WO2024100695A1

WO2024100695A1 - Power converter

Info

Publication number: WO2024100695A1
Application number: PCT/JP2022/041305
Authority: WO
Inventors: 雄希木村; 浩之清永
Original assignee: 三菱電機株式会社
Priority date: 2022-11-07
Filing date: 2022-11-07
Publication date: 2024-05-16
Also published as: JP7241996B1

Abstract

An inverter (50), which is an example of a power conversion device, comprises a power module (40) incorporating legs (20a to 20c) constituted by sets of two switching elements (1a, 2a), (3a, 4a), and (5a, 6a), respectively, that are electrically connected in series, and operates the power module (40) to supply load power to a load device (8). When the temperature of at least one of the legs (20a to 20c) during a non-driving period, in which the supply of load power to the load device (8) is stopped, decreases by at least a certain value as compared to the temperature of the leg immediately after the supply of load power is stopped, the inverter (50) implements short circuit control by repeatedly performing the operation of electrically shorting, for a specified period of time, the switching elements of the upper and lower arms of at least the leg where the temperature has decreases by at least a certain value.

Description

Power Conversion Equipment

This disclosure relates to a power conversion device incorporating a power semiconductor element.

Examples of power conversion devices include inverters, converters, and uninterruptible power supplies (UPS). This type of power conversion device has multiple built-in power semiconductor elements, and power conversion is performed by a drive circuit that controls the switching of the multiple power semiconductor elements. Generally, IGBTs (Insulated Gate Bipolar Transistors) and MOS-FETs (Metal Oxide Semiconductor Field-Effect Transistors) are used as power semiconductor elements.

The power conversion device has at least one leg consisting of at least two power semiconductor elements connected in series. If there are multiple legs, the multiple legs are connected in parallel to each other. This connection form is called a "bridge connection."

Typically, one or more power semiconductor elements used in power conversion devices are often sealed and configured as a package. The sealed package is called a "power module." Power semiconductor elements are packaged to simplify the electrical connection between the power semiconductor elements or between the power semiconductor elements and other electrical components, and to improve the heat dissipation of the power semiconductor elements. A power module is configured with silicon chips that make up the IGBTs or MOS-FETs, silicon chips that make up the rectifier elements, metal pads for wire bonding, external terminals of the module, metal wires that connect the silicon chips, etc.

In a power conversion device, power conversion is performed by switching the power semiconductor elements built into the power module. During this process, the power semiconductor elements generate a lot of heat. Therefore, when a power conversion device is operated intermittently, the power semiconductor elements experience rapid temperature changes.

The linear expansion coefficient of the silicon chip is different from that of the metal wire. For this reason, it is known that shear stress occurs between the silicon chip and the metal wire with each temperature change, causing the wire to peel off. If the wire peeling progresses, the electrical connection by the metal wire is severed, causing the power module to malfunction and leading to failure of the device equipped with the power module. The resistance to the shear stress that occurs between the silicon chip and the metal wire when the temperature changes is generally called the "power cycle resistance."

As mentioned above, power modules are components with a finite lifespan, and so it has been common to predict the lifespan of a power module based on its power cycle tolerance. For example, the following Patent Document 1 proposes a method of detecting an increase in thermal resistance between a metal base and a power device, and detecting failure of the power module in advance based on the degree of increase in thermal resistance. Patent Document 1 also describes that by determining the timing of replacing a power module based on the predicted lifespan, it is possible to reduce the margin beyond the margin that should be maintained for the predicted time of failure, and to extend the maintenance cycle for replacement, etc.

JP 2017-017822 A

However, the technology in Patent Document 1 merely predicts the lifespan of a power module in order to reduce margins in maintenance cycles such as replacement, and is not a technology that directly extends the lifespan of a power module. In addition, the technology in Patent Document 1 does not have the effect of mitigating the shear stress that occurs between the silicon chip and the metal wire, and if the power module is used under conditions in which temperature changes occur frequently, the lifespan of the power module will be shortened.

The present disclosure has been made in consideration of the above, and aims to obtain a power conversion device that can suppress shortening of the lifespan of a power module, even when the power module is used under operating conditions in which temperature changes occur frequently.

In order to solve the above-mentioned problems and achieve the object, the power conversion device according to the present disclosure includes a power module incorporating at least one of the legs formed by electrically connecting at least two or more semiconductor elements in series, and supplies load power to a load device by operating the power module. During a non-driving period in which the supply of load power to the load device is stopped, when the temperature of at least one leg drops by a certain value or more compared to the temperature of the leg immediately after the supply of load power is stopped, the power conversion device performs short-circuit control by repeatedly performing an operation of electrically shorting, for a specified time, at least the semiconductor elements of the upper and lower arms of the leg whose temperature has dropped by the certain value or more.

The power conversion device disclosed herein has the effect of preventing shortening of the lifespan of the power module, even when the power module is used under operating conditions in which temperature changes occur frequently.

Electrical circuit configuration diagram of an inverter according to the first embodiment FIG. 1 is a plan view of a power module included in an inverter according to a first embodiment; FIG. 2 is a diagram in which a calculation unit, a drive circuit, and a thermistor are added to the electric circuit configuration diagram of the inverter according to the first embodiment shown in FIG. 1. A comparative example showing the temperature change when a switching element built into a power module is driven using a conventional method. FIG. 13 is a diagram showing a state of temperature change when a switching element built into a power module is driven using the method of the first embodiment. 1 is a flowchart used to explain a control flow according to the first embodiment. Electric circuit configuration diagram of an inverter according to a second embodiment 1 is a flowchart used to explain a control flow according to the second embodiment.

Below, a power conversion device according to an embodiment of the present disclosure will be described in detail with reference to the attached drawings. Note that in the following embodiment, an inverter that converts direct current to alternating current will be described as an example of a power conversion device, but this is not intended to exclude application to power conversion devices other than inverters. In other words, the technology of the present disclosure can also be applied to power conversion devices other than inverters.

Embodiment 1.
Fig. 1 is an electric circuit diagram of an inverter 50 according to the first embodiment. As shown in Fig. 1, the inverter 50 includes a DC power supply 10 that outputs a DC voltage, a capacitor 9 that smoothes the DC voltage output by the DC power supply 10, and an inverter main circuit unit 7. The inverter main circuit unit 7 includes switching elements 1a to 6a that perform switching, and rectifier elements 1b to 6b that are connected in parallel to the switching elements 1a to 6a, respectively. The inverter main circuit unit 7 supplies three-phase AC power to a load device 8. Examples of the load device 8 include an induction motor and a permanent magnet motor.

Each of the switching elements 1a to 6a is a power semiconductor element. Typical power semiconductor elements include IGBTs and MOS-FETs. The rectifier elements 1b to 6b include diodes and thyristors. If each of the switching elements 1a to 6a is a MOS-FET, the parasitic diode of the MOS-FET may be used as the rectifier elements 1b to 6b.

Capacitor 9 is arranged to stabilize the voltage of the DC section of inverter 50. The DC section is the electrical wiring that electrically connects capacitor 9 to inverter main circuit section 7. When inverter main circuit section 7 supplies three-phase AC power to load device 8, the capacitor voltage, which is the voltage across capacitor 9, is maintained within a certain range of voltage values. This voltage maintained within a certain range is called the "bus voltage."

In the inverter main circuit section 7, switching

elements

1a and 2a are connected in series to form leg 20a, switching

elements

3a and 4a are connected in series to form leg 20b, and switching

elements

5a and 6a are connected in series to form leg 20c. Of the switching elements 1a to 6a that make up the legs, the

switching elements

1a, 3a, and 5a located on the high potential side are called the "upper arm switching elements," and the

switching elements

2a, 4a, and 6a located on the low potential side are called the "lower arm switching elements."

The connection points of each switching element in legs 20a to 20c form intermediate

potential points

18a, 18b, and 18c. In the inverter main circuit section 7, wiring is drawn from each of these intermediate

potential points

18a, 18b, and 18c and connected to the load device 8.

The inverter 50 supplies three-phase AC power to the load device 8, for example, by PWM (Pulse Width Modulation) control. Note that PWM control uses known technology and will not be described in this specification.

The inverter main circuit section 7 shown in FIG. 1 has three legs 20a-20c and has a three-phase configuration that supplies three-phase AC power to the load device 8, but is not limited to this configuration. The number of legs may be one or two, or may be four or more. When there is one leg, it is called a "half bridge", and when there are two legs, it is called a "single-phase bridge", "full bridge", etc. Also, in each of the legs 20a-20c, the number of elements connected in series is two, but this example is not limiting. The number of elements connected in series may be three or more.

In the inverter 50 configured as described above, the switching elements 1a to 6a and the rectifier elements 1b to 6b are high heat generating components. Therefore, these high heat generating components are sealed with resin and configured as a single power module 40. This configuration has the advantage that it is only necessary to provide a heat dissipation mechanism for the power module 40, making it possible to simplify the heat dissipation mechanism.

The power module 40 is mounted on a printed circuit board (not shown in FIG. 1) and is electrically connected to the load device 8 and the capacitor 9 via the printed circuit board. A heat dissipation component (not shown) is attached to the power module 40. An example of a heat dissipation component is a heat dissipation fin. The heat dissipation component operates to keep the temperature of the high heat generating components built into the power module 40 below an allowable temperature.

FIG. 2 is a plan view of the power module 40 included in the inverter 50 according to the first embodiment. In FIG. 2, the components shown in FIG. 1 are indicated with the same reference numerals.

Silicon chips

11 and 12 are mounted on the printed circuit board 45. The silicon chip 11 corresponds to the switching elements 1a to 6a, and the silicon chip 12 corresponds to the rectifying elements 1b to 6b. The silicon chip 11 and the metal pad 14 are electrically connected by wire bonding the metal wire 13. For the metal wire 13, a metal wire such as gold, aluminum, or copper is used. The metal wire 13 is used when electrically connecting the

silicon chips

11 and 12 to other electrical components, and between the

silicon chips

11 and 12. For example, in FIG. 2, the

silicon chips

11 and 12, and the silicon chip 12 and the metal pad 14 are also electrically connected by the metal wire 13.

Module external terminals 15 are also provided on the printed circuit board 45. The module external terminals 15 are inserted into through holes provided in the printed circuit board 45 and connected with solder or the like. The module external terminals 15 are also electrically connected to the metal pads 14 by wiring. This electrically connects the module external terminals 15 to the circuit pattern formed on the printed circuit board 45.

FIG. 3 is a diagram in which the calculation unit 30, drive circuit 60, and thermistor 90 have been added to the electrical circuit configuration diagram of the inverter 50 according to the first embodiment shown in FIG. 1.

In FIG. 3, a shunt resistor 16 is inserted in each of legs 20a to 20c on the low potential side, i.e., the emitter terminal side, of the lower

arm switching elements

2a, 4a, and 6a, and a voltage measurement circuit 17 is connected to both ends of the shunt resistor 16. The inverter 50 also includes a thermistor 90.

The shunt resistor 16 is a current measuring resistor used to measure the current flowing through the

switching elements

2a, 4a, and 6a of the lower arm. The shunt resistor 16 may be disposed inside the power module 40, or may be disposed on the printed circuit board 45 on which the power module 40 is mounted. The voltage measuring circuit 17 is composed of an isolation element, for example a photocoupler or an isolation amplifier, and a signal amplification element, such as an operational amplifier. Here, the isolation element is used to electrically isolate the legs 20a to 20c from the calculation unit 30.

Thermistor 90 is used to measure the ambient temperature of inverter 50. Thermistor 90 is typically attached to the housing of inverter 50 (not shown), but is not limited to this configuration. Thermistor 90 can be attached anywhere on inverter 50 as long as it can measure the ambient temperature of inverter 50.

Information about the ambient temperature of the inverter 50 measured by the thermistor 90 is input to the calculation unit 30. The thermistor 90 may be an element having a nonlinear temperature-resistance characteristic, such as an NTC (Negative Temperature Coefficient) type, a PTC (Positive Temperature Coefficient) type, or a CTR (Critical Temperature Resistor) type. Note that the method of reading temperature information from the resistance characteristic of the thermistor 90 is a publicly known technique, and will not be described in this specification. Note that in this document, the part of the circuit that includes the thermistor 90 and transmits the measurement results of the thermistor 90 to the calculation unit 30 may be referred to as the "first temperature measurement circuit."

The voltage across the shunt resistor 16 is input to the calculation unit 30 via the voltage measurement circuit 17. The calculation unit 30 can be realized by a processing circuit having a processor and a memory. The calculation unit 30 may also be realized by a dedicated processing circuit instead of a processor and a memory. As the dedicated processing circuit, an integrated circuit such as an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a microcomputer (microcomputer) is used. The calculation unit 30 also includes a memory area 30a. The memory area 30a may be the memory of the processing circuit. The temperature information measured by the thermistor 90 and the voltage information measured by the voltage measurement circuit 17 are stored in the memory area 30a.

An external command 80 is input to the calculation unit 30. Here, the external command 80 is a drive command input from outside the inverter 50 to operate the inverter 50. The calculation unit 30 inputs an operation command for the switching elements 1a to 6a to the drive circuit 60 based on the external command 80. The drive circuit 60 drives the inverter main circuit unit 7 by outputting a drive signal 70 to the switching elements 1a to 6a.

While switching elements 1a to 6a are being driven by drive signal 70, calculation unit 30 estimates the current flowing through legs 20a to 20c based on the voltage information of shunt resistor 16 input via voltage measurement circuit 17. The current estimated by calculation unit 30 is stored as an estimated current in memory area 30a.

Here, the memory area 30a stores a conversion table that converts the current flowing through the legs 20a to 20c into temperature. The calculation unit 30 calculates the temperature of the legs 20a to 20c based on the estimated current of the legs 20a to 20c stored in the memory area 30a. The conversion table stored in the memory area 30a is specific to each power module 40 used, and is provided for each power module 40. In addition, this conversion table is constructed for each power module 40 by measuring in advance the relationship between the current flowing through the power module 40 and the temperature in the legs 20a to 20c. In addition, the memory area 30a stores the thermal resistance value between the legs 20a to 20c and the heat dissipation components attached to the power module 40. This thermal resistance value is a value specific to each inverter 50.

Since the calculation unit 30 provides the drive signal 70 to the switching elements 1a to 6a based on the external command 80, the calculation unit 30 itself can determine whether the inverter 50 is operating or not. The external command 80 also includes a drive stop command to stop the operation of the inverter 50. Therefore, the calculation unit 30 can store the temperature information of the legs 20a to 20c when the inverter 50 stops driving in the memory area 30a, just as when the inverter 50 is operating.

When the inverter 50 is operating, current flows through the switching elements 1a to 6a, generating heat loss due to conduction and heat loss due to switching operation. These heat losses cause the power module 40, which encapsulates the switching elements 1a to 6a, to generate heat. At this time, the temperature of the switching elements 1a to 6a inside the power module 40 becomes higher than the ambient temperature of the inverter 50.

When the inverter 50 is in a resting state, the temperature of the switching elements 1a to 6a is approximately the same as the ambient temperature of the inverter 50. Therefore, when comparing when the inverter 50 is driven with when the inverter 50 is in a resting state, a temperature difference ΔT occurs between the two. As mentioned above, the linear expansion coefficients of the switching elements 1a to 6a and the metal wire 13 are different, so every time the temperature of the switching elements 1a to 6a changes, shear stress is generated between the switching elements 1a to 6a and the metal wire 13, which causes wire peeling, in which the metal wire 13 peels off.

On the other hand, if the temperature difference ΔT between the switching elements 1a to 6a when the inverter 50 is operating and when the inverter 50 is in a resting state can be reduced, the shear stress generated between the switching elements 1a to 6a and the metal wire 13 can be mitigated. This can extend the life of the power module 40 due to its power cycle resistance.

Next, the control method of the first embodiment for reducing the temperature difference ΔT in the switching elements 1a to 6a built into the power module 40 will be described with reference to Figs. 4 to 6. Fig. 4 is a diagram showing, as a comparative example, how the temperature changes when the switching elements 1a to 6a built into the power module 40 are driven using a conventional method. Fig. 5 is a diagram showing how the temperature changes when the switching elements 1a to 6a built into the power module 40 are driven using the method of the first embodiment. Fig. 6 is a flowchart used to explain the control flow relating to the method of the first embodiment.

4 and 5, the upper part shows the waveform of the current flowing through one leg, and the lower part shows the waveform of the temperature change of the power semiconductor element belonging to that leg. In each figure, _TR represents the inverter ambient temperature before the inverter drive command is input, i.e., before the inverter is driven, and _TE represents the temperature of the legs 20a to 20c immediately after the inverter is stopped.

When an inverter drive command is input to the calculation unit 30 by an external command 80, the calculation unit 30 provides a drive signal 70 to the switching elements 1a to 6a via the drive circuit 60. This causes the inverter 50 to start driving. When driving starts, three-phase AC power is supplied to the load device 8, and current flows through the legs 20a to 20c. The switching elements 1a to 6a generate heat loss due to conduction and heat loss due to switching operations. Furthermore, the rectifier elements 1b to 6b generate heat loss due to conduction. These losses cause the temperatures of the legs 20a to 20c to rise. Furthermore, after a certain time has passed, the temperatures of the legs 20a to 20c saturate depending on the amount of current flowing through the legs 20a to 20c.

When an inverter drive stop command is input to the calculation unit 30 by the external command 80, the calculation unit 30 stops outputting the drive signal 70. As a result, the inverter 50 stops supplying three-phase AC power to the load device 8, and no current flows through the legs 20a to 20c. When the drive of the inverter 50 is stopped, the current that generates the heat loss disappears. Here, in the comparative example shown in FIG. 4, when the drive of the inverter 50 is stopped and no current is applied, no current flows through the legs 20a to 20c. Therefore, the temperature of the legs 20a to 20c when no current is applied is approximately the same as the inverter ambient temperature T _R. Therefore, a large temperature difference ΔT _J ′ occurs between the temperature of the switching elements 1a to 6a that are being driven and the temperature of the switching elements 1a to 6a that are not being driven.

In contrast, the operating waveforms when driven using the method of the first embodiment are as shown in FIG. 5. The difference from the conventional method is the operation after the inverter drive stop command is input. When an inverter drive command is input to the calculation unit 30 by an external command 80, the calculation unit 30 provides a drive signal 70 to the switching elements 1a to 6a through the drive circuit 60. This causes the inverter 50 to start driving. When driving starts, three-phase AC power is supplied to the load device 8, and current flows through the legs 20a to 20c. The switching elements 1a to 6a generate heat loss due to conduction and heat loss due to switching operation. In addition, the rectifier elements 1b to 6b generate heat loss due to conduction. These losses cause the temperature of the legs 20a to 20c to rise. In addition, after a certain time has passed, the temperature of the legs 20a to 20c saturates depending on the amount of current flowing through the legs 20a to 20c. The operation up to this point is the same as in the comparative example.

The calculation unit 30 stores the temperature T _E immediately after the inverters of the legs 20a to 20c are stopped at the time of driving end in the storage area 30a. The calculation unit 30 also performs calculation processing related to temperature estimation of the power module 40 at regular time intervals.

As described above, the storage area 30a stores thermal resistance values between the legs 20a to 20c and the heat dissipation components attached to the power module 40. The storage area 30a also stores the temperature estimates of the legs 20a to 20c and the inverter ambient temperature T _R input from the thermistor 90. The amounts of heat dissipated in the legs 20a to 20c can be calculated using the temperatures of the legs 20a to 20c, the temperature difference between the temperatures of the legs 20a to 20c and the inverter ambient temperature T _R , and the thermal resistance values between the legs 20a to 20c and the heat dissipation components. This allows the calculation unit 30 to calculate the temperatures of the legs 20a to 20c after driving is stopped.

When the calculated temperature of at least one of the legs 20a to 20c falls by a certain value or more below the temperature T _E immediately after the inverter is stopped, the calculation unit 30 instructs the drive circuit 60 to output a drive signal 70 for turning on the switching elements of the upper and lower arms of the leg whose temperature has fallen by a certain value or more. In this paper, this operation is called a "short-circuit operation". This short-circuit operation is performed for a predetermined specified time. Note that the legs on which the short-circuit operation is performed do not necessarily include only the upper and lower arms of the leg whose temperature has fallen by a certain value or more, but may include at least the leg whose temperature has fallen by a certain value or more. For example, the switching elements of the upper and lower arms of all the legs may be turned on. That is, the power conversion device according to the first embodiment performs control to electrically short-circuit the switching elements of the upper and lower arms of at least the leg whose temperature has fallen by a certain value or more among the legs 20a to 20c for a specified time when the temperature of at least one of the legs 20a to 20c falls by a certain value or more below the temperature _{T E} immediately after the inverter is stopped.

As an example of the constant value, it can be any value between 1 and 100°C. In addition, the time of the short circuit operation that turns on the upper and lower arm switching elements in at least one leg of the switching elements 1a to 6a depends on the thermal resistance value that characterizes the temperature rise of the switching elements 1a to 6a, but can be any time between 0.1 μs and 1 ms, for example.

When the switching elements 1a to 6a are short-circuited, a current flows through the switching elements 1a to 6a for a specified time via the DC power supply 10 and the capacitor 9. At this time, the calculation unit 30 raises the temperature of the switching elements 1a to 6a by conduction loss, and increases the temperature to a value close to the temperature T _E immediately after the inverter is stopped. Note that the conversion table stored in the memory area 30a is assumed to contain the amount of temperature rise of the legs 20a to 20c when the legs 20a to 20c are short-circuited for an arbitrary period of time in advance. The calculation unit 30 can estimate the temperature of the legs 20a to 20c after the short-circuit operation is performed based on the amount of temperature rise recorded in the conversion table in the memory area 30a.

The calculation unit 30 raises the temperature of the switching elements 1a to 6a to a value near the temperature T _E , and then commands the drive circuit 60 to turn off all of the switching elements 1a to 6a, i.e., to stop outputting the drive signal 70. When the output of the drive signal 70 stops, the temperature of the legs 20a to 20c starts to drop again. The calculation unit 30 repeats the flow of performing a temperature estimation calculation of the legs 20a to 20c, and performing a short-circuit operation again when the temperature of the legs 20a to 20c drops. This repeated control is referred to as "short-circuit control" in this paper. Note that this short-circuit control corresponds to the processing of steps S6 to S9 described below, and the temperature estimation calculation in the short-circuit control corresponds to the processing of step S6 in the steps S6 to S9.

By the short circuit control, the temperatures of the legs 20a to 20c have a periodic waveform in which temperature drops and temperature rises are repeated. In addition, if the specified time is set appropriately, the temperature rise due to the short circuit operation for the specified time and the temperature drop due to the rest time between the short circuit operations are harmonized, and the temperatures of the legs 20a to 20c have a waveform in which temperature drops and temperature rises are repeated around the temperature T _E immediately after the inverter is stopped, as shown in FIG.

Furthermore, the temperature difference ΔT _J , which is the amount of temperature change in the legs 20a to 20c when the short circuit control is performed, is smaller than the temperature difference ΔT when the short circuit control is not performed.

In this document, it is assumed that the user or administrator can decide whether or not to implement short circuit control. If the information regarding whether or not short circuit control is implemented is notified to the calculation unit 30 by an external command 80, there is an advantage in that there is no need to provide a special changeover switch or the like, and the system configuration can be simplified. In this case, the calculation unit 30 receives the information regarding whether or not short circuit control is implemented and stores it in the memory area 30a.

Next, the control flow for the short-circuit operation of the power conversion device according to the first embodiment as seen from the calculation unit 30 will be described with reference to FIG. 6. First, when a DC voltage is output from the DC power source 10 and an external command 80 is input to the calculation unit 30, the inverter 50 is ready to start supplying three-phase power to the load device 8.

The calculation unit 30 inputs the drive signal 70 to the switching elements 1a to 6a through the drive circuit 60 (step S1). Step S1 causes the inverter 50 to start operating, and three-phase AC power is supplied to the load device 8.

The calculation unit 30 calculates the temperatures of the legs 20a to 20c when the drive signal 70 is input, and stores the calculated values in the memory area 30a (step S2). As described above, the temperatures of the legs 20a to 20c can be calculated by using a conversion table that converts the current values of the legs 20a to 20c stored in the memory area 30a into the temperatures of the legs 20a to 20c.

After step S2, it is determined whether an inverter drive stop command has been input to the calculation unit 30 (step S3). When it becomes unnecessary to supply three-phase power to the load device 8, an inverter drive stop command is input to the calculation unit 30 by an external command 80. If an inverter drive stop command has not been input to the calculation unit 30 (step S3, No), the process returns to step S2 and the process from step S2 is repeated. If an inverter drive stop command has been input to the calculation unit 30 (step S3, Yes), the calculation unit 30 stops outputting the drive signal 70. When the output of the drive signal 70 is stopped, the inverter 50 stops operating.

After step S3, the calculation unit 30 checks whether the short circuit control is enabled (step S4). As described above, whether or not to implement the short circuit control is determined by the user or administrator, and the information is stored in the memory area 30a. The calculation unit 30 checks the memory area 30a to determine whether the short circuit control is enabled, i.e., whether or not to implement the short circuit control. If the short circuit control is not enabled (step S4, No), the process flow of FIG. 6 is terminated without implementing the short circuit control. If the short circuit control is enabled (step S4, Yes), the calculation unit 30 stores the temperature of the legs 20a to 20c immediately after the inverter drive is stopped as temperature T _E in the memory area 30a (step S5).

After step S5, the calculation unit 30 calculates the temperatures of the legs 20a to 20c after the inverter is stopped, and stores the calculated values in the memory area 30a (step S6). The calculation in step S6 can be performed based on the temperature T _E immediately after the inverter is stopped, the temperature difference between the temperature T _E immediately after the inverter is stopped and the inverter ambient temperature T _R , and the thermal resistance value between the legs 20a to 20c and the heat dissipation components.

After step S6, the calculation unit 30 judges whether or not the temperature of at least one of the calculated temperatures of the legs 20a to 20c is lower than the temperature T _E immediately after the inverter is stopped by a certain value or more (step S7). If all of the calculated temperatures of the legs 20a to 20c are not lower than the temperature T _E immediately after the inverter is stopped by a certain value or more (step S7, No), the calculation unit 30 returns to step S6 and repeats the processing from step S6 onwards. On the other hand, if the calculated temperature of at least one of the legs 20a to 20c is lower than the temperature T _E immediately after the inverter is stopped by a certain value or more (step S7, Yes), the calculation unit 30 performs the above-mentioned short-circuit control for a specified time (step S8). After step S8, it is judged whether or not an inverter drive command has been input to the calculation unit 30 (step S9). If an inverter drive command has been input to the calculation unit 30 (step S9, Yes), the calculation unit 30 returns to step S2 and repeats the processing from step S2 onwards. If an inverter drive command has not been input to the calculation unit 30 (step S9, No), the process returns to step S6, and the processes from step S6 onwards are repeated.

As described above, the power conversion device according to the first embodiment supplies load power to a load device by operating a power module incorporating at least one of legs formed by electrically connecting at least two or more semiconductor elements in series. During a non-driving period in which the supply of load power to the load device is stopped, when the temperature of at least one leg drops by a certain value or more compared to the temperature of the leg immediately after the supply of load power is stopped, the power conversion device performs short-circuit control by repeatedly shorting the switching elements of the upper and lower arms of at least the leg whose temperature has dropped by the certain value or more for a specified time. By performing such short-circuit control, it is possible to reduce the shear stress between the switching elements and the metal wire caused by temperature changes when the power conversion device repeatedly drives and stops driving. This makes it possible to extend the time until the wire peels off, thereby increasing the lifespan of the power module and the power conversion device. In addition, even when the power module is used under operating conditions in which temperature changes occur frequently, it is possible to suppress shortening of the lifespan of the power module.

The power conversion device according to the first embodiment can be configured to include a current measurement resistor electrically connected in series to the legs, a first temperature measurement circuit capable of measuring the ambient temperature of the power conversion device, and a calculation unit that performs short circuit control. With this configuration, the calculation unit can calculate the temperature of the legs based on the voltage across the current measurement resistor and the measurement result of the first temperature measurement circuit. Note that it is sufficient that a current measurement resistor is provided for at least one leg. The temperature for a leg that does not have a current measurement resistor can be estimated based on the calculation result for a leg that has a current measurement resistor.

In addition, if a heat dissipation component is attached to the power module, the calculation unit calculates the amount of heat dissipation in the leg based on the thermal resistance value between the leg and the heat dissipation component, the temperature of the leg immediately after driving is stopped, and the temperature difference between the temperature of the leg immediately after driving is stopped and the ambient temperature of the power conversion device. This calculation process makes it possible to estimate the temperature of the leg during the short circuit control period.

Embodiment 2.
Fig. 7 is an electric circuit diagram of an inverter 50A according to embodiment 2. In Fig. 7, thermistors 90a to 90c are provided instead of the shunt resistor 16, the voltage measurement circuit 17, and thermistor 90 in the inverter 50 according to embodiment 1 shown in Fig. 3. The other configurations are the same as or equivalent to those of the inverter 50 according to embodiment 1 shown in Fig. 3, and the same or equivalent components are denoted by the same reference numerals, and duplicated explanations will be omitted as appropriate.

Thermistors 90a to 90c are used to measure the temperatures of legs 20a to 20c, respectively. Thermistors 90a to 90c may be attached to any location on legs 20a to 20c or inverter 50 as long as they are capable of measuring the temperatures of legs 20a to 20c.

Information about the temperatures of legs 20a-20c measured by thermistors 90a-90c is input to calculation unit 30. This enables calculation unit 30 to obtain temperature information about legs 20a-20c when switching elements 1a-6a are driven and when they are not driven. Note that in this document, the part of the circuit that includes thermistors 90a-90c and transmits the measurement results of thermistors 90a-90c to calculation unit 30 is sometimes referred to as the "second temperature measurement circuit."

Since the temperature information of legs 20a to 20c is constantly input to the calculation unit 30, the power conversion device according to embodiment 2 can be operated with a control flow equivalent to the control flow shown in FIG. 6.

FIG. 8 is a flowchart used to explain the control flow relating to the method of embodiment 2. Note that in FIG. 8, processing steps that are the same as or equivalent to those in FIG. 6 are indicated with the same step numbers, and duplicate explanations will be omitted as appropriate.

First, in step S1, the inverter 50 starts operating and three-phase AC power is supplied to the load device 8. After step S1, the calculation unit 30 receives temperature information of the legs 20a to 20c at the time when the drive signal 70 is input from the thermistors 90a to 90c and stores it in the memory area 30a (step S20).

As in the first embodiment, when short circuit control is performed, the temperatures T _E in the legs 20a to 20c immediately after the inverter drive is stopped are stored in the memory area 30a (step S5). After step S5, the calculation unit 30 receives temperature information of the legs 20a to 20c after the inverter drive is stopped from the thermistors 90a to 90c and stores the information in the memory area 30a (step S21).

After step S21, the calculation unit 30 judges whether or not the temperature of at least one of the received temperatures of the legs 20a to 20c is lower than the temperature T _E immediately after the inverter is stopped by a certain value or more (step S22). If the temperature of at least one of the received temperatures of the legs 20a to 20c is lower than the temperature T _E immediately after the inverter is stopped by a certain value or more (step S22, Yes), the short circuit control described above is performed for a specified time (step S8). The subsequent operations are the same as those in the first embodiment. Also, if all of the received temperatures of the legs 20a to 20c are not lower than the temperature T _E immediately after the inverter is stopped by a certain value or more (step S22, No), the process returns to step S21 and repeats the processes from step S21 onwards. The above processes can provide the same effects as those in the first embodiment.

As described above, the power conversion device according to the second embodiment can be configured to include a second temperature measurement circuit capable of measuring the temperature of the power module, and a calculation unit that performs short circuit control. With this configuration, the calculation unit can receive the measurement result of the second temperature measurement circuit as temperature information and store it in a memory area. This allows the calculation unit to calculate the temperature of the leg based on the measurement result of the second temperature measurement circuit, and to perform the above-mentioned short circuit control. This allows the same effect as in the first embodiment to be obtained.

The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or the embodiments may be combined with each other. In addition, parts of the configurations may be omitted or modified without departing from the spirit of the invention.

1a-6a switching elements, 1b-6b rectifier elements, 7 inverter main circuit section, 8 load device, 9 capacitor, 10 DC power supply, 11, 12 silicon chip, 13 metal wire, 14 metal pad, 15 module external terminal, 16 shunt resistor, 17 voltage measurement circuit, 18a, 18b, 18c midpoint potential point, 20a, 20b, 20c leg, 30 calculation section, 30a memory area, 40 power module, 45 printed circuit board, 50, 50A inverter, 60 drive circuit, 70 drive signal, 80 external command, 90, 90a-90c thermistor.

Claims

A power conversion device includes a power module having at least one built-in leg formed by electrically connecting at least two or more semiconductor elements in series, and supplies load power to a load device by operating the power module,
a power conversion device which performs short-circuit control in which, when the temperature of at least one of the legs drops by a certain value or more compared to the temperature of the leg immediately after the supply of the load power is stopped during a non-driving period in which the supply of the load power to the load device is stopped, the device repeats an operation of electrically short-circuiting at least the upper and lower arm semiconductor elements of the leg whose temperature has dropped by the certain value or more for a specified period of time.
a current measuring resistor electrically connected in series with at least one of the legs;
A first temperature measuring circuit capable of measuring an ambient temperature of the power conversion device;
A calculation unit that performs the short circuit control,
The power conversion device according to claim 1 , wherein the calculation unit calculates the temperature of the leg based on a voltage across the current measuring resistor and a measurement result of the first temperature measuring circuit.
The calculation unit is
calculating a temperature of the leg when the load power is being supplied to the load device, based on a current flowing through the leg estimated based on a voltage across the current measuring resistor and a conversion table for converting the current flowing through the leg into a temperature;
The power conversion device according to claim 2 , wherein the temperature of the leg during the short circuit control is calculated based on the measurement result of the first temperature measurement circuit.
The power module is provided with a heat dissipation component,
4. The power conversion device according to claim 2 or 3, wherein the calculation unit estimates the temperature of the leg during the short-circuit control by calculating an amount of heat dissipation in the leg based on a thermal resistance value between the leg and the heat dissipation component, a temperature of the leg immediately after driving is stopped, and a temperature difference between the temperature of the leg immediately after driving is stopped and an ambient temperature of the power conversion device.
The power conversion device according to claim 2 , wherein the first temperature measurement circuit includes a thermistor.
a second temperature measurement circuit capable of measuring a temperature of the power module;
A calculation unit that performs the short circuit control,
The power conversion device according to claim 1 , wherein the calculation unit calculates the temperature of the leg based on a measurement result of the second temperature measurement circuit.
The power conversion device according to claim 6 , wherein the second temperature measurement circuit includes a thermistor.