FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERTER, MOTOR DRIVE SYSTEM, AND POWER CONVERSION
METHOD
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Field
[0001] The present disclosure relates to a power
converter that converts input power into desired output
power, a motor drive system, and a power conversion method.5
Background
[0002] As one of power converters that convert input
power into desired output power, there is a power converter
having a configuration in which a smoothing capacitor is10
connected to a converter circuit such as a diode rectifier
circuit. For this power converter, studies have been made
for protecting the smoothing capacitor from a high voltage
when an alternating current input voltage to the converter
circuit is high.15
[0003] For example, in a power converter described in
Patent Literature 1, a smoothing capacitor (first
capacitor) having high breakdown voltage and low
capacitance and a smoothing capacitor (second capacitor)
having low breakdown voltage and high capacitance are20
connected in parallel. In the power converter described in
Patent Literature 1, when a potential difference across the
first capacitor is higher than or equal to a reference
value, a switch connected in series with the second
capacitor is turned off so that the second capacitor is25
protected.
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent Application30
Laid-open No. 2012-60855
Summary of Invention
3
Problem to be solved by the Invention
[0005] However, in the technique of Patent Literature 1
above, when the potential difference across the first
capacitor is higher than or equal to the reference value,
the operation is continued only with the first capacitor5
having low capacitance. At this time, in a case where the
power converter has a configuration in which an inverter
circuit and a motor are connected in addition to the
converter circuit and the smoothing capacitor, the decrease
in the capacitance of the smoothing capacitor results in10
pulsation of various voltages and various currents. As a
result, in the power converter of Patent Literature 1, the
ripple current in the smoothing capacitor increases to
exceed the rated ripple current in some cases. When the
ripple current exceeding the rated ripple current flows15
through the smoothing capacitor for a long time, there is a
problem that the life of the smoothing capacitor is
significantly reduced.
[0006] The present disclosure has been made in view of
the above, and an object thereof is to provide a power20
converter that can prevent a reduction in life of a
smoothing capacitor connected to a converter circuit.
Means to Solve the Problem
[0007] In order to solve the above problem and achieve25
the object, a power converter of the present disclosure
comprises: a first converter circuit to convert an
alternating current voltage from an alternating current
power supply into a direct current voltage; an inverter
circuit to convert the direct current voltage obtained by30
conversion by the first converter circuit into an
alternating current voltage, and supply the alternating
current voltage to a motor; a first smoothing unit
4
connected between the first converter circuit and the
inverter circuit, the first smoothing unit including a
first smoothing capacitor and a second smoothing capacitor,
the first smoothing capacitor having a first breakdown
voltage equal to a second voltage threshold, the second5
smoothing capacitor having a second breakdown voltage
higher than a first voltage threshold, the first voltage
threshold being a value higher than or equal to the second
voltage threshold, the first smoothing capacitor and the
second smoothing capacitor being connected in parallel; a10
first interrupting device connected in series to the first
smoothing capacitor; and a first voltage detector to detect
an applied voltage across the second smoothing capacitor.
The power converter of the present disclosure further
comprises a controller to, in a case where a first detected15
value as a detected value of the applied voltage detected
by the first voltage detector is higher than or equal to
the second voltage threshold, open the first interrupting
device and control a rotation speed of the motor such that
a ripple current flowing through the second smoothing20
capacitor is less than or equal to a rated ripple current.
Effects of the Invention
[0008] The power converter according to the present
disclosure has an effect of preventing a reduction in life25
of the smoothing capacitor connected to the converter
circuit.
Brief Description of Drawings
[0009] FIG. 1 is a diagram illustrating a configuration30
of a motor drive system including a power converter
according to a first embodiment.
FIG. 2 is a diagram illustrating a configuration of a
5
controller included in the power converter according to the
first embodiment.
FIG. 3 is a diagram illustrating an example of a
hardware configuration of the controller included in the
power converter according to the first embodiment.5
FIG. 4 is a block diagram illustrating an example of a
software configuration in the controller included in the
power converter according to the first embodiment.
FIG. 5 is a graph for explaining correlation data
indicating a relationship between motor rotation speed and10
ripple current flowing through a second smoothing capacitor
when a first interrupting device included in the power
converter according to the first embodiment is open.
FIG. 6 is a graph for explaining the motor rotation
speed that is set using the correlation data by the power15
converter according to the first embodiment.
FIG. 7 is a flowchart illustrating a procedure of
control processing by the controller of the power converter
according to the first embodiment.
FIG. 8 is a diagram illustrating a configuration of a20
motor drive system including the power converter according
to a second embodiment.
FIG. 9 is a diagram illustrating a configuration of a
controller included in the power converter according to the
second embodiment.25
FIG. 10 is a block diagram illustrating an example of
a software configuration in the controller included in the
power converter according to the second embodiment.
FIG. 11 is a diagram illustrating a configuration of a
motor drive system including the power converter according30
to a third embodiment.
FIG. 12 is a diagram illustrating a configuration of a
controller included in the power converter according to the
6
third embodiment.
FIG. 13 is a block diagram illustrating an example of
a software configuration in the controller included in the
power converter according to the third embodiment.
FIG. 14 is a flowchart illustrating a procedure of5
control processing by the controller of the power converter
according to the third embodiment.
FIG. 15 is a diagram illustrating a configuration of a
motor drive system including the power converter according
to a fourth embodiment.10
FIG. 16 is a diagram illustrating a configuration of a
controller included in the power converter according to the
fourth embodiment.
FIG. 17 is a block diagram illustrating an example of
a software configuration in the controller included in the15
power converter according to the fourth embodiment.
FIG. 18 is a flowchart illustrating a procedure of
control processing by the controller of the power converter
according to the fourth embodiment.
FIG. 19 is a diagram illustrating an example of20
another configuration of a motor drive system including the
power converter according to the fourth embodiment.
Description of Embodiments
[0010] Hereinafter, a power converter, a motor drive25
system, and a power conversion method according to
embodiments of the present disclosure will be described in
detail with reference to the drawings. The magnitude
relationship among breakdown voltages and voltage
thresholds described in first to fourth embodiments below30
is: “a breakdown voltage of a first smoothing capacitor
(first breakdown voltage)”=“a second voltage threshold”≤“a
first voltage threshold”<“a third voltage threshold”=“a
7
breakdown voltage of a second smoothing capacitor (second
breakdown voltage)”≤“a breakdown voltage of a third
smoothing capacitor”. These breakdown voltages and voltage
thresholds will be described later.
[0011] First Embodiment.5
FIG. 1 is a diagram illustrating a configuration of a
motor drive system including a power converter according to
a first embodiment. A motor drive system 301 is connected
to an alternating current power supply 1. The motor drive
system 301 includes a power converter 10, a motor 6, and a10
current detector 32.
[0012] The motor drive system 301 is a system that
converts input power into desired output power by the power
converter 10 and supplies the converted power to the motor
6. In the motor drive system 301, the alternating current15
power supply 1 inputs alternating current power to the
power converter 10, and the motor 6 is driven by three-
phase power generated by the power converter 10.
[0013] The power converter 10 is a motor controller that
controls the motor 6 by supplying the power to the motor 6.20
The power converter 10 includes a first converter circuit 2,
a first smoothing unit 11, an inverter circuit 5, and a
first interrupting device 21. The first smoothing unit 11
includes a first smoothing capacitor 3 and a second
smoothing capacitor 4.25
[0014] The power converter 10 also includes a first
voltage detector 31 and a controller 7A. The controller 7A
controls, on the basis of detection signals from the first
voltage detector 31 and the current detector 32, opening
and closing of the first interrupting device 21 and30
switching on and off of each switching element of the
inverter circuit 5.
[0015] The alternating current power supply 1 is a
8
commercial alternating current system, a private power
generator, or the like. The motor 6 is a permanent magnet
motor including a three-phase, Y-connected stator in which
three-phase windings including a U-phase winding, a V-phase
winding, and a W-phase winding are connected in a Y shape,5
and a permanent magnet rotor. Note that the alternating
current power supply 1 and the motor 6 are not limited to
the above configuration, and, for example, the stator in
the motor 6 may be a three-phase, Δ-connected stator in
which the three-phase windings are connected in a Δ shape.10
[0016] The first converter circuit 2 converts an
alternating current voltage from the alternating current
power supply 1 into a direct current voltage. The first
converter circuit 2 is a diode rectifier circuit in which
four diode elements are bridge-connected. Note that the15
type of the diode element used in the first converter
circuit 2 is not limited to a fast recovery diode (FRD) or
soft recovery diode (SBD). The diode element used in the
first converter circuit 2 may be an element using material
such as silicon carbide (SiC), gallium nitride (GaN), or20
gallium oxide (Ga2O3). Also, the first converter circuit 2
may be a circuit that uses switching elements to form a
step-up circuit, a step-down circuit, a step-up/down
circuit, or the like.
[0017] The alternating current power supply 1 and the25
first converter circuit 2 are connected via connection
lines 61 and 62. The first converter circuit 2 and the
inverter circuit 5 are connected via connection lines 63
and 64.
[0018] A connection point 51 disposed on the connection30
line 63 and a connection point 53 disposed on the
connection line 64 are connected via a connection line 65.
A connection point 52 disposed on the connection line 63
9
and a connection point 54 disposed on the connection line
64 are connected via a connection line 66. The connection
point 52 is a connection point on a side of a subsequent
stage of the connection point 51, and the connection point
54 is a connection point on a side of a subsequent stage of5
the connection point 53.
[0019] The first interrupting device 21 and the first
smoothing capacitor 3 are connected in series on the
connection line 65. That is, the connection point 51 is
connected to the connection point 53 via the first10
interrupting device 21 and the first smoothing capacitor 3.
When the first interrupting device 21 is closed, the first
smoothing capacitor 3 and the connection point 51 are
connected, and when the first interrupting device 21 is
opened, the first smoothing capacitor 3 and the connection15
point 51 are disconnected. The second smoothing capacitor
4 is disposed on the connection line 66. That is, the
connection point 52 is connected to the connection point 54
via the second smoothing capacitor 4.
[0020] Accordingly, in the first smoothing unit 11 of20
the power converter 10, the first smoothing capacitor 3 and
the second smoothing capacitor 4 are connected in parallel
to each other. When the first voltage threshold is a value
higher than or equal to the second voltage threshold
(“first voltage threshold”≥“second voltage threshold”), the25
first breakdown voltage that is the breakdown voltage of
the first smoothing capacitor (low breakdown voltage
capacitor) 3 has the same value as the second voltage
threshold.
[0021] Moreover, the second breakdown voltage that is30
the breakdown voltage of the second smoothing capacitor 4
is higher than the first voltage threshold. The first
smoothing capacitor 3 and the second smoothing capacitor 4
10
smooth the direct current voltage, which is obtained by
conversion by the first converter circuit 2, by converting
the direct current voltage into a stable direct current
voltage having a constant magnitude.
[0022] Note that the first smoothing capacitor 3 and the5
second smoothing capacitor 4 have capacitances that: allow
the ripple current less than or equal to the rated ripple
current to flow through each smoothing capacitor under all
predetermined rotation speed conditions with the first
interrupting device 21 closed; and allow the ripple current10
less than or equal to the rated ripple current to flow
through the second smoothing capacitor 4 under at least one
of the rotation speed conditions with the first
interrupting device 21 open.
[0023] Furthermore, the first smoothing capacitor 3 and15
the second smoothing capacitor 4 each have breakdown
voltage and capacitance such that all the predetermined
rotation speed conditions are satisfied when the first
interrupting device 21 is closed, and at least one of the
rotation speed conditions is satisfied when the first20
interrupting device 21 is open. The first smoothing
capacitor 3 and the second smoothing capacitor 4 each have
the breakdown voltage and the capacitance such that a
ripple amount (ripple voltage) of an applied voltage across
each smoothing capacitor is less than or equal to a value25
(multiplied value) obtained by multiplying the breakdown
voltage of each smoothing capacitor by a percentage (for
example, 20 to 40%) determined by chemical properties of
the smoothing capacitor. That is, the smoothing capacitors
each having the breakdown voltage and capacitance such that30
the ripple amount of the applied voltage is less than or
equal to the multiplied value are used, whereby the
operation is performed under all the predetermined rotation
11
speed conditions when the first interrupting device 21 is
closed, and the operation is performed under at least one
of the rotation speed conditions when the first
interrupting device 21 is open.
[0024] With the first smoothing capacitor 3 and the5
second smoothing capacitor 4 each having the capacitance
described above, the power converter 10 can realize optimum
operation with the capacitor capacitance that is needed.
[0025] The first smoothing unit 11 is not limited to the
above configuration, and may have any configuration as long10
as the voltage can be properly smoothed. For example, the
first smoothing unit 11 may have a configuration in which
three or more smoothing capacitors including the first
smoothing capacitor 3 and the second smoothing capacitor 4
are connected in parallel, and an interrupting device is15
connected in series to all the smoothing capacitors each
having a breakdown voltage lower than or equal to the
second voltage threshold. With this configuration, the
power converter 10 can realize optimum operation with the
capacitor capacitance that is needed. Also, the first20
smoothing unit 11 may be configured such that at least one
of the first smoothing capacitor 3 and the second smoothing
capacitor 4 includes a plurality of smoothing capacitors
connected in series. In a case where the first smoothing
unit 11 includes three or more smoothing capacitors25
connected in parallel as well, each of the smoothing
capacitors has the breakdown voltage and capacitance
described above.
[0026] For the first interrupting device 21, a
mechanical relay is used, but a switching element formed of30
a semiconductor including a wide band gap semiconductor may
be used. That is, for the first interrupting device 21, a
switching element such as an insulated gate bipolar
12
transistor (IGBT), a metal oxide semiconductor field effect
transistor (MOSFET), a SiC-MOSFET, a GaN-FET, a GaN-high
electron mobility transistor (HEMT), or a Ga2O3-MOSFET may
be used.
[0027] The inverter circuit 5 converts the direct5
current voltage, which is obtained by conversion by the
first converter circuit 2 and smoothed by the first
smoothing capacitor 3 and the second smoothing capacitor 4,
into the alternating current voltage and supplies the
alternating current voltage to the motor 6.10
[0028] In the inverter circuit 5, three switching
element pairs (hereinafter referred to as arms) each
including two switching elements connected in series are
connected in parallel, and a midpoint of each arm is
connected to the corresponding winding of the motor 6. The15
power converter 10 can drive the motor 6 at a desired
number of revolutions (rotation speed) by controlling the
alternating current voltage, that is, alternating current
power output from the inverter circuit 5. The switching
element included in the inverter circuit 5 and formed of a20
semiconductor including a wide band gap semiconductor is
not limited to an IGBT or a MOSFET, and may be a SiC-MOSFET,
a GaN-FET, a GaN-HEMT, or a Ga2O3-MOSFET.
[0029] The first voltage detector 31 detects the applied
voltage across the second smoothing capacitor 4 and outputs25
the detected value as a detected value Vdc1 to the
controller 7A. The applied voltage across the second
smoothing capacitor 4 and the applied voltage across the
first smoothing capacitor 3 are the same. Therefore, the
first voltage detector 31 may detect the applied voltage30
across the first smoothing capacitor 3. The detected value
Vdc1 detected by the first voltage detector 31 is a first
detected value.
13
[0030] The current detector 32 is disposed on a
connection line connecting the inverter circuit 5 and the
motor 6, detects a phase current flowing from the inverter
circuit 5 to the motor 6, and outputs a detected value as a
detected value Iuvw to the controller 7A. The current5
detector 32 may be a current detector using a current
transformer (CT), or may be a current detector using a
shunt resistor.
[0031] FIG. 2 is a diagram illustrating a configuration
of the controller included in the power converter according10
to the first embodiment. The controller 7A included in the
power converter 10 of the first embodiment receives the
detected value Vdc1 transmitted from the first voltage
detector 31. The controller 7A also receives the detected
value Iuvw transmitted from the current detector 32.15
[0032] In addition, on the basis of the detected value
Vdc1 from the first voltage detector 31, the controller 7A
transmits a switching signal X to the first interrupting
device 21. The switching signal X is a signal for
switching an open/closed state of the first interrupting20
device 21.
[0033] Moreover, on the basis of the detected value Vdc1
from the first voltage detector 31 and the detected value
Iuvw from the current detector 32, the controller 7A
transmits drive signals S1 to S6 to the switching elements25
of the inverter circuit 5. The drive signals S1 to S6 are
signals for controlling switching on and off of the
switching elements of the inverter circuit 5. The
controller 7A can thus control opening and closing of the
first interrupting device 21 and switching on and off of30
the switching elements of the inverter circuit 5.
[0034] Note that, in a case where the first converter
circuit 2 includes switching elements, the controller 7A
14
transmits the drive signals S1 to S6 for controlling
switching on and off of the switching elements of the first
converter circuit 2 to the first converter circuit 2.
[0035] FIG. 3 is a diagram illustrating an example of a
hardware configuration of the controller included in the5
power converter according to the first embodiment. The
controller 7A is configured using processing circuitry such
as a microcomputer. The controller 7A is configured using
a processor 100 and a storage 101. Although not
illustrated in FIG. 3, the storage 101 includes a volatile10
storage such as a random access memory and a non-volatile
auxiliary storage such as a flash memory. Instead of the
flash memory, the storage 101 may include the auxiliary
storage such as a hard disk.
[0036] In the case where the controller 7A incudes the15
processor 100 and the storage 101, the functions of the
controller 7A are implemented by software, firmware, or a
combination of software and firmware. The software or
firmware is described as a program and stored in the
storage 101.20
[0037] The processor 100 executes the program input from
the storage 101, thereby outputting the switching signal X
and the drive signals S1 to S6. In this case, the program
is input from the auxiliary storage to the processor 100
via the volatile storage. This program can also be said to25
be a program for causing the controller 7A to execute the
functions implemented by the processing circuitry. This
program may be provided by a storage medium storing the
program, or may be provided by other means such as a
communication medium. The processor 100 may also output30
data such as a calculation result to the volatile storage
of the storage 101, or may save the data in the auxiliary
storage via the volatile storage.
15
[0038] The processor 100 is, for example, a central
processing unit (CPU) or a system large scale integration
(LSI), the CPU being also referred to as a central
processor, a processing unit, an arithmetic unit, a
microprocessor, a microcomputer, or a digital signal5
processor (DSP).
[0039] FIG. 4 is a block diagram illustrating an example
of a software configuration in the controller included in
the power converter according to the first embodiment. The
software in the controller 7A includes a position/speed10
specification unit 200, a dq-axis coordinate transformation
unit 201, an opening/closing signal generation unit 202A, a
rotation command generation unit 203, a current control
unit 204, and a drive signal generation unit 205.
[0040] In order to perform vector control on the motor 6,15
the position/speed specification unit 200 estimates a
magnetic pole position and a rotation speed of the motor 6
using a voltage command value output from the current
control unit 204 and a dq-axis current Idq output from the
dq-axis coordinate transformation unit 201. As such an20
estimation method, an estimation method called an adaptive
observer is generally known. Note that the estimation
method executed by the position/speed specification unit
200 is not limited to the above estimation method, and any
estimation method may be used as long as the magnetic pole25
position and the rotation speed of the motor 6 can be
properly estimated by the estimation method. Also, a
position detector may be attached to the motor 6 and be
used as the position/speed specification unit 200.
[0041] The position/speed specification unit 200 outputs30
the estimated magnetic pole position (estimated position)
to the dq-axis coordinate transformation unit 201. The
position/speed specification unit 200 also outputs the
16
estimated rotation speed (estimated speed) to the rotation
command generation unit 203 and the current control unit
204.
[0042] The dq-axis coordinate transformation unit 201
receives the detected value Iuvw transmitted from the5
current detector 32. The dq-axis coordinate transformation
unit 201 uses the estimated position of the motor 6 output
from the position/speed specification unit 200 to transform
the detected value Iuvw from the current detector 32 into a
current value (dq-axis current Idq) in dq-axis coordinates10
as rotating coordinates. The dq-axis coordinates are a
coordinate system generally used in vector control of a
rotating body such as the motor 6. The dq-axis coordinate
transformation unit 201 outputs the dq-axis current Idq to
the position/speed specification unit 200 and the current15
control unit 204.
[0043] The opening/closing signal generation unit 202A
receives the detected value Vdc1 transmitted from the first
voltage detector 31. The opening/closing signal generation
unit 202A compares the second voltage threshold (≤ first20
voltage threshold) with the detected value Vdc1. In a case
where the detected value Vdc1 is higher than or equal to
the second voltage threshold, the opening/closing signal
generation unit 202A generates the switching signal X for
opening the first interrupting device 21. On the other25
hand, in a case where the detected value Vdc1 is lower than
the second voltage threshold, the opening/closing signal
generation unit 202A generates the switching signal X for
closing the first interrupting device 21. The
opening/closing signal generation unit 202A transmits the30
generated switching signal X to the first interrupting
device 21 and the rotation command generation unit 203.
[0044] Note that the method of generating the switching
17
signal X by the opening/closing signal generation unit 202A
is not limited to the above generation method, and any
generation method may be used as long as the switching
signal X can be properly generated by the generation method.
For example, in a case where the power converter 105
includes a timer function, the opening/closing signal
generation unit 202A may generate the switching signal X
for closing the first interrupting device 21 when the first
interrupting device 21 is open for a specific time or
longer.10
[0045] The rotation command generation unit 203
generates a rotation speed command value for the motor 6 on
the basis of the switching signal X output from the
opening/closing signal generation unit 202A. Specifically,
in a case where the switching signal X is a signal as an15
instruction to close the first interrupting device 21, the
rotation command generation unit 203 freely sets the
rotation speed command value corresponding to the operation
request for the motor 6. On the other hand, in a case
where the switching signal X is a signal as an instruction20
to open the first interrupting device 21, the rotation
command generation unit 203 sets the rotation speed command
value for the motor 6 on the basis of correlation data 80
described below.
[0046] Here, the correlation data 80 will be described.25
FIG. 5 is a graph for explaining the correlation data
indicating a relationship between the motor rotation speed
and the ripple current flowing through the second smoothing
capacitor when the first interrupting device included in
the power converter according to the first embodiment is30
open.
[0047] In the graph illustrated in FIG. 5, the
horizontal axis represents the motor rotation speed that is
18
the rotation speed of the motor 6, and the vertical axis
represents the ripple current flowing through the second
smoothing capacitor 4. The correlation data 80 is data
indicating the correlation between the motor rotation speed
and an effective value of the ripple current flowing5
through the second smoothing capacitor 4 when the first
interrupting device 21 is open. Note that the correlation
data 80 may be represented by the graph as illustrated in
FIG. 5, or may be represented by table data in which the
motor rotation speed and the effective value of the ripple10
current flowing through the second smoothing capacitor 4
are associated with each other.
[0048] The correlation data 80 can be obtained by, for
example, a method such as a test or simulation actually
using the power converter 10. In this case, data actually15
acquired is subjected to linear interpolation or fitting
with an appropriate function so that, even for the motor
rotation speed at which data is not actually acquired, the
effective value of the ripple current flowing through the
second smoothing capacitor 4 can be obtained.20
[0049] When receiving the switching signal X as the
instruction to open the first interrupting device 21 from
the opening/closing signal generation unit 202A, the
rotation command generation unit 203 sets, on the basis of
the correlation data 80, the motor rotation speed at which25
the effective value of the ripple current flowing through
the second smoothing capacitor 4 is less than or equal to a
rated ripple current Ic_lim.
[0050] FIG. 6 is a graph for explaining the motor
rotation speed that is set using the correlation data by30
the power converter according to the first embodiment.
Upon receiving the switching signal X as the instruction to
open the first interrupting device 21, the rotation command
19
generation unit 203 included in the controller 7A of the
power converter 10 reads the correlation data 80.
[0051] The rotation command generation unit 203 sets the
motor rotation speed on the basis of the correlation data
80. Specifically, the rotation command generation unit 2035
acquires, from the correlation data 80, the effective value
of the ripple current flowing through the second smoothing
capacitor 4 at a motor rotation speed N1 at the time point
(hereinafter referred to as an open instruction time point
in some cases) of receiving the switching signal X as the10
instruction to open the first interrupting device 21 The
motor rotation speed N1 at the open instruction time point
may be the rotation speed command value at the open
instruction time point, or may be calculated on the basis
of the estimated speed transmitted from the position/speed15
specification unit 200 at the open instruction time point.
[0052] In a case where the motor rotation speed N1
acquired from the correlation data 80 is larger than the
rated ripple current Ic_lim, the rotation command
generation unit 203 selects the motor rotation speed (in20
FIG. 6, for example, a motor rotation speed N2) at which
the effective value of the ripple current flowing through
the second smoothing capacitor 4 is less than or equal to
the rated ripple current Ic_lim. That is, the rotation
command generation unit 203 selects, from among the motor25
rotation speeds included in the correlation data 80, the
motor rotation speed at which the effective value of the
ripple current is less than or equal to the rated ripple
current Ic_lim.
[0053] For example, the rotation command generation unit30
203 may select a motor rotation speed obtained by
subtracting a specific value from the motor rotation speed
at the rated ripple current Ic_lim, or may select a motor
20
rotation speed obtained by multiplying the motor rotation
speed at the rated ripple current Ic_lim by a specific
value (a value larger than 0 and smaller than or equal to
1). Note that the rotation command generation unit 203 may
select the motor rotation speed using not only these5
selection methods but using another selection method. The
rotation command generation unit 203 outputs the selected
motor rotation speed as the rotation speed command value.
[0054] On the other hand, in a case where the effective
value of the ripple current flowing through the second10
smoothing capacitor 4 at the motor rotation speed N1 is
less than or equal to the rated ripple current Ic_lim, the
rotation command generation unit 203 continues the
operation with the current rotation speed command value.
[0055] Note that the correlation data 80 illustrated in15
FIGS. 5 and 6 may be held in the controller 7A or may be
held in a cloud or the like. In a case where the
correlation data 80 is held in the cloud or the like, an
external device may determine the rotation speed command
value on the basis of the correlation data 80. In this20
case, the power converter 10 receives the rotation speed
command value determined by the external device and
generates a voltage command value for driving the inverter
circuit 5. Note that even in the case where the
correlation data 80 is held in the cloud or the like, the25
power converter 10 may determine the rotation speed command
value on the basis of the correlation data 80.
[0056] Furthermore, the correlation data 80 illustrated
in FIGS. 5 and 6 is not limited to the configuration
described above. The correlation data 80 may have any30
configuration as long as the relationship between the motor
rotation speed and the effective value of the ripple
current flowing through the second smoothing capacitor 4
21
when the first interrupting device 21 is open can be
properly obtained from the data. For example, a voltage
detector may be installed in the alternating current power
supply 1, and data considering dependency of an input
voltage from the alternating current power supply 1 to the5
power converter 10 may be used as the correlation data 80.
Alternatively, the detected value Vdc1 obtained from the
first voltage detector 31 may be used, and data considering
dependency of an output voltage from the power converter 10
may be used as the correlation data 80.10
[0057] The current control unit 204 generates the
voltage command value for driving the inverter circuit 5 on
the basis of the dq-axis current Idq output from the dq-
axis coordinate transformation unit 201, the rotation speed
command value output from the rotation command generation15
unit 203, and the estimated speed of the motor 6 output
from the position/speed specification unit 200. As a
method of generating such a voltage command value, a
generation method using a proportional integral (PI)
controller is generally known.20
[0058] Note that the method of generating the voltage
command value by the current control unit 204 is not
limited to the above generation method, and any generation
method may be used as long as the dq-axis current Idq is
appropriately controlled by the generation method. For25
example, in order to intentionally cause the output of the
motor 6 to pulsate, the current control unit 204 may add a
method of generating the voltage command value that causes
pulsation of the dq-axis current Idq.
[0059] On the basis of the voltage command value output30
from the current control unit 204, the drive signal
generation unit 205 generates the drive signals S1 to S6
for performing pulse width modulation (PWM) control of
22
switching on or off the switching elements of the inverter
circuit 5. The PWM control is a method generally used for
generating the drive signals S1 to S6 of the switching
elements from the voltage command value or a current
command value. The drive signal generation unit 2055
transmits the drive signals S1 to S6 generated to the
inverter circuit 5.
[0060] Among control processing executed by the
controller 7A, a description will be made of an example of
processing that generates the switching signal X and the10
rotation speed command value on the basis of the detected
value Vdc1 detected by the first voltage detector 31.
[0061] FIG. 7 is a flowchart illustrating a procedure of
the control processing by the controller of the power
converter according to the first embodiment. The flowchart15
of FIG. 7 illustrates the procedure of the processing in
which the controller 7A generates the switching signal X
and the rotation speed command value on the basis of the
detected value Vdc1.
[0062] The opening/closing signal generation unit 202A20
of the controller 7A receives the detected value Vdc1 from
the first voltage detector 31. The opening/closing signal
generation unit 202A compares the detected value Vdc1 from
the first voltage detector 31 with the second voltage
threshold, and determines whether or not “the detected25
value Vdc1 from the first voltage detector 31”≥“the second
voltage threshold” is satisfied (step ST1).
[0063] If “the detected value Vdc1 from the first
voltage detector 31”≥“the second voltage threshold” is
satisfied (Yes in step ST1), the opening/closing signal30
generation unit 202A generates and transmits the switching
signal X as the instruction to open the first interrupting
device 21 (step ST2). In this case, the opening/closing
23
signal generation unit 202A transmits the switching signal
X generated to the first interrupting device 21 and the
rotation command generation unit 203.
[0064] The rotation command generation unit 203 acquires,
from the correlation data 80, the effective value of the5
ripple current flowing through the second smoothing
capacitor 4 at the motor rotation speed N1 at the time
point of receiving the switching signal X as the
instruction to open the first interrupting device 21 That
is, the rotation command generation unit 203 acquires, from10
the correlation data 80, the effective value of the ripple
current corresponding to the motor rotation speed N1 at the
open instruction time point.
[0065] The rotation command generation unit 203 compares
the effective value of the ripple current flowing through15
the second smoothing capacitor 4 at the motor rotation
speed N1 with the rated ripple current. The rotation
command generation unit 203 determines whether or not “the
effective value of the ripple current flowing through the
second smoothing capacitor 4 at the motor rotation speed20
N1”>“the rated ripple current” is satisfied (step ST3).
[0066] If “the effective value of the ripple current
flowing through the second smoothing capacitor 4 at the
motor rotation speed N1”>“the rated ripple current” is
satisfied (Yes in step ST3), the rotation command25
generation unit 203 selects the rotation speed command
value of the motor 6 with which the effective value of the
ripple current flowing through the second smoothing
capacitor 4 is less than or equal to the rated ripple
current (step ST4). The rotation command generation unit30
203 selects, for example, the motor rotation speed N2
illustrated in FIG. 6. The rotation command generation
unit 203 outputs the selected rotation speed command value
24
to the current control unit 204.
[0067] If “the effective value of the ripple current
flowing through the second smoothing capacitor 4 at the
motor rotation speed N1”≤“the rated ripple current” is
satisfied (No in step ST3), the rotation command generation5
unit 203 continues the operation with the current rotation
speed command value (step ST5). That is, the rotation
command generation unit 203 outputs the current rotation
speed command value to the current control unit 204.
[0068] In the processing of step ST1, if “the detected10
value Vdc1 from the first voltage detector 31”<“the second
voltage threshold” is satisfied (No in step ST1), the
opening/closing signal generation unit 202A generates and
transmits the switching signal X as the instruction to
close the first interrupting device 21 (step ST6). That is,15
if “the detected value Vdc1”<“the second voltage threshold”
is satisfied with the first interrupting device 21 being
open, the opening/closing signal generation unit 202A
generates and transmits the switching signal X as the
instruction to close the first interrupting device 21. In20
this case, the opening/closing signal generation unit 202A
transmits the switching signal X generated to the first
interrupting device 21 and the rotation command generation
unit 203.
[0069] Since the first interrupting device 21 is closed,25
the rotation command generation unit 203 freely sets the
rotation speed command value of the motor 6 according to
the operation request (step ST7). The rotation command
generation unit 203 outputs the set rotation speed command
value to the current control unit 204.30
[0070] After steps ST4, ST5, and ST7, the current
control unit 204 generates the voltage command value using
the rotation speed command value output from the rotation
25
command generation unit 203, the dq-axis current Idq output
from the dq-axis coordinate transformation unit 201, and
the estimated speed of the motor 6 output from the
position/speed specification unit 200. The current control
unit 204 outputs the generated voltage command value to the5
position/speed specification unit 200 and the drive signal
generation unit 205.
[0071] On the basis of the voltage command value output
from the current control unit 204, the drive signal
generation unit 205 generates the drive signals S1 to S610
for performing PWM control of switching on or off the
switching elements of the inverter circuit 5. The drive
signal generation unit 205 transmits the drive signals S1
to S6 generated to the inverter circuit 5.
[0072] As described above, in the first embodiment, the15
first voltage detector 31 detects, as the detected value
Vdc1, the voltage applied to the second smoothing capacitor
4 having the second breakdown voltage higher than the first
voltage threshold as the breakdown voltage. The detected
value Vdc1 corresponds to the voltage applied to the first20
smoothing capacitor 3.
[0073] In a case where the detected value Vdc1 detected
by the first voltage detector 31 is higher than or equal to
the second voltage threshold, the controller 7A opens the
first interrupting device 21 connected in series to the25
first smoothing capacitor 3. Furthermore, the controller
7A controls the rotation speed of the motor 6 such that the
ripple current flowing through the second smoothing
capacitor 4 whose breakdown voltage is higher than the
first voltage threshold is less than or equal to the rated30
ripple current.
[0074] As a result, the power converter 10 can operate
with high reliability. That is, the power converter 10 can
26
operate with high reliability by keeping the ripple current
flowing through the second smoothing capacitor 4 to the
rated ripple current or less while keeping the applied
voltage across the first smoothing capacitor 3 to its
breakdown voltage or lower.5
[0075] As described above, in the first embodiment, the
power converter 10 opens the first interrupting device 21
in the case where the detected value Vdc1 detected by the
first voltage detector 31 is higher than or equal to the
second voltage threshold. Furthermore, the power converter10
10 controls the rotation speed of the motor 6 such that the
ripple current flowing through the second smoothing
capacitor 4 is less than or equal to the rated ripple
current. As a result, the power converter 10 can keep the
ripple current flowing through the second smoothing15
capacitor 4 to the rated ripple current or less. Therefore,
the power converter 10 can prevent a reduction in life of
the second smoothing capacitor 4.
[0076] Second Embodiment.
Next, a second embodiment will be described with20
reference to FIGS. 8 to 10. In the second embodiment, the
power converter 10 drives and controls the motor 6 in a
motor drive system in which a second converter circuit is
connected in parallel to the first converter circuit 2.
[0077] FIG. 8 is a diagram illustrating a configuration25
of the motor drive system including the power converter
according to the second embodiment. Components in FIG. 8
that achieve the same functions as those of the motor drive
system 301 of the first embodiment illustrated in FIG. 1
are assigned the same reference numerals as those in FIG. 1,30
and redundant description will be omitted. Note that FIG.
8 omits the illustration of reference numerals of the
connection points 51 to 54 and the connection lines 63 to
27
66.
[0078] A motor drive system 302 includes the power
converter 10, the motor 6, the current detector 32, and a
drive unit 40. That is, the motor drive system 302
includes the drive unit 40 in addition to the components of5
the motor drive system 301.
[0079] The drive unit 40 includes a second converter
circuit 41 connected in parallel with the first converter
circuit 2, a second smoothing unit 43 including a third
smoothing capacitor 42, a second voltage detector 44, and a10
load 45. The drive unit 40 is connected to connection
lines 67 and 68. The connection line 67 is connected to a
connection point 55 on the connection line 61, and the
connection line 68 is connected to a connection point 56 on
the connection line 62.15
[0080] In the drive unit 40, the second converter
circuit 41 is connected to the connection lines 67 and 68.
Moreover, the second converter circuit 41 and the load 45
are connected via connection lines 69 and 70.
[0081] A connection point 57 disposed on the connection20
line 69 and a connection point 58 disposed on the
connection line 70 are connected via a connection line 71.
The third smoothing capacitor 42 is disposed on the
connection line 71. That is, the connection point 57 is
connected to the connection point 58 via the third25
smoothing capacitor 42.
[0082] Moreover, the power converter 10 includes a
controller 7B instead of the controller 7A. The controller
7B controls, on the basis of detection signals from the
first voltage detector 31, the second voltage detector 44,30
and the current detector 32, opening and closing of the
first interrupting device 21 and switching on and off of
each switching element of the inverter circuit 5.
28
[0083] As with the first converter circuit 2, the second
converter circuit 41 is a diode rectifier circuit in which
four diode elements are bridge-connected. Note that, as
with the first converter circuit 2, the type of the diode
element used in the second converter circuit 41 is not5
limited to the fast recovery diode or the soft recovery
diode. The diode element used in the second converter
circuit 41 may be an element using a material such as SiC,
GaN, or Ga2O3. Also, the second converter circuit 41 may
be a circuit that uses switching elements to form a step-up10
circuit, a step-down circuit, a step-up/down circuit, or
the like.
[0084] A third breakdown voltage that is a breakdown
voltage of the third smoothing capacitor 42 is higher than
or equal to the second breakdown voltage of the second15
smoothing capacitor 4. Note that the third smoothing
capacitor 42 has such a capacitance that the ripple current
flowing through the third smoothing capacitor 42 is less
than or equal to the rated ripple current for all
predetermined rotation speed conditions.20
[0085] Moreover, the third smoothing capacitor 42 has
the breakdown voltage and the capacitance such that a
ripple amount of an applied voltage is less than or equal
to a value obtained by multiplying the breakdown voltage of
the smoothing capacitor by a percentage (for example, 20 to25
40%) determined by chemical properties of the smoothing
capacitor.
[0086] The second smoothing unit 43 is not limited to
the above configuration, and may have any configuration as
long as the voltage can be properly smoothed. For example,30
the second smoothing unit 43 (third smoothing capacitor 42)
may have a configuration (smoothing capacitor group) in
which two or more smoothing capacitors are connected in
29
series such that the total breakdown voltage (third
breakdown voltage) is higher than or equal to the second
breakdown voltage of the second smoothing capacitor 4.
[0087] The second smoothing unit 43 may also have a
configuration in which either two or more of smoothing5
capacitors each having a breakdown voltage higher than or
equal to the second breakdown voltage of the second
smoothing capacitor 4, or the smoothing capacitor groups
described above are connected in parallel.
[0088] The load 45 includes an inverter circuit and a10
motor similar to the inverter circuit 5 and the motor 6.
Note that the load 45 is not limited to the above
configuration, and a load having any configuration may be
used.
[0089] The second voltage detector 44 detects the15
applied voltage across the third smoothing capacitor 42 and
outputs the detected value as a detected value Vdc2 to the
controller 7B. The detected value Vdc2 detected by the
second voltage detector 44 is a second detected value.
[0090] FIG. 9 is a diagram illustrating a configuration20
of the controller included in the power converter according
to the second embodiment. The controller 7B included in
the power converter 10 of the second embodiment receives
the detected value Vdc1 transmitted from the first voltage
detector 31. The controller 7B also receives the detected25
value Vdc2 transmitted from the second voltage detector 44.
The controller 7B also receives the detected value Iuvw
transmitted from the current detector 32.
[0091] In addition, on the basis of the detected value
Vdc1 from the first voltage detector 31 or the detected30
value Vdc2 from the second voltage detector 44, the
controller 7B transmits the switching signal X to the first
interrupting device 21. Moreover, on the basis of the
30
detected value Vdc1 from the first voltage detector 31 or
the detected value Vdc2 from the second voltage detector 44
and the detected value Iuvw from the current detector 32,
the controller 7B transmits the drive signals S1 to S6 to
the switching elements of the inverter circuit 5. The5
controller 7B can thus control opening and closing of the
first interrupting device 21 and switching on and off of
the switching elements of the inverter circuit 5.
[0092] Note that, in a case where the first converter
circuit 2, the second converter circuit 41, or the load 4510
includes switching elements, the controller 7B transmits
the drive signals S1 to S6 for controlling switching on and
off of these switching elements to these switching elements.
[0093] FIG. 10 is a block diagram illustrating an
example of a software configuration in the controller15
included in the power converter according to the second
embodiment. Components in FIG. 10 that achieve the same
functions as those of the controller 7A of the first
embodiment illustrated in FIG. 4 are assigned the same
reference numerals as those in FIG. 4, and redundant20
description will be omitted.
[0094] The software in the controller 7B includes the
position/speed specification unit 200, the dq-axis
coordinate transformation unit 201, an opening/closing
signal generation unit 202B, the rotation command25
generation unit 203, the current control unit 204, and the
drive signal generation unit 205. That is, as compared
with the software in the controller 7A, the software in the
controller 7B includes the opening/closing signal
generation unit 202B instead of the opening/closing signal30
generation unit 202A.
[0095] The opening/closing signal generation unit 202B
receives at least one of the detected value Vdc1
31
transmitted from the first voltage detector 31 and the
detected value Vdc2 transmitted from the second voltage
detector 44.
[0096] Note that in a case where the first voltage
detector 31 transmits the detected value Vdc1 to the5
opening/closing signal generation unit 202B, the power
converter 10 need not include the second voltage detector
44. Similarly, in a case where the second voltage detector
44 transmits the detected value Vdc2 to the opening/closing
signal generation unit 202B, the power converter 10 need10
not include the first voltage detector 31. That is, since
the detected value Vdc1 and the detected value Vdc2 are
substantially the same value, either the detected value
Vdc1 or the detected value Vdc2 need only be input to the
opening/closing signal generation unit 202B.15
[0097] The opening/closing signal generation unit 202B
adopts either the detected value Vdc1 from the first
voltage detector 31 or the detected value Vdc2 from the
second voltage detector 44 as a voltage value (hereinafter
referred to as a switching voltage value in some cases) for20
generating the switching signal X.
[0098] The opening/closing signal generation unit 202B
compares the second voltage threshold with the switching
voltage value. In a case where the switching voltage value
is higher than or equal to the second voltage threshold,25
the opening/closing signal generation unit 202B generates
the switching signal X for opening the first interrupting
device 21. On the other hand, in a case where the
switching voltage value is lower than the second voltage
threshold, the opening/closing signal generation unit 202B30
generates the switching signal X for closing the first
interrupting device 21. The opening/closing signal
generation unit 202B transmits the generated switching
32
signal X to the first interrupting device 21 and the
rotation command generation unit 203.
[0099] Note that the method of generating the switching
signal X by the opening/closing signal generation unit 202B
is not limited to the above generation method, and any5
generation method may be used as long as the switching
signal X can be properly generated by the generation method.
For example, in a case where both the detected value Vdc1
from the first voltage detector 31 and the detected value
Vdc2 from the second voltage detector 44 are higher than or10
equal to the second voltage threshold, the opening/closing
signal generation unit 202B may generate the switching
signal X for opening the first interrupting device 21. The
opening/closing signal generation unit 202B may also adopt
an average value of the detected value Vdc1 from the first15
voltage detector 31 and the detected value Vdc2 from the
second voltage detector 44 as the switching voltage value.
[0100] Moreover, in a case where the power converter 10
includes a timer function, the opening/closing signal
generation unit 202B may generate the switching signal X20
for closing the first interrupting device 21 when the first
interrupting device 21 is open for a specific time or
longer.
[0101] The processing in which the controller 7B
generates the switching signal X and the rotation speed25
command value is different only in step ST1 from the
procedure described with reference to FIG. 7 of the first
embodiment. Specifically, in the first embodiment, the
opening/closing signal generation unit 202A determines
whether or not “the detected value Vdc1 from the first30
voltage detector 31”≥“the second voltage threshold” is
satisfied, whereas in the second embodiment, the
opening/closing signal generation unit 202A determines
33
whether or not “the switching voltage value”≥“the second
voltage threshold” is satisfied.
[0102] That is, in the processing in which the
controllers 7A and 7B generate the switching signal X and
the rotation speed command value, in the flowchart of FIG.5
7, the detected value Vdc1 from the first voltage detector
31 used in step ST1 is simply replaced with the switching
voltage value. The processing in which the controllers 7A
and 7B generate the switching signal X and the rotation
speed command value is the same in step ST2 and subsequent10
steps.
[0103] As described above, in the second embodiment, the
first voltage detector 31 detects the voltage applied to
the first smoothing capacitor 3, or the second voltage
detector 44 detects the voltage applied to the third15
smoothing capacitor 42. In a case where the switching
voltage value determined by the detected value from at
least one of the first voltage detector 31 and the second
voltage detector 44 is higher than or equal to the second
voltage threshold, the controller 7B opens the first20
interrupting device 21 connected in series to the first
smoothing capacitor 3. Furthermore, the controller 7B
controls the rotation speed of the motor 6 such that the
ripple current flowing through the second smoothing
capacitor 4 whose breakdown voltage is higher than the25
first voltage threshold is less than or equal to the rated
ripple current.
[0104] Therefore, the power converter 10 of the second
embodiment can obtain an effect similar to that of the
power converter 10 of the first embodiment. That is, in30
the second embodiment as well, the power converter 10 can
operate with high reliability and can prevent a reduction
in life of the second smoothing capacitor 4.
34
[0105] Third Embodiment.
Next, a third embodiment will be described with
reference to FIGS. 11 to 14. In the third embodiment, a
second interrupting device is disposed on the connection
line 61 between the alternating current power supply 1 and5
the first converter circuit 2, and the power converter 10
controls opening and closing of the second interrupting
device.
[0106] FIG. 11 is a diagram illustrating a configuration
of a motor drive system including the power converter10
according to the third embodiment. Components in FIG. 11
that achieve the same functions as those of the motor drive
system 301 of the first embodiment illustrated in FIG. 1
are assigned the same reference numerals as those in FIG. 1,
and redundant description will be omitted. Note that FIG.15
11 omits the illustration of reference numerals of the
connection points 51 to 54 and the connection lines 63 to
66.
[0107] A motor drive system 303 includes the power
converter 10, the motor 6, the current detector 32, and a20
second interrupting device 22. That is, the motor drive
system 303 includes the second interrupting device 22 in
addition to the components of the motor drive system 301.
[0108] The second interrupting device 22 is disposed on
the connection line 61. That is, the second interrupting25
device 22 is disposed between the alternating current power
supply 1 and the first converter circuit 2. Note that the
second interrupting device 22 may be disposed inside the
power converter 10 or may be disposed outside the power
converter 10.30
[0109] Moreover, the power converter 10 includes a
controller 7C instead of the controller 7A. The controller
7C controls, on the basis of detection signals from the
35
first voltage detector 31 and the current detector 32,
opening and closing of the first interrupting device 21,
opening and closing of the second interrupting device 22,
and switching on and off of each switching element of the
inverter circuit 5.5
[0110] For the second interrupting device 22, a
mechanical relay is used as with the first interrupting
device 21, but a switching element formed of a
semiconductor including a wide band gap semiconductor may
be used. That is, for the second interrupting device 22, a10
switching element such as an IGBT, a MOSFET, a SiC-MOSFET,
a GaN-FET, a GaN-HEMT, or a Ga2O3-MOSFET may be used.
[0111] FIG. 12 is a diagram illustrating a configuration
of the controller included in the power converter according
to the third embodiment. The controller 7C included in the15
power converter 10 of the third embodiment receives the
detected value Vdc1 transmitted from the first voltage
detector 31. The controller 7C also receives the detected
value Iuvw transmitted from the current detector 32.
[0112] In addition, on the basis of the detected value20
Vdc1, the controller 7C transmits the switching signal X to
the first interrupting device 21. Also, on the basis of
the detected value Vdc1, the controller 7C transmits a
switching signal Y to the second interrupting device 22.
The switching signal Y is a signal for switching an25
open/closed state of the second interrupting device 22.
Moreover, on the basis of the detected value Vdc1 and the
detected value Iuvw, the controller 7C transmits the drive
signals S1 to S6 to the switching elements of the inverter
circuit 5. The controller 7C can thus control opening and30
closing of the first interrupting device 21, opening and
closing of the second interrupting device 22, and switching
on and off of the switching elements of the inverter
36
circuit 5.
[0113] FIG. 13 is a block diagram illustrating an
example of a software configuration in the controller
included in the power converter according to the third
embodiment. Components in FIG. 13 that achieve the same5
functions as those of the controller 7A of the first
embodiment illustrated in FIG. 4 are assigned the same
reference numerals as those in FIG. 4, and redundant
description will be omitted.
[0114] The software in the controller 7C includes the10
position/speed specification unit 200, the dq-axis
coordinate transformation unit 201, an opening/closing
signal generation unit 202C, the rotation command
generation unit 203, the current control unit 204, and the
drive signal generation unit 205. That is, as compared15
with the software in the controller 7A, the software in the
controller 7C includes the opening/closing signal
generation unit 202C instead of the opening/closing signal
generation unit 202A.
[0115] The opening/closing signal generation unit 202C20
receives the detected value Vdc1 transmitted from the first
voltage detector 31. The opening/closing signal generation
unit 202C compares the second voltage threshold with the
detected value Vdc1 from the first voltage detector 31. In
a case where the detected value Vdc1 is higher than or25
equal to the second voltage threshold, the opening/closing
signal generation unit 202C generates the switching signal
X for opening the first interrupting device 21. On the
other hand, in a case where the detected value Vdc1 is
lower than the second voltage threshold, the30
opening/closing signal generation unit 202C generates the
switching signal X for closing the first interrupting
device 21.
37
[0116] In addition, the opening/closing signal
generation unit 202C compares the detected value Vdc1 with
the third voltage threshold that is higher than the first
voltage threshold and has the same value as the second
breakdown voltage of the second smoothing capacitor 45
(“first voltage threshold”<“third voltage
threshold”≤“second breakdown voltage”). In a case where
the detected value Vdc1 is higher than or equal to the
third voltage threshold, the opening/closing signal
generation unit 202C generates the switching signal Y for10
opening the second interrupting device 22. On the other
hand, in a case where the detected value Vdc1 is lower than
the third voltage threshold, the opening/closing signal
generation unit 202C generates the switching signal Y for
closing the second interrupting device 22.15
[0117] The opening/closing signal generation unit 202C
transmits the generated switching signal X to the first
interrupting device 21 and the rotation command generation
unit 203. The opening/closing signal generation unit 202C
also transmits the generated switching signal Y to the20
second interrupting device 22.
[0118] In addition, the opening/closing signal
generation unit 202C has a function of closing the
interrupting devices in order, i.e., the first interrupting
device 21 and subsequently the second interrupting device25
22 when an open state of both of the first interrupting
device 21 and the second interrupting device 22 lasts for a
specific time or longer.
[0119] Note that the method of generating the switching
signals X and Y by the opening/closing signal generation30
unit 202C is not limited to the above generation method,
and any generation method may be used as long as the
switching signals X and Y can be properly generated by the
38
generation method.
[0120] Among control processing executed by the
controller 7C, a description will be made of an example of
processing that generates the switching signals X and Y and
the rotation speed command value on the basis of the5
detected value Vdc1 detected by the first voltage detector
31.
[0121] FIG. 14 is a flowchart illustrating a procedure
of the control processing by the controller of the power
converter according to the third embodiment. The flowchart10
of FIG. 14 illustrates the processing in which the
controller 7C generates the switching signals X and Y and
the rotation speed command value on the basis of the
detected value Vdc1.
[0122] The opening/closing signal generation unit 202C15
of the controller 7C determines the open/closed states of
the first interrupting device 21 and the second
interrupting device 22 at the end of the previous
processing. Specifically, the opening/closing signal
generation unit 202C determines whether or not the first20
interrupting device 21 and the second interrupting device
22 (hereinafter referred to as first and second
interrupting devices in some cases) are both open at the
end of the previous processing (step ST11).
[0123] If determining that the first and second25
interrupting devices are both open at the end of the
previous processing (Yes in step ST11), the opening/closing
signal generation unit 202C acquires the duration of the
state in which the first and second interrupting devices
are both open. The duration of the state in which the30
first and second interrupting devices are both open is
measured using a timer function or the like.
[0124] The opening/closing signal generation unit 202C
39
determines whether or not the duration of the state in
which the first and second interrupting devices are both
open is shorter than a specific time (step ST12a). In
other words, the opening/closing signal generation unit
202C determines whether or not the continuation of the5
state in which the first and second interrupting devices
are both open has passed a specific time.
[0125] If determining that the duration of the state in
which the first and second interrupting devices are both
open is shorter than the specific time (Yes in step ST12a),10
the opening/closing signal generation unit 202C allows the
continuation of the state in which the first and second
interrupting devices are both open (step ST13). That is,
the opening/closing signal generation unit 202C generates
the switching signals X and Y for allowing the continuation15
of the state in which the first and second interrupting
devices are both open.
[0126] The opening/closing signal generation unit 202C
transmits the generated switching signal X to the first
interrupting device 21 and the rotation command generation20
unit 203. The opening/closing signal generation unit 202C
also transmits the generated switching signal Y to the
second interrupting device 22.
[0127] If determining that the duration of the state in
which the first and second interrupting devices are both25
open is longer than or equal to the specific time (No in
step ST12a), the opening/closing signal generation unit
202C closes the interrupting devices in the order of the
first interrupting device 21 and the second interrupting
device 22 (step ST14). As a result, the motor drive system30
303 can return to the normal operation.
[0128] The opening/closing signal generation unit 202C
closes the interrupting devices in the order of the first
40
interrupting device 21 and the second interrupting device
22, thereby being able to prevent an excessive inrush
current from flowing into the power converter 10.
[0129] The opening/closing signal generation unit 202C
closes the interrupting devices in the order of the first5
interrupting device 21 and the second interrupting device
22, and then compares the detected value Vdc1 from the
first voltage detector 31 with the third voltage threshold.
The opening/closing signal generation unit 202C then
determines whether or not “the detected value Vdc1 from the10
first voltage detector 31”≥“the third voltage threshold” is
satisfied (step ST15).
[0130] If “the detected value Vdc1 from the first
voltage detector 31”≥“the third voltage threshold” is
satisfied (Yes in step ST15), the opening/closing signal15
generation unit 202C generates the switching signal Y as
the instruction to open the second interrupting device 22
and transmits the switching signal Y to the second
interrupting device 22 (step ST16). The controller 7C
thereafter stops the operation of the motor 6 (step ST17).20
[0131] Also, in the processing of step ST11, if the
opening/closing signal generation unit 202C determines that
either the first or second interrupting device is closed at
the end of the previous processing (No in step ST11), the
controller 7C executes the processing of step ST15 and25
subsequent steps.
[0132] In the processing of step ST15, if the
opening/closing signal generation unit 202C determines that
“the detected value Vdc1 from the first voltage detector
31”<“the third voltage threshold” is satisfied (No in step30
ST15), the opening/closing signal generation unit 202C
generates the switching signal Y as the instruction to
close the second interrupting device 22 and transmits the
41
switching signal Y to the second interrupting device 22
(step ST18).
[0133] The controller 7C thereafter executes the
processing of steps ST1 to ST7 described with reference to
FIG. 7. That is, the controller 7C generates and transmits5
the switching signal X and the rotation speed command value
(steps ST1 to ST7).
[0134] Note that the opening/closing signal generation
unit 202C executes the processing of both steps ST16 and
ST17 if “the detected value Vdc1 from the first voltage10
detector 31”≥“the third voltage threshold” is satisfied,
but the opening/closing signal generation unit 202C may
execute the processing of at least one of steps ST16 and
ST17.
[0135] As described above, in the third embodiment, the15
controller 7C opens the second interrupting device 22 and
stop the operation of the motor 6 in the case where the
detected value Vdc1 of the voltage applied to the second
smoothing capacitor 4 having the breakdown voltage higher
than the first voltage threshold is higher than or equal to20
the third voltage threshold that is greater than the first
voltage threshold and has the same value as the breakdown
voltage of the second smoothing capacitor 4.
[0136] Moreover, in the third embodiment, in the case
where the detected value Vdc1 of the voltage applied to the25
second smoothing capacitor 4 is higher than or equal to the
second voltage threshold, the controller 7C opens the first
interrupting device 21 connected in series to the first
smoothing capacitor 3. Furthermore, the controller 7C
controls the rotation speed of the motor 6 such that the30
ripple current flowing through the second smoothing
capacitor 4 is less than or equal to the rated ripple
current. Therefore, as with the first embodiment, the
42
power converter 10 can operate with high reliability and
can prevent a reduction in life of the second smoothing
capacitor 4.
[0137] Fourth Embodiment.
Next, a fourth embodiment will be described with5
reference to FIGS. 15 to 19. In the fourth embodiment, a
motor drive system has a configuration that is a
combination of the motor drive systems 302 and 303. That
is, in the motor drive system of the fourth embodiment, the
second converter circuit 41 is connected in parallel to the10
first converter circuit 2, and the second interrupting
device 22 is disposed on the connection line 61 between the
alternating current power supply 1 and the first converter
circuit 2.
[0138] FIG. 15 is a diagram illustrating the15
configuration of the motor drive system including the power
converter according to the fourth embodiment. Components
in FIG. 15 that achieve the same functions as those of the
motor drive system 302 of the second embodiment or the
motor drive system 303 of the third embodiment are assigned20
the same reference numerals as those in the corresponding
motor drive system of the second or third embodiment, and
redundant description will be omitted. Note that FIG. 15
omits the illustration of reference numerals of the
connection points 51 to 54, 57, and 58 and the connection25
lines 63 to 70.
[0139] A motor drive system 304 includes the power
converter 10, the motor 6, the current detector 32, the
second interrupting device 22, and the drive unit 40. That
is, the motor drive system 304 includes the second30
interrupting device 22 in addition to the components of the
motor drive system 302.
[0140] In the fourth embodiment, the second interrupting
43
device 22 is disposed between the connection point 55 and
the first converter circuit 2 on the connection line 61.
Note that the second interrupting device 22 may be disposed
inside the power converter 10 or may be disposed outside
the power converter 10.5
[0141] Moreover, the power converter 10 includes a
controller 7D instead of the controller 7A. On the basis
of detection signals from the first voltage detector 31,
the second voltage detector 44, and the current detector 32,
the controller 7D controls opening and closing of the first10
interrupting device 21, opening and closing of the second
interrupting device 22, and switching on and off of each
switching element of the inverter circuit 5.
[0142] FIG. 16 is a diagram illustrating a configuration
of the controller included in the power converter according15
to the fourth embodiment. The controller 7D included in
the power converter 10 of the fourth embodiment receives
the detected value Vdc1 transmitted from the first voltage
detector 31. The controller 7D also receives the detected
value Vdc2 transmitted from the second voltage detector 44.20
The controller 7D also receives the detected value Iuvw
transmitted from the current detector 32.
[0143] In addition, on the basis of the detected value
Vdc1 from the first voltage detector 31, the controller 7D
transmits the switching signal X to the first interrupting25
device 21. Also, on the basis of the detected value Vdc2
from the second voltage detector 44, the controller 7D
transmits the switching signal Y to the second interrupting
device 22. Moreover, on the basis of the detected value
Vdc1 from the first voltage detector 31 and the detected30
value Iuvw from the current detector 32, the controller 7D
transmits the drive signals S1 to S6 to the switching
elements of the inverter circuit 5. The controller 7D can
44
thus control opening and closing of the first interrupting
device 21, opening and closing of the second interrupting
device 22, and switching on and off of the switching
elements of the inverter circuit 5.
[0144] Note that, in a case where the first converter5
circuit 2, the second converter circuit 41, or the load 45
includes switching elements, the controller 7D transmits
the drive signals S1 to S6 for controlling switching on and
off of these switching elements to these switching elements.
[0145] FIG. 17 is a block diagram illustrating an10
example of a software configuration in the controller
included in the power converter according to the fourth
embodiment. Components in FIG. 17 that achieve the same
functions as those of the controller 7A of the second
embodiment illustrated in FIG. 4 are assigned the same15
reference numerals as those in FIG. 4, and redundant
description will be omitted.
[0146] The software in the controller 7D includes the
position/speed specification unit 200, the dq-axis
coordinate transformation unit 201, an opening/closing20
signal generation unit 202D, the rotation command
generation unit 203, the current control unit 204, and the
drive signal generation unit 205. That is, as compared
with the software in the controller 7A, the software in the
controller 7D includes the opening/closing signal25
generation unit 202D instead of the opening/closing signal
generation unit 202A.
[0147] The opening/closing signal generation unit 202D
receives the detected value Vdc1 transmitted from the first
voltage detector 31 and the detected value Vdc2 transmitted30
from the second voltage detector 44.
[0148] The opening/closing signal generation unit 202D
compares the second voltage threshold with the detected
45
value Vdc2 from the second voltage detector 44. In a case
where the detected value Vdc2 is higher than or equal to
the second voltage threshold, the opening/closing signal
generation unit 202D closes the interrupting devices in the
order of the first interrupting device 21 and the second5
interrupting device 22.
[0149] In addition, the opening/closing signal
generation unit 202D compares the detected value Vdc1 with
the third voltage threshold that is higher than the first
voltage threshold and has the same value as the second10
breakdown voltage of the second smoothing capacitor 4. In
a case where the detected value Vdc1 is higher than or
equal to the third voltage threshold, the opening/closing
signal generation unit 202D generates the switching signal
Y for opening the second interrupting device 22. On the15
other hand, in a case where the detected value Vdc1 is
lower than the third voltage threshold, the opening/closing
signal generation unit 202D generates the switching signal
Y for closing the second interrupting device 22.
[0150] The opening/closing signal generation unit 202D20
also compares the second voltage threshold with the
detected value Vdc2 from the second voltage detector 44.
In a case where the detected value Vdc2 is higher than or
equal to the second voltage threshold, the opening/closing
signal generation unit 202D generates the switching signal25
X for opening the first interrupting device 21, as with the
opening/closing signal generation unit 202A. On the other
hand, in a case where the detected value Vdc2 is lower than
the second voltage threshold, the opening/closing signal
generation unit 202D generates the switching signal X for30
closing the first interrupting device 21.
[0151] The opening/closing signal generation unit 202D
transmits the generated switching signal X to the first
46
interrupting device 21 and the rotation command generation
unit 203. The opening/closing signal generation unit 202D
also transmits the generated switching signal Y to the
second interrupting device 22.
[0152] As described above, the opening/closing signal5
generation unit 202D has both the function of the
opening/closing signal generation unit 202B and the
function of the opening/closing signal generation unit 202C.
[0153] Note that the method of generating the switching
signals X and Y by the opening/closing signal generation10
unit 202D is not limited to the above generation method,
and any generation method may be used as long as the
switching signals X and Y can be properly generated by the
generation method.
[0154] Among control processing executed by the15
controller 7D, a description will be made of an example of
processing that generates the switching signals X and Y and
the rotation speed command value on the basis of the
detected value Vdc1 detected by the first voltage detector
31 and the detected value Vdc2 detected by the second20
voltage detector 44.
[0155] FIG. 18 is a flowchart illustrating a procedure
of the control processing by the controller of the power
converter according to the fourth embodiment. The
flowchart of FIG. 18 illustrates the processing in which25
the controller 7D generates the switching signals X and Y
and the rotation speed command value on the basis of the
detected value Vdc1 and the detected value Vdc2.
[0156] While the controller 7C executes the processing
of step ST12a, the controller 7D executes processing of30
step ST12b. The processing of steps ST11, ST13 to ST18,
and ST1 to ST7 executed by the controller 7C and the
processing of steps ST11, ST13 to ST18, and ST1 to ST7
47
executed by the controller 7D are the same processing and
are executed in the same procedure.
[0157] If determining that the first and second
interrupting devices are both open at the end of the
previous processing (Yes in step ST11), the controller 7D5
acquires the duration of the state in which the first and
second interrupting devices are both open using a timer
function or the like.
[0158] The opening/closing signal generation unit 202D
then compares the detected value Vdc2 from the second10
voltage detector 44 with the second voltage threshold, and
determines whether or not “the detected value Vdc2 from the
second voltage detector 44”≥“the second voltage threshold”
is satisfied (step ST12b).
[0159] If “the detected value Vdc2 from the second15
voltage detector 44”≥“the second voltage threshold” is
satisfied (Yes in step ST12b), the opening/closing signal
generation unit 202D executes the processing of step ST13.
On the other hand, if “the detected value Vdc2 from the
second voltage detector 44”<“the second voltage threshold”20
is satisfied (No in step ST12b), the opening/closing signal
generation unit 202D executes the processing of step ST14
and subsequent steps. As a result, the controller 7D need
not to stop the operation of the motor 6 for a specific
time.25
[0160] FIG. 19 is a diagram illustrating an example of
another configuration of a motor drive system including the
power converter according to the fourth embodiment.
Components in FIG. 19 that achieve the same functions as
those of the motor drive system 304 illustrated in FIG. 1530
are assigned the same reference numerals as those in FIG.
15, and redundant description will be omitted. Note that,
as in FIG. 15, FIG. 19 omits the illustration of reference
48
numerals of the connection points 51 to 54, 57, and 58 and
the connection lines 63 to 70.
[0161] As with the motor drive system 304, a motor drive
system 305 includes the power converter 10, the motor 6,
the current detector 32, the second interrupting device 22,5
and the drive unit 40.
[0162] In the motor drive system 305, the second
interrupting device 22 is disposed between the connection
point 55 and the alternating current power supply 1 on the
connection line 61. In the motor drive system 305, the10
power converter 10 executes the operation similar to that
in the motor drive system 304. Thus, the preferred
operation of the motor drive system 305 can be implemented
by combining the operations described in the first to
fourth embodiments.15
[0163] Note that, in the motor drive system 305, when
the controller 7D generates the switching signals X and Y
and the rotation speed command value, the switching voltage
value may be used instead of the detected value Vdc2
detected by the second voltage detector 44. That is, the20
opening/closing signal generation unit 202D may compare the
second voltage threshold with the detected value Vdc1
instead of comparing the second voltage threshold with the
detected value Vdc2.
[0164] Thus, in the fourth embodiment, the controller 7D25
opens the second interrupting device 22 and stop the
operation of the motor 6 in a case where the detected value
Vdc1 of the voltage applied to the second smoothing
capacitor 4, the breakdown voltage of which is higher than
the first voltage threshold, is higher than or equal to the30
third voltage threshold that is greater than the first
voltage threshold and has the same value as the breakdown
voltage of the second smoothing capacitor 4.
49
[0165] Moreover, in the fourth embodiment, in a case
where the detected value Vdc1 of the voltage applied to the
second smoothing capacitor 4 is higher than or equal to the
second voltage threshold, the controller 7D opens the first
interrupting device 21 connected in series to the first5
smoothing capacitor 3 whose breakdown voltage is equal to
the second voltage threshold. Furthermore, the controller
7D controls the rotation speed of the motor 6 such that the
ripple current flowing through the second smoothing
capacitor 4 whose breakdown voltage is higher than the10
first voltage threshold is less than or equal to the rated
ripple current. Therefore, as with the first embodiment,
the power converter 10 can operate with high reliability
and can prevent a reduction in life of the second smoothing
capacitor 4.15
[0166] The configurations illustrated in the above
embodiments each merely illustrate an example so that
another known technique can be combined, the embodiments
can be combined together, or the configurations can be
partially omitted and/or modified without departing from20
the scope of the present disclosure.
Reference Signs List
[0167] 1 alternating current power supply; 2 first
converter circuit; 3 first smoothing capacitor; 4 second25
smoothing capacitor; 5 inverter circuit; 6 motor; 7A to
7D controller; 10 power converter; 11 first smoothing
unit; 21 first interrupting device; 22 second
interrupting device; 31 first voltage detector; 32
current detector; 40 drive unit; 41 second converter30
circuit; 42 third smoothing capacitor; 43 second
smoothing unit; 44 second voltage detector; 45 load; 51
to 58 connection point; 61 to 71 connection line; 80
50
correlation data; 100 processor; 101 storage; 200
position/speed specification unit; 201 dq-axis coordinate
transformation unit; 202A to 202D opening/closing signal
generation unit; 203 rotation command generation unit; 204
current control unit; 205 drive signal generation unit;5
301 to 305 motor drive system.
51
WE CLAIM:
[Claim 1] A power converter comprising:
a first converter circuit to convert an alternating
current voltage from an alternating current power supply
into a direct current voltage;5
an inverter circuit to convert the direct current
voltage obtained by conversion by the first converter
circuit into an alternating current voltage, and supply the
alternating current voltage to a motor;
a first smoothing unit connected between the first10
converter circuit and the inverter circuit, the first
smoothing unit including a first smoothing capacitor and a
second smoothing capacitor, the first smoothing capacitor
having a first breakdown voltage equal to a second voltage
threshold, the second smoothing capacitor having a second15
breakdown voltage higher than a first voltage threshold,
the first voltage threshold being a value higher than or
equal to the second voltage threshold, the first smoothing
capacitor and the second smoothing capacitor being
connected in parallel;20
a first interrupting device connected in series to the
first smoothing capacitor;
a first voltage detector to detect an applied voltage
across the second smoothing capacitor; and
a controller to, in a case where a first detected25
value as a detected value of the applied voltage detected
by the first voltage detector is higher than or equal to
the second voltage threshold, open the first interrupting
device and control a rotation speed of the motor such that
a ripple current flowing through the second smoothing30
capacitor is less than or equal to a rated ripple current.
[Claim 2] The power converter according to claim 1, wherein
52
the controller
closes the first interrupting device in a case where
the first detected value is lower than the second voltage
threshold.
5
[Claim 3] The power converter according to claim 1 or 2,
wherein
the controller
closes the first interrupting device in a case where
an open state of the first interrupting device lasts a10
specific time.
[Claim 4] The power converter according to any one of
claims 1 to 3, further comprising:
a second converter circuit connected in parallel to15
the first converter circuit to convert the alternating
current voltage from the alternating current power supply
into a direct current voltage;
a load to be supplied with the direct current voltage
obtained by conversion by the second converter circuit;20
a second smoothing unit connected between the second
converter circuit and the load, the second smoothing unit
including a third smoothing capacitor having a third
breakdown voltage higher than or equal to the second
breakdown voltage; and25
a second voltage detector to detect an applied voltage
across the third smoothing capacitor, wherein
the controller
opens the first interrupting device in a case where a
switching voltage value is higher than or equal to the30
second voltage threshold, the switching voltage being a
detected value of at least one of the applied voltage
detected by the first voltage detector and the applied
53
voltage detected by the second voltage detector.
[Claim 5] The power converter according to any one of
claims 1 to 3, further comprising
a second interrupting device connected between the5
alternating current power supply and the first converter
circuit, wherein
the controller
opens the second interrupting device and stop the
operation of the motor in a case where the first detected10
value is higher than or equal to a third voltage threshold,
the third voltage threshold being a value larger than the
first voltage threshold and equal to the second breakdown
voltage.
15
[Claim 6] The power converter according to claim 5, wherein
the controller
closes the first interrupting device and subsequently
closes the second interrupting device in a case where an
open state of both of the first interrupting device and the20
second interrupting device lasts a specific time.
[Claim 7] The power converter according to any one of
claims 1 to 3, further comprising:
a second converter circuit connected in parallel to25
the first converter circuit to convert the alternating
current voltage from the alternating current power supply
into a direct current voltage;
a load to be supplied with the direct current voltage
obtained by conversion by the second converter circuit;30
a second smoothing unit connected between the second
converter circuit and the load, the second smoothing unit
including a third smoothing capacitor having a third
54
breakdown voltage higher than or equal to the second
breakdown voltage;
a second interrupting device connected between the
alternating current power supply and the first converter
circuit; and5
a second voltage detector to detect an applied voltage
across the third smoothing capacitor, wherein
the controller
opens the second interrupting device and stop the
operation of the motor in a case where the first detected10
value is higher than or equal to a third voltage threshold,
the third voltage threshold being a value larger than the
first voltage threshold and equal to the second breakdown
voltage.
15
[Claim 8] The power converter according to claim 7, wherein
the controller
closes the first interrupting device and subsequently
closes the second interrupting device in a case where a
second detected value is lower than the second voltage20
threshold with the first interrupting device and the second
interrupting device both open, the second detected value
being a detected value of the applied voltage detected by
the second voltage detector.
25
[Claim 9] The power converter according to any one of
claims 1 to 8, wherein
on the basis of correlation data in which the rotation
speed of the motor is associated with an effective value of
the ripple current flowing through the second smoothing30
capacitor, the controller
controls the rotation speed of the motor such that the
current flowing through the second smoothing capacitor is
55
less than or equal to the rated ripple current.
[Claim 10] The power converter according to claim 9,
wherein
the controller5
selects, from among the rotation speeds included in
the correlation data, one rotation speed at which the
ripple current flowing through the second smoothing
capacitor is less than or equal to the rated ripple current,
and controls the rotation speed of the motor to achieve the10
selected rotation speed.
[Claim 11] The power converter according to any one of
claims 1 to 10, wherein
in the first smoothing unit,15
three or more smoothing capacitors including the first
smoothing capacitor and the second smoothing capacitor are
connected in parallel, wherein
of the three or more smoothing capacitors, low
breakdown voltage capacitors each having a breakdown20
voltage lower than or equal to the first voltage threshold
and connected in series to a specific interrupting device,
and wherein,
of the low breakdown voltage capacitors, the first
smoothing capacitor is connected in series to the first25
interrupting device.
[Claim 12] The power converter according to any one of
claims 1 to 11, wherein
the first smoothing capacitor and the second smoothing30
capacitor have
capacitances that: allow a ripple current less than or
equal to the rated ripple current to flow through each of
56
the first smoothing capacitor and the second smoothing
capacitor under all predetermined rotation speed conditions
with the first interrupting device closed; and allow a
ripple current less than or equal to the rated ripple
current to flow through the second smoothing capacitor5
under at least one of the rotation speed conditions with
the first interrupting device open.
[Claim 13] The power converter according to claim 4 or
7, wherein10
the third smoothing capacitor is
a smoothing capacitor group including two or more
smoothing capacitors connected in series and having a total
breakdown voltage that is the third breakdown voltage.
15
[Claim 14] The power converter according to claim 4 or
7, wherein
the third smoothing capacitor is defined by:
two or more parallel-connected smoothing capacitors
each having the third breakdown voltage; or20
two or more parallel-connected smoothing capacitor
groups each including two or more smoothing capacitors
connected in series and having a total breakdown voltage
that is the third breakdown voltage.
25
[Claim 15] The power converter according to any one of
claims 1 to 14, wherein
the first smoothing capacitor and the second smoothing
capacitor have
the first breakdown voltage and capacitances such that,30
with the first interrupting device closed, all
predetermined rotation speed conditions are satisfied, and
with the first interrupting device open, at least one of
57
the rotation speed conditions is satisfied.
[Claim 16] The power converter according to any one of
claims 1 to 15, wherein
the first interrupting device is a mechanical relay or5
a switching element formed of a semiconductor including a
wide band gap semiconductor.
[Claim 17] A motor drive system comprising:
a motor; and10
a power converter to convert and supply, to the motor,
an alternating current voltage from an alternating current
power supply, wherein
the power converter includes:
a first converter circuit to convert the alternating15
current voltage from the alternating current power supply
into a direct current voltage;
an inverter circuit to convert the direct current
voltage obtained by conversion by the first converter
circuit into an alternating current voltage, and supply the20
alternating current voltage to the motor;
a first smoothing unit connected between the first
converter circuit and the inverter circuit, the first
smoothing including a first smoothing capacitor and a
second smoothing capacitor, the first smoothing capacitor25
having a first breakdown voltage equal to a second voltage
threshold, the second smoothing capacitor having a second
breakdown voltage higher than a first voltage threshold,
the first voltage threshold being a value higher than or
equal to the second voltage threshold, the first smoothing30
capacitor and the second smoothing capacitor being
connected in parallel;
a first interrupting device connected in series to the
58
first smoothing capacitor;
a first voltage detector to detect an applied voltage
across the second smoothing capacitor; and
a controller to, in a case where a first detected
value as a detected value of the applied voltage detected5
by the first voltage detector is higher than or equal to
the second voltage threshold, open the first interrupting
device and control a rotation speed of the motor such that
a ripple current flowing through the second smoothing
capacitor is less than or equal to a rated ripple current.10
[Claim 18] A power conversion method comprising:
a first conversion step in which a first converter
circuit converts an alternating current voltage from an
alternating current power supply into a direct current15
voltage;
a smoothing step in which a first smoothing capacitor
having a first breakdown voltage equal to a second voltage
threshold and a second smoothing capacitor connected in
parallel to the first smoothing capacitor and having a20
second breakdown voltage higher than a first voltage
threshold smooth the direct current voltage, the first
voltage threshold being a value higher than or equal to the
second voltage threshold;
a second conversion step in which an inverter circuit25
converts the smoothed direct current voltage into an
alternating current voltage, and supplies the alternating
current voltage to a motor;
a detection step in which a first voltage detector
detects an applied voltage across the second smoothing30
capacitor; and
a control step of, in a case where a first detected
value as a detected value of the applied voltage detected
59
by the first voltage detector is higher than or equal to
the second voltage threshold, opening a first interrupting
device connected in series to the first smoothing capacitor
and controlling a rotation speed of the motor such that a
ripple current flowing through the second smoothing5
capacitor is less than or equal to a rated ripple current.