of the AC power does not vary, it is not
20 necessary to consider a variation (temporal variation) of the eddy current that is
generated in the edge portion of the steel strip 10. Therefore, when the control unit 100
is used in the induction heating system, even when operational conditions vary, a
temperature increase in the vicinity of the edge can be appropriately controlled by the
shielding plate 301. Furthermore, since the depressed portions 51 and 52 are formed in
25 the shielding plate 301, even when the relative permeability varies in response to a
heated state of the steel sheet, the temperature distribution in the vicinity of the edge can
45
be appropriately controlled due to the depressed portions 51 and 52. Therefore, in the
configuration according to this embodiment, it is possible to cope with a change in
heating speed in a relatively flexible manner.
In addition, in the above-described embodiments (the first embodiment to the
5 third embodiment), the shielding plates 31 and 301 are not limited to a plate made of
copper. That is, the shielding plates 3 1 and 301 may be formed by any material as long
as this material is a conductor having a relative permeability of 1 (for example, metal that
is a paramagnetic substance or a diamagnetic substance). For example, the shielding
plate 3 1 may be formed of aluminum.
10 In addition, in this embodiment, the positional relationship between the steel
strip 10 and the shielding plate 301 is not particularly limited as long as the depressed
portions of the shielding plate 301 and the steel strip 10 (also including a plane extended
from the steel strip 10) are opposite to each other in a region that is present on the edge
10a side compared to the maximum current passing region 56. However, it is preferable
15 that a region between the maximum current passing region 56 and the edge 10a of the
steel strip 10, and at least a part of the depressed portions of the shielding plate be
opposite to each other as shown in FIG 9B in order for a repulsive force to be reliably
generated between the eddy current flowing through the shielding plate 30 1 and the eddy
current flowing through the steel strip 10.
20 100531
In addition, in this embodiment, a description has been made with respect to a
case in which the two depressed portions are formed in the shielding plate as an example,
but the number of the depressed portion formed in the shielding plate is not limited.
In addition, in this embodiment, an illustration has been made with respect to a
25 case in which the shape of the depressed portions 51 and 52 is a rhombic shape as an
example. However, the shape of the depressed portions 5 1 and 52 may be any shape as
46
long as the eddy current may be made to flow through the steel strip 10 along the edge
portion of the depressed portions 51 and 52. The shape of the depressed portions 51
and 52 may be, for example, an ellipse, a rectangle other than a rhombic shape, or other
square shapes. At this time, when a depressed portion in which the length in the sheet
5 conveyance direction is longer than that in a direction orthogonal to the sheet conveyance
direction is formed, the eddy current can be easily made to flow along an edge portion of
the depressed portion. Therefore, it is preferable to form a depressed portion in which
the length in the sheet conveyance direction is longer than that in the direction orthogonal
to the sheet conveyance direction. In addition, the shape of the depressed portion in the
10 shielding plate is not necessary to have a closed shape. For example, the depressed
portion may be formed in an end portion of the shielding plate.
Furthermore, copper is normally used for the upper side heating coil 24 and the
lower side heating coil 28, but a conductor (metal) other than copper may be used. In
addition, an induction heating system other than the continuous annealing line may be
15 adopted. In addition, the dimensions of the cores 23 and 27 shown in FIG. 2A may be
appropriately determined within a range in which the cores 23 and 27 are not
magnetically saturated. Here, the generation of magnetic saturation in the cores 23 and
27 may be determined from magnetic field strength [Alm] that is calculated from the
current flowing through the heating coils 24 and 28.
20 In addition, in the above-described embodiments, both of the upper side inductor
21 and the lower side inductor 22 are provided as an example, but either the upper side
inductor 21 or the lower side inductor 22 may be provided. Furthermore, the size of the
gap is not particularly limited.
[0054]
25 In addition, all of the above-described embodiments of the present invention
illustrate only a specific example for executing the present invention, and a technical
47
scope of the present invention is not limited to the embodiments. That is, the present
invention may be executed with various forms without departing from the technical
scope or critical features thereof.
5 Industrial Applicability
[0055]
It is possible to provide a control unit of an induction heating unit, an induction
heating system, and a control method of the induction heating unit, in which a
temperature distribution in the sheet width direction of a conductive sheet is made more
10 uniform compared to that in the conventional techniques, even when the sheet
conveyance speed of the conductive sheet varies in a case where the conductive sheet is
heated using a transverse type induction heating unit.
Reference Symbol List
15 [0056]
10: Steel strip (Conductive sheet)
20: Induction heating unit
23,27: Core (Magnetic core)
24: Upper side heating coil (Heating coil)
28: Lower side heating coil (Heating coil)
3 1 a to 3 1 d: Shielding plate
5 1,52: Depressed portion (Valley portion)
100,200: Control unit of induction heating unit
1 10: Rectifying unit
120: Reactor
130: Magnetic energy recovery switch (MERS)
48
13 1 to 134: First to fourth reverse conductivity type semiconductor switches
140: Gate control unit
150: Output current setting unit
160: AC power supply
170: Current transformer (Current measuring unit)
1 80: Frequency setting unit
2 1 0: Output transformer
30 1 : Shielding plate
S1 to S4: Semiconductor switches
Dl to D4: Diodes

What is claimed is:
1. A control unit of an induction heating unit, in which the control &it controls an AC
power output to a heating coil of a transverse type induction heating unit allowing an
5 alternating magnetic field to intersect a sheet surface of a conductive sheet which is being
conveyed to inductively heat the conductive sheet, the control unit comprising:
a magnetic energy recovery switch which outputs the AC power to the heating
coil;
a frequency setting unit which sets an output frequency in response to at least
10 one of a relative permeability, a resistivity, and a sheet thickness of the conductive sheet;
and
a gate control unit which controls a switching operation of the magnetic energy
recovery switch on the basis of the output frequency set by the frequency setting unit.
15 2. The control unit of the induction heating unit according to claim 1,
wherein the frequency setting unit acquires an attribute information which
specifies the relative permeability, resistivity, and sheet thickness of the conductive sheet,
and selects a frequency corresponding to the acquired attribute information as the output
fiequency with reference to a table in which the relative permeability, resistivity, and
20 sheet thickness of the conductive sheet, and the frequency are correlated with each other
and are registered in advance.
3. The control unit of the induction heating unit according to claim 1 or 2, further
comprising:
25 an output current setting unit which sets an output current value in response to at
least one of the relative permeability, resistivity, and sheet thickness of the conductive
5 0
sheet;
a current measuring unit which measures an alternating current which flows
through the induction heating unit; and
a power supply unit which supplies a DC power to the magnetic energy recovery
5 switch and adjusts an alternating current which is measured by the current measuring unit
to the output current value which is set by the output current setting unit,
wherein the magnetic energy recovery switch is supplied with the DC power by
the power supply unit and outputs the AC power to the heating coil.
10 4. The control unit of the induction heating unit according to claim 3,
wherein the output current setting unit acquires an attribute information which
specifies the relative permeability, resistivity, and sheet thickness of the conductive sheet,
and selects a current value corresponding to the acquired attribute information as the
output current value with reference to a table in which the relative permeability,
15 resistivity, and sheet thickness of the conductive sheet, and the current value are
correlated with each other and are registered in advance.
5. The control unit of the induction heating unit according to any one of claims 1 to 4,
further comprising:
20 an output transformer which is disposed between the magnetic energy recovery
switch and the induction heating unit, lowers an AC voltage which is output from the
magnetic energy recovery switch, and outputs the lowered AC voltage to the heating coil.
6. The control unit of the induction heating unit according to any one of claims 1 to 5,
25 wherein the magnetic energy recovery switch includes,
first and second AC terminals which are connected to one end and an other end
of the heating coil, respectively,
first and second DC terminals which are connected to an output terminal of a
power supply unit,
a first reverse conductivity type semiconductor switch which is connected
5 between the first AC terminal and the first DC terminal,
a second reverse conductivity type semiconductor switch which is connected
between the first AC terminal and the second DC terminal,
a third reverse conductivity type semiconductor switch which is connected
between the second AC terminal and the second DC terminal,
10 a fourth reverse conductivity type semiconductor switch which is connected
between the second AC terminal and the first DC terminal, and
a capacitor which is connected between the first and second DC terminals;
the first reverse conductivity type semiconductor switch and the fourth reverse
conductivity type semiconductor switch are connected in series in such a manner that
15 conduction directions at the time of a switch-off become opposite to each other;
the second reverse conductivity type semiconductor switch and the third reverse
conductivity type semiconductor switch are connected in series in such a manner that
conduction directions at the time of the switch-off become opposite to each other;
the first reverse conductivity type semiconductor switch and the third reverse
20 conductivity type semiconductor switch have the same conduction direction at the time
of the switch-off as each other;
the second reverse conductivity type semiconductor switch and the fourth
reverse conductivity type semiconductor switch have the same conduction direction at
the time of the switch-off as each other; and
25 the gate control unit controls a switching operation time of the first and third
reverse conductivity type semiconductor switches and a switching operation time of the
second and fourth reverse conductivity type semiconductor switches on the basis of the
output frequency which is set by the frequency setting unit.
7. An induction heating system which allows an alternating magnetic field to intersect a
5 sheet surface of a conductive sheet which is being conveyed to inductively heat the
conductive sheet, the induction heating system comprising:
the control unit of the induction heating unit according to any one of claims 1 to 6;
a heating coil which is disposed to face the sheet surface of the conductive sheet;
a core around which the heating coil is wound; and
10 a shielding plate which is disposed to face a region including an edge of the conductive
sheet in a width direction and is formed from a conductor having a relative permeability
of 1.
8. The induction heating system according to claim 7,
15 wherein the shielding plate has a depressed portion.
9. The induction heating system according to claim 8,
wherein the shielding plate is disposed in such a manner that a region, which is
closer to the edge of the conductive sheet than a region in which an eddy current flowing
20 to the conductive sheet becomes a maximum, and the depressed portion face each other.
10. A method of controlling an induction heating unit by controlling an AC power,
which is output to a heating coil of a transverse type induction heating unit allowing an
alternating magnetic field to intersect a sheet surface of a conductive sheet which is being
25 conveyed to inductively heat the conductive sheet, the method comprising:
outputting the AC power to the heating coil by a magnetic energy recovery
switch;
setting an output frequency in response to at least one of a relative permeability,
a resistivity, and a sheet thickness of the conductive sheet; and
controlling a switching operation of the magnetic energy recovery switch on the
5 basis of the output frequency which is set.
11. The method of controlling the induction heating unit according to claim 10,
wherein the output frequency is set by acquiring an attribute information which
specifies the relative permeability, resistivity, and sheet thickness of the conductive sheet,
10 and by selecting a frequency corresponding to the acquired attribute information as the
output frequency with reference to a table in which the relative permeability, resistivity,
and sheet thickness of the conductive sheet, and the frequency are correlated with each
other and are registered in advance.
15 12. The method of controlling the induction heating unit according to claim 10 or 11,
the method further comprising:
setting an output current value in response to at least one of the relative
permeability, resistivity, and sheet thickness of the conductive sheet;
measuring an alternating current which flows to the induction heating unit; and
20 supplying an DC power, which is necessary for adjusting an alternating current
which is measured to the output current value which is set, to the magnetic energy
recovery switch.
13. The method of controlling the induction heating unit according to claim 12, .
25 wherein the output current value is set by acquiring an attribute information
which specifies the relative permeability, resistivity, and sheet thickness of the
54
conductive sheet, and by selecting a current value corresponding to the acquired attribute
information as the output current value with reference to a table in which the relative
permeability, resistivity, and sheet thickness of the conductive sheet, and the current
value are correlated with each other and are registered in advance.
5
14. The method of controlling the induction heating unit according to any one of claims
10 to 13,
wherein an AC voltage which is output fiom the magnetic energy recovery
switch is lowered by an output transformer, and the lowered AC voltage is output to the
10 heating coil.
15. The method of controlling the induction heating unit according to any one of claims
1Oto 14,
wherein the magnetic energy recovery switch includes,
15 first and second AC terminals which are connected to one end and the other end
of the heating coil, respectively,
first and second DC terminals which are connected to an output terminal of the
power supply unit,
a first reverse conductivity type semiconductor switch which is connected
20 between the first AC terminal and the first DC terminal,
a second reverse conductivity type semiconductor switch which is connected
between the first AC terminal and the second DC terminal,
a third reverse conductivity type semiconductor switch which is connected
between the second AC terminal and the second DC terminal,
25 a fourth reverse conductivity type semiconductor switch which is connected
between the second AC terminal and the first DC terminal, and