U.S. patent application number 15/969804 was filed with the patent office on 2019-05-30 for power conversion system.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Akiko GOTO.
Application Number | 20190165664 15/969804 |
Document ID | / |
Family ID | 66442164 |
Filed Date | 2019-05-30 |
United States Patent
Application |
20190165664 |
Kind Code |
A1 |
GOTO; Akiko |
May 30, 2019 |
POWER CONVERSION SYSTEM
Abstract
A power conversion system includes: a plurality of power modules
connected in parallel to each other, a plurality of drive circuits
driving the plurality of power modules based on input signals
respectively; a plurality of correction sections correcting the
input signals inputted to the plurality of drive circuits based on
a plurality of correction values respectively; a temperature
detection section detecting operating temperatures of the plurality
of power modules; and a calculation section estimating current
switching characteristics of the plurality of power modules based
on the measured operating temperatures and temperature dependency
of switching characteristics of the plurality of power modules, and
calculating the plurality of correction values based on the
estimated current switching characteristics so as to reduce
variations of currents flowing through the plurality of power
modules.
Inventors: |
GOTO; Akiko; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
66442164 |
Appl. No.: |
15/969804 |
Filed: |
May 3, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 1/088 20130101;
H02M 7/537 20130101; H02M 1/08 20130101; H02M 7/493 20130101; H02M
1/32 20130101; H02M 2001/327 20130101; H02M 2001/0025 20130101 |
International
Class: |
H02M 1/08 20060101
H02M001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2017 |
JP |
2017-228236 |
Claims
1. (canceled)
2. A power conversion system comprising: a plurality of power
modules connected in parallel to each other, a plurality of drive
circuits driving the plurality of power modules based on input
signals respectively; a plurality of correction sections correcting
the input signals inputted to the plurality of drive circuits based
on a plurality of correction values respectively; a temperature
detection section detecting operating temperatures of the plurality
of power modules; and a calculation section estimating current
switching characteristics of the plurality of power modules based
on the detected operating temperatures and temperature dependencies
of switching characteristics of the plurality of power modules, and
calculating the plurality of correction values based on the
estimated current switching characteristics so as to reduce
variations of currents flowing through the plurality of power
modules, wherein the switching characteristic is at least one of a
rising time, a falling time, a time period required to turn on, a
time period required to turn off, a turn-on delay time, a turn-off
delay time, a total value of a turn-on delay time and a rising
time, and a total value of a turn-off delay time and a falling
time.
3. A power conversion system comprising: a plurality of power
modules connected in parallel to each other; a plurality of drive
circuits driving the plurality of power modules based on input
signals respectively; a plurality of correction sections correcting
the input signals inputted to the plurality of drive circuits based
on a plurality of correction values respectively; a temperature
detection section detecting operating temperatures of the plurality
of power modules; a calculation section estimating current
switching characteristics of the plurality of power modules based
on the detected operating temperatures and temperature dependencies
of switching characteristics of the plurality of power modules, and
calculating the plurality of correction values based on the
estimated current switching characteristics so as to reduce
variations of currents flowing through the plurality of power
modules; and a recording section recording inspection results of
switching characteristics of the plurality of power modules and
inspection temperatures as shipment inspection results, wherein the
calculation section estimates the temperature dependencies of the
switching characteristics of the plurality of power modules based
on the shipment inspection results.
4. The power conversion system according to claim 2, further
comprising a recording section recording inspection results of
switching characteristics of the plurality of power modules and
inspection temperatures as shipment inspection results, wherein the
calculation section estimates the temperature dependencies of the
switching characteristics of the plurality of power modules based
on the shipment inspection results.
5. The power conversion system according to claim 3, wherein the
recording section includes a plurality of recording sections
provided in the plurality of power modules respectively and
recording the shipment inspection results of the plurality of power
modules respectively.
6. The power conversion system according to claim 4, wherein the
recording section includes a plurality of recording sections
provided in the plurality of power modules respectively and
recording the shipment inspection results of the plurality of power
modules respectively.
7. The power conversion system according to claim 5, wherein the
plurality of drive circuits and the plurality of correction
sections are provided in the plurality of power modules
respectively, and the plurality of recording sections records the
plurality of calculated correction values respectively.
8. The power conversion system according to claim 6, wherein the
plurality of drive circuits and the plurality of correction
sections are provided in the plurality of power modules
respectively, and the plurality of recording sections records the
plurality of calculated correction values respectively.
9. (canceled)
10. The power conversion system according to claim 2, wherein the
plurality of power modules includes a plurality of switching
devices made of a wide-band-gap semiconductor respectively.
11. The power conversion system according to claim 3, wherein the
plurality of power modules includes a plurality of switching
devices made of a wide-band-gap semiconductor respectively.
12. The power conversion system according to claim 4, wherein the
plurality of power modules includes a plurality of switching
devices made of a wide-band-gap semiconductor respectively.
13. The power conversion system according to claim 5, wherein the
plurality of power modules includes a plurality of switching
devices made of a wide-band-gap semiconductor respectively.
14. The power conversion system according to claim 6, wherein the
plurality of power modules includes a plurality of switching
devices made of a wide-band-gap semiconductor respectively.
15. The power conversion system according to claim 7, wherein the
plurality of power modules includes a plurality of switching
devices made of a wide-band-gap semiconductor respectively.
16. The power conversion system according to claim 8, wherein the
plurality of power modules includes a plurality of switching
devices made of a wide-band-gap semiconductor respectively.
Description
BACKGROUND OF THE INVENTION
Field
[0001] The present invention relates to a power conversion system
capable of reducing variations of currents flowing through a
plurality of power modules connected in parallel to each other.
Background
[0002] A power conversion system such as an inverter device is
constructed of a plurality of power modules equipped with switching
devices such as IGBTs or MOSFETs connected in parallel to each
other and configured to achieve a necessary output capacity by
causing these power modules to perform switching operations.
Unbalanced current sharing caused by variations of characteristics
of the plurality of power modules is known to cause not only an
operation defect of a system or adverse effects on the
characteristics but also a temperature rise due to current
concentration, malfunctioning or reduction in the service life of
the system. A method is proposed which adjusts ON/OFF timings of a
plurality of switching devices connected in parallel to each other
based on electrical characteristic information of the switching
devices created on the basis of test results (e.g., see Patent
Literature 1: JP 2009-225531 A).
SUMMARY
[0003] However, the switching characteristics of the power modules
connected in parallel to each other are not determined by the
characteristics of the respective switching devices alone. For
example, a temperature variation may occur due to influences of an
arrangement of power modules on a cooling system, which produces
variations in currents flowing through the plurality of power
modules in actual use, resulting in a deviation of adjustment of
the switching characteristics.
[0004] The present invention has been implemented to solve the
above-described problems and it is an object of the present
invention to provide a power conversion system capable of reducing
variations of currents flowing through a plurality of power modules
connected in parallel to each other.
[0005] A power conversion system according to the present invention
includes: a plurality of power modules connected in parallel to
each other, a plurality of drive circuits driving the plurality of
power modules based on input signals respectively; a plurality of
correction sections correcting the input signals inputted to the
plurality of drive circuits based on a plurality of correction
values respectively; a temperature detection section detecting
operating temperatures of the plurality of power modules; and a
calculation section estimating current switching characteristics of
the plurality of power modules based on the measured operating
temperatures and temperature dependency of switching
characteristics of the plurality of power modules, and calculating
the plurality of correction values based on the estimated current
switching characteristics so as to reduce variations of currents
flowing through the plurality of power modules.
[0006] In the present invention, the current switching
characteristics of the plurality of power modules are estimated
based on the measured operating temperature and temperature
dependency of the switching characteristics, and a plurality of
correction values are calculated based on the estimated current
switching characteristics so as to reduce variations of the
currents flowing through the plurality of power modules. A
plurality of input signals to be inputted to the plurality of drive
circuits are corrected based on the plurality of correction values
respectively.
[0007] It is thereby possible to reduce variations of currents
flowing through the plurality of power modules connected in
parallel to each other.
[0008] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a diagram illustrating a power conversion system
according to a first embodiment.
[0010] FIG. 2 is a diagram illustrating a collector current Ic and
a collector-emitter voltage Vee of the switching device driven
based on an input signal VIN.
[0011] FIG. 3 is a diagram illustrating a method of estimating the
switching characteristic.
[0012] FIG. 4 is a diagram illustrating a flowing current when ON
timings of the two power modules do not coincide with each
other.
[0013] FIG. 5 is a diagram illustrating a flowing current when ON
timings of the two power modules are aligned.
[0014] FIG. 6 is a diagram illustrating a power conversion system
according to a second embodiment.
[0015] FIG. 7 is a diagram illustrating a power conversion system
according to a third embodiment.
DESCRIPTION OF EMBODIMENTS
[0016] A power conversion system according to the embodiments of
the present invention will be described with reference to the
drawings. The same components will be denoted by the same symbols,
and the repeated description thereof may be omitted.
First Embodiment
[0017] FIG. 1 is a diagram illustrating a power conversion system
according to a first embodiment. A plurality of power modules 1 and
2 connected in parallel to each other operate in-phase with each
other. Each of power modules 1 and 2 is a half bridge circuit
including two switching devices SW1 and SW2 such as IGBTs or
MOSFETs. Free-wheel diodes D1 and D2 are connected inversely
parallel to the switching devices SW1 and SW2 respectively.
[0018] The power modules 1 and 2 are each provided with a
temperature detection section 3 and the temperature detection
section 3 outputs an operating temperature of the corresponding
power module. The temperature detection section 3 is, for example,
a temperature sensing diode disposed on the switching device SW1 or
SW2 such as a thermistor disposed on a current path or in the
vicinity of the switching device SW1 or SW2.
[0019] A control section 4 controls the switching devices SW1 of
the power modules 1 and 2, and a control section 5 controls the
switching devices SW2 of the power modules 1 and 2. A configuration
of the control section 4 will be described below, and a similar
configuration also applies to the control section 5. In the control
section 4, an input signal generation section 6 such as a CPU
generates an input signal. A plurality of drive circuits 7 and 8
drive the switching devices SW1 of the plurality of power modules 1
and 2 based on their respective input signals.
[0020] FIG. 2 is a diagram illustrating a collector current Ic and
a collector-emitter voltage Vce of the switching device driven
based on an input signal V.sub.IN. Reference character "tr" denotes
a rising time, which is also referred to as an elevating time,
representing a time period required for a flowing current to
increase from 10% to 90% when, for example, an ON-state flowing
current is assumed to be 100%. Reference character "tf" denotes a
falling time, which is also referred to as a lowering time,
representing a time period required for a flowing current to
decrease from 90% to 10%. Reference character "tc (on)" denotes a
time period required to turn on, representing a time period
required after the flowing current increases to 10% until an
applied voltage decreases down to 10%, where, for example, an
ON-state flowing current is assumed to be 100% and an OFF-state
applied voltage is assumed to be 100%. Reference character "tc
(off)" denotes a time period required to turn off, representing,
for example, a time period required after the applied voltage
increases to 10% until the flowing current decreases down to
10%.
[0021] Reference character "td (on)" denotes a turn-on delay time,
representing, for example, a time period required after an input
signal turns ON until the flowing current flows by 10%.
[0022] Reference character "td (off)" denotes a turn-off delay
time, representing, for example, a time period required after the
input signal turns OFF until the flowing current decreases down to
90%.
[0023] Reference character "ton" denotes a total value of td (on)
and tr. Reference character "toff" denotes a total value of td
(off) and tf.
[0024] A plurality of correction sections 9 and 10 correct input
signals inputted to the plurality of drive circuits 7 and 8 based
on a plurality of correction values respectively. The correction
sections 9 and 10 are delay circuits or the like that advance or
delay an input signal in accordance with the correction values.
[0025] A recording section 11 records inspection results of the
switching characteristics of the plurality of power modules 1 and 2
subjected to shipment inspections and inspection temperatures which
are operating temperatures during the inspections as shipment
inspection results. The recording section 11 also records matrix
data showing a correlation between the switching characteristics
and the operating temperatures as a calculation table. Note that
the calculation table can be created using typical switching
characteristic information plotted with operating temperatures and
flowing currents provided by a power module maker. Without being
limited to this, the calculation table may also be created based on
results of confirming temperature dependency of switching
characteristics in actual use of the power modules mounted on the
actual power conversion system within ranges of expected operating
temperatures, applied voltages and flowing currents.
[0026] Examples of common shipment inspections include a DC current
flowing test (static characteristic evaluation), insulation test,
switching test under single-pulse or multi-pulse current flowing on
an L load half bridge circuit. The inspected switching
characteristics are at least one of tr, tf, tc (on), to (off), td
(on), td (off), ton and toff. The power modules are each assigned
an identification number such as a lot number, running number and
thereby shipped in a one-to-one correspondence with several values
of the shipment inspection results.
[0027] A calculation section 12 estimates temperature dependency of
the switching characteristics of the plurality of power modules 1
and 2 based on the shipment inspection results and estimates the
current switching characteristics of the plurality of power modules
1 and 2 based on the measured operating temperature and the
estimated temperature dependency of the switching characteristics.
Note that since the temperature dependency of the switching
characteristics of each of power modules 1 and 2 is specific to
each power module and invariable, these may be saved in the
recording section 11 to shorten the calculation time.
[0028] FIG. 3 is a diagram illustrating a method of estimating the
switching characteristic. If the switching characteristic of the
power module 1 has first temperature dependency and the operating
temperature of the power module 1 is T1, the current switching
characteristic of the power module 1 is estimated to be a rising
time tr1. Similarly, if the switching characteristic of the power
module 2 has second temperature dependency and the operating
temperature of the power module 2 is 2, the current switching
characteristic of the power module 2 is estimated to be a rising
time tr2.
[0029] FIG. 4 is a diagram illustrating a flowing current when ON
timings of the two power modules do not coincide with each other. A
common input signal VM is inputted to the two power modules, but
since their rising times tr1 and tr2 are different, ON timings do
not coincide with each other. In this case, a flowing current
transiently and intensively flows through the power module which is
started earlier. After that, when the other power module is
started, the flowing current is distributed between the two power
modules according to an extent of opening of gates of the modules,
an inductance component of an external or internal wiring, capacity
components of the modules or the like. In this case, di/dt and
dv/dt fluctuate. Transient current concentration may cause greater
switching loss than expected and repetition of such loss may cause
concern about a temperature rise and an extreme reduction of the
service life of the power modules.
[0030] Therefore, the calculation section 12 aligns switching
ON/OFF timings of the plurality of power modules 1 and 2 based on
the estimated current switching characteristics and calculates a
plurality of correction values so as to reduce variations of
currents flowing through the plurality of power modules 1 and 2.
Here, a difference .DELTA.t between the estimated rising times of
the power modules 1 and 2 is used as a correction value.
[0031] FIG. 5 is a diagram illustrating a flowing current when ON
timings of the two power modules are aligned. The ON timings are
aligned by adjusting delay amounts of input signals V.sub.IN1 and
V.sub.IN2 to be inputted to the two power modules respectively.
After both of the two power modules are placed in an ON stationary
state, the flowing current is distributed so that a voltage drop
during energization of both modules becomes constant. This prevents
the flowing current from concentrating on one power module, and can
thereby prevent an increase in switching loss, an accompanying
temperature rise of the switching devices and an extreme reduction
of the service life. Furthermore, since excessive concentration of
the flowing current can be suppressed, the variation of device
temperature also decreases and the variations of di/dt and dv/dt
also decrease as a consequence.
[0032] When the calculation section 12 is of a timer type, the
calculation section 12 reads temperature information again every
constant periods and recalculates a correction value. When the
calculation section 12 is of an event type, the calculation section
12 recalculates a correction value at timing at which an operating
temperature increases or decreases by a certain amount, for
example, 5.degree. C. from the previous calculation. Since the
recalculated correction value needs to be applied in an OFF state
or in a situation in which the flowing current is 0 A or the like,
a process is performed whereby an old correction value held is
discarded for an application of the next or an arbitrary input
signal so as to be replaced by a new correction value. Furthermore,
when the switching characteristic of each power module is estimated
at a certain operating temperature and a correction value is
calculated, the correction value may be held for a certain time
period and input signals such as PWM (pulse width modulation)
signals may be continuously corrected in a simplified manner. This
allows switching characteristics during actual use to be fed back
without increasing a calculation load.
[0033] As described above, in the present embodiment, the current
switching characteristics of the plurality of power modules 1 and 2
are estimated based on the measured operating temperature and
temperature dependency of the switching characteristics, and a
plurality of correction values are calculated based on the
estimated current switching characteristics so as to reduce
variations of the currents flowing through the plurality of power
modules 1 and 2. A plurality of input signals to be inputted to the
plurality of drive circuits 7 and 8 are corrected based on the
plurality of correction values respectively. It is thereby possible
to reduce variations of currents flowing through the plurality of
power modules 1 and 2 connected in parallel to each other.
[0034] The switching characteristics fluctuate according to an
operating temperature, applied voltage, flowing current, circuit
conditions or the like. However, compared to fluctuations according
to an applied voltage and flowing current, greater fluctuations are
generally attributable to circuit conditions such as routing of
main electrodes or signal wiring and temperatures. Therefore, in
the case of a power conversion system such as an inverter with
fixed ranges of applied voltage and flowing current, it is possible
to estimate the current switching characteristics of the power
modules based on the measured operating temperature and temperature
dependency of the switching characteristics.
[0035] When the switching characteristics, fluctuations of which
are large relative to that of the flowing current or applied
voltage are used as shipment inspection results, there are concerns
that the correction accuracy may deteriorate when the flowing
current or applied voltage fluctuates considerably at startup or
during high load operation or the like. Therefore, the switching
characteristics are preferably at least one of tr, tf, to (on), to
(off), td (on), td (off), ton and toff. Since fluctuations of these
switching times caused by a current or voltage are small, it is
possible to correct switching timing more accurately by simple
calculations and improve current unbalance. Note that switching
times generally have small current dependency, but the current
dependency differs depending on the structure of a switching device
such as an IGBT or MOSFET, and the material such as Si or SiC.
Therefore, it is necessary to select a shipment inspection result
according to the characteristics. For example, in the case of a
power module equipped with an IGBT of a Si material, td (on), td
(off), ton, toff or the like generally has small current dependency
and is suitable for shipment inspection results. On the other hand,
in the case of a power module equipped with a drive circuit, since
td (on), td (off), ton or toff includes a delay time of the drive
circuit, such a power module has an advantage that corrections can
be made with characteristic variations taken into
consideration.
[0036] The calculation section 12 is implemented by a processing
circuit such as a CPU or a system LSI that executes a program
stored in memory. Furthermore, a plurality of processing circuits
may operate in cooperation to execute the above-described
functions. An input signal may be corrected by software using the
calculation section 12 but correcting an input signal by hardware
through the correction sections 9 and 10 can further reduce the
load and the number of output pins of the calculation section
12.
[0037] Variations of a flowing current are generated under the
influence of an arrangement of the switching devices SW1 and SW2 in
the power modules 1 and 2, arrangement of the power modules 1 and 2
connected in parallel to each other, position of the power supply
or electrolytic capacitor or the like relative to a DC voltage
source, length or routing of main wiring or outside wiring such as
signal wiring or the like. Furthermore, variations of switching
characteristics are also generated under the influence of
temperature variations due to an arrangement of power modules on a
cooling system. In such a case, it is preferable to improve the
arrangement of the switching devices or the power modules, routing
of signal wiring or the like. However, there may be cases where
uniform arrangement is not possible due to apparatus constraints.
Thus, it is preferable to confirm effects on the switching
characteristics of the arrangement of the switching devices or
power modules, routing of wiring or the like through evaluations of
initial products of the power conversion system or the like, and
reflect the effects in the calculation table. By superimposing
these effects on the characteristics of each power module estimated
based on the operating temperature and the shipment inspection
results, it is possible to more accurately calculate a correction
value of each power module.
[0038] When, for example, a three-phase inverter circuit is
constructed by connecting two power modules having six switching
devices in parallel to each other, correction values of the
switching devices with the respective phases are deduced using a
common calculation table and corrections are made according to the
position relative to the main electrode and circuit conditions such
as routing of signal wiring. Therefore, even when the shipment
inspection result and the operating temperature are the same,
correction values may vary from one phase to another.
[0039] As the power modules 1 and 2, power modules with one device
or six devices or power modules for a single-phase inverter or a
three-phase inverter circuit or the like may be used. Protective
circuits for overheat protection, short circuit protection, supply
voltage reduction protection or the like may be provided. Although
the input signal generation section 6 is provided separately from
the calculation section 12, an input signal may be generated by
software using the calculation section 12 and the recording section
11. Although a drive circuit is connected for each switching
device, the plurality of switching devices in one power module or
the plurality of power modules 1 and 2 may be switched by a common
drive circuit such as an LVIC. An input signal may be level-shifted
using a drive circuit such as an HVIC and the P side (high side)
and the N side (low side) of the same phase or a plurality of
phases such as all phases of the P side may be switched using a
common drive circuit.
Second Embodiment
[0040] FIG. 6 is a diagram illustrating a power conversion system
according to a second embodiment. In the present embodiment, the
power modules 1 and 2 are each provided with a recording section
13. The recording section 13 records a shipment inspection result
of the corresponding power module. This easily makes sure to bring
the power modules into one-to-one correspondence with their
shipment inspection results. The control section 4 reads the
shipment inspection results from the power modules 1 and 2 upon the
initial starting or at every start, and records the shipment
inspection results in the recording section 11. A product
assembling step can be simplified because the shipment inspection
results of the respective power modules 1 and 2 need not be
inputted to the recording section 11 of the control section 4 in
assembling the power conversion system. Furthermore, the power
modules can be replaced or changed as field maintenance at the
installation place after shipment of the power conversion system.
In that case, the system may be reset and read again after the
maintenance. Note that when the shipment inspection results are
held in the recording section 11 of the control section 4 upon the
initial starting, the system may be reset and read again after
field maintenance.
Third Embodiment
[0041] FIG. 7 is a diagram illustrating a power conversion system
according to a third embodiment. In the present embodiment, the
power module 1 is provided with not only the recording section 13
but also a drive circuit 7 such as an HVIC or LVIC and a correction
section 9. Similarly, the power module 2 is provided with a drive
circuit 8 and a correction section 10. The recording section 13
records not only shipment inspection results but also calculated
correction values.
[0042] At switching OFF timing, the drive circuit 7 reads a
correction value from the recording section 13 every time or once
every several times. The drive circuit 7 selects a delay circuit of
the correction section 9 according to the correction value and the
correction section 9 corrects input signals with a specific phase
or all phases. Note that the drive circuit 7 may also read a
correction value at timing at which the correction value is
rewritten or at timing at which all the three phases of the input
signals are turned OFF according to an instruction from the
calculation section 12 of the control section 4.
[0043] Since input signals are corrected in the power modules 1 and
2, the input signals applied to the power modules 1 and 2 are made
common. Since this makes routing of wiring in the control section 4
simpler, the design of the control section 4 becomes simple and it
is possible to use an inexpensive wiring board and signal wiring as
the control section 4.
[0044] Note that a control circuit that selects a delay circuit of
the correction section 9 may be provided in the power device. When
the correction value is changed due to a change in the temperature
condition or the like, a new correction value may be overwritten at
the same address of the recording section 13. It is possible to
read data from and write data to the recording section 13 from the
calculation section such as the microcomputer, CPU or DSP of the
control section 4 outside the power modules 1 and 2. At least one
of the correction section 9 and the recording section 13 may be
equipped in the drive circuit 7, which makes it possible to improve
accuracy and reduce a transmission delay time.
[0045] The correction section 9 is not limited to a delay circuit
that corrects an input signal by hardware, but may be a
microcomputer that corrects an input signal by software. When an
input signal is corrected by software, since the input signal
corrected for each of the power modules 1 and 2 is calculated and
outputted in the first and second embodiments, the number of
outputs of the microcomputer increases according to the number of
power modules connected in parallel to each other. On the other
hand, in the third embodiment, since the common input signal is
applied to the power modules 1 and 2, there is no need to increase
the number of outputs of the microcomputer or the like. For
example, in the case of a three-phase PWM control system in which
two power modules, each including 6 devices, are connected in
parallel to each other and driven, the number of necessary outputs
of the microcomputer is 6 devices.times.2=12 pins in the first and
second embodiments, whereas it is 6 pins in the third embodiment.
Thus, the design of substrate wiring becomes simpler and a more
inexpensive PCB substrate can be used.
[0046] Without being limited to the configuration in which the
recording section 13 and the drive circuit 7 are connected to each
of the switching devices SW1 and SW2, a configuration may be
adopted in which a common recording section and a common drive
circuit are connected to a plurality of switching devices or a
plurality of phases. A configuration may also be adopted in which
an input signal is level-shifted by a drive circuit such as an
HVIC, and the P side (high side) and the N side (low side) of the
same phase or a plurality of phases such as all phases of the P
side are switched using a common memory and a common drive
circuit.
[0047] Note that the switching devices SW1 and SW2 are not limited
to ones formed of silicon, but may also be formed of a wide
band-gap semiconductor having a greater band-gap than that of
silicon. The wide band-gap semiconductor is, for example, silicon
carbide, nitride gallium-based material or diamond. An device
formed of such a wide band-gap semiconductor has high withstand
voltage or high allowable current density, and can thereby be
downsized. Using this downsized device also makes it possible to
downsize and highly integrate a power conversion system
incorporating this device. In addition, since the device exhibits
high heat resistance, it is possible to downsize radiator fins of a
heat sink, replace a water-cooling section with an air-cooling
system, and thereby further downsize the power conversion system.
Moreover, since the device exhibits low power loss and high
efficiency, it is possible to increase efficiency of the power
conversion system.
[0048] Furthermore, when the power module is driven, conduction
loss and switching loss occur, and temperature rises. As the
temperature rises, electric resistance increases causing less
current to flow, and so current unbalance among a plurality of
power modules connected in parallel to each other tends to be
improved. On the other hand, a power module equipped with a silicon
carbide switching device has significantly lower conduction loss
and switching loss than those of a silicon switching device. For
example, in an inverter operation using power modules of the same
current rating, an inverter using a silicon carbide switching
device has switching loss of approximately 30% of that in an
inverter using a silicon switching device and has a smaller
temperature rise than that of the inverter using a silicon
switching device. Therefore, when the silicon carbide switching
device is used, an improvement of current unbalance caused by
temperatures cannot be expected, and so it is necessary to reduce
variations of currents flowing through a plurality of power modules
as in the case of the present embodiment.
[0049] Furthermore, there may also be a case where as the
temperature rises, the electric resistance of the switching devices
decreases, which facilitates the current flow. In this case,
current concentration is more likely to occur, and so an
improvement cannot be expected either due to the temperature rise,
and it is therefore necessary to reduce variations of currents
flowing through the plurality of power modules as in the case of
the present embodiment.
[0050] A silicon carbide switching device using a new material and
structure, compared to a silicon switching device, has insufficient
technology and know-how accumulation such as quality stability of
materials such as wafers, manufacturing constraints and a chip
structure. For this reason, there are concerns about variations of
stationary characteristics or switching characteristics. Correcting
variations of switching characteristics according to the present
embodiment makes it possible to relax the product standard of power
modules, lead to an improvement of manufacturing yield and stable
production, provide and use more inexpensive silicon carbide power
modules.
[0051] Obviously many modifications and variations of the present
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
[0052] The entire disclosure of Japanese Patent Application No.
2017-228236, filed on Nov. 28, 2017 including specification,
claims, drawings and summary, on which the Convention priority of
the present application is based, is incorporated herein by
reference in its entirety.
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