JP7313416B2 - power converter - Google Patents

Description

The present application relates to a power converter.

There are the following types of power converters that convert the output form of power. They are an AC/DC converter that converts AC power to DC power (Alternate Current/Direct Current Converter), an inverter that converts DC power to AC power, and a DC/DC converter that changes the voltage and current levels of DC power and outputs them (Direct Current/Direct Current Converter). These power converters have a configuration including switching elements.

The temperature of the switching elements increases with driving with increasing power losses in the switching elements. That is, the temperature of the switching element rises when the power converter outputs a large amount of power, when it is driven at a high switching frequency, and the like.

Moreover, the temperature of the switching element also depends on the environment in which the power converter is arranged. A power conversion device includes a cooler that cools a heat generating portion of a switching element. Depending on the environment in which the power converter is arranged, the temperature of the cooling medium in the cooler increases. Therefore, the temperature of the switching element further increases. In particular, when the flow of the cooling medium is stopped due to a failure of a device for flowing the cooling medium into the cooler, the heat cannot be released from the cooler. Therefore, the temperature of the switching element may continue to rise sharply.

In relation to the arrangement environment of the switching elements in the power conversion device, it is assumed that the temperature of the switching elements may continue to rise due to an abnormal state. In that case, the operating limit temperature of the switching element may be reached. If the temperature of the switching element rises excessively, it is conceivable that the power converter will malfunction, deteriorate in performance, and shorten its life. As a countermeasure, a technique has been proposed in which a temperature sensor monitors the temperature of the switching element and limits the load factor of the power conversion device when the temperature reaches a threshold value (for example, Patent Document 1).

WO2012/124073

The conventional technique disclosed in Patent Document 1 is to provide a temperature sensor for measuring the temperature of the switching element and monitor the output of the temperature sensor. When the temperature of the switching element detected by the temperature sensor exceeds a predetermined threshold, the load factor of the rotating electric machine driven by the power converter (inverter) is limited to protect the switching element from overheating.

Japanese Patent Laid-Open No. 2004-200001 discloses a technique for suppressing temperature rise of a switching element by operating to change driving conditions of a power conversion device when a temperature detection value exceeds a predetermined threshold value. This threshold value is set with some leeway in consideration of the drive conditions of the power conversion device, the arrangement environment, the determination error of the temperature sensor, the variations in the amount of heat generated by the switching elements, the variations in the amount of inflow of the cooling medium, and the like.

The threshold value is set high so as not to erroneously determine abnormality when the power converter is normal. Therefore, when the power conversion device becomes abnormal, it takes a long time for the detected temperature value to reach a relatively high threshold value. In other words, there is a delay time from when an abnormality occurs to when the determination is made. A delay in detecting an overheated state of the switching element may cause failure, deterioration of performance, and shortening of the life of the power converter.

The present application discloses a technique for solving these problems, and detects an abnormal state by obtaining a rate of increase in temperature based on the temperature of the switching element detected by a temperature sensor. Accordingly, it is an object of the present invention to provide a power conversion device that realizes continuation of power conversion while quickly detecting an abnormal state and preventing failure, deterioration of performance, and shortening of the life of the power conversion device due to reaching the operation limit temperature of a switching element.

The power conversion device according to the present application is
switching element,
a temperature sensor that detects the temperature of the switching element;
A power conversion device comprising a control device that controls a switching element and limits the operation of the switching element when the temperature rise rate detected by the temperature sensor during a predetermined determination period is greater than a predetermined temperature rise rate value ,
In the control device, the temperature rise rate value is set to a value smaller than the maximum temperature rise rate detected by the temperature sensor when the power conversion device is in the normal state and the switching element outputs the rated output.

According to the power converter according to the present application, the temperature rise rate is obtained based on the temperature of the switching element detected by the temperature sensor, and an abnormal state is detected. As a result, it is possible to quickly detect an abnormal state, prevent the switching element from reaching its operating limit temperature, which causes failure, deterioration of performance, and shortening of the life of the power conversion device, while realizing continuation of power conversion.

1 is a configuration diagram of a power converter according to Embodiment 1; FIG. 2 is a hardware configuration diagram of a control device for the power conversion device according to Embodiment 1. FIG. 2 is a functional block diagram of a control device for the power converter according to Embodiment 1; FIG. 4 is a functional block diagram of an output suppression unit of the control device for the power conversion device according to Embodiment 1; FIG. 4 is a diagram showing changes in temperature of switching elements and temperature detection values of the power converter according to Embodiment 1. FIG. FIG. 4 is a diagram showing changes in temperature rise rate of switching elements of the power conversion device according to Embodiment 1; 4 is a diagram showing a temperature rise rate, a temperature rise rate continuation period, and a determination value of a switching element of the power converter according to Embodiment 1; FIG. It is a figure which shows the temperature of the switching element of the power converter device which concerns on a comparative example, and determination temperature. FIG. 4 is a diagram showing transition of temperature up to the operation limit of the switching element of the power converter according to Embodiment 1; FIG. 4 is a diagram showing transition of temperature rise rate up to operation limitation of switching elements of the power converter according to Embodiment 1; FIG. 4 is a diagram showing changes in temperature during operation restriction of switching elements of the power converter according to Embodiment 1; FIG. 5 is a diagram showing changes in temperature rise rate during operation restriction of switching elements of the power converter according to Embodiment 1; FIG. 4 is a diagram for explaining variation in temperature rise rate of switching elements of the power conversion device according to Embodiment 1; FIG. 9 is a diagram showing a temperature rise rate, a temperature rise rate continuation period, and a determination value of a switching element of a power conversion device according to Embodiment 2; FIG. 11 is a functional block diagram of an output suppression unit of a control device for a power conversion device according to Embodiment 3;

Power converters according to Embodiments 1 to 3 of the power converters according to the present application will be described below. In addition, in each figure, the same code|symbol is attached|subjected to the same part or a corresponding part. Further, each embodiment exemplifies a power converter applied to a three-phase inverter having U-phase, V-phase and W-phase for driving an AC motor.

1. Embodiment 1
<Switching element>
Semiconductor switching elements (hereinafter referred to as switching elements) include diodes that allow current to flow in only one direction, thyristors that are suitable for handling large currents, and power transistors that can operate at high switching frequencies. Among switching elements, power transistors in particular are used in a wide range of fields such as automobiles, refrigerators, and air conditioners. Power transistors include IGBTs (Insulated Gate Bipolar Transistors), MOS-FETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and the like, and these power transistors are used for various purposes.

In recent years, wide band gap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have attracted attention as materials for switching elements. Switching elements made of these materials have a lower resistance value in the ON state than conventional switching elements using silicon (Si), and can reduce power loss. Also, the electron saturation speed is high, switching between on and off states is quick, and power loss can be reduced.

Compared to silicon, switching elements using silicon carbide or gallium nitride can be driven in higher temperature environments. However, the operating limit temperature of the switching element is fixed, and if the switching element continues to be driven even after the operating limit temperature is exceeded, the switching element may be damaged.

In relation to the arrangement environment of the switching elements in the power conversion device, it is assumed that the temperature of the switching elements and the like may continue to rise due to an abnormal state. In that case, the operating limit temperature of the switching element may be reached. If the temperature of the switching element rises excessively, it is conceivable that the power converter will malfunction, deteriorate in performance, and shorten its life. In this case, it is possible to cool down the temperature of the switching element and the temperature of the cooling medium by stopping the power converter.

However, there are cases where a power conversion device mounted on a vehicle is used to drive a rotating electric machine that is a driving source of the vehicle. In such a case, the drive source cannot be suddenly stopped during operation. Moreover, the power conversion device may be used in an electric power steering device mounted on an automobile. Since the electric power steering system controls a motor that assists the steering of the vehicle, it is undesirable to suddenly stop the power conversion system while the vehicle is being driven. Even if the switching element is in a high temperature state, it is necessary to keep driving the power converter without damaging the switching element.

As described above, there is a possibility that the temperature of the switching element rises to the temperature at which the switching element is damaged, depending on the drive conditions, arrangement environment, etc. of the power converter. The temperature at which the switching element is damaged is hereinafter referred to as the operating limit temperature. Therefore, in order to prevent the switching element from reaching the operating limit temperature and continue to drive the power conversion device, it is necessary to drive the power conversion device under appropriate driving conditions and placement environment.

In particular, in the arrangement environment of the switching elements that make up the power conversion device, when heat conduction between the cooler and the switching elements is hindered, when the inflow of the cooling medium flowing through the cooler is stopped, or when the cooling medium disappears, it is necessary to detect an abnormal state (hereinafter referred to as an abnormal state) of the cooler without delay. Under these abnormal conditions, it is necessary to change and control the driving conditions of the power conversion device to avoid the switching elements from reaching the operating limit temperature.

Conventionally, when the temperature detection value exceeds a predetermined threshold value, an operation is performed to change the drive conditions of the power conversion device, thereby suppressing the temperature rise of the switching element. This threshold value is set with some leeway in consideration of the drive conditions of the power conversion device, the arrangement environment, the determination error of the temperature sensor, the variations in the amount of heat generated by the switching elements, the variations in the amount of inflow of the cooling medium, and the like.

The threshold value is set high so as not to erroneously determine abnormality when the power converter is normal. Therefore, when the power conversion device becomes abnormal, it takes a long time for the detected temperature value to reach a relatively high threshold value. In other words, there is a delay time from when an abnormality occurs to when the determination is made. A delay in detecting an overheated state of the switching element may cause failure, deterioration of performance, and shortening of the life of the power converter.

In particular, the temperature of the semiconductor switching element continues to rise sharply in the case of a failure in which the inflow of the cooling medium is stopped or the cooling medium disappears. Therefore, the attained temperature of the semiconductor switching element increases in proportion to the time from the occurrence of the abnormality to the determination. In the prior art, in order to prevent damage to the switching element, an expensive switching element such as a switching element with higher heat resistance or a low-loss switching element is required, which increases the cost.

<Configuration of power converter>
FIG. 1 is a configuration diagram of a power converter 100 according to Embodiment 1. As shown in FIG. In FIG. 1 , the power conversion device 100 includes a power supply section 2 , a power conversion section 3 , a cooler 4 , a rotation angle sensor 5 , a motor temperature sensor 6 , a switching element temperature sensor 7 , a command generator 8 and a control device 9 . The electric motor 1 is a load device of the power conversion device 100 . The load device is not limited to the electric motor 1 and may be other than the electric motor 1 .

The electric motor 1 is controlled by a PWM (Pulse Width Modulation) method. The electric motor 1 is, for example, an in-vehicle electric motor. Here, the vehicle-mounted electric motor is specifically an electric motor for driving a vehicle, an electric fan, an oil pump, a water pump, and an electric power steering device for assisting the steering operation of the vehicle. Further, the electric motor 1 is not limited to a vehicle-mounted motor, and may be a motor other than a vehicle-mounted motor.

The following description assumes that the electric motor 1 is a three-phase brushless motor having a rotor and a stator. The rotor (not shown) is a disc-shaped member and has field poles made of permanent magnets fixed on its surface. The stator accommodates the rotor inside so as to be relatively rotatable. The stator has a plurality of protrusions protruding toward the rotor at predetermined angles, and U-phase coil 11, V-phase coil 12, and W-phase coil 13 are wound around the protrusions.

The power supply unit 2 is a power supply for driving the electric motor 1 and outputs DC power to the power conversion unit 3 . As a specific configuration example of the power supply unit 2 , the power supply unit 2 includes a battery 21 , which is an example of a DC power supply that outputs DC power, a smoothing capacitor 22 , and a choke coil 23 .

The smoothing capacitor 22 and the choke coil 23 are arranged between the battery 21 and an inverter section 31, which will be described later, and constitute a power filter. With this configuration, it is possible to reduce noise transmitted from other devices sharing the battery 21 to the inverter section 31 side, and reduce noise transmitted from the inverter section 31 side to other devices sharing the battery 21. The smoothing capacitor 22 stores electric charge to assist power supply to the switching elements 311 to 316, and further suppresses noise components such as surge current. The power supply unit 2 also supplies power to the control device 9 (not shown).

The power conversion unit 3 converts the DC power supplied from the power supply unit 2 into AC power, and outputs the converted AC power to the electric motor 1 . As a specific configuration example of the power conversion section 3 , the power conversion section 3 has an inverter section 31 , a current detector 32 , an amplifier circuit 33 and a drive circuit 34 .

The inverter unit 31 has a plurality of half bridge circuits connected in parallel, each of which has a switching element in each of the upper arm and the lower arm. Switching elements 311 to 316 are controlled to be switched on and off according to the PWM signal. As a result, the DC power output from the power supply unit 2 is converted into AC power, and the converted AC power is output to the electric motor 1 .

FIG. 1 illustrates a case where the inverter unit 31 is configured by three half-bridge circuits. The inverter unit 31 is a three-phase inverter including switching elements 311-316. Six switching elements 311 to 316 are bridge-connected to switch energization to each of the U-phase coil 11, the V-phase coil 12, and the W-phase coil 13. FIG. As the switching elements 311 to 316, MOS-FETs, which are a kind of field effect transistors, may be used. Alternatively, transistors other than MOS-FETs, IGBTs, or the like may be used.

The drains of the three switching elements 311 , 312 and 313 are connected to the positive electrode side of the battery 21 . The sources of switching elements 311, 312 and 313 are connected to the drains of switching elements 314, 315 and 316, respectively. The sources of switching elements 314 , 315 and 316 are connected to the negative electrode side of battery 21 .

A connection point connecting the pair of switching elements 311 and 314 is connected to one end of the U-phase coil 11 of the electric motor 1 . A connection point connecting the pair of switching elements 312 and 315 is connected to one end of the V-phase coil 12 of the electric motor 1 . Furthermore, the connection point connecting the pair of switching elements 313 and 316 is connected to one end of the W-phase coil 13 of the electric motor 1 .

Three switching elements 311, 312, and 313 arranged on the high potential side of the inverter section 31 constitute switching elements of a U-phase upper arm, a V-phase upper arm, and a W-phase upper arm, respectively. Three switching elements 314, 315, and 316 arranged on the low potential side of the inverter section 31 constitute switching elements of a U-phase lower arm, a V-phase lower arm, and a W-phase lower arm, respectively.

The current detector 32 is composed of a U-phase current detector 321 , a V-phase current detector 322 and a W-phase current detector 323 . The U-phase current detector 321, the V-phase current detector 322, and the W-phase current detector 323 are configured using, for example, shunt resistors. U-phase current detector 321 outputs a U-phase current detection value corresponding to U-phase current Iu flowing in U-phase coil 11 . The V-phase current detector 322 outputs a V-phase current detection value corresponding to the V-phase current Iv flowing through the V-phase coil 12 . The W-phase current detector 323 outputs a W-phase current detection value corresponding to the W-phase current Iw flowing through the W-phase coil 13 . In the following description, the U-phase current detection value, the V-phase current detection value, and the W-phase current detection value may be collectively referred to as current detection values.

Although not shown, instead of current detector 32 or together with current detector 32, a voltage detector for detecting the voltage applied to switching elements 311-316 may be provided. In this case, the output state of the power converter 3 is calculated based on at least one of the detected value of the current detector 32, the detected value of the voltage detector, and the command value for commanding the output of the power converter.

The U-phase current detection value, V-phase current detection value, and W-phase current detection value output from U-phase current detection unit 321 , V-phase current detection unit 322 , and W-phase current detection unit 323 are input to control device 9 via amplifier circuit 33 . The amplifier circuit 33 is for taking in the U-phase current detection value, the V-phase current detection value, and the W-phase current detection value as appropriate values that can be processed within the control device 9 .

Drive circuit 34 is controlled based on a PWM signal input from control device 9 . The drive circuit 34 has a function of switching the switching elements 311 to 316 on and off.

Cooler 4 cools smoothing capacitor 22 , choke coil 23 and power converter 3 . The cooler 4 is, for example, a water-cooled cooler. Specifically, a water-cooled cooler, a radiator, a motor-driven water pump, and the like are connected by a hose, and a cooling medium such as water, oil, or LLC (Long Life Coolant) flows from the motor-driven water pump to the water-cooled cooler. Note that the cooler 4 is not limited to a water-cooled cooler, and may be an air-cooled cooler or the like. The cooler 4 may be a heat sink connected to the switching elements 311-316 to conduct heat.

The rotation angle sensor 5 is attached to the electric motor 1 and detects position information representing the rotor position of the electric motor 1 . The rotation angle sensor 5 specifically detects the rotation angle θm of the rotor. The rotation angle sensor 5 is configured using, for example, a resolver. The rotation angle sensor 5 is configured to convert the detected rotation angle θm into an electrical angle θe based on the number of pole pairs of the permanent magnets of the electric motor 1 . The rotation angle θm and electrical angle θe are input to the controller 9 .

A motor temperature sensor 6 detects the temperature of the motor 1 . The motor temperature sensor 6 is composed of temperature sensors such as thermistors attached to the U-phase coil 11, the V-phase coil 12 and the W-phase coil 13, for example. The temperature of the electric motor 1 is input to the controller 9 .

The switching element temperature sensor 7 detects temperatures of the switching elements 311-316. Specifically, for example, the switching element temperature sensor 7 is installed near each of the switching elements 311 to 316, and indirectly measures each temperature Tj of the switching elements 311 to 316. FIG. The switching element temperature sensor 7 may directly detect the temperature Tj of the switching elements 311-316. For example, the temperature may be detected by a temperature detection diode or the like arranged on the semiconductor substrate of the switching elements 311-316.

When the temperature detection value Tj_sens output by the switching element temperature sensor 7 is based on the temperature near the switching elements 311-316, the temperature near the switching elements 311-316 corresponds to the temperature Tj of the switching elements 311-316. Therefore, the temperature detection value Tj_sens output by the switching element temperature sensor 7 corresponds to the temperature Tj of the switching elements 311-316. A temperature detection value Tj_sens of the switching element temperature sensor 7 is input to the control device 9 .

A command generator 8 generates a control command for controlling the electric motor 1 . The command generator 8 then outputs the control command to the control device 9 . For example, when the electric motor 1 is used as a drive source for a vehicle such as an electric vehicle, the command generator 8 outputs a control command corresponding to the depression angle of the accelerator pedal operated by the driver of the vehicle. The control commands generated by the command generator 8 are periodically transmitted to the control device 9 by communication.

<Hardware configuration of control device>
FIG. 2 is a hardware configuration diagram of the control device 9 of the power conversion device 100 according to Embodiment 1. As shown in FIG. In this embodiment, the control device 9 is a control device that controls the power conversion device 100 . Each function of the control device 9 is implemented by a processing circuit provided in the control device 9 . Specifically, the control device 9 includes, as processing circuits, an arithmetic processing unit 80 (computer) such as a CPU (Central Processing Unit), a storage device 81 for exchanging data with the arithmetic processing unit 80, an input circuit 82 for inputting an external signal to the arithmetic processing unit 80, and an output circuit 83 for outputting a signal from the arithmetic processing unit 80 to the outside.

As the arithmetic processing device 80, an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, various signal processing circuits, and the like may be provided. Further, as the arithmetic processing unit 80, a plurality of units of the same type or different types may be provided, and each process may be shared and executed. As the storage device 81, a RAM (random access memory) capable of reading and writing data from the arithmetic processing unit 80, a ROM (read only memory) capable of reading data from the arithmetic processing unit 80, and the like are provided. The input circuit 82 includes the rotation angle sensor 5, the motor temperature sensor 6, the switching element temperature sensor 7, and the amplifier circuit 33, and is connected to various sensors and switches. The output circuit 83 includes the drive circuit 34 and is connected to electrical loads such as switching elements and actuators. The output circuit 83 is provided with interface circuits such as a drive circuit and a communication circuit for converting and outputting an output signal from the arithmetic processing unit 80 to these electrical loads.

Each function provided by the control device 9 is realized by the arithmetic processing device 80 executing software (program) stored in a storage device 81 such as a ROM and cooperating with other hardware of the control device 9 such as the storage device 81, the input circuit 82, and the output circuit 83. Setting data such as threshold values and determination values used by the control device 9 are stored in a storage device 81 such as a ROM as a part of software (program).

Each function installed inside the control device 9 of FIG. 1 may be configured by a software module, or may be configured by a combination of software and hardware.

<Functional block of control device>
FIG. 3 is a functional block diagram of the control device 9 of the power conversion device 100 according to Embodiment 1. As shown in FIG. In FIG. 3, the control device 9 includes an output suppression unit 91, a rotation speed calculation unit 92, a torque/current command conversion unit 93, a three-phase/two-phase conversion unit 94, a voltage command generation unit 95, a two-phase/three-phase conversion unit 96, a duty conversion unit 97, and a PWM signal generation unit 98.

The output suppression unit 91 receives the torque command Trqc from the command generator 8 . Control commands for controlling the electric motor 1 include, for example, torque commands, current commands, voltage commands, and the like. Embodiment 1 will exemplify a case where the torque command Trqc is employed as the control command. Output suppression unit 91 receives temperature detection value Tj_sens from switching element temperature sensor 7 .

The output suppression unit 91 generates a torque control command Trqc_ctl and an output stop signal Sig_stop so that the temperature Tj of the switching elements 311 to 316 does not reach the operating limit temperature. A more detailed configuration of the output suppression unit 91 will be described later. Further, in Embodiment 1, the output power of the power conversion device 100 is suppressed by the means for suppressing the torque command Trqc.

A rotation speed calculation unit 92 integrates the rotation angle θm acquired from the rotation angle sensor 5 and converts it into the rotation speed N of the electric motor 1 . The rotational speed calculator 92 outputs the calculated rotational speed N to the torque/current command converter 93 .

A torque/current command conversion unit 93 calculates a d-axis current command Idc and a q-axis current command Iqc from the rotation speed N of the electric motor 1 obtained from the rotation speed calculation unit 92 and the torque control command Trqc_ctl obtained from the output suppression unit 91. Specifically, for example, the torque/current command conversion unit 93 is configured to convert these values into the d-axis current command Idc and the q-axis current command Iqc by using a torque/current command conversion table with the rotational speed N of the electric motor 1 and the torque control command Trqc_ctl as axes. Note that the torque/current command conversion unit 93 may be configured to calculate the d-axis current command Idc and the q-axis current command Iqc without using the torque/current command conversion table.

The three-phase/two-phase converter 94 calculates the d-axis current detection value Id and the q-axis current detection value Iq from the current detection value of the current detector 32 received via the amplifier circuit 33 and the angle detection value corresponding to the electrical angle θe detected by the rotation angle sensor 5. Here, the current detection value of current detector 32 is composed of a U-phase current detection value corresponding to U-phase current Iu detected by U-phase current detection section 321, a V-phase current detection value corresponding to V-phase current Iv detected by V-phase current detection section 322, and a W-phase current detection value corresponding to W-phase current Iw detected by W-phase current detection section 323.

Voltage command generator 95 calculates d-axis voltage command Vdc and q-axis voltage command Vqc by performing current feedback calculation from d-axis current command Idc and q-axis current command Iqc and d-axis current detection value Id and q-axis current detection value Iq. Specifically, for example, the voltage command generator 95 is configured to calculate the d-axis voltage command Vdc and the q-axis voltage command Vqc so that the current deviation ΔId, which is the deviation between the d-axis current command Idc and the d-axis current detection value Id, and the current deviation ΔIq, which is the deviation between the q-axis current command Iqc and the q-axis current detection value Iq, both converge to “0”. (ΔId and ΔIq are not shown)

A two-phase/three-phase conversion unit 96 calculates three-phase voltage commands Vuc, Vvc, and Vwc from the d-axis voltage command Vdc and the q-axis voltage command Vqc obtained from the voltage command generation unit 95 and the electrical angle θe obtained from the rotation angle sensor 5. The three-phase voltage commands Vuc, Vvc, and Vwc are preferably set to be equal to or lower than the DC power supply voltage input to the inverter section 31, that is, the voltage Vcon of the smoothing capacitor 22. FIG.

The duty conversion unit 97 generates duty commands Du, Dv, Dw for each of the three phases from the three-phase voltage commands Vuc, Vvc, Vwc acquired from the two-phase/three-phase conversion unit 96 and the voltage Vcon of the smoothing capacitor 22 . The duty converter 97 generates and outputs duty commands Du, Dv, and Dw corresponding to the optimum correction control commands.

A PWM signal generator 98 generates a PWM signal. The PWM signal generation unit 98 uses the output stop signal Sig_stop obtained from the output suppression unit 91 and the duty commands Du, Dv, and Dw of each phase obtained from the duty conversion unit 97 to generate a PWM signal for switching on and off each of the switching elements 311 to 316.

Specifically, for example, when the state of the output stop signal Sig_stop indicates that the output is permitted, the PWM signal generator 98 generates the PWM signal by comparing the duty commands Du, Dv, and Dw of each phase with the carrier wave. When the state of the output stop signal Sig_stop is output prohibited, a PWM signal is generated so that all of the switching elements 311 to 316 are turned off. The PWM signal generation unit 98 is configured to generate a PWM signal by adopting, for example, a triangular wave comparison method, a sawtooth wave comparison method, or the like using a triangular wave having an isosceles triangle shape whose rising speed and falling speed are equal to each other as a carrier.

In FIG. 3, the PWM signals generated by the PWM signal generator 98 include a PWM signal UH_SW applied to the U-phase upper arm switching element 311, a PWM signal VH_SW applied to the V-phase upper arm switching element 312, a PWM signal WH_SW applied to the W-phase upper arm switching element 313, a PWM signal UL_SW applied to the U-phase lower arm switching element 314, and a PW applied to the V-phase lower arm switching element 315. The M signal VL_SW and the PWM signal WL_SW given to the W-phase lower arm switching element 316 are shown, respectively.

<Functional block of output suppressor>
FIG. 4 is a functional block diagram of the output suppression unit 91 of the control device 9 of the power conversion device 100 according to Embodiment 1. As shown in FIG. In FIG. 4 , the output suppressing section 91 is composed of a temperature increase rate determining section 911 , a torque command suppressing section 912 and an output stop determining section 913 .

A temperature rise rate determination unit 911 inputs the temperature detection value Tj_sens of the switching element temperature sensor 7 . Then, abnormal heat generation of the switching elements 311 to 316, an abnormal state of the cooler 4, and the like are detected, and the determination result is output to the torque command suppression section 912 and the output stop determination section 913.

Specifically, temperature rise rate determination unit 911 calculates temperature rise rate Tj_sens_rat, which is the amount of rise per unit time of temperature detection value Tj_sens of switching element temperature sensor 7 (hereinafter, temperature rise rate Tj_sens_rat, which is the amount of rise of temperature detection value Tj_sens per unit time, is simply referred to as temperature rise rate). Then, the temperature rise rate Tj_sens_rat is compared with a predetermined temperature rise rate value Th1.

As a result of the comparison, when the temperature rise rate Tj_sens_rat exceeds the temperature rise rate value Th1 and continues for the temperature rise rate continuation period Δt1, the temperature rise rate determination unit 911 determines that there is abnormal heat generation in the switching elements 311 to 316 or an abnormal state in the cooler 4. Then, the temperature increase rate determination unit 911 generates an error signal Sig_err indicating an abnormal state and outputs it to the torque command suppression unit 912 and the output stop determination unit 913 . A method of setting the temperature rise rate value Th1 and the temperature rise rate continuation period Δt1 will be described later.

A unit time for calculating the temperature rise rate Tj_sens_rat from the temperature detection value Tj_sens is sufficiently shorter than the time constant of the switching element temperature sensor 7 . Also, the unit time for calculating the temperature rise rate Tj_sens_rat is desirably set to a time that is not affected by switching noise of the switching elements 311-316.

Torque command suppression unit 912 generates torque control command Trqc_ctl converted based on torque command Trqc and the state of error signal Sig_err. Specifically, for example, when the error signal Sig_err indicates an error state, the torque command suppression unit 912 may generate and output a torque control command Trqc_ctl having a value lower than the torque command Trqc by multiplying the torque command Trqc by a predetermined ratio.

On the other hand, when the error signal Sig_err indicates the normal state, the torque command suppression unit 912 outputs the torque command Trqc as it is as the torque control command Trqc_ctl. When the error signal Sig_err indicates an error state, the torque command suppression unit 912 generates the torque control command Trqc_ctl by multiplying the torque command Trqc by a predetermined ratio. The method of generating the torque control command Trqc_ctl is not limited to this. The torque control command Trqc_ctl may be calculated and generated by changing this ratio according to the temperature detection value Tj_sens of the switching element temperature sensor 7 .

Based on the temperature detection value Tj_sens of the switching element temperature sensor 7 and the state of the error signal Sig_err, the output stop determination unit 913 outputs an output stop signal Sig_stop that stops the output of the inverter unit 31 . Specifically, for example, when the error signal Sig_err continues for a predetermined limited operation period in an error state, the output stop determination unit 913 transmits the output stop signal Sig_stop to the PWM signal generation unit 98 to prohibit the output of the PWM signal.

Here, the predetermined restricted operation period will be described. The predetermined limited driving period refers to, for example, the time until the vehicle can run and stop at a place where there is no problem. In the case of a vehicle such as an electric vehicle or a hybrid vehicle whose drive source is an electric motor, it is undesirable for the vehicle to suddenly stop even if the switching elements 311 to 316 generate abnormal heat or the cooler 4 is in an abnormal state. Even if an abnormality occurs, the vehicle must be able to drive itself, evacuate to a safe place, and stop.

Furthermore, when the content of the error signal Sig_err indicates an error state, the output stop determination unit 913 compares the temperature detection value Tj_sens of the switching element temperature sensor 7 with a predetermined stop determination temperature Th3 (Th3 is not shown). This is to prevent the temperature Tj of the switching elements 311 to 316 from reaching the breakdown temperature, which is the operating limit temperature. When the temperature detection value Tj_sens exceeds the stop determination temperature Th3, the output stop determination unit 913 outputs an output stop signal Sig_stop indicating prohibition of driving.

That is, the output stop determination unit 913 outputs the output stop signal Sig_stop having the content of prohibition of driving when at least one of the case where the content of the error signal Sig_err indicates an error state and the operation continues for a predetermined limited operation time, and the case where the temperature detection value Tj_sens of the switching element temperature sensor 7 exceeds the predetermined stop determination temperature Th3 is established.

<Transition of temperature rise rate of switching element>
FIG. 5 is a diagram showing changes in the temperature of the switching element and the detected temperature value of the power converter 100 according to the first embodiment. The vertical axis in FIG. 5 indicates temperature, and the horizontal axis indicates time. FIG. 6 is a diagram showing transition of the temperature rise rate of the switching element of the power converter 100 according to the first embodiment. The vertical axis indicates the rate of temperature rise, and the horizontal axis indicates time. Specifically, FIGS. 5 and 6 show changes in the temperature Tj of the switching element 311, the temperature detection value Tj_sens of the switching element temperature sensor 7, and the temperature rise rate Tj_sens_rat when the cooling medium in the cooler 4 disappears after a sufficient amount of time has passed after the output of the inverter unit 31 is changed from "0" to a constant output value.

Note that the switching element temperature Tj and the temperature detection value Tj_sens shown in FIG. 5 are for the switching element 311, for example. However, not only the switching element 311 but also one of the other switching elements 312, 313, 314, 315, and 316 shows a similar temperature transition.

FIGS. 5 and 6 show the situation when the power conversion unit 3 changes from the output “0” state to a constant output value at time t1, and the operation is continued in this state for a sufficient amount of time. A situation is shown in which the cooling medium in the cooler 4 has disappeared at time t2.

As shown in FIG. 5, before the cooling medium in the cooler 4 disappears at time t2, the cooler 4 is operating normally. The temperature Tj of the switching element and the temperature detection value Tj_sens of the switching element temperature sensor 7 are stabilized at a substantially constant temperature after a sufficient period of time determined based on the loss of the switching element 311 and the performance of the cooler 4 has passed. Since the temperature detection value Tj_sens of the switching element temperature sensor 7 indirectly measures the temperature Tj of the switching element 311, it has a longer time constant and a lower settling temperature than the temperature Tj of the switching element 311. FIG.

When the cooling medium in the cooler 4 disappears at time t2, the temperature of the cooler 4 sharply rises due to the heat generation of the switching element 311 . As the temperature of the cooler 4 rises, the temperature Tj of the switching element 311 and the temperature detection value Tj_sens of the switching element temperature sensor 7 rise. Therefore, as shown in FIG. 6, the temperature increase rate Tj_sens_rat increases.

<Temperature rise rate value and temperature rise rate duration setting>
FIG. 7 is a diagram showing the temperature rise rate, the temperature rise rate continuation period, and the determination value of the switching element of the power converter 100 according to the first embodiment. A procedure for setting the temperature rise rate value Th1 and the temperature rise rate continuation period Δt1 in the temperature rise rate determination unit 911 will be described. The vertical axis in FIG. 7 indicates the temperature rise rate, and the horizontal axis indicates time.

FIG. 7 shows the normal rated output temperature rise rate Tj_sens_rat_nH when the output of the inverter changes from 0 to the rated output in the normal state (hereinafter referred to as the temperature rise rate at the rated output in the normal state). This is a waveform corresponding to the transition from t1 to t2 in FIG. 6, and shows the temperature rise rate Tj_sens_rat when the power conversion unit 3 changes from the output “0” state to the rated output value at time t3, and a sufficient amount of time has passed in that state.

In the power conversion device 100, output power variations occur due to determination variations of the current determiner, the voltage determiner, the rotation angle sensor 5, and the like. The rated output refers to the maximum output state within the performance range of the power converter 100 including these variations. The normal rated output temperature rise rate Tj_sens_rat_nH, which is the temperature rise rate at the rated output in the normal state, is the transition of the maximum temperature rise rate in the normal state including the manufacturing variation of the cooler 4 and the observation error of the temperature sensor.

In the abnormal state at the rated output, the abnormal rated output temperature rise rate Tj_sens_rat_fH is a waveform corresponding to transition after t2 in FIG. FIG. 7 shows the transition of the temperature rise rate when the cooling medium in the cooler 4 disappears at time t3 at the rated output.

Similarly, the abnormal partial output temperature rise rate Tj_sens_rat_fL in an abnormal state during partial output is a waveform corresponding to the transition after t2 in FIG. FIG. 7 shows the transition when the cooling medium in the cooler 4 disappears at time t3 during partial output. The partial output indicates the lower limit of the output state of the power converter 3 that should be protected by the power converter 100 according to the first embodiment. That is, although it is not a rated output but a partial output state, it indicates an output state in which the operation of the switching element should be limited when the cooler malfunctions. It shows an output state in which it is necessary to realize continuation of power conversion while preventing failure, deterioration of performance, and shortening of the life of the power conversion device due to the switching element reaching its operating limit temperature.

The temperature rise rate value Th1 in the temperature rise rate determination unit 911 is set to be equal to or less than the peak value of the abnormal partial output temperature rise rate Tj_sens_rat_fL in an abnormal state during partial output. When an abnormal state occurs during output between partial output and rated output, the temperature rise rate Tj_sens_rat transitions to an abnormal partial output temperature rise rate Tj_sens_rat_fL or more in an abnormal state during partial output. Therefore, it is possible to determine an abnormal state in the entire region to be protected by the temperature rise rate value Th1.

Next, the temperature rise rate continuation period Δt1 will be described. The temperature rise rate continuation period Δt1 is set to be longer than the time during which the temperature rise rate during normal operation exceeds the temperature rise rate value Th1 in order to prevent erroneous determination. Specifically, the temperature rise rate continuation period Δt1 is set to be longer than the period during which the normal rated output temperature rise rate Tj_sens_rat_nH (the upward convex temperature rise rate in FIG. 7) exceeds the temperature rise rate value Th1 at the rated output in the normal state.

The temperature rise rate Tj_sens_rat below the rated output is smaller than the temperature rise rate Tj_sens_rat at the rated output. Therefore, by setting the temperature rise rate continuation period Δt1 in consideration of transition of the temperature rise rate Tj_sens_rat at the rated output, erroneous determination can be prevented at all outputs to be protected.

Note that the temperature rise rate continuation period Δt1 takes into account at least variations in the loss of the switching elements 311 to 316, variations in the performance of the cooler 4, detection errors of the switching element temperature sensor 7, and the like, and is set to a period that does not reach even if the normal rated output temperature increase rate Tj_sens_rat_nH at the rated output in the normal state fluctuates to the high value side.

FIG. 8 is a diagram showing temperatures of switching elements and determination temperatures of a power converter according to a comparative example. FIG. 10 is an explanatory diagram showing transitions of the temperature Tj of the switching element and the temperature detection value Tj_sens until an abnormality determination is made when temperatures are detected and compared in the same manner as in the conventional technology; The vertical axis is temperature and the horizontal axis is time. In FIG. 8, a judgment temperature Th0 for judging abnormality by comparison with the detected temperature value Tj_sens and a time t4 of the abnormality judgment X1 are added to FIG.

In FIG. 8, the determination temperature Th0 is set so as not to erroneously determine an abnormality when the driving conditions of the power converter 3, the arrangement environment of the switching elements 311 to 316, and the like are normal. In other words, it is set high taking into account the determination error of the switching element temperature sensor 7, variations in the amount of heat generated by the switching elements 311 to 316, variations in the amount of cooling medium flowing into the cooler 4, and the like.

Therefore, as shown in FIG. 8, when the cooling medium of the cooler 4 disappears at time t2, the time [t4-t2] from the temperature detection value Tj_sens reaching the determination temperature Th0 to the abnormality determination X1 (time t4) becomes longer. In other words, when the conventional technology is applied, the time until the abnormality determination X1 is long, and the temperature of the switching element 311 becomes Tj_X1, which increases.

<Transition of temperature rise rate when cooling medium in cooler disappears>
FIG. 9 is a diagram showing transition of temperature up to the operation limit of the switching element of the power converter 100 according to the first embodiment. The vertical axis indicates temperature and the horizontal axis indicates time. FIG. 10 is a diagram showing the transition of the temperature rise rate up to the operation limit of the switching elements of the power conversion device 100 according to the first embodiment. The vertical axis indicates the rate of temperature rise, and the horizontal axis indicates time.

9 and 10 show the temperature detection value Tj_sens and the temperature rise rate Tj_sens_rat of the switching element in a normal state up to time t2. At time t1, the output of inverter section 31 rises from "0". Along with this change, the temperature rise rate Tj_sens_rat based on the temperature detection value Tj_sens rises dramatically. Then, the temperature rise rate Tj_sens_rat reaches the maximum value in the normal state at time t11 immediately after time t1.

After that, the temperature increase rate Tj_sens_rat gradually decreases, and at time t12 after a sufficient time has passed since time t11, the temperature detection value Tj_sens settles. Therefore, the temperature rise rate Tj_sens_rat is "0".

At time t2, the cooling medium in cooler 4 disappears. The temperature detection value Tj_sens increases. A temperature increase rate Tj_sens_rat based on the temperature detection value Tj_sens rises sharply and reaches a temperature increase rate value Th1 at time t21a. At time t21b when the temperature rise rate Tj_sens_rat exceeds the temperature rise rate value Th1 for the temperature rise rate continuation period Δt1, an abnormality is determined.

The time [t21b-t2] from the abnormality occurrence time t2 to the abnormality determination time t21b in FIG. 10 is shorter than the time [t4-t2] from the abnormality occurrence time t2 to the abnormality determination time t4 according to the comparative example in FIG. That is, the abnormal state can be determined more quickly. The temperature of the switching element 311 at this time is Tj_X2b. Therefore, temperature Tj_X2b at the time of abnormality determination according to the first embodiment is lower than temperature Tj_X1 of switching element 311 when abnormality is determined by the conventional method shown in FIG. Therefore, compared to simply comparing the temperature detection value Tj_sens with the determination temperature Th0, the abnormality determination according to the first embodiment, which detects that the temperature increase rate Tj_sens_rat has exceeded the temperature increase rate value Th1 for the temperature increase rate continuation period Δt1, is more advantageous.

Note that the unit time for calculating the temperature rise rate Tj_sens_rat from the temperature detection value Tj_sens is set long in order to avoid the influence of noise, and the transition is indicated by a ramp function. However, this is not necessarily the case, and the unit time for calculating the temperature increase rate Tj_sens_rat from the temperature detection value Tj_sens may be shortened.

In this case, it is possible to shorten the time from the time t2 when the abnormality occurs to the time t21a at the crossing point X2 of the temperature rise rate value Th1 and the temperature rise rate Tj_sens_rat and the abnormality determination time t21b. Thereby, it is possible to more effectively suppress the temperature rise of the switching element 311 .

<Temperature change at the time of operation restriction>
FIG. 11 is a diagram showing changes in temperature during operation restriction of the switching elements of the power conversion device 100 according to the first embodiment. The vertical axis indicates temperature and the horizontal axis indicates time. FIG. 12 is a diagram showing changes in the temperature rise rate when the operation of the switching elements of the power conversion device 100 according to Embodiment 1 is restricted. The vertical axis indicates the rate of temperature rise, and the horizontal axis indicates time.

In FIGS. 11 and 12, the abnormality determination is completed at time t21b. After this, the error signal Sig_err of the temperature rise rate determination unit 911 shown in FIG. 4 indicates an error state. At this time, the torque control command Trqc_ctl is calculated by multiplying the torque command Trqc by a predetermined ratio by the torque command suppression unit 912 . Therefore, torque control command Trqc_ctl, which is lower than torque command Trqc, is output from torque command suppressing portion 912 .

Since the torque control command Trqc_ctl is a lower value obtained by adding a predetermined limit to the torque command Trqc, the output of the inverter unit 31 decreases. At this time, the switching element temperature Tj becomes the temperature Tj_21b. A temperature increase rate Tj_sens_rat based on the temperature detection value Tj_sens by the switching element temperature sensor 7 decreases from time t21b. Thereafter, the temperature rise rate Tj_sens_rat falls below the temperature rise rate value Th1.

However, the error signal Sig_err continues to indicate the error condition. Therefore, even if the temperature rise rate Tj_sens_rat decreases, the torque control command Trqc_ctl is kept under the predetermined limitation, and the overheated state of the switching element can be continuously dealt with. As a result, the continuation of power conversion can be realized while preventing the switching element from reaching the operating limit temperature and causing failure, performance deterioration, and shortening of the life of the power converter.

At time t22 after the limited operation period Δt2, which is a predetermined time [t22−t21b] from time t21b of the abnormality determination, the switching element is stopped. At time t22, the output stop signal Sig_stop output from the output stop determination unit 913 shown in FIG. 3 indicates that driving is prohibited, and the output of the inverter unit 31 becomes "0". Therefore, the temperature Tj of the switching element at time t22 shown in FIG. As a result, it is possible to prevent failure, deterioration of performance, and shortening of the life of the power converter.

As shown in FIG. 12, the power converter 100 according to Embodiment 1 operates for a predetermined limited operation period Δt2 or longer after the temperature rise rate Tj_sens_rat exceeds the temperature rise rate value Th1 for the temperature rise rate duration Δt1. As a result, when the electric motor 1 is used as a driving source of a vehicle such as an electric vehicle, for example, when an abnormal state occurs at a problematic place such as an intersection, the vehicle can be driven by itself and moved until it can be stopped at a trouble-free place.

The power converter 100 according to Embodiment 1 limits the output by suppressing the torque control command Trqc_ctl after determining the abnormal state. As a result, the temperature rise after determination of the abnormal state is reduced. Therefore, it is possible to set a longer limited operation period Δt2 from time t21b to time t22, which is the time from when the abnormal state is determined until the power converter 100 is stopped.

Therefore, for example, when the electric motor 1 is used as a drive source for a vehicle such as an electric vehicle, it is possible to appropriately respond when an abnormal state occurs at a problematic location such as an intersection. The vehicle can be self-propelled for a sufficient amount of time until it can stop at a place where there is no obstacle. Therefore, it is possible to configure the power conversion device 100 that is capable of responding appropriately while ensuring reliability when an abnormal state occurs.

As described above, after the temperature rise rate Tj_sens_rat exceeds the temperature rise rate value Th1, it falls below the temperature rise rate value Th1 at time t21c in FIG. 12, but the error signal Sig_err continues to indicate the error state. As a result, it is possible to reliably continue the operation of the power converter 100 during the limited operation period Δt2 while preventing damage to the switching elements.

As described above, after the abnormal state is determined at time t21b and the operation is restricted, the output stop signal Sig_stop output from the output stop determination unit 913 shown in FIG. As a result, it is possible to continue the operation for the predetermined limited operation period Δt2 after determining the abnormal state, and to stop the operation before the switching element 311 reaches the operation limit temperature.

The switching elements 311 to 316 of the inverter section 31 may be configured using any semiconductor element. For example, it can be configured using a wide bandgap semiconductor. Examples of wide bandgap semiconductor materials include SiC and GaN. By using these semiconductors, the heat resistance of the switching element can be improved, which contributes to improving the performance.

However, the switching elements 311 to 316 configured using wide bandgap semiconductors are more expensive than conventional switching elements configured using Si. Therefore, the cost of the inverter section 31 including the wide bandgap semiconductor is high.

By lowering the maximum reaching temperature of the switching element, it becomes possible to use an element with low heat resistance. Alternatively, it becomes possible to use an element with a high loss. Furthermore, since the temperature rise of the semiconductor can be appropriately controlled, the maximum attainable temperature of the semiconductor can be brought close to the operating limit temperature. For this reason, it is possible to cope with the size reduction of semiconductors whose heat radiation performance is lowered, and the cost can be further reduced.

Further, as described above, one arm of the inverter section 31 may be configured with one switching element. However, in order to reduce the current flowing per switching element, one arm may be configured by connecting a plurality of switching elements in parallel. In this case, if one switching element temperature sensor 7 is mounted for one switching element, the number of switching element temperature sensors 7 becomes enormous. As a result, the cost is high and the scale of the temperature acquisition circuit is increased. In order to avoid this, one switching element temperature sensor 7 may be installed for one arm to comprehensively acquire the temperatures of a plurality of switching elements.

In this way, even if one switching element generates excessive heat, by arranging the temperature sensor at a position where an average temperature can be obtained, it is possible to reduce the influence of variations in the obtained temperature. Then, an abnormal state can be determined quickly. The temperature rise rate value Th1 and the temperature rise rate continuation period Δt1 can be set in consideration of variations in the amount of heat generated by the switching elements.

As described above, the power conversion device 100 according to Embodiment 1 monitors the temperature rise rate from the temperature detection value of the switching element temperature sensor 7 that detects the temperature of the peripheral portion where the switching elements 311 to 316 are installed. By monitoring, it is possible to quickly determine whether the inflow of the cooling medium flowing to the cooler 4 has stopped or disappeared. Thereby, the maximum temperature reached by the switching element can be lowered. Optimal control can be realized by devising the drive conditions of the power conversion device 100 . The power conversion device 100 can continue to be driven while preventing the switching elements 311 to 316 from being damaged by high temperatures.

<Disparity in temperature rise rate>
13A and 13B are diagrams for explaining variations in temperature rise rate of switching elements of the power converter according to Embodiment 1. FIG. In FIG. 13, let Z0 be the maximum value of the temperature rise rate in the actual output state in the normal state, Z1 be the maximum value of the temperature rise rate in the output state observed to be small due to the observation accuracy in the normal state, Z2 be the maximum value of the temperature rise rate in the output state observed to be large due to the observation accuracy in the normal state, and Za be the maximum value of the temperature rise rate when the actual output state becomes abnormal.

In FIG. 13, when the output state is observed to be small due to the observation accuracy, the temperature rise rate value Th1a is set above the maximum value Z1 of the temperature rise rate in the output state observed to be small. However, since the maximum value Z0 of the temperature rise rate in the actual output state is larger than the temperature rise rate value Th1a, the temperature rise rate in the normal state exceeds the temperature rise rate value Th1a, and although it is not an abnormal state, it is determined as an abnormal state and an erroneous determination occurs.

Therefore, considering the observation accuracy, consider a case where a value higher than the maximum value Z2 when the output state is observed to be large, that is, a temperature rise rate value Th1b is set instead of the temperature rise rate value Th1a. In this case, the temperature rise rate value Th1b is higher than the maximum value Za of the temperature rise rate when the abnormal state occurs in the actual output state, so the abnormal state cannot be determined. The smaller the output, the smaller the difference between the maximum temperature rise rate Za under abnormal conditions and the maximum temperature rise rate Z0 under actual output conditions.

In the power conversion device 100, it is necessary to improve the accuracy of the current detector and the voltage detector in order to prevent erroneous determination. For that purpose, there is a problem that the performance of the components of the determination circuit is improved and the cost is increased. In the power converter 100 according to the first embodiment, abnormality determination is performed using the temperature rise rate Tj_sens_rat, the temperature rise rate value Th1, and the temperature rise rate duration Δt1 without monitoring the output state using a current detector and a voltage detector. This makes it possible to eliminate the influence of the variation described above and determine an abnormal state for a wide range of output states.

2. Embodiment 2
FIG. 14 is a diagram showing the temperature rise rate, the temperature rise rate continuation period, and the determination value of the switching element of the power converter 100 according to the second embodiment. In the second embodiment, the hardware configuration and functional blocks shown in FIGS. 1 to 4 are used. It is assumed that the abnormality determination and operation restriction according to the temperature of the switching element and the temperature rise rate can be realized by changing the software, and the symbols of each part are not changed. However, in realizing the power conversion device 100 according to the second embodiment, hardware changes are not excluded. It may be realized by cooperation of changed hardware and changed software. In the following, the description of the parts that are the same as or corresponding to those of the first embodiment will be omitted, and the description will focus on the points that differ from the first embodiment.

Embodiment 2 differs from the temperature rise rate determining unit 911 of the power converter 100 according to Embodiment 1 shown in FIG. 4 in that a plurality of temperature rise rate values Th1 and temperature rise rate continuation periods Δt1 are provided. FIG. 14 shows the temperature rise rate, the temperature rise rate duration period and the judgment value according to the second embodiment, in contrast to the temperature rise rate, the temperature rise rate duration period and the judgment value according to the first embodiment shown in FIG. In FIG. 14, a temperature rise rate value Th11, a second temperature rise rate value Th12, a temperature rise rate continuation period Δt11, and a second temperature rise rate continuation period Δt12 are provided. Furthermore, a third temperature rise rate value Th13 is provided as a value higher than the maximum value of the normal rated output temperature rise rate Tj_sens_rat_nH at the rated output in the normal state.

In the first embodiment, as shown in FIG. 7, the temperature rise rate value Th1 is set below the peak value of the abnormal partial output temperature rise rate Tj_sens_rat_fL in an abnormal state during partial output, and a temperature rise rate continuation period Δt1 is provided to prevent erroneous determination based on the temperature rise rate value. However, when an abnormal condition occurs at the rated output, the output is large and the temperature Tj rises rapidly. Therefore, the temperature Tj of the switching element reaches the operating limit temperature before the temperature rise rate continuation period Δt1 elapses, and there is a possibility that the switching element will be damaged due to the high temperature.

Therefore, in the second embodiment, as shown in FIG. 14, a second temperature rise rate value Th12, which is a threshold value higher than the temperature rise rate value Th11, and a second temperature rise rate continuation period Δt12, which is a shorter determination time than the temperature rise rate continuation period Δt11, are added to the first embodiment. As a result, it is possible to quickly determine an abnormality and limit the operation of the switching element when the output is high. Although two temperature rise rate values and two temperature rise rate continuation periods are provided in the second embodiment, three or more may be provided.

A procedure for setting the temperature rise rate value, the temperature rise rate continuation period, and the third temperature rise rate value Th13 in the second embodiment will be described with reference to FIG. The vertical axis indicates the rate of temperature rise, and the horizontal axis indicates time.

FIG. 14 sets temperature rise rate value Th11 and second temperature rise rate value Th12, which are a plurality of temperature rise rate values, in FIG. Furthermore, a third temperature rise rate value Th13 and a third temperature rise rate continuation period Δt3 may be newly provided (Δt3 is not shown).

<Setting the third temperature rise rate value>
First, a method of setting the third temperature rise rate value Th13 and the third temperature rise rate continuation period Δt3 will be described. The third temperature rise rate value Th13 is set to a value higher than the maximum value of the normal rated output temperature rise rate Tj_sens_rat_nH at the rated output in the normal state in FIG. Erroneous determination can be prevented by setting a threshold value to a rate of temperature rise that cannot be reached in a normal state. Further, since the temperature does not reach in a normal state, the determination time can be shortened. As a result, when an abnormal state occurs at rated or near-rated high output, the abnormality can be determined quickly. In order to determine a sudden rise in temperature rise rate without delay, the third temperature rise rate continuation period Δt3 may be set to a very short period.

Here, the maximum allowable temperature is obtained by subtracting the temperature rise (temperature rise from Tj_21b to Tj_22 in FIG. 11) when the operation continues after the determination of the abnormal state from the operating limit temperature. The third temperature rise rate continuation period Δt3 is equal to or less than the time from when the abnormal rated output temperature rise rate Tj_sens_rat_fH in an abnormal state at the rated output reaches the third temperature rise rate value Th13 at X3 to when the temperature Tj of the switching element reaches the maximum allowable temperature (not shown). As a result, it is possible to determine the abnormal state before the temperature Tj of the switching element reaches the maximum allowable temperature at rated or near-rated high output.

The third temperature rise rate value Th13 is set to a value lower than the maximum value of the abnormal rated output temperature rise rate Tj_sens_rat_fH in an abnormal state at the rated output. As a result, the temperature rise rate reliably reaches the third temperature rise rate value Th13 when the abnormal state occurs at the rated output, so that the abnormal state can be reliably determined.

The third temperature rise rate continuation period Δt3 may be the unit time during which the temperature rise rate is calculated, and if the temperature rise rate, which is the amount of rise per unit time, exceeds the third temperature rise rate value Th13 even once, it may be determined as an abnormal state, and the error signal Sig_err may indicate the error state. As a result, the abnormal state can be determined in the shortest time when the output is rated or near rated.

<Setting of temperature rise rate value and second temperature rise rate value>
Next, a method of setting a plurality of temperature rise rate values Th11, a second temperature rise rate value Th12, and a temperature rise rate duration Δt11 and a second temperature rise rate duration Δt12, which are a plurality of temperature rise rate durations, will be described. The temperature rise rate value Th11 is set to be equal to or less than the peak value of the abnormal partial output temperature rise rate Tj_sens_rat_fL in an abnormal state during partial output in FIG. The partial output indicates the lower limit output to be protected by the power converter 100 among the output states of the power converter 3 . That is, although it is not a rated output but a partial output state, it indicates an output state in which the operation of the switching element should be limited when the cooler malfunctions.

The temperature rise rate continuation period Δt11 corresponding to the temperature rise rate value Th11 is longer than the period during which the normal rated output temperature rise rate Tj_sens_rat_nH exceeds the temperature rise rate value Th11 at the rated output in the normal state. As a result, it is possible to determine an abnormality such as a cooler abnormality at an output equal to or greater than the partial output while preventing erroneous determination.

A second temperature rise rate value Th12 is set by selecting a temperature rise rate value that is equal to or less than the maximum temperature rise rate of the normal rated output temperature rise rate Tj_sens_rat_nH at the rated output in the normal state and is greater than the temperature rise rate value Th11. A second temperature rise rate continuation period Δt12 is set as a period shorter than the temperature rise rate continuation period Δt11 and longer than the period during which the normal rated output temperature rise rate Tj_sens_rat_nH exceeds the second temperature rise rate value Th12. As a result, with respect to the temperature rise rate greater than the temperature rise rate value Th11, the second temperature rise rate continuation period Δt12, which is a period shorter than the temperature rise rate continuation period Δt11, can prevent erroneous judgments and quickly make an abnormality judgment. At this time, the second temperature rise rate value Th12 may be set to be equal to or lower than the third temperature rise rate value Th13.

That is, in the case of the abnormal partial output temperature rise rate Tj_sens_rat_fL in an abnormal state, the combination of the temperature rise rate value Th11 and the temperature rise rate continuation period Δt11 can prevent an erroneous judgment and make an abnormality judgment. Although this makes it possible to limit the operation of the switching element, the abnormality determination requires a temperature increase rate continuation period Δt11. On the other hand, the combination of the second temperature rise rate value Th12 and the second temperature rise rate continuation period Δt12 cannot limit the operation of the switching elements of the abnormal partial output temperature rise rate Tj_sens_rat_fL. However, for an abnormality exceeding the second temperature increase rate value Th12, which is a larger temperature increase rate value, an erroneous determination can be prevented, and the abnormality can be quickly determined in the second temperature increase rate continuation period Δt12, which is a shorter period, and the operation of the switching element can be restricted.

According to the power conversion device 100 according to Embodiment 2 described above, the temperature rise rate value and the temperature rise rate duration period are set so that the higher the temperature rise rate value, the shorter the temperature rise rate duration period corresponding to the temperature rise rate value. That is, it is possible to determine an abnormal state early according to the output in the entire range of the rated output or less and the partial output or more, and by performing operation restriction to suppress the output of the power converter 100, the switching elements 311 to 316 are damaged due to high temperature.

3. Embodiment 3
FIG. 15 is a functional block diagram of the output suppression unit 91 of the power converter 100 according to Embodiment 3. As shown in FIG. In Embodiment 3, the hardware configuration and functional blocks shown in FIGS. 1 to 3 are used. In the configuration of the power converter 100 according to Embodiment 1, the output suppression unit 91 shown in FIG. 4 is changed to the output suppression unit 91 shown in FIG. Specifically, the output suppression unit 91 of FIG. 15 is obtained by changing the output destination of the temperature rise rate determination unit 911 of the output suppression unit 91 of FIG. 4 and adding a temperature rise determination unit 914 and an abnormality determination unit 915 .

The change of the function block of the output suppression unit 91 and the implementation of abnormality determination and operation restriction according to the temperature of the switching element and the temperature rise rate will be explained as being realized by changing the software, and the reference numerals of each part will not be changed. However, in realizing the power conversion device 100 according to the third embodiment, hardware changes are not excluded. It may be realized by cooperation of changed hardware and changed software. In the following, the description of the parts that are the same as or corresponding to those of the first embodiment will be omitted, and the description will focus on the points that differ from the first embodiment.

In FIG. 15 , the output of temperature rise rate determination section 911 is input to abnormality determination section 915 . The temperature increase determination unit 914 is a function provided in parallel with the function of the temperature increase rate determination unit 911 . Specifically, the temperature rise determination unit 914 compares the temperature detection value Tj_sens with a predetermined determination temperature Th2 to detect abnormal heat generation of the switching elements 311 to 316, an abnormal state of the cooler 4, etc., and inputs the result to the abnormality determination unit 915 (Th2 is not shown).

The determination temperature Th2 is set so that, for example, even if the cooling medium in the cooler 4 disappears, the temperature increase rate determination unit 911 cannot determine an abnormality, that is, when the inverter unit 31 outputs low power, the temperature increase determination unit 914 can determine an abnormality. Even if the detected temperature value Tj_sens drops below the determination temperature Th2 after determining the abnormal state, the temperature rise determination unit 914 continues to determine the abnormal state.

Abnormality determination unit 915 monitors the output results of temperature increase rate determination unit 911 and temperature increase determination unit 914, and when at least one of temperature increase rate determination unit 911 and temperature increase determination unit 914 is determined to be abnormal, it outputs error signal Sig_err in an abnormal state.

Here, the power conversion device described in Patent Document 1 and the power conversion device 100 according to the third embodiment are compared. Both have the same function of comparing the temperature detection value Tj_sens with a predetermined judgment temperature (threshold) and starting operation restriction when the temperature detection value Tj_sens exceeds the judgment temperature. However, in the third embodiment, temperature rise rate determination section 911 determines abnormality based on temperature rise rate value Th1 in the high output region of inverter section 31, and temperature rise determination section 914 determines abnormality based on determination temperature Th2 in the low output region.

As described above, the problem is that the maximum temperature reached by the switching elements 311 to 316 increases. As shown in the third embodiment, if the temperature detection value Tj_sens is compared with a predetermined determination temperature Th2, the maximum reaching temperature of the switching elements 311 to 316 is the sum of the difference between the temperature Tj of the switching elements 311 to 316 and the temperature detection value Tj_sens, and the determination temperature Th2.

The determination temperature Th2 is a temperature that does not reach when the power conversion device 100 operates normally, and therefore cannot be lowered. On the other hand, comparing the difference between the temperature Tj of the switching element and the detected temperature value Tj_sens at low output of the inverter unit 31 and the difference between the temperature Tj of the switching element and the detected temperature value Tj_sens at high output, the difference is smaller at low output than at high output. Therefore, the difference between the temperature Tj of the switching element and the temperature detection value Tj_sens at the point when the determination temperature Th2 is reached when the output of the inverter unit 31 is low becomes small. Therefore, the maximum temperature reached by the switching element can be lowered when the output is low.

The output suppression unit 91 of the control device 9 of the power conversion device 100 according to Embodiment 3 compares the temperature detection value Tj_sens of the switching element temperature sensor 7 with a predetermined determination temperature Th2, and includes a temperature rise determination unit 914 that determines that the temperature detection value Tj_sens exceeds the determination temperature Th2. Then, the temperature rise rate determination unit 911 described above is provided. At least one of the temperature increase rate determination unit 911 and the temperature increase determination unit 914 is configured to perform operation restriction to suppress the output of the power conversion unit 3 when it determines that the corresponding threshold value has been exceeded. As a result, when the output is high, the temperature rise rate determination unit 911 determines the abnormal state, and when the output is low, the temperature rise determination unit 914 determines the abnormal state, so it is possible to determine the abnormality corresponding to various outputs.

The determination temperature Th2 is set at least to a value higher than the temperature detection value Tj_sens that the power conversion unit 3 reaches during rated operation in a normal state. As a result, the temperature rise determination section 914 does not determine abnormality in the normal state, so that erroneous determination by the temperature rise determination section 914 can be prevented.

The determination temperature Th2 is set to a value that allows the power conversion unit 3 to operate for a predetermined limited operation period after the temperature detection value Tj_sens of the switching element temperature sensor 7 exceeds the determination temperature Th2. This allows time to take necessary measures before the power electronics device 100 stops functioning.

The determination temperature Th2 is set so that the temperature of the switching element that reaches due to the abnormality of the cooler in the case of partial output can be detected. The partial output indicates the lower limit output to be protected by the power converter 100 among the output states of the power converter 3 . That is, although it is not a rated output but a partial output state, it indicates an output state in which the operation of the switching element should be limited when the cooler malfunctions.

For this reason, in the case of partial output, which is the lower limit output to be protected, the determination temperature Th2 is set to be less than the maximum value of the temperature detection value Tj_sens of the switching element that reaches when the cooler malfunctions. As a result, the control device 9 of the power conversion device 100 can detect the temperature abnormality of the switching element and perform the protection operation even in a low output region. It is possible to secure a high output region in which abnormality can be determined at the temperature rise rate Tj_sens_rat and a low output region in which abnormality can be determined based on the temperature detection value Tj_sens. As a result, the output range that cannot be determined can be reduced. In a wide output range, the abnormal state can be determined by either the abnormality determination based on the temperature rise rate or the abnormality determination based on the temperature detection value. Further, when the power conversion device 100 is in operation and the temperature detection value Tj_sens of the switching element when the cooler is abnormal even with no load exceeds the temperature detection value Tj_sens of the switching element when the cooler is in normal rated operation, by setting the determination temperature Th2 during this period, it is possible to determine the abnormal state in the entire output range.

Here, let us consider the temperature rise rate abnormality judgment possible output lower limit value, which is the lower limit of the output region in which an abnormality judgment can be made at the temperature rise rate Tj_sens_rat. Then, consider the lower temperature abnormality determination output lower limit value, which is the lower limit of the output range in which abnormality determination is possible with the temperature detection value Tj_sens. The temperature rise rate abnormality determination output lower limit value and the temperature abnormality determination output lower limit value may be matched, and this may be used as a partial output. With such a setting, the output range in which an abnormality can be determined based on the temperature rise rate and the output range in which an abnormality can be determined based on the temperature overlap. As a result, it is possible to reliably determine the abnormality in the overlapping output range by two methods, so that the reliability of the abnormality determination can be improved.

The control device 9 is configured such that at least one of the temperature increase rate determination unit 911 and the temperature increase determination unit 914 determines an abnormality, and then performs operation restriction to suppress the output of the power conversion unit 3 . As a result, the temperature rise after determination of the abnormal state is reduced. Therefore, it is possible to ensure a longer limited operation period from when the abnormal state is determined to when the engine is stopped. For example, when the electric motor 1 is used as a drive source for a vehicle such as an electric vehicle, when an abnormal condition occurs at a problematic location such as an intersection, the power conversion device 100 can be obtained to move the vehicle to a safe location such as a road shoulder using the restricted operation period.

Further, the control device 9 of the power conversion device 100 continues the operation restriction for suppressing the output of the power conversion section 3 even when the temperature of the switching element is lowered. When at least one of a state in which the temperature rise rate Tj_sens_rat falls below the temperature rise rate value Th1 and a state in which the detected temperature value Tj_sens falls below the determination temperature Th2 during the operation limitation of the switching element, the power conversion device 100 is configured to continue the operation limitation to suppress the output of the power conversion unit 3. As a result, it is possible to reliably continue the operation of the power converter 100 for a period equal to or longer than the predetermined limited operation period while preventing damage to the switching elements.

Furthermore, the control device 9 of the power conversion device 100 may be configured to stop the output of the power conversion unit 3 after a predetermined period of time (for example, a limited operation period) after executing the operation restriction that suppresses the output of the power conversion unit 3. Further, the control device 9 may include an output stop determination unit 913 that, after performing operation restriction to suppress the output of the power conversion unit 3, compares a predetermined stop determination temperature Th3 with a detected temperature value Tj_sens, and stops the output of the power conversion unit 3 when the detected temperature value Tj_sens exceeds the stop determination temperature Th3. As a result, the operation can be continued after the abnormal state is determined, and the operation can be stopped before the switching element 311 reaches the operation limit temperature.

Each of the switching elements 311 to 316 forming one arm of the power converter 3 may be configured by connecting a plurality of switching elements in parallel. The switching element temperature sensor 7 may be configured to detect the average temperature of all switching elements.

According to the power converter 100 according to Embodiment 3 described above, when the output of the inverter unit 31 is high, it is possible to quickly determine the abnormality of the cooler 4 based on the temperature rise rate Tj_sens_rat. Then, when the output of the inverter unit 31 is low, it is possible to determine whether the cooler 4 is abnormal based on the temperature detection value Tj_sens.

It has been explained that the partial output indicates the lower limit of the output state of the power converter 3 that the power converter 100 should protect. Now consider the maximum rate of temperature rise value if the heat transfer function of the cooler is lost in this partial power condition. A temperature rise rate value Th4 that is smaller than the maximum temperature rise rate value at this time is determined (Th4 is not shown). This temperature rise rate value Th4 may be set as the temperature rise rate value Th1 to be compared with the temperature rise rate Tj_sens_rat in the temperature rise rate determination unit 911 .

In this way, loss of heat transfer function of the cooler during partial power conditions can be detected more quickly. As a result, it is possible to overlap a high-output region in which an abnormality is detected based on the temperature rise rate value and a low-output region in which an abnormality is detected based on the temperature detection value. As a result, the output range that cannot be determined can be eliminated. In the entire output range, the abnormal state can be determined by either the abnormality determination based on the temperature rise rate or the abnormality determination based on the temperature detection value.

Although this application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of particular embodiments, but are applicable to the embodiments singly or in various combinations. Accordingly, numerous variations not illustrated are envisioned within the scope of the technology disclosed herein. For example, modification, addition or omission of at least one component, extraction of at least one component, and combination with components of other embodiments shall be included.

1 electric motor 3 power conversion unit 4 cooler 7 switching element temperature sensor 8 command generator 9 control device 100 power conversion device 311, 312, 313, 314, 315, 316 switching element 33 amplifier circuit 34 drive circuit 91 output suppression unit 911 temperature rise rate determination unit 912 torque command suppression unit 913 output stop determination unit 914 temperature rise determination Tj_sens Temperature detection value Tj_sens_rat Temperature rise rate Tj_sens_rat_nH Normal rated output temperature rise rate Tj_sens_rat_fL Abnormal partial output temperature rise rate Tj_sens_rat_fH Abnormal rated output temperature rise rate Th1, Th11, Th4 Temperature rise rate value Th12 Second Temperature rise rate value Th13 Third temperature rise rate value Th2 Judgment temperature Th3 Stop judgment temperature Δt1, Δt11 Temperature rise rate continuation period Δt2 Limited operation period Δt12 Second temperature rise rate continuation period Δt3 Third temperature rise rate continuation period

Claims (18)

switching element,
a temperature sensor that detects the temperature of the switching element;
A power conversion device comprising: a control device that controls the switching element and limits the operation of the switching element when the rate of temperature increase detected by the temperature sensor during a predetermined determination period is greater than a predetermined rate of temperature increase ,
In the control device, the temperature rise rate value is set to a value smaller than the maximum rate of temperature rise detected by the temperature sensor when the power converter is in a normal state and the switching element outputs rated output, and the determination period is set to a period longer than a period during which the temperature rise rate detected by the temperature sensor continues to be greater than the temperature rise rate value when the power converter is normal and the switching element outputs the rated output. 2. The power converter according to claim 1 , wherein the control device has a second temperature rise rate value larger than the temperature rise rate value and a second judgment period shorter than the judgment period, and restricts the operation of the switching element when the temperature rise rate detected by the temperature sensor is higher than the temperature rise rate value during the judgment period or when the temperature rise rate detected by the temperature sensor is higher than the second temperature rise rate value during the second judgment period. 3. The power conversion device according to claim 2 , wherein the second determination period is set to a value smaller than the maximum rate of temperature rise detected by the temperature sensor when the power conversion device is in a normal state and the rated output of the switching element, and the second determination period is set to a longer period than a period during which the rate of temperature increase detected by the temperature sensor is greater than the second temperature rise rate value when the power conversion device is normal . The power conversion device according to any one of claims 1 to 3 , wherein the control device has a predetermined third temperature rise rate value, and further limits the operation of the switching element when the maximum value of the temperature rise rate detected by the temperature sensor is greater than the third temperature rise rate value. A cooler that cools the switching element,
5. The power converter according to claim 4 , wherein the control device sets the third temperature rise rate value to be equal to or less than the maximum temperature rise rate of the switching element at the time of rated output when the heat transfer function of the cooler is lost. The power conversion device according to any one of claims 1 to 5 , wherein the control device continues limiting the operation of the switching element when the rate of increase in the temperature detected by the temperature sensor after starting the limitation of operation of the switching element is equal to or lower than the predetermined temperature increase rate value. The power converter according to any one of claims 1 to 6 , wherein the control device restricts the operation of the switching element when the rate of temperature increase detected by the temperature sensor is greater than the temperature rate of increase during the determination period, or when the temperature detected by the temperature sensor is higher than a predetermined determination temperature. 8. The power conversion device according to claim 7 , wherein the control device sets the judgment temperature to a value higher than the temperature of the switching element at the rated output when the power conversion device is normal. A cooler that cools the switching element,
9. The power converter according to claim 7 , wherein the control device sets the judgment temperature according to an output for limiting the operation of the switching element when the heat transfer function of the cooler is lost. A cooler that cools the switching element,
10. The power converter according to any one of claims 7 to 9 , wherein the control device sets the temperature rise rate value according to an output for limiting the operation of the switching element when the heat transfer function of the cooler is lost. 11. The power converter according to claim 10 , wherein the control device sets the temperature rise rate value to be equal to or less than the maximum temperature rise rate at the time of output that limits the operation of the switching element when the heat transfer function of the cooler is lost. The power conversion device according to any one of claims 7 to 11 , wherein the control device continues to limit the operation of the switching element when the rate of increase in the temperature detected by the temperature sensor after starting the limitation of operation of the switching element is equal to or lower than the predetermined temperature increase rate value and the temperature detected by the temperature sensor is equal to or lower than the determination temperature. The power converter according to any one of claims 1 to 12 , wherein the control device limits the operation of the switching element by controlling the switching element to a predetermined output. 14. The power converter according to claim 13 , wherein the control device limits and controls the switching element to a predetermined output for a predetermined limited operation period after starting the operation limitation of the switching element. 15. The power converter according to any one of claims 1 to 14 , wherein the control device stops the operation of the switching element after a predetermined limited operation period after starting the operation limitation of the switching element. The power conversion device according to any one of claims 1 to 15 , wherein the control device stops the operation of the switching element when the temperature detected by the temperature sensor is higher than a predetermined stop determination temperature after starting the operation limitation of the switching element. comprising a plurality of switching elements connected in parallel,
The power converter according to any one of claims 1 to 16 , wherein the temperature sensor detects temperatures of a plurality of switching elements. 18. The power converter according to any one of claims 1 to 17 , wherein said switching element is composed of a wide bandgap semiconductor.

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