1. A 3-level power conversion device, comprising: a plurality of power conversion main circuits each configured to convert a DC voltage into an AC voltage having an arbitrary frequency and amplitude and vice versa, the plurality of power conversion main circuits being connected to each other; wherein the plurality of power conversion main circuits are arranged in parallel rows to each other in a structure body in which a switching element structure body having power switching elements of same operation units being arrayed and a diode element structure body having diode elements being arrayed are configured in mounting regardless of up/down and left/right.

2. The 3-level power conversion device (1) according to claim 1, wherein the switching element structure body has an array of constructs in each of which two or more power switching elements each capable of detecting application of an overvoltage are connected in series; and each of the power conversion main circuits stops, when an overvoltage is applied to one of the power switching elements thereof connected in series, operation of the other power switching elements connected in series.

3. The 3-level power conversion device according to claim 1, wherein each of the plurality of power conversion main circuits includes: a first switching element structure body connected at one end thereof to a positive electrode side DC terminal; a second switching element structure body connected between the first switching element structure body and an AC terminal; a fourth switching element structure body connected at one end thereof to a negative electrode side DC terminal; and a third switching element structure body connected between the fourth switching element structure body and the AC terminal; and the diode element structure body includes a first diode element 28 connected from a neutral point to other end of the first switching element structure body and a second diode element connected from the neutral point to other end of the fourth switching element structure body.

4. The 3-level power conversion device according to claim 3, wherein the first switching element structure body and the fourth switching element structure body are arranged in plane symmetry across a bus connected to the neutral point.

5. The 3-level power conversion device according to claim 3, wherein the first diode element and the second diode element configuring the diode element structure body are arranged in plane symmetry.

6. The 3-level power conversion device according to claim 5, wherein the second switching element structure body and the third switching element structure body are arranged in plane symmetry across the diode element structure body.

Specification
[Title of the Invention] 3-level power conversion device
[Technical Field]
[0001]
The present invention relates to a 3-level power conversion device
configured using a plurality of power switching elements.
[Background Art]
[0002]
A power conversion device has an AC power generation function for
operating a plurality of power switching elements to convert AC power into a
voltage equivalent to an AC voltage instruction of an arbitrary amplitude and
frequency and a DC power generation function for performing conversion
reverse to that of the AC power generation function. A power conversion
device capable of outputting a positive voltage, a negative voltage and a zero
voltage to the AC terminal side is referred to as 3-level power conversion device.
The 3-level power conversion device includes a circuit configuration having, for
example, four kinds of switching operation divisions. The 3-level power
conversion device applies an instruction signal of a switching pattern to gate
drivers in response to the AC voltage instruction to perform an on/off operation
of the power switching elements and outputs a voltage equivalent to the AC
voltage instruction from an AC output end thereof. Also it is possible for the
3-level power conversion device to convert an AC voltage of an arbitrary
amplitude and frequency into a DC voltage.
[0003]
Generally, in order to increase the output capacity of a 3-level power
conversion device for which power switching elements are used, a method is
available in which a plurality of power conversion cells (power switching
element aggregates) in which a plurality of power conversion main circuits are
aggregated in a box-shaped housing are connected in parallel to each other.
Each of the power conversion cells includes the four kinds of switching
operation divisions described above.
[0004]
Together with increase of the capacity of an AC induction motor in
recent years, the 3-level power conversion device are demanded to have an
3
increased capacity and a reduced size. The solving means of the abstract of
Patent Document 1 describes: “In a 3-level power conversion device, power
conversion modules 1 to 4 each including a switching element and a reflux
diode are arranged in a power conversion module aggregate 20 such that the
longitudinal direction thereof coincides with a direction parallel to the bottom
face of a device housing. The power conversion modules 1 to 4 are arrayed
and arranged in order in a direction parallel to the device housing within a range
of a defined length, and the power conversion modules 1 to 4 within a range
exceeding the defined length are arranged on a different stage.”
[Prior Art Document]
[Patent Document]
[0005]
[Patent Document 1] JP-2014-116995-A
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0006]
In the power conversion device described above, a conventional
power conversion cell is configured such that parts are arranged in a plane such
that a 3-level power conversion device by one phase is included. If, in such a
configuration as just described, two or more series of power switching elements
are configured in order to increase an application voltage, then there is the
possibility that the circuit scale may be increased to increase the size of the
power conversion device.
Similarly, also where the power switching elements are configured in
parallel rows in order to increase the power capacity of the device, there is the
possibility that the degree of freedom of the design may be decreased by
restriction in mounting and, as a result, the size of the power conversion device
may increase.
[0007]
Further, when an accident such as damage to conduction occurs with
the power switching element, in order to restore the power conversion device, it
is necessary for the power switching elements to have a uniformized
characteristic among the parallel rows. Therefore, not only the power
conversion cell including the damaged power conversion switching element but
4
also some other power conversion cell that forms a parallel construct to the
power conversion cell are included in a range of exchange. Therefore, since
the exchange range is great in comparison with the failure range, there is the
possibility that the restoration time and the restoration expense may increase.
In addition, when a failure such as short-circuiting occurs with a
power switching element in a power conversion cell during operation of the
power conversion device, there is the possibility that an influence may spread in
a chain also to some other power switching element on the path of the shortcircuiting.
Therefore, prevention of secondary damage upon a failure is
demanded.
Therefore, it is a subject of the present disclosure to implement
downsizing of a power conversion device and reduce secondary damage upon a
failure.
[Means for Solving the Problems]
[0008]
In order to solve the subject described above, there is provided a 3-
level power conversion device including a plurality of power conversion main
circuits each configured to convert a DC voltage into an AC voltage having an
arbitrary frequency and amplitude and vice versa, the plurality of power
conversion main circuits being connected to each other. The plurality of power
conversion main circuits are arranged in parallel rows to each other in a
structure body in which a switching element structure body having power
switching elements of same operation units being arrayed and a diode element
structure body having diode elements being arrayed are configured in mounting
regardless of up/down and left/right.
The other means will be described in the description of the preferred
embodiment.
[Effects of the Invention]
[0009]
With the present invention, a power conversion device can be
provided which can achieve downsizing thereof and can reduce secondary
damage upon a failure.
[Brief Description of the Drawings]
[0010]
5
[FIG. 1] FIG. 1 is a block diagram of a 3-level power conversion
device according to an embodiment.
[FIG. 2] FIG. 2 is a circuit diagram depicting the 3-level power
conversion circuit according to the embodiment.
[FIG. 3] FIG. 3 is a circuit diagram depicting details of an IGBT cell.
[FIG. 4] FIG. 4 is a view illustrating that a failure occurs with the 3-
level power conversion circuit according to the embodiment.
[FIG. 5] FIG. 5 is a view illustrating that the 3-level power conversion
circuit according to the present embodiment stops after the failure.
[FIG. 6] FIG. 6 is a front elevational view of the 3-level power
conversion circuit.
[FIG. 7] FIG. 7 is a circuit diagram depicting a 3-level power
conversion circuit for one phase.
[FIG. 8] FIG. 8 is a front elevational view of a power conversion cell.
[FIG. 9] FIG. 9 is a side elevational view of the power conversion cell.
[FIG. 10] FIG. 10 is a perspective view of the power conversion cell.
[FIG. 11] FIG. 11 is a front elevational view depicting a clamp diode
cell.
[FIG. 12] FIG. 12 is a side elevational view depicting the clamp diode
cell.
[FIG. 13] FIG. 13 is a perspective view depicting the clamp diode cell.
[FIG. 14] FIG. 14 is a block diagram of a 3-level power conversion
device of a comparative example.
[FIG. 15] FIG. 15 is a circuit diagram depicting the 3-level power
conversion circuit of the comparative example.
[FIG. 16] FIG. 16 is a circuit diagram depicting details of an IGBT
element and a gate driver.
[FIG. 17] FIG. 17 is a view illustrating that a failure occurs with the 3-
level power conversion circuit of the comparative example.
[FIG. 18] FIG. 18 is a view illustrating that damage to conduction of
elements is caused by a failure of the 3-level power conversion circuit of the
comparative example.
[Mode for Carrying out the Invention]
[0011]
6
In the following, a mode for carrying out the present invention is
described with reference to the drawings. It is to be noted that, in the drawings,
like elements are denoted by like reference characters and overlapping
description of them is omitted herein.
3-level power conversion device in a comparative example and the
present embodiment are inverters that convert a DC voltage into an AC voltage
of an arbitrary frequency and amplitude. The 3-level power conversion device
is applied to driving control of an AC induction motor used, for example, in a
steel rolling plant.
[0012]
<<3-level power conversion device of Comparative Example>>
FIG. 14 is a block diagram of a 3-level power conversion device 9 of a
comparative example.
The 3-level power conversion device 9 is configured from three-phase
circuits including a U-phase circuit 91u, a V-phase circuit 91v and a W-phase
circuit 91w. The V-phase circuit 91v and the W-phase circuit 91w have a
configuration same as that of the U-phase circuit 91u.
The U-phase circuit 91u is configured from power conversion main
circuits 92a to 92c connected in parallel to each other. The power conversion
main circuits 92a to 92c are connected to a positive side DC power supply bus
(hereinafter referred to as “P bus”), a neutral point bus (hereinafter referred to as
“C bus”) and a negative side DC power supply bus (hereinafter referred to as “N
bus”), respectively, such that DC voltages are supplied to the power conversion
main circuits 92a to 92c and an AC voltage of the U-phase is outputted to a node
UACO of the power conversion main circuits 92a to 92c. The power
conversion main circuits 92b and 92c have a circuit configuration same as that
of the power conversion main circuit 92a.
[0013]
The V-phase circuit 91v is configured from power conversion main
circuits 92d to 92f connected in parallel to each other. The power conversion
main circuits 92d to 92f are connected to the P bus, C bus and N bus,
respectively, such that DC voltages are supplied to the power conversion main
circuits 92d to 92f and an AC voltage of the V-phase is outputted to a node
VACO of the power conversion main circuits 92d to 92f. The power
7
conversion main circuits 92e and 92f have a circuit configuration same as that of
the power conversion main circuit 92d.
The W-phase circuit 91w is configured from power conversion main
circuits 92g to 92i connected in parallel to each other. The power conversion
main circuits 92g to 92i are connected to the P bus, C bus and N bus,
respectively, such that DC voltages are supplied to the power conversion main
circuits 92g to 92i and an AC voltage of the W-phase is outputted to a node
WACO of the power conversion main circuits 92g to 92i. The power
conversion main circuits 92h and 92i have a circuit configuration same as that of
the power conversion main circuit 92g.
In the following description, where the power conversion main
circuits 92a to 92i are not specifically distinguished from each other, each of
them is referred to simply as power conversion main circuit 92.
[0014]
A load L is connected to the nodes UACO, VACO and WACO, and an
AC voltage is applied to the load L. The load L is, for example, an AC
induction motor.
The U-phase circuit 91u, V-phase circuit 91v and W-phase circuit 91w
have configurations same as each other among the three phases. By connecting
a plurality of power conversion main circuits 92, which are similar to each other,
in parallel to each other for the three phases of the U-phase circuit 91u, V-phase
circuit 91v and W-phase circuit 91w, the output capacity of the 3-level power
conversion device 9 can be increased.
[0015]
FIG. 15 is a circuit diagram depicting the power conversion main
circuit 92 of the comparative example.
The power conversion main circuit 92 is a neutral point clamped
(NPC) type power conversion circuit in which IGBT elements Q11 to Q14 are
used as power switching elements and clamping to a neutral point is performed
by diode elements D3 and D4. Each of the IGBT elements Q11 to Q14 is an
element including an insulated gate bipolar transistor (IGBT: hereinafter referred
to as “IGBT”) and a reflux diode connected between the collector and the
emitter. A gate driver 18 is connected to each of the IGBT elements Q11 to
Q14 and controlled by a control unit 90. Details of the IGBT elements Q11 to
8
Q14 are hereinafter described with reference to FIG. 16.
[0016]
In the comparative example, the IGBT element Q11 at the positive
side outputs a potential of the P bus to a node ACO through the IGBT element
Q12. A DC voltage is applied to the P bus by a DC power supply Ep.
The IGBT element Q12 at a first neutral point and the IGBT element
Q13 at a second neutral point output a potential of the C bus to the node ACO
when the IGBT elements Q11 and Q12 are off.
[0017]
The IGBT element Q14 at the negative side outputs a potential of the
N bus to the node ACO through the IGBT element Q13. The IGBT elements
Q11 to Q14 are connected in series between the P bus and the N bus. The gate
drivers 18 are connected to the control unit 90 and individually supply a driving
signal to the gate of the IGBT elements Q11 to Q14.
[0018]
Further, the power conversion main circuit 92 is configured including
two clamp diode elements D3 and D4. Each of the diode element D3 for the
positive side clamping and the diode element D4 for the negative side clamping
is a 2-in-1 diode element. The diode element D3 for the positive side clamping
for outputting a potential of the C bus is connected between the connection point
of the IGBT elements Q11 and Q12 and the C bus. Further, the diode element
D4 for the negative side clamp for outputting a potential of the C bus is
connected between the connection point of the IGBT elements Q13 and Q14 and
the C bus. In the power conversion main circuit 92, the IGBT elements Q11 to
Q14 perform switching operation to output AC power from the node ACO that is
an outputting point to the load L.
[0019]
<>
When a pulse of a positive voltage is to be outputted to the node ACO,
the control unit 90 controls the IGBT elements Q11 and Q12 to an on state and
controls the IGBT elements Q13 and Q14 to an off state. Consequently, the
potential of the P bus is outputted to the node ACO.
On the other hand, when the zero voltage is to be outputted to the node
ACO, the control unit 90 controls the IGBT elements Q12 and Q13 to an on
9
state and controls the IGBT elements Q11 and Q14 to an off state.
Consequently, the potential of the C bus is outputted to the node ACO.
[0020]
When a pulse of a negative voltage is to be outputted to the node ACO,
the control unit 90 controls the IGBT elements Q13 and Q14 to an on state and
controls the IGBT elements Q11 and Q12 to an off state. Consequently, the
potential of the N bus is outputted to the node ACO.
The control unit 90 of the power conversion main circuit 92 outputs a
pulse width modulation (PWM) pulse configured from such a positive pulse and
a negative pulse centered at the zero point as described above. Therefore, an
AC voltage having a waveform more proximate to a sine waveform can be
outputted to the node ACO in comparison with a 2-level power conversion
circuit.
[0021]
FIG. 16 is a circuit diagram depicting details of the IGBT element Q11,
gate driver 18 and so forth.
The gate driver 18, an overvoltage detection circuit 19 and an
overvoltage suppression circuit 20 are connected to the IGBT element Q11 of
the comparative example.
The overvoltage suppression circuit 20 is configured by including a
Zener diode (not depicted) connected in parallel between the collector and the
gate of the IGBT element Q11. If an overvoltage is applied between the
collector and the gate of the overvoltage suppression circuit 20, then current
flows through the Zener diode and charging current is supplied to the gate of the
IGBT element Q11. Consequently, the impedance of the IGBT element Q11 is
decreased thereby to protect the IGBT element Q11 from the overvoltage.
The overvoltage detection circuit 19 and the gate driver 18 are
connected between the gate and the emitter of the IGBT element Q11. The
gate driver 18 supplies an instruction signal to the gate of the IGBT element Q11.
The overvoltage detection circuit 19 decides that an overvoltage is generated if
it recognizes that an output signal of the overvoltage suppression circuit 20 and
the instruction signal supplied from the gate driver 18 to the IGBT element Q11
do not coincide with each other. Consequently, the control unit 90 (refer to FIG.
15) can stop operation to prevent damage to conduction of an element.
10
[0022]
<>
The power conversion main circuit 92 of the comparative example has
the possibility that secondary element damage may occur when damage to
conduction occurs with one of the IGBT elements Q11 to Q14. This problem
is described with reference to FIGS. 17 and 18.
FIG. 17 is a view illustrating that a failure occurs with the power
conversion main circuit 92 of the comparative example.
Electric current flowing to the power conversion main circuit 92 when
the IGBT elements Q11 and Q12 are placed into a on state and the IGBT
elements Q13 and Q14 are placed in an off state is indicated by a route 73. The
current flows from the P bus to the load L through the IGBT elements Q11 and
Q12 and the node ACO. At this time, if the IGBT element Q13 is turned on by
mistake or damage to conduction occurs, then also some other element is
damaged as depicted in FIG. 18.
[0023]
FIG. 18 is a view illustrating that damage to conduction occurs with
some elements by failure.
Electric current flowing to the power conversion main circuit 92 at
this time is indicated by a route 74. The current flows from the P bus to the C
bus through the IGBT elements Q11, Q12 and Q13 and the diode element D4.
By such DC short-circuiting as just described, the IGBT elements Q11 and Q12
and the diode element D4 are broken.
While a voltage corresponding to four elements of the IGBT elements
Q11 to Q14 is applied to the IGBT element Q11 connected in series and the
voltage of the IGBT element Q11 increased, further damage can be suppressed
by detecting a failure of a neighboring IGBT element using the overvoltage
detection circuit 19 (refer to FIG. 16) and stopping driving of the neighboring
IGBT element. However, if it is taken into consideration that the IGBT
element Q13 suffers from damage by an overvoltage, it is necessary to exchange
the IGBT elements Q11 to Q14 and the diode element D4 after stopping of
operation. In other words, a construct for one phase must be exchanged.
[0024]
<>
A 3-level power conversion device 1 depicted in FIG. 1 includes a Uphase
circuit 11u, a V-phase circuit 11v and a W-phase circuit 11w for three
phases each using three power conversion main circuits 12 (refer to FIG. 2) for
converting a DC voltage into an AC voltage of an arbitrary frequency and
amplitude. The V-phase circuit 11v and the W-phase circuit 11w have a
configuration same as that of the U-phase circuit 11u.
[0025]
The U-phase circuit 11u is configured by including power conversion
main circuits 12a to 12c connected in parallel to each other. The power
conversion main circuits 12a to 12c are connected to the P bus, C bus and N bus,
respectively, and supplied with a DC voltage and output a U-phase AC voltage
to the node UACO. The circuit configuration of the power conversion main
circuits 12b and 12c is same as that of the power conversion main circuit 12a.
Further, the power conversion main circuits 12a to 12c share IGBT cells 14 to
17 in each of which IGBT elements of same operation units are arrayed and a
clamp diode cell 13 in which diodes are arrayed. The power conversion main
circuits 12a to 12c are connected in parallel to each other in a structure body in
which the IGBT cells 14 to 17 and the clamp diode cell 13 are configured in
mounting regardless of up/down and left/right. Since the IGBT elements and
the diodes are cellularized in a same operation unit, exchange in a same
operation unit can be easily performed.
[0026]
The IGBT cell 14 of FIG. 1 is denoted by “QP” indicative of an
operation unit and operates similarly to the IGBT element Q11 (refer to FIG. 15)
of the comparative example. The IGBT cell 15 is denoted by “QPC” indicative
of an operation unit and operates similarly to the IGBT element Q12 (refer to
FIG. 15) of the comparative example. The IGBT cell 16 is denoted by “QNC”
indicative of an operation unit and operates similarly to the IGBT element Q13
(refer to FIG. 15) of the comparative example. The IGBT cell 17 is denoted by
“QN” indicative of an operation unit and operates similarly to the IGBT element
Q14 (refer to FIG. 15) of the comparative example. The clamp diode cell 13 is
denoted by “D” indicative of an operation unit.
[0027]
12
The V-phase circuit 11v is configured by including power conversion
main circuits 12d to 12f connected in parallel to each other. The power
conversion main circuits 12d to 12f are connected to the P bus, C bus and N bus,
respectively, and supplied with a DC voltage and output a V-phase AC voltage
to the node VACO. The power conversion main circuits 12e and 12f have a
configuration same as that of the power conversion main circuit 12d. Further,
the power conversion main circuits 12d to 12f share the IGBT cells 14 to 17 in
each of which IGBT elements of same operation units are arrayed and the clamp
diode cell 13 in which diodes of same operation units are arrayed.
Consequently, the IGBT elements and the diodes can be exchanged in the same
operation unit.
[0028]
The W-phase circuit 11w is configured by including power conversion
main circuits 12g to 12i connected in parallel to each other. The power
conversion main circuits 12h to 12i are connected to the P bus, C bus and N bus,
respectively, and supplied with a DC voltage and output a W-phase AC voltage
to the node WACO. The power conversion main circuits 12g and 12i have a
configuration same as that of the power conversion main circuit 12g. Further,
the power conversion main circuits 12g to 12i share the IGBT cells 14 to 17 in
which IGBT elements of same operation units are arrayed and the clamp diode
cell 13 in which diodes of same operation units are arrayed. Consequently, the
IGBT elements and the diodes can be exchanged in the same operation unit.
In the following description, when the power conversion main circuits
12a to 12i are not specifically distinguished, each of them is referred to simply
as power conversion main circuit 12.
[0029]
In the U-phase circuit 11u, V-phase circuit 11v and W-phase circuit
11w, elements are arranged in three parallel rows in each cell such that three
power conversion main circuits 12 are configured. Therefore, the output of the
AC power of the 3-level power conversion device 1 is an output of the sum of
the AC power of the three power conversion main circuits 12.
[0030]
FIG. 2 is a circuit diagram depicting each power conversion main
circuit 12 in the present embodiment.
13
The power conversion main circuit 12 of the present embodiment is
different from the power conversion main circuit 92 of the comparative example
(refer to FIG. 15) in that a power conversion cell is configured by connecting
two IGBT elements, which perform switching operations similar to each other,
in series. Consequently, a rated voltage of the power conversion cell can be
shared by the two IGBT elements, and consequently, an inputted DC voltage can
be increased to approximately two times and increase of the capacity of the
output can be implemented.
[0031]
The power conversion main circuit 12 is an NPC type power
conversion circuit in which the IGBT cells 14 to 17 are used as power
conversion cells and clamping to the neutral point is performed by the clamp
diode cell 13. The IGBT cell 14 is configured from a series connection of the
IGBT elements Q1 and Q2 that perform switching operations similar to each
other. The IGBT cell 15 is configured from a series connection of the IGBT
elements Q3 and Q4 that perform switching operations similar to each other.
The IGBT cell 16 is configured from a series connection of the IGBT elements
Q5 and Q6 that perform switching operations similar to each other. The IGBT
cell 17 is configured from a series connection of the IGBT elements Q7 and Q8
that perform switching operations similar to each other. Each of the IGBT cells
14 to 17 is a switching element structure body in which two IGBT elements
connected in series are arrayed over three rows. Meanwhile, the clamp diode
cell 13 is a diode element structure body in which the diode elements D1 and D2
are arrayed over three rows. Consequently, as depicted in FIG. 1, the three
power conversion main circuits 12 can be arrayed in parallel to each other.
Each of the IGBT elements Q1 to Q8 is an element including an insulating gate
bipolar transistor and a reflux diode connected between the collector and the
emitter.
[0032]
FIG. 3 is a circuit diagram depicting details of an IGBT cell.
Similarly as in the comparative example depicted in FIG. 16, the gate
driver 18, overvoltage detection circuit 19 and overvoltage suppression circuit
20 are connected to each of the IGBT elements Q1 and Q2.
If an overvoltage is applied between the collector and the gate of any
14
of the IGBT elements Q1 and Q2, then the overvoltage suppression circuit 20
supplies charging current to the gate of the current IGBT element.
Consequently, the impedance of the IGBT element Q1 or Q2 is decreased and
the IGBT elements Q1 and Q2 are protected from the overvoltage.
The overvoltage detection circuit 19 and the gate driver 18 are
connected between the gate and the emitter of each of the IGBT elements Q1
and Q2. The gate driver 18 supplies an instruction signal to the gate of the
IGBT element Q1 or Q2. The overvoltage detection circuit 19 decides that an
overvoltage is generated in each IGBT element by recognizing that the output
signal of the overvoltage suppression circuit 20 and the instruction signal
flowing from the gate driver 18 to the IGBT elements Q1 and Q2 do not
coincide with each other.
[0033]
Consequently, the IGBT cell 14 can detect application of an
overvoltage to the IGBT elements Q1 and Q2. When an overvoltage is applied
to one of the IGBT elements Q1 and Q2, the control unit 10 of the power
conversion main circuit 12 stops operation of the other IGBT element to reduce
secondary damage upon accident.
Similarly, the IGBT cell 15 can detect application of an overvoltage to
the IGBT elements Q3 and Q4. When an overvoltage is applied to one of the
IGBT elements Q3 and Q4, the power conversion main circuit 12 stops
operation of the other IGBT element to reduce secondary damage upon accident.
[0034]
The IGBT cell 16 can detect application of an overvoltage to the IGBT
elements Q5 and Q6. When an overvoltage is applied to one of the IGBT
elements Q5 and Q6, the power conversion main circuit 12 stops operation of
the other IGBT element to reduce secondary damage upon accident.
The IGBT cell 17 can detect application of an overvoltage to the IGBT
elements Q7 and Q8. When an overvoltage is applied to one of the IGBT
elements Q7 and Q8, the power conversion main circuit 12 stops operation of
the other IGBT element to reduce secondary damage upon accident.
[0035]
In the present embodiment, the IGBT cell 14 at the positive side
outputs a potential of the P bus to the node ACO. The DC voltage is applied to
15
the P bus by a DC power supply Ep.
The IGBT cell 15 at a first neutral point and the IGBT cell 16 at a
second neutral point output a potential of the C bus to the node ACO.
[0036]
The IGBT cell 17 at the negative side outputs a potential of the N bus
to the node ACO. The IGBT cells 14 to 17 are connected in series between the
P bus and the N bus. The gate drivers 18 are connected to the control unit 10
and supply a driving signal to the gate of the IGBT elements Q1 to Q8 provided
in the IGBT cells 14 to 17.
[0037]
Further, the power conversion main circuit 12 is configured by
including two diode elements D1 and D2 for clamping. Each of the diode
element D1 for the positive side clamping and the diode element D2 for the
negative side clamping is a 2-in-1 diode element. The diode element D1 for
the positive side clamping for outputting a potential of the C bus is connected
between a connection point of the IGBT cells 14 and 15 and the C bus. Further,
the diode element D2 for the negative side clamping for outputting a potential of
the C bus is connected between a connection point of the IGBT cells 16 and 17
and the C bus. In the power conversion main circuit 12, when the IGBT
elements Q1 to Q8 included in the IGBT cells 14 to 17 perform a switching
operation, AC power is outputted from the node ACO that is an outputting point
to the load L.
[0038]
<>
When a pulse of a positive voltage is to be outputted to the node ACO,
the control unit 10 controls the IGBT elements Q1 to Q4 provided in the IGBT
cells 14 and 15 to an on state and controls the IGBT elements Q5 to Q8 provided
in the IGBT cells 16 and 17 to an off state. Consequently, the potential of the P
bus is outputted to the node ACO.
Meanwhile, when the zero voltage is to be outputted to the node ACO,
the control unit 10 controls the IGBT elements Q3 to Q6 provided in the IGBT
cells 15 and 16 to an on state and controls the IGBT elements Q1 and Q2
provided in the IGBT cell 14 and the IGBT elements Q7 and Q8 provided in the
IGBT cell 17 to an off state. Consequently, the potential of the C bus is
16
outputted to the node ACO.
[0039]
When a pulse of a negative voltage is to be outputted to the node ACO,
the control unit 10 controls the IGBT elements Q5 to Q8 provided in the IGBT
cells 16 and 17 to an on state and controls the IGBT elements Q1 to Q4 provided
in the IGBT cells 14 and 15 to an off state. Consequently, the potential of the
N bus is outputted to the node ACO.
The control unit 10 of the power conversion main circuit 12 can
output, using such a pulse width modulation (PWM) pulse formed from a
positive pulse and a negative pulse centered at the zero point as described
hereinabove, an AC voltage of a waveform nearer to a sine wave in comparison
with that of a 2-level power conversion circuit to the node ACO.
[0040]
<>
In the power conversion main circuit 12 of the present embodiment,
two IGBT elements that perform switching operations similar to each other are
connected in series to the IGBT cells 14 to 17. According to this connection
scheme, since a rated voltage of the IGBT cells 14 to 17 is shared by two IGBT
elements, an inputted DC voltage can be increased to approximately twice.
Also, there is an advantageous effect that secondary element damage is reduced
when some IGBT element is damaged in conduction. This is described with
reference to FIGS. 4 and 5.
[0041]
FIG. 4 is a view illustrating that a failure occurs with the power
conversion main circuit 12 in the present embodiment.
Electric current flowing in the power conversion main circuit 12 when
the IGBT elements Q1 to Q4 are turned on and the IGBT elements Q5 to Q8 are
turned off is indicated by a route 71. The current flows from the P bus to the
load L through the IGBT elements Q1 to Q4 and the node ACO. At this time,
it is assumed that the IGBT element Q5 turns on by mistake or is damaged in
conduction.
[0042]
FIG. 5 is a view illustrating that the IGBT Q5 stops after the failure.
As indicated by a route 72, a voltage applied to the P bus is applied
17
also to the collector terminal of the IGBT element Q6. To the IGBT element
Q6, a voltage corresponding to five elements of the IGBT elements Q1 to Q5 is
applied, and the voltage of the IGBT element Q6 rises. However, the control
unit 10 detects a failure of the neighboring IGBT element by the overvoltage
suppression circuit 20 and the overvoltage detection circuit 19 and stops
operation of the power conversion main circuit 12. Consequently, the power
conversion main circuit 12 can avoid further damage.
[0043]
In the present embodiment, since the IGBT element Q6 is off, DC
short-circuit current is not generated. Therefore, what is to be exchanged due
to the failure is only the IGBT element Q5 and the IGBT element Q6 that has
been damaged by an overvoltage. Since the 3-level power conversion device 1
of the present embodiment involves cellularization for each switching operation
unit, only the IGBT cell 16 is an exchange point. Therefore, the number of
parts to be exchanged decreases in comparison with the comparative example.
Accordingly, the power conversion main circuit 12 of the present embodiment
can reduce secondary damage by a failure of an IGBT element and suppress the
recovery time and the recovery expense in comparison with the power
conversion main circuit 92 of the comparative example.
It is to be noted that each of the IGBT cells 14 to 17 may be a series
connection of three or more IGBT elements that perform similar switching
operations to each other and is not restricted particularly.
[0044]
<>
FIG. 6 depicts an example of arrangement of unit structures of the
IGBT cells 14 to 17 and the clamp diode cell 13 configuring the power
conversion main circuit 12 in the present embodiment.
The unit structures of FIG. 6 are arranged in three parallel rows in the
depthwise direction of FIG.6 within a structure body configured from the IGBT
cells 14 to 17 and the clamp diode cell 13 mounted regardless of up/down and
left/right. Thus, it is possible to easily provide the three power conversion
main circuits 12a to 12c being arrayed in parallel to each other, for example, in
the U-phase circuit 11u.
18
It is to be noted that, in the unit structure example of FIG. 6, all of the
IGBT cells 14 to 17 have a same structure. Consequently, the number of types
of exchange parts for preparations for a failure of an IGBT cell can be restricted
to one, and the number of kinds and the stock number of exchange parts can be
reduced.
[0045]
The IGBT cell 14 disposed at the left upper position in FIG. 6 is
configured including an IGBT element Q1 connected at the collector terminal
thereof to a bus 21 and at the emitter terminal thereof to another bus 22 and an
IGBT element Q2 connected at the collector terminal thereof to the bus 22 and
at the emitter terminal thereof to a further bus 23.
In this IGBT cell 14, the collector terminal of the IGBT element Q1 is
connected to the P bus through the bus 21, and the emitter terminal of the IGBT
element Q2 is connected to the IGBT cell 15 through the buses 23 and 24.
[0046]
The IGBT cell 15 disposed at the right upper position in FIG. 6 is
configured including an IGBT element Q3 connected at the collector terminal
thereof to a bus 25 and connected at the emitter terminal thereof to another bus
26 and an IGBT element Q4 connected at the collector terminal thereof to the
bus 26 and at the emitter terminal thereof to a further bus 27.
In this IGBT cell 15, the collector terminal of the IGBT element Q3 is
connected to the emitter terminal of the IGBT element Q2 through the buses 25,
24 and 23 and to the cathode terminal of a diode element D1 through the buses
25 and 32. Further, the emitter terminal of the IGBT element Q4 is connected
to a bus 28 through the bus 27. This bus 28 serves as the node ACO that
outputs power outputted from the power conversion main circuit 12.
[0047]
The clamp diode cell 13 disposed at a right central position in FIG. 6
includes the diode element D1 connected at the anode terminal thereof to a bus
31 and at the cathode terminal thereof to the bus 32. The clamp diode cell 13
further includes a diode element D2 connected at the cathode terminal thereof to
a bus 33 and at the anode terminal thereof to another bus 34.
The anode terminal of the diode element D1 is connected to a bus 30
having a potential equal to that of the C bus through the bus 31. The cathode
19
terminal of the diode element D1 is connected to the connection point of the
IGBT cell 14 and the IGBT cell 15 through the bus 32.
[0048]
The cathode terminal of the diode element D2 is connected to the bus
30 having a potential equal to that of the C bus through the bus 33. The anode
terminal of the diode element D1 is connected to the connection point of the
IGBT cell 16 and the IGBT cell 17 through the bus 44.
The diode elements D1 and D2 and the buses 31 and 32 and the buses
33 and 34 connected to the diode elements D1 and D2, respectively, are
arranged in a plane symmetrical relationship to each other.
[0049]
The IGBT cell 17 disposed at a left lower position in FIG. 6 is
configured including an IGBT element Q8 connected at the emitter terminal
thereof to a bus 41 and at the collector terminal thereof to another bus 42, and an
IGBT element Q7 connected at the emitter terminal thereof to the bus 42 and at
the collector terminal thereof to a further bus 43.
In this IGBT cell 17, the emitter terminal of the IGBT element Q8 is
connected to an N bus through the bus 41, and the collector terminal of the
IGBT element Q7 is connected to the IGBT cell 16 through the buses 43 and 44.
[0050]
The IGBT cell 16 disposed at a right lower position in FIG. 6 is
configured including an IGBT element Q6 connected at the emitter terminal
thereof to a bus 45 and at the collector terminal thereof to another bus 46, and an
IGBT element Q5 connected at the emitter terminal thereof to the bus 46 and at
the collector terminal thereof to a further bus 47.
In this IGBT cell 16, the emitter terminal of the IGBT element Q6 is
connected to the collector terminal of the IGBT element Q7 through the buses
45, 44 and 43 and connected to the anode terminal of the diode element D2
through the buses 45 and 34. Further, the collector terminal of the IGBT
element Q5 is connected to the bus 28 that serves as the node ACO through the
bus 47.
[0051]
As depicted in FIG. 6, the IGBT cell 14 and the IGBT cell 17 are
arranged in plane symmetry across the bus 30. The IGBT cell 14 is arranged in
20
a vertically reversed relationship from the IGBT cell 17.
Further, the IGBT cell 15 and the IGBT cell 16 are arranged in plane
symmetry across the clamp diode cell 13. The IGBT cell 15 is arranged in a
vertically reversed relationship from the IGBT cell 16.
Further, the diode element D1 and the diode element D2 of the clamp
diode cell 13 are arranged in plane symmetry relative to each other.
Consequently, the width of the 3-level power conversion device 1 can be
suppressed.
[0052]
Further, a plurality of power conversion main circuits 12 can be
arranged in parallel rows by arraying IGBT elements and diode elements of the
IGBT cells 14 to 17 and the clamp diode cell 13 in the depthwise direction of the
3-level power conversion device 1. Therefore, by increasing the number of
cell wiring buses to a number equal to the number of parallel rows, it is possible
to increase the output capacity of the 3-level power conversion device 1 without
increasing the dimension of the 3-level power conversion device 1 in the
widthwise direction and the vertical direction in FIG. 6.
[0053]
Further, in the 3-level power conversion device 1, the buses 32 and 34
are arranged in such a manner as to sandwich the buses 31, 30 and 33
therebetween, and the buses 25, 26 and 45, 46 are arranged in such a manner as
to sandwich the buses 32 and 34 therebetween. Further, in the 3-level power
conversion device 1, the buses 21, 22, 23 and 24 and the buses 41, 42, 43 and 44
are arranged in such a manner as to sandwich the bus 30 therebetween. With
the 3-level power conversion device 1, by arranging the IGBT cells 14 to 17 and
positioning the buses in the proximity of each other in this manner, it is possible
to reduce the distance between the buses to reduce the mutual inductance of
them thereby to reduce an influence of a bounce voltage of the IGBT elements
upon switching operation. Here, the buses are preferably arranged at distances
at which a short-circuiting accident by contact does not occur and besides the
mutual inductance between the buses decreases even if the tolerance in part
dimension is taken into consideration. The distance between two buses
preferably is, for example, 0.1 to 10.0 mm, and more preferably is 1.0 to 5.0 mm.
[0054]
21
The widthwise dimension of the 3-level power conversion device 1 of
the present embodiment can be suppressed to approximately 1,400 mm. A
conventional product having a similar capacity has a widthwise dimension of
approximately 3,000 mm when it is compared in a three-parallel row
configuration that is a maximum parallel row configuration in the present
embodiment.
[0055]
It is to be noted that, since the structure body in the present
embodiment is complicated, a circuit diagram in which the IGBT cells 14 to 17
and the clamp diode cell 13 are arranged similarly as in FIG. 6 in order to
promote understandings is depicted in FIG. 7.
[0056]
FIG. 7 depicts the circuit diagram of the power conversion main
circuit 12 depicted in FIG. 2 in arrangement similar to that of FIG. 6.
At the left side in FIG. 7, the P bus, C bus and N bus are arranged.
The IGBT cells 14 and 15 are connected in series between the P bus and the
node ACO. The IGBT cells 16 and 17 are connected in series between the
node ACO and the N bus. The clamp diode cell 13 includes diode elements D1
and D2. The diode element D1 is connected from the C bus toward the
connection node of the IGBT cells 14 and 15. The diode element D2 is
connected from the connection node of the IGBT cells 16 and 17 toward the C
bus.
The IGBT cell 14 is a first switching element structure body
connected at one end thereof to a positive electrode side DC terminal of the P
bus. The IGBT cell 15 is a second switching element structure body connected
between the IGBT cell 14 and the node ACO (AC terminal).
Further, the IGBT cell 17 is a fourth switching element structure body
connected at one end thereof to a negative electrode side DC terminal of the N
bus. The IGBT cell 16 is a third switching element structure body connected
between the IGBT cell 17 and the node ACO (AC terminal).
The diode element D1 is a first diode element connected to the other
end of the IGBT cell 14 from the C bus (neutral point). The diode element D2
is connected to the other end of the IGBT cell 17 from the C bus (neutral point).
[0057]
22
<>
FIGS. 8 to 10 depict an example of a structure of the IGBT cells 14 to
17 configuring the power conversion main circuit 12 in the present embodiment.
Since all of the IGBT cells 14 to 17 have a similar configuration, description
here is given of the IGBT cell 14 while description of the IGBT cells 15 to 17 is
omitted herein.
FIG. 8 is a front elevational view of the IGBT cell 14. In FIG. 8, the
IGBT cell 14 reversed in the upward and downward direction is viewed from a
direction similar to that in FIG. 6.
[0058]
The IGBT cell 14 is an aggregate of electrical parts configured from
an array of three sets of IGBT elements Q1 and Q2 and buses 21, 22 and 23
arrayed on heat sinks 50a and 50b. It is to be noted that, in FIG. 8, only one set
from the array of the three sets is depicted while the other two sets are hidden
behind the one set. The IGBT cell 14 is configured further including a metal
plate 53 to which the heat sinks 50a and 50b are fixed, a support member 51 that
supports the metal plate 53 and the heat sinks 50a and 50b, and another metal
plate 52 in the form of a flat plate.
The metal plate 53 fixes the heat sinks 50a and 50b and further fixes
the support member 51. The support member 51 is formed such that it has a Ushaped
cross section and is fixed at the upper side thereof to the metal plate 53.
The metal plate 52 is in the form of a flat plate and is fixed to the support
member 51 at the opposite side to the metal plate 53 and the heat sinks 50a and
50b.
[0059]
FIG. 9 is a side elevational view of the IGBT cell 14. In FIG. 9, the
IGBT cell 14 is viewed from the left side face in FIG. 8.
Referring to FIG. 9, the array of the three elements of the IGBT
elements Q2 and the buses 23, metal plate 53, support member 51 and metal
plate 52 of the IGBT cell 14 are depicted. The buses 22 and 21 and the IGBT
element Q1 are hidden behind the IGBT elements Q2 and the buses 23. The
heat sinks 50a and 50b are hidden behind the metal plate 53.
[0060]
FIG. 10 is a perspective view of a power conversion cell. In FIG. 10,
23
the IGBT cell 14 is viewed from the oblique right upper side in FIG. 8.
Referring to FIG. 10, it is depicted that the IGBT cell 14 is configured
from the array of the three sets of the IGBT elements Q1 and Q2 and the buses
21, 22 and 23 on the heat sinks 50a and 50b. The three sets of the buses 21, 22
and 23 are disposed so as to form a same plane on the upper side in FIG. 10.
The three sets of the buses 21, 22 and 23 are disposed in the proximity of the
three rows of the planar buses 30 (refer to FIG. 6).
Each of the buses 21 connects the P bus and the collector terminal of
an IGBT element Q1 in an equal potential. Each of the buses 22 connects the
emitter terminal of the IGBT element Q1 and the collector terminal of the IGBT
element Q2 to each other. Each of the buses 23 connects the emitter terminal
of the IGBT element Q2 and the collector terminal of an IGBT element Q3 of
the adjacent IGBT cell 15.
[0061]
The three rows of the IGBT elements Q1 are fixed to the heat sink 50b,
and the three rows of the IGBT elements Q2 are fixed to the heat sink 50a. The
heat sinks 50a and 50b are fixed to the metal plate 53 and supported by the
support member 51. The support member 51 is fixed to the metal plate 52 in
the form of a flat plate.
[0062]
<>
FIGS. 11 to 13 depict an example of a structure of the clamp diode
cell 13 configuring the power conversion main circuit 12 in the present
embodiment.
FIG. 11 is a front elevational view of the clamp diode cell 13. In FIG.
11, the clamp diode cell 13 is viewed in an upward and downwardly reversed
relationship from a direction similar to that of FIG. 6.
[0063]
The clamp diode cell 13 is an aggregate of electrical parts configured
from an array of three sets of a diode element D1 and buses 31 and 32 on a heat
sink 60p and another array of three sets of a diode element D2 and buses 33 and
34 on a heat sink 60n. It is to be noted that, in FIG. 11, only one set from
among the array of the three sets is depicted while the other two sets are hidden
behind the one set. The heat sink 60p is fixed to one face of a support plate 61
24
while the heat sink 60n is fixed to the other face of the support plate 61.
The diode elements D1 are P-side (2-in-1) clamp diodes. The diode
elements D2 are N-side (2-in-1) clamp diodes.
[0064]
Each of the buses 32 connects the connection point between the
emitter terminal of an IGBT element Q2 and the collector terminal of an
associated IGBT element Q3 and the cathode terminal of the diode element D1
as depicted in FIG. 6. The bus 31 connects the anode terminal of the diode
element D1 and the bus 30 that is a neutral point.
The bus 34 connects the connection point between the collector
terminal of the IGBT element Q7 and the emitter terminal of the IGBT element
Q6 and the anode terminal of the diode element D2 as depicted in FIG. 6. The
bus 33 connects the cathode terminal of the diode element D2 and the bus 30
that is a neutral point.
[0065]
FIG. 12 is a side elevational view depicting a clamp diode cell 13. In
FIG. 12, the clamp diode cell 13 is viewed from the left side face side in FIG. 11.
Referring to FIG. 12, the clamp diode cell 13 includes three sets of a
diode element D1 and buses 31 and 32 arrayed on the heat sink 60p and three
sets of a diode element D2 and buses 33 and 34 arrayed on the heat sink 60n.
[0066]
FIG. 13 is a perspective view depicting a clamp diode cell 13. In FIG.
13, the clamp diode cell 13 is viewed from the oblique right upper side in FIG.
11.
Referring to FIG. 13, a manner of the clamp diode cell 13 in which
three sets of a diode element D1 and buses 31 and 32 are arrayed on the heat
sink 60p is illustrated. This heat sink 60p is fixed to one of faces of the support
plate 61. While three sets of a bus 33 and one set of a bus 34 on the nearer side
are depicted on the lower side of the support plate 61, three sets of a diode
element D2 and two sets of a bus 34 and a heat sink 60n on the interior side are
hidden by the support plate 61.
[0067]
Although the embodiment of the present invention has been described
in detail, the present invention is not limited to the embodiment and it is a matter
25
of course that the present invention can be carried out in various other
modifications and applications without departing from the subject matter
described in the claims.
[0068]
For example, the embodiment described above has been described in
detail in order to facilitate understandings of the present invention, and the
present invention is not necessarily limited to the embodiment including all
features described hereinabove. Further, it is possible to add part of constructs
of each embodiment to constructs of a different embodiment. Further, it is
possible to add, delete or replace part of constructs of each embodiment to, from
or with other constructs. In addition, those of controls lines and information
lines which are considered necessary for description are depicted, but all control
lines or information lines necessary for a product are not necessarily depicted.
Actually, it may be considered that almost all constructs are connected to each
other.
[0069]
The present invention can be carried out in such modified forms, for
example, as described in the following items (a) to (e).
(a) The power conversion main circuit of the present invention is not limited to
that of the NPC type but may be configured as that of the A-NPC (Advanced-
NPC) type.
(b) The conversion operation of the power conversion main circuit is not limited
to an inverter operation but may be a converter operation.
(c) The power conversion cell is not limited to a series connection circuit of two
power switching elements.
(d) The number of parallel rows of power conversion cells is not limited to three
rows.
(e) The power switching element to be used in the power conversion cell is not
limited to an IGBT but may be, for example, a gate turn-off thyristor.
[Description of Reference Symbols]
[0070]
1: 3-level power conversion device
10: Control unit
11u: U-phase circuit
26
11v: V-phase circuit
11w: W-phase circuit
12, 12a to 12i: Power conversion main circuit
13: Clamp diode cell (diode element structure body)
14: IGBT cell (first switching element structure body)
15: IGBT cell (second switching element structure body)
16: IGBT cell (third switching element structure body)
17: IGBT cell (fourth switching element structure body)
18: Gate driver
19: Overvoltage detection circuit
20: Overvoltage suppression circuit
21 to 28, 30 to 34: Bus
41 to 48: Bus
50a, 50b: Heat sink
51: Support member
52: Metal plate
53: Metal plate
60p, 60n: heat sink
61: Support plate
9: 3-level power conversion device
90: Control unit
91u: U-phase circuit
91v: V-phase circuit
91w: W-phase circuit
92, 92a to 92i: Power conversion main circuit

We Claim:
1. A 3-level power conversion device, comprising:
a plurality of power conversion main circuits each configured to
convert a DC voltage into an AC voltage having an arbitrary frequency and
amplitude and vice versa, the plurality of power conversion main circuits being
connected to each other; wherein
the plurality of power conversion main circuits are arranged in parallel
rows to each other in a structure body in which
a switching element structure body having power switching elements
of same operation units being arrayed and
a diode element structure body having diode elements being arrayed
are configured in mounting regardless of up/down and left/right.
2. The 3-level power conversion device (1) according to claim 1,
wherein the switching element structure body has an array of
constructs in each of which two or more power switching elements each capable
of detecting application of an overvoltage are connected in series; and
each of the power conversion main circuits stops, when an overvoltage
is applied to one of the power switching elements thereof connected in series,
operation of the other power switching elements connected in series.
3. The 3-level power conversion device according to claim 1,
wherein each of the plurality of power conversion main circuits
includes:
a first switching element structure body connected at one end thereof
to a positive electrode side DC terminal;
a second switching element structure body connected between the first
switching element structure body and an AC terminal;
a fourth switching element structure body connected at one end
thereof to a negative electrode side DC terminal; and
a third switching element structure body connected between the fourth
switching element structure body and the AC terminal; and
the diode element structure body includes a first diode element
28
connected from a neutral point to other end of the first switching element
structure body and a second diode element connected from the neutral point to
other end of the fourth switching element structure body.
4. The 3-level power conversion device according to claim 3,
wherein the first switching element structure body and the fourth
switching element structure body are arranged in plane symmetry across a bus
connected to the neutral point.
5. The 3-level power conversion device according to claim 3,
wherein the first diode element and the second diode element
configuring the diode element structure body are arranged in plane symmetry.
6. The 3-level power conversion device according to claim 5, wherein the
second switching element structure body and the third switching element
structure body are arranged in plane symmetry across the diode element
structure body.