Power converter

Abstract

To provide an efficient power conversion device that suppresses excessive limitation on an output of the power conversion device while appropriately preventing overheating of a semiconductor switching element.SOLUTION: A power conversion device includes: a switching element for conducting and interrupting a current; an element temperature detector for detecting temperature of the switching element; a cooler for cooling the switching element; a refrigerant status detector for detecting a status of a refrigerant passing through the cooler; and a control device for controlling the switching element to perform power conversion and performing overheating prevention control of the switching element. The control device determines a temperature threshold for determining necessity of the overheating prevention control based on a state of the refrigerant detected by the refrigerant state detector and performs the overheating prevention control by limiting operation of the switching element when temperature detected by the element temperature detector is higher than the temperature threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to a power conversion device.

Background Art

[0002] A power conversion device is used to convert the output form of electric power. As power conversion devices, there are an AC / DC converter (Alternate Current / Direct Current Converter) that converts AC power to DC power, an inverter that converts DC power to AC power, a DC / DC converter (Direct Current / Direct Current Converter) that changes the levels of the input voltage and output voltage of DC power, and so on. These power conversion devices often have a configuration including semiconductor switching elements.

[0003] The power conversion device controls the current flowing by the switching operation of the semiconductor switching element. And the input power is converted by this switching operation to obtain the output power. In the semiconductor switching element, power loss occurs due to the current flowing through the semiconductor switching element. Most of the power loss becomes heat, raising the temperature of the semiconductor switching element. The semiconductor switching element has a determined maximum operating temperature Tjmax, and if it continues to be driven even exceeding this maximum operating temperature Tjmax, the semiconductor switching element may deteriorate in performance or be damaged due to overheating. Therefore, the power conversion device may include a cooler that cools the heat generating part to prevent overheating of the semiconductor switching element. (The maximum operating temperature Tjmax is not shown in the figure)

[0004] To prevent overheating of the semiconductor switching element of the power conversion device, a technique is disclosed that includes a temperature detector capable of detecting the temperature of the semiconductor switching element and reduces the output of the power conversion device when the detected temperature exceeds a predetermined threshold value. By reducing the output of the power conversion device, it is possible to protect the semiconductor switching element so that its temperature does not exceed the maximum operating temperature Tjmax (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-169401 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the technology described in Patent Document 1, the output of the power converter is uniformly limited when the temperature detected by a temperature detector of some semiconductor switching elements exceeds a predetermined threshold. However, this cannot cope with situations where the behavior of the temperature rise at the junction of the semiconductor switching elements changes depending on the state of the cooler that cools the semiconductor switching elements. As a result, depending on the state of the cooler, the detected temperature may exceed the predetermined threshold and the output may be excessively limited even when the behavior of the temperature rise at the junction of the semiconductor switching elements is still acceptable. In such cases, the power converter will limit the capabilities of the semiconductor switching elements more than necessary, and will not be able to fully perform.

[0007] This invention discloses a technology for solving the above-mentioned problems. In a power converter having a cooler, the threshold temperature for determining the limit of the output of the power converter is changed based on the state of the cooling medium flowing through the cooler. The aim is to provide an efficient power converter by preventing excessive limiting of the output of the power converter while more appropriately preventing overheating of semiconductor switching elements. [Means for solving the problem]

[0008] The power conversion device relating to this application is A switching element that conducts and interrupts electric current. A temperature detector for detecting the temperature of a switching element. Cool the switching elements. It is cooled by a cooling medium, and when the temperature of the cooling medium decreases, the viscosity of the cooling medium decreases, the flow rate of the cooling medium decreases, and the cooling efficiency decreases. cooler, A cooling medium state detector that detects the state of the cooling medium passing through the cooler, and A power conversion device equipped with a control device that controls switching elements to perform power conversion and also controls overheating prevention of the switching elements, The control device determines a temperature threshold for determining whether overheat prevention control is necessary based on the state of the cooling medium detected by the cooling medium state detector, and if the temperature detected by the element temperature detector is higher than the temperature threshold, it restricts the operation of the switching element to perform overheat prevention control. And, A cooling medium state detector is a cooling medium flow detector that detects the flow rate of the cooling medium. It is. Furthermore, the power conversion device relating to this application is A switching element that conducts and interrupts electric current. A temperature detector for detecting the temperature of a switching element. A cooler that cools switching elements and is also cooled by a cooling medium, where the viscosity of the cooling medium decreases and the flow rate of the cooling medium decreases when the temperature of the cooling medium drops, resulting in a decrease in cooling efficiency. A cooling medium state detector that detects the state of the cooling medium passing through the cooler, and A power conversion device equipped with a control device that controls switching elements to perform power conversion and also controls overheating prevention of the switching elements, The control device is a power converter that determines a temperature threshold for determining whether overheat prevention control is necessary based on the state of the cooling medium detected by a cooling medium state detector, and restricts the operation of the switching element to perform overheat prevention control when the temperature detected by the element temperature detector is higher than the temperature threshold, The cooling medium state detector includes a cooling medium temperature detector for detecting the temperature of the cooling medium and a cooling medium flow rate detector for detecting the flow rate of the cooling medium. The control device determines a temperature threshold based on the temperature of the cooling medium detected by the cooling medium temperature detector and the flow rate of the cooling medium detected by the cooling medium flow rate detector. [Effects of the Invention]

[0009] According to this invention, in a power converter having a cooler, the detection temperature threshold for determining the limit of the power converter's output is changed based on the state of the cooling medium flowing through the cooler. The power converter's output can be limited when the temperature detected by the semiconductor switching element's temperature detector is higher than this temperature threshold. This makes it possible to more appropriately prevent overheating of the semiconductor switching element while suppressing excessive limiting of the power converter's output, thereby providing an efficient power converter. [Brief explanation of the drawing]

[0010] [Figure 1] This is a configuration diagram of the power conversion device according to Embodiment 1. [Figure 2] This is a hardware configuration diagram of the control device for the power conversion device according to Embodiment 1. [Figure 3] It is a functional block diagram of a control device of a power conversion device according to Embodiment 1. [Figure 4] It is a first diagram for explaining the relationship between a fixed temperature threshold value and an element temperature of a power conversion device according to Embodiment 1. [Figure 5] It is a second diagram for explaining the relationship between a fixed temperature threshold value and an element temperature of a power conversion device according to Embodiment 1. [Figure 6] It is a diagram for explaining the relationship between a cooling medium temperature and a variably set temperature threshold value of a power conversion device according to Embodiment 1. [Figure 7] It is a first time chart showing the temperature transition during overheat prevention by a fixed temperature threshold value of a power conversion device according to Embodiment 1. [Figure 8] It is a second time chart showing the temperature transition during overheat prevention by a fixed temperature threshold value of a power conversion device according to Embodiment 1. [Figure 9] ] It is a first time chart showing the temperature transition during overheat prevention by a variably set temperature threshold value of a power conversion device according to Embodiment 1. [Figure 10] It is a second time chart showing the temperature transition during overheat prevention by a variably set temperature threshold value of a power conversion device according to Embodiment 1. [Figure 11] It is a diagram showing the relationship between a cooling medium temperature and an element temperature during overheat prevention by a fixed temperature threshold value of a power conversion device according to Embodiment 1. [Figure 12] It is a diagram showing the relationship between a cooling medium temperature and an element temperature during overheat prevention by a variably set temperature threshold value of a power conversion device according to Embodiment 1. [Figure 13] It is a configuration diagram of a second embodiment of a power conversion device according to Embodiment 1. [Figure 14] It is a configuration diagram of a third embodiment of a power conversion device according to Embodiment 1. [Figure 15] It is a configuration diagram of a fourth embodiment of a power conversion device according to Embodiment 1. [Figure 16] It is a configuration diagram of a fifth embodiment of a power conversion device according to Embodiment 1. [Figure 17] This is a configuration diagram of the sixth embodiment of the power conversion device according to Embodiment 1. [Figure 18] This is a diagram showing the configuration of a power conversion device according to Embodiment 2. [Figure 19] This is a functional block diagram of the control device for the power conversion device according to Embodiment 2. [Figure 20] This is the first figure illustrating the relationship between a fixed temperature threshold and element temperature in a power conversion device according to Embodiment 2. [Figure 21] This is a second diagram illustrating the relationship between a fixed temperature threshold and element temperature in a power conversion device according to Embodiment 2. [Figure 22] This figure illustrates the relationship between the cooling medium flow rate and the variable temperature threshold of the power conversion device according to Embodiment 2. [Figure 23] This is a first time chart showing the temperature changes during overheat prevention using a fixed temperature threshold for the power converter according to Embodiment 2. [Figure 24] This is a second time chart showing the temperature changes during overheat prevention using a fixed temperature threshold for the power converter according to Embodiment 2. [Figure 25] This is a first time chart showing the temperature changes during overheat prevention based on a variablely set temperature threshold for the power converter according to Embodiment 2. [Figure 26] This is a second time chart showing the temperature changes during overheat prevention based on a variablely set temperature threshold for the power converter according to Embodiment 2. [Figure 27] This figure shows the relationship between the cooling medium flow rate and element temperature when overheating is prevented by a fixed temperature threshold in the power conversion device according to Embodiment 2. [Figure 28] This figure shows the relationship between the cooling medium flow rate and element temperature when overheating is prevented by a variablely set temperature threshold in the power conversion device according to Embodiment 2. [Figure 29] This is a configuration diagram of the power conversion device according to Embodiment 3. [Figure 30] This is a functional block diagram of the control device for the power conversion device according to Embodiment 3. [Figure 31] This figure illustrates the relationship between the cooling capacity of the power converter according to Embodiment 3 and the variablely set temperature threshold. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the power conversion device according to the present application will be described with reference to the drawings.

[0012] 1. Embodiment 1 <Configuration of a power converter> Figure 1 is a diagram showing the configuration of a power converter 100 according to Embodiment 1. The power converter 100 may be used in electric vehicles such as electric vehicles and plug-in hybrid vehicles. A power converter for driving a motor powered by the electricity of a high-voltage battery can be envisioned.

[0013] The power converter 100 comprises semiconductor switching elements 51 to 56 that convert power through switching operation, a cooler 351, a control device 90, and element temperature detectors 71 to 76. The cooler 351 cools the semiconductor switching elements 51 to 56. The control device 90 controls the semiconductor switching elements 51 to 56. The element temperature detectors 71 to 76 detect the temperature of the semiconductor switching elements 51 to 56.

[0014] The control device 90 restricts the operation of semiconductor switching elements 51 to 56 to suppress the temperature rise of the semiconductor switching elements 51 to 56 when the temperature detection values ​​T1 to T6 of the element temperature detectors 71 to 76 are higher than a predetermined temperature threshold OT. The control that prevents overheating of the semiconductor switching elements 51 to 56 is generally also called overheat protection control.

[0015] The cooler 351 is provided with a cooling medium state detection means for detecting the state of the cooling medium flowing through the cooler 351. In Figure 1, a water temperature sensor 36 is provided as the cooling medium state detection means for detecting the temperature of the cooling water flowing into the cooler 351. The control device 90 sets a temperature threshold based on the temperature TW of the cooling medium detected by the water temperature sensor 36.

[0016] Figure 1 shows a DC power source 12, such as a battery, which supplies DC power to the power converter 100 and is charged by regenerative power, and a rotating electric machine 10 to be controlled. The controlled object is not limited to the rotating electric machine 10, but may be something other than the rotating electric machine 10.

[0017] In Figure 1, the power converter 100 is connected to the DC power supply 12 by a positive DC bus 1a and a negative DC bus 1b, and exchanges drive power and regenerative power with the DC power supply 12. The power converter 100 is also connected to the rotating electric machine 10 by an AC bus 2, and exchanges drive power and regenerative power with the rotating electric machine 10.

[0018] The rotating electric machine 10 is equipped with a rotation angle sensor 11 that detects the rotation angle θm of the rotating electric machine 10. The rotating electric machine 10 rotates the load and can regenerate the rotational energy of the load as electrical energy. For example, a permanent magnet three-phase AC synchronous motor or a three-phase brushless motor may be used. (The rotation angle θm is not shown.)

[0019] The power conversion device 100 includes a power conversion unit 20, and a cooler 351 is assembled to cool the heat-generating part of the power conversion unit 20. The power conversion unit 20 has a positive DC bus 1a and a negative DC bus 1b connected to the DC power supply 12, a capacitor 21 connected between them, and a voltage detection unit 24 for detecting the DC bus voltage of the power conversion unit 20. The power conversion unit 20 is composed of a plurality of semiconductor switching elements 51 to 56 and includes an inverter circuit 25 that performs DC / AC power conversion, and a current detection unit 26 that detects the current of the rotating electric machine 10 flowing through the AC bus 2. The power conversion unit 20 also includes a drive circuit 27 for switching the semiconductor switching elements 51 to 56 on and off. The power conversion unit 20 is controlled by a control device 90.

[0020] Capacitor 21 has functions such as suppressing ripple in the DC bus voltage, lowering the power supply impedance of the power conversion unit 20 to improve its AC current driving capability, and absorbing surge voltage. The voltage detection unit 24 divides the DC bus voltage into voltages that can be read by the control device 90 using voltage divider resistors, etc., and outputs the DC bus voltage information to the control device 90.

[0021] The inverter circuit 25 is an inverter that uses a full bridge connection of six commonly known semiconductor switching elements 51 to 56. That is, as shown in Figure 1, semiconductor switching elements 51, 52, 53, 54, 55, and 56 are the upper and lower semiconductor switching elements, respectively. The upper and lower semiconductor switching elements are connected in series and connected in parallel to the DC power supply 12.

[0022] Furthermore, the midpoints of semiconductor switching elements 51 and 52 are connected to the U-phase input of the rotating electric machine 10. The midpoints of semiconductor switching elements 53 and 54 are connected to the V-phase input of the rotating electric machine 10. And the midpoints of semiconductor switching elements 55 and 56 are connected to the W-phase input of the rotating electric machine 10. Semiconductor switching elements 51 to 56 are each built into semiconductor modules 61 to 66.

[0023] <Semiconductor switching element> Semiconductor switching elements include diodes, which allow current to flow in only one direction; thyristors, which are suitable for handling large currents; and power transistors, which are power semiconductor switching elements capable of operating at high switching frequencies. Power transistors are used in a wide range of fields, such as automobiles, refrigerators, and air conditioners. Among power transistors, there are IGBTs (Insulated Gate Bipolar Transistors) and MOS-FETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and these power transistors are used differently depending on the application.

[0024] In recent years, silicon carbide (SiC) and gallium nitride (GaN) have attracted attention as materials for semiconductor switching elements. Semiconductor switching elements formed from these materials have lower resistance in the ON state compared to conventional silicon (Si) semiconductor switching elements, thus reducing power loss. In addition, they have a high electron saturation rate, which allows for faster switching between the ON and OFF states, further reducing power loss. Furthermore, compared to silicon, semiconductor switching elements using silicon carbide or gallium nitride can be operated in higher temperature environments.

[0025] The semiconductor switching elements 51 to 56 are, for example, MOS-FETs with a diode built into the source-drain junction, as shown in Figure 1. However, the type and number of semiconductor switching elements are not limited to these. The semiconductor switching elements may also be, for example, IGBTs and SiC MOSFETs.

[0026] Furthermore, the inverter circuit 25 is equipped with element temperature detectors 71 to 76 located inside or near the semiconductor modules 61 to 66, respectively, to detect the temperature of the semiconductor switching elements 51 to 56. The temperature detection values ​​T1 to T6 detected by the element temperature detectors 71 to 76 are input to the control device 90. The element temperature detectors 71 to 76 are the element temperature detectors in Embodiment 1.

[0027] The element temperature detectors 71 to 76, which detect the temperature of the semiconductor switching elements 51 to 56, may be installed inside the semiconductor modules 61 to 66. Alternatively, the element temperature detectors 71 to 76 may be installed on the substrate on which the semiconductor modules 61 to 66 are installed, or in the vicinity of the semiconductor modules 61 to 66. The element temperature detectors 71 to 76 are assumed to be thermistors. However, the temperature detectors are not limited to thermistors, and the temperature may be detected by temperature-sensing diodes or the like, which are placed on the semiconductor substrate of the semiconductor switching elements 51 to 56.

[0028] The current detection unit 26 is composed of a U-phase current detection unit 261, a V-phase current detection unit 262, and a W-phase current detection unit 263. The U-phase current detection unit 261, V-phase current detection unit 262, and W-phase current detection unit 263 are configured, for example, using shunt resistors. The U-phase current detection unit 261 outputs a U-phase current detection value corresponding to the U-phase current Iu to the control device 90. The V-phase current detection unit 262 outputs a V-phase current detection value corresponding to the V-phase current Iv to the control device 90. The W-phase current detection unit 263 outputs a W-phase current detection value corresponding to the W-phase current Iw to the control device 90. In the following description, the U-phase current detection value, V-phase current detection value, and W-phase current detection value may be collectively referred to as the current detection value. The current detection unit 26 may also be a current sensor using a Hall element or the like.

[0029] The drive circuit 27 is controlled based on a PWM signal input from the control device 90. The drive circuit 27 has the function of switching the semiconductor switching elements 51 to 56 on and off.

[0030] The rotation angle sensor 11 detects the rotor rotation angle θm of the rotating electric machine 10 using a resolver, encoder, etc. The rotor rotation angle θm detected by the rotation angle sensor 11 is output to the control device 90. The rotor rotation angle θm is converted to an electrical angle θe based on the number of pole pairs of the rotating electric machine 10.

[0031] The cooler 351 of the cooling system 350 cools the semiconductor switching elements 51 to 56. The cooling system 350 is, for example, a water-cooled cooling system. Specifically, the cooling system 350 is configured to connect a water-cooled cooler 351, a radiator 352, a water pump 353, etc., with cooling water piping such as hoses. A cooling medium such as water, oil, or LLC (Long Life Coolant) flows from the water pump 353 through the radiator 352 to the cooler 351. The direction of the flow of the cooling medium may be from the radiator 352 through the water pump 353 to the cooler 351.

[0032] The water temperature sensor 36 is a means for detecting the state of the cooling medium in Embodiment 1, and detects the temperature TW of the cooling medium flowing inside the cooling water piping and outputs it to the control device 90. The water temperature sensor 36 is placed, for example, in the cooler directly below the semiconductor module. Note that the water temperature sensor 36 is not limited to being placed inside the cooler, but may also be placed inside the cooling water piping.

[0033] <Control device hardware configuration> Figure 2 is a hardware configuration diagram of the control device 90 of the power converter 100 according to Embodiment 1. Although Figure 2 can also be applied to control devices 90A and 90B, the control device 90 will be described as a representative example here. In this embodiment, the control device 90 is a control device that controls the power converter 100. Each function of the control device 90 is realized by the processing circuits provided in the control device 90. Specifically, the control device 90 includes, as processing circuits, a arithmetic processing unit 80 (computer) such as a CPU (Central Processing Unit), a storage device 81 that exchanges data with the arithmetic processing unit 80, an input circuit 82 that inputs external signals to the arithmetic processing unit 80, and an output circuit 83 that outputs signals from the arithmetic processing unit 80 to the outside.

[0034] The arithmetic processing unit 80 may include an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits. Furthermore, multiple arithmetic processing units 80 of the same or different types may be provided, with each unit performing a portion of the processing. The storage device 81 may include a RAM (Random Access Memory) configured to read and write data from the arithmetic processing unit 80, or a ROM (Read Only Memory) configured to read data from the arithmetic processing unit 80. The input circuit 82 includes a rotation angle sensor 11, a voltage detection unit 24, a current detection unit 26, element temperature detectors 71 to 76, and a water temperature sensor 36. Various sensors and switches are connected to the input circuit, and the input circuit includes an AD conversion unit and other interface circuits that input the output signals from these sensors and switches to the arithmetic processing unit 80. The output circuit 83 includes a drive circuit 27, to which electrical loads such as switching elements and actuators are connected, and is equipped with interface circuits such as a drive circuit and a communication circuit that convert and output the output signals from the arithmetic processing unit 80 to these electrical loads.

[0035] Each function of the control device 90 is realized by the arithmetic processing unit 80 executing software (programs) stored in a storage device 81 such as ROM, and cooperating with other hardware of the control device 90, such as the storage device 81, input circuit 82, and output circuit 83. Setting data such as thresholds and judgment values ​​used by the control device 90 are stored in the storage device 81 such as ROM as part of the software (program).

[0036] Each function installed inside the control device 90 may be composed of a software module. However, each function installed inside the control device 90 may also be composed of a combination of software and hardware.

[0037] <Functional blocks of the control unit> Figure 3 is a functional block diagram of the control device 90 of the power converter 100 according to Embodiment 1. In Figure 3, the control device 90 includes a temperature threshold setting unit 91, an overheat protection control unit 92, a current command generation unit 93, a three-phase to two-phase conversion unit 94, a voltage command generation unit 95, a two-phase to three-phase conversion unit 96, a duty cycle conversion unit 97, and a PWM signal generation unit 98.

[0038] The current command generation unit 93 receives a torque command value Trq* from a higher-level system (not shown). Examples of control commands for controlling the rotating electric machine 10 include torque commands, current commands, voltage commands, etc. Embodiment 1 illustrates the case where the torque command value Trq* is used as the control command. Based on this torque command value Trq*, the current command generation unit 93 generates a d-axis current command value Id* and a q-axis current command value Iq*.

[0039] Here, the d-axis represents the magnetic pole position of the rotating electric machine 10, i.e., the direction of the magnetic flux, and the q-axis represents the direction electrically perpendicular to the d-axis, thus constituting a dq-axis coordinate system. The dq-axis coordinate system is a rotating coordinate system, and when the rotor of the rotating electric machine 10, which has magnets, rotates, the dq-axis coordinate system also rotates.

[0040] The temperature threshold setting unit 91 has a function, which is a feature of the present invention, to calculate a temperature threshold for implementing overheat protection control based on the state of the cooling medium.

[0041] The temperature threshold setting unit 91 receives the temperature TW of the cooling medium from the water temperature sensor 36 and calculates the temperature threshold OT for implementing overheat protection control based on this temperature TW of the cooling medium. It then outputs the temperature threshold OT to the overheat protection control unit 92. A more detailed configuration of the temperature threshold setting unit 91 will be described later.

[0042] The overheat protection control unit 92 has a function, which is a feature of the present invention, to control the operation of the switching element to limit the current based on a temperature threshold OT calculated based on the temperature TW of the cooling medium. The overheat protection control unit 92 receives the d-axis current command value Id*, the q-axis current command value Iq*, the temperature threshold OT, and temperature detection values ​​T1 to T6 from the element temperature detectors 71 to 76 as input. If the maximum value of the temperature detection values ​​T1 to T6 is greater than the temperature threshold OT, the d-axis current command value Id* and the q-axis current command value Iq* are limited to predetermined current command values ​​to generate the d-axis current command value Idc and the q-axis current command value Iqc. If the maximum value of the temperature detection values ​​T1 to T6 is less than the temperature threshold OT, the d-axis current command value Id* and the q-axis current command value Iq* are generated as the d-axis current command value Idc and the q-axis current command value Iqc.

[0043] The three-phase to two-phase conversion unit 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 detection unit 26 and the angle detection value corresponding to the electrical angle θe detected by the rotation angle sensor 11. Here, the current detection value of the current detection unit 26 is composed of the U-phase current detection value corresponding to the U-phase current Iu detected by the U-phase current detection unit 261, the V-phase current detection value corresponding to the V-phase current Iv detected by the V-phase current detection unit 262, and the W-phase current detection value corresponding to the W-phase current Iw detected by the W-phase current detection unit 263.

[0044] The voltage command generation unit 95 calculates the d-axis voltage command Vdc and the q-axis voltage command Vqc by performing a current feedback calculation from the d-axis current command value Idc and the q-axis current command value Iqc, and the d-axis current detection value Id and the q-axis current detection value Iq. Specifically, for example, the voltage command generation unit 95 is configured to calculate the d-axis voltage command Vdc and the q-axis voltage command Vqc such that the current deviation ΔId, which is the difference between the d-axis current command value Idc and the d-axis current detection value Id, and the current deviation ΔIq, which is the difference between the q-axis current command value Iqc and the q-axis current detection value Iq, both converge to "0". (ΔId and ΔIq are not shown.)

[0045] The two-phase to three-phase conversion unit 96 calculates three-phase voltage commands Vuc, Vvc, and Vwc from the d-axis voltage command Vdc and q-axis voltage command Vqc obtained from the voltage command generation unit 95 and the electrical angle θe obtained from the rotation angle sensor 11. Preferably, the three-phase voltage commands Vuc, Vvc, and Vwc are set to be less than or equal to the DC power supply voltage input to the power conversion unit 20, i.e., the input voltage Vpn detected by the voltage detection unit 24.

[0046] The duty cycle conversion unit 97 generates duty cycle commands Du, Dv, and Dw for each phase of the three-phase system from the three-phase voltage commands Vuc, Vvc, and Vwc obtained from the two-phase to three-phase conversion unit 96 and the input voltage Vpn. The duty cycle conversion unit 97 generates and outputs duty cycle commands Du, Dv, and Dw corresponding to the optimal correction control command.

[0047] The PWM signal generation unit 98 generates a PWM signal. The PWM signal generation unit 98 generates a PWM signal for switching each of the semiconductor switching elements 51 to 56 on and off from the duty cycle commands Du, Dv, and Dw for each phase obtained from the duty cycle conversion unit 97.

[0048] Specifically, the PWM signal generation unit 98 generates a PWM signal by comparing the duty cycle commands Du, Dv, and Dw for each phase with the carrier wave. The PWM signal generation unit 98 is configured to generate a PWM signal by employing, for example, a triangular wave comparison method or a sawtooth wave comparison method, which use a triangular wave having the shape of an isosceles triangle with equal rising and falling speeds as the carrier.

[0049] In Figure 3, the PWM signals generated by the PWM signal generation unit 98 are shown as follows: PWM signal UH_SW applied to the semiconductor switching element 51 of the U-phase upper arm, PWM signal VH_SW applied to the switching element 53 of the V-phase upper arm, and PWM signal WH_SW applied to the switching element 55 of the W-phase upper arm. Similarly, the PWM signals generated by the PWM signal generation unit 98 are shown as follows: PWM signal UL_SW applied to the switching element 52 of the U-phase lower arm, PWM signal VL_SW applied to the switching element 54 of the V-phase lower arm, and PWM signal WL_SW applied to the switching element 56 of the W-phase lower arm.

[0050] The PWM signal generated by the PWM signal generation unit 98 is input from the control device 90 to the drive circuit 27 of the power conversion unit 20. The drive circuit 27 converts DC power to AC power and supplies it to the rotating electric machine 10 by switching semiconductor switching elements 51 to 56 on and off based on the PWM signal, and also charges the DC power supply 12 with regenerative power generated when the rotating electric machine 10 is in a regenerative state.

[0051] Herein, a feature of the power converter 100 according to Embodiment 1 is that the control device 90 is equipped with a temperature threshold setting unit 91 and an overheat protection control unit 92. The temperature threshold setting unit 91 sets a temperature threshold OT based on the temperature TW of the cooling medium, and the overheat protection control unit 92 limits the d-axis current command value and the q-axis current command value to predetermined current command values ​​based on the temperature detection values ​​T1 to T6 and the temperature threshold OT. Furthermore, a feature of the power converter according to Embodiment 1 is that the temperature threshold setting unit 91 sets a higher temperature threshold OT as the temperature TW of the cooling medium increases.

[0052] <When the temperature threshold OT is a fixed value> Here, in order to explain the effect of setting the temperature threshold OT based on the temperature TW of the cooling medium, which is a feature of the power converter 100 according to Embodiment 1, we will describe the case where the temperature threshold OT is a fixed value. When the temperature threshold OT is a fixed value, depending on the state of the cooling medium, there are cases where the output is excessively limited even though the temperature rise from semiconductor switching elements 51 to 56 is still permissible. This case will be explained using Figures 4 and 5.

[0053] Figure 4 is a first diagram illustrating the relationship between the fixed temperature threshold OT and the element junction temperature TJ of the power converter 100 according to Embodiment 1. Figure 5 is a second diagram illustrating the relationship between the temperature threshold OT and the element junction temperature TJ. The cooling medium is a liquid such as water, oil, or LLC.

[0054] Figure 4 schematically shows a time chart of the junction temperature TJ of semiconductor switching elements 51 to 56 and the detected temperature TD by element temperature detectors 71 to 76 when the power converter 100 is driven from a stopped state to a constant load, with the cooling medium temperature TW being low. Here, the junction temperature TJ is the junction temperature of the semiconductor switching element measured or estimated by special test equipment or additional temperature sensors, and is difficult to measure in products applied to the market. The temperature detected values ​​T1 to T6 by element temperature detectors 71 to 76 will be collectively referred to as the detected temperature TD below.

[0055] Figure 5 schematically shows the time charts of the actual junction temperatures TJ of semiconductor switching elements 51 to 56 and the detected temperatures TD by element temperature detectors 71 to 76 when the power converter is driven from a stopped state to a constant load, under the condition that the cooling medium temperature TW is high. Note that, regarding the time charts of element junction temperature TJ and detected temperature TD, Figures 4 and 5 show the temperature time charts when overheat protection is not implemented, in order to clearly show the difference in temperature rise depending on the cooling medium temperature TW. In both Figures 4 and 5, at the starting point of the graph, both the detected temperature TD and the junction temperature TJ are equal to the cooling medium temperature TW.

[0056] In a power converter 100 equipped with a cooler 351 for cooling the heat-generating elements of semiconductor switching elements 51 to 56, when the temperature TW of the cooling medium is low, the difference between the temperature of the cooling medium and the operating limit temperature OTJ of the semiconductor switching elements becomes large. In other words, the allowable temperature rise of the semiconductor switching elements relative to the temperature of the cooling medium becomes larger. Therefore, when the temperature of the cooling medium is low, it is possible to reduce the cooling performance (cooling capacity) compared to when the temperature of the cooling medium is high, and it is common practice to reduce the flow rate of the cooling medium in order to reduce the power consumption of auxiliary pump equipment such as the water pump 353 that circulates the cooling medium. In addition, liquids that serve as cooling medium have the characteristic of becoming more viscous and less flowable as the temperature decreases, which may also cause a decrease in the flow rate of the cooling medium.

[0057] In this state, the flow rate of the cooling medium is lower and the cooling performance is lower compared to when the temperature of the cooling medium is high. Therefore, as shown in Figure 4, when driving is performed so that the losses of semiconductor switching elements 51 to 56 are the same, the temperature rise of the semiconductor switching elements starts at a lower temperature and the slope of the temperature rise is steeper compared to when the temperature of the cooling medium is high.

[0058] As mentioned above, the element temperature detectors 71 to 76, which detect the temperature of semiconductor switching elements 51 to 56, have temperature sensors such as thermistors and temperature-sensing diodes placed inside or near the semiconductor module. However, it is difficult to directly measure the junction temperature TJ, where the temperature of the semiconductor switching element is highest, and the detected temperature TD deviates from the junction temperature TJ of the semiconductor switching element.

[0059] Furthermore, there is a time delay (response delay) before the temperature TD detected by the element temperature detectors 71 to 76 matches the temperature of the object being measured. Therefore, when the temperature rise of the semiconductor switching elements 51 to 56 is rapid, the discrepancy between the net element junction temperature TJ of the semiconductor switching elements 51 to 56 and the temperature TD detected by the element temperature detectors 71 to 76 becomes larger compared to when the temperature rise is gradual, as shown in Figure 4. For this reason, when the temperature TW of the cooling medium is low, the temperature TD detected by the element temperature detectors 71 to 76 when the junction temperature TJ of the semiconductor switching elements 51 to 56 reaches the operating limit temperature OTJ needs to be sufficiently low, as shown in Figure 4, compared to when the temperature TW of the cooling medium is high.

[0060] In other words, in the comparative example where overheating of semiconductor switching elements is prevented by reducing the output of the power converter when the detected temperature TD exceeds a fixed temperature threshold OT, it is necessary to set the temperature threshold OT to a sufficiently low value from the temperature TD detected by the element temperature detectors 71 to 76 when the junction temperature TJ of the semiconductor switching element reaches the operating limit temperature OTJ, in accordance with the case where the temperature TW of the cooling medium is low (low cooling performance) as shown in Figure 4. In this case, as shown in Figure 5, when the temperature TW of the cooling medium is high (high cooling performance), even though the junction temperature TJ of the semiconductor switching elements 51 to 56 has not yet reached the operating limit temperature OTJ and a temperature rise is still permissible, the temperature TD detected by the element temperature detectors 71 to 76 exceeds the predetermined temperature threshold OT, resulting in excessive overheat protection.

[0061] <When the temperature threshold OT is set to a variable value> Therefore, in the power conversion device 100 according to Embodiment 1, the temperature threshold setting unit 91 is configured to set the temperature threshold OT based on the temperature TW of the cooling medium. The higher the temperature TW of the cooling medium, the higher the temperature threshold OT is set.

[0062] Figure 6 illustrates the relationship between the cooling medium temperature TW and the variable temperature threshold OT of the power converter 100 according to Embodiment 1. The operation of the temperature threshold setting unit 91 and the overheat protection control unit 92, which are features of the power converter 100 according to Embodiment 1, will be described below.

[0063] The temperature threshold setting unit 91 takes the temperature TW of the cooling medium from the water temperature sensor 36 as input and outputs a temperature threshold OT for implementing overheat protection control. The temperature threshold setting unit 91 is equipped with a pre-defined threshold setting map of the temperature threshold OT for the temperature TW of the cooling medium. The temperature threshold OT for the temperature TW of the cooling medium must be set so that the junction temperature TJ of the semiconductor switching element does not exceed the operating limit temperature OTJ even under the most severe operating conditions, in order to prevent thermal damage to the semiconductor switching element.

[0064] A temperature threshold OT is determined for the temperature TW of the cooling medium. In each state of the cooling medium temperature TW, when the power converter 100 is driven under the driving conditions that result in the greatest power loss in the semiconductor switching elements 51 to 56, the temperature threshold OT is set to a temperature that is a predetermined margin lower than the detected temperature TD of the element temperature detectors 71 to 76 at the point when the junction temperature TJ of the semiconductor switching elements 51 to 56 reaches the operating limit temperature OTJ.

[0065] Here, the temperature TD detected by the element temperature detector at the point when the junction temperature TJ of semiconductor switching elements 51 to 56 reaches the operating limit temperature OTJ is lower when the cooling medium temperature is lower compared to when it is higher, as explained using Figures 4 and 5. Therefore, the threshold setting map for the temperature threshold OT with respect to the cooling medium temperature TW is set so that the temperature threshold OT tends to increase as the cooling medium temperature TW increases, as shown in Figure 6.

[0066] The overheat protection control unit 92 has the function of controlling the operation of semiconductor switching elements 51 to 56 to limit the current based on a temperature threshold OT calculated based on the temperature TW of the cooling medium. The overheat protection control unit 92 receives the d-axis current command value Id* and the q-axis current command value Iq* from the current command generation unit 93, the temperature threshold OT from the temperature threshold setting unit 91, and temperature detection values ​​T1 to T6 from the element temperature detectors 71 to 76.

[0067] In the overheat protection control unit 92, the maximum temperature Tmax from temperature detection values ​​T1 to T6 is compared with the temperature threshold OT. If the maximum temperature Tmax is greater than the temperature threshold OT, command values ​​are generated as the d-axis current command value Idc and the q-axis current command value Iqc by multiplying the d-axis current command value Id* and the q-axis current command value Iq* by a ratio less than 1 (overheat protection gain G), and these are output to the voltage command generation unit 95. This overheat protection gain G is set to a smaller value as the maximum temperature Tmax increases. However, the setting of the overheat protection gain G is not limited to this, and it may be set to a predetermined value less than 1. (Tmax is not shown)

[0068] If the maximum temperature Tmax from temperature detection values ​​T1 to T6 is less than the temperature threshold OT, the d-axis current command value Id* and the q-axis current command value Iq* are generated as d-axis current command value Idc and q-axis current command value Iqc. These are then output to the voltage command generation unit 95. In addition, when comparing the maximum temperature Tmax and the temperature threshold OT, a predetermined hysteresis may be provided to avoid oscillation due to switching of overheat protection control.

[0069] Furthermore, the overheat protection control unit 92 sets a limit release temperature threshold Trst, which is lower than the temperature threshold OT, as a temperature threshold for releasing the overheat protection limit. If the maximum temperature Tmax exceeds the temperature threshold OT, it continues the current command value limiting process described above until the maximum temperature Tmax becomes lower than the limit release temperature threshold Trst. (The limit release temperature threshold Trst is not shown.)

[0070] As a result, when the element junction temperature TJ of semiconductor switching elements 51 to 56 is likely to exceed the operating limit temperature OTJ, the operation is restricted to reduce the current flowing through the semiconductor switching elements 51 to 56. This reduces the losses of the semiconductor switching elements 51 to 56, suppressing the temperature rise of the semiconductor switching elements 51 to 56, and preventing thermal breakdown due to the junction temperature TJ exceeding the operating limit temperature OTJ.

[0071] Furthermore, the overheat protection control unit 92 generates command values ​​for the d-axis current command value Id* and the q-axis current command value Iqc by multiplying the d-axis current command value Id* and the q-axis current command value Iq* by a ratio less than 1 (overheat protection gain G) when the maximum temperature Tmax from temperature detection value T1 to T6 is greater than the temperature threshold OT. However, this is not the only way to limit the current command value. For example, the d-axis current command value Id* and the q-axis current command value Iq* may be limited to predetermined current command values ​​and then generated as the d-axis current command value Idc and the q-axis current command value Iqc.

[0072] <Comparison of effects> Here, using Figures 7 to 10, we will explain the effects of applying the above control compared to the comparative example. We will explain that the power converter 100 can reliably prevent thermal damage to the semiconductor switching elements 51 to 56 while suppressing excessive limiting of the power converter's output.

[0073] Figure 7 is a first time chart showing the temperature changes during overheat prevention using a fixed temperature threshold OT for the power converter 100 according to Embodiment 1. Figure 8 is a second time chart showing the temperature changes during overheat prevention using a fixed temperature threshold.

[0074] Figures 7 and 8 are time charts of the junction temperature TJ of semiconductor switching elements 51 to 56 and the detected temperature TD by element temperature detectors 71 to 76. Figure 7 is a time chart when the power converter 100 is driven from a stopped state to a constant load when the temperature TW of the cooling medium is low. Figure 8 is a time chart when the power converter 100 is driven from a stopped state to a constant load when the temperature TW of the cooling medium is high.

[0075] Figure 9 is a first time chart showing the temperature changes during overheat prevention using a variable temperature threshold OT for the power converter 100 according to Embodiment 1. Figure 10 is a second time chart showing the temperature changes during overheat prevention using a variable temperature threshold OT.

[0076] Figures 9 and 10 are time charts of the junction temperature TJ of semiconductor switching elements 51 to 56 and the detected temperature TD by element temperature detectors 71 to 76 when overheat protection limiting by a variable temperature threshold OT is applied. Figure 9 is a time chart when the power converter is driven from a stopped state to a constant load when the temperature TW of the cooling medium is low, and Figure 10 is a time chart when the power converter is driven from a stopped state to a constant load when the temperature TW of the cooling medium is high. In all of Figures 7 to 10, at the starting point of the graph, both the detected temperature TD and the junction temperature TJ are equal to the temperature TW of the cooling medium.

[0077] When overheat protection is applied using a fixed temperature threshold OT, the overheat protection is implemented at the same fixed temperature threshold OT regardless of the temperature of the cooling medium. Therefore, as shown in Figure 8, when the temperature of the cooling medium is high, the overheat protection is activated even though the junction temperature TJ of the semiconductor switching elements 51 to 56 is sufficiently low compared to the operating limit temperature OTJ. As a result, the power converter 100 unnecessarily limits the capabilities of the semiconductor switching elements 51 to 56, preventing them from performing at their full potential.

[0078] On the other hand, when applying overheat protection limiting using a variable temperature threshold OT, as shown in Figure 6, the temperature threshold OT is set low when the temperature TW of the cooling medium is low, and the temperature threshold OT is set higher as the temperature TW of the cooling medium increases, thereby implementing overheat protection limiting. Therefore, as shown in Figure 10, even when the temperature TW of the cooling medium is high, the overheat protection limiting operates when the junction temperature TJ of the semiconductor switching elements 51 to 56 is close to the operating limit temperature OTJ.

[0079] Figure 11 shows the relationship between the cooling medium temperature TW and the element temperature when overheating is prevented by a fixed temperature threshold OT in the power converter 100 according to Embodiment 1. Figure 12 shows the relationship between the cooling medium temperature TW and the element temperature when overheating is prevented by a variable temperature threshold OT. Figures 11 and 12 show the relationship between the cooling medium temperature TW, the setting of the overheat protection limit temperature threshold OT, the actual maximum junction temperature OTJC of the semiconductor switching element when the overheat protection limit is applied, and the operating limit temperature OTJ of the semiconductor switching element.

[0080] In overheat protection limiting using a fixed temperature threshold OT, a constant overheat protection limit temperature threshold OT is applied regardless of the temperature of the cooling medium, as shown in Figure 11. Therefore, when the temperature TW of the cooling medium is high, the maximum junction temperature OTJC that is actually limited to the semiconductor switching elements 51 to 56 will be lower than the operating limit temperature OTJ. In other words, when the temperature of the cooling medium is high, the system will excessively implement overheat protection limiting even though there is a margin above the operating limit temperature OTJ.

[0081] On the other hand, in overheat protection limiting using a variablely set temperature threshold OT, as shown in Figure 12, the temperature threshold OT of the overheat protection limit is applied, which increases as the temperature of the cooling medium increases. Therefore, even when the temperature TW of the cooling medium is high, the maximum junction temperature OTJC that is actually limited to the semiconductor switching elements 51 to 56 will be close to the operating limit temperature OTJ. In other words, even when the temperature TW of the cooling medium is high, it is possible to prevent the operating limit temperature OTJ of the semiconductor switching elements 51 to 56 from being exceeded, while suppressing excessive limitation of the output of the power converter and providing an efficient power converter. <Summary>

[0082] As described above, the power converter 100 of Embodiment 1 has a water temperature sensor 36 for detecting the temperature of the cooling medium as a cooling medium state detection means for detecting the state of the cooling medium flowing through the cooler 351, and sets the temperature threshold OT for overheat protection limit based on the temperature TW of the cooling medium. For this reason, the higher the temperature TW of the cooling medium, the higher the temperature threshold OT for overheat protection limit can be set. This makes it possible to properly prevent overheating of the semiconductor switching elements 51 to 56, suppress excessive limiting of the output of the power converter, and provide an efficient power converter.

[0083] As mentioned above, the semiconductor switching elements 51 to 56 of the inverter circuit 25 can be made up of any type of semiconductor element. For example, they can be made up using wide-bandgap semiconductors. Examples of wide-bandgap semiconductor materials include SiC and GaN.

[0084] The semiconductor switching elements 51 to 56, constructed using wide-bandgap semiconductors, have improved heat resistance compared to conventional switching elements constructed using silicon semiconductors, allowing for a higher operating limit temperature (OTJ). In other words, wide-bandgap semiconductors have a larger difference between the operating limit temperature (OTJ) and the cooling medium temperature (TW) compared to conventional silicon semiconductors, resulting in a larger allowable temperature rise.

[0085] In this case, the discrepancy between the semiconductor switching element and the temperature TD detected by the element temperature detector becomes relatively larger. Consequently, the difference between the high and low temperatures of the cooling medium TW and the high and low temperature threshold OT for overheat protection also becomes larger. In other words, in a power conversion device using a switching element made of a wide-bandgap semiconductor, by changing and setting the temperature threshold OT based on the temperature TW of the cooling medium, which is a feature of this embodiment, it is possible to more effectively prevent excessive limiting of the output of the power conversion device.

[0086] Furthermore, the element temperature detectors 71 to 76 that detect the temperature of the semiconductor switching elements 51 to 56 are thermistors, temperature-sensing diodes, etc. Although it depends on where the element temperature detectors are mounted, generally, thermistors have a worse temperature detection response than temperature-sensing diodes, and the discrepancy between the temperature of the semiconductor switching element and the temperature TD detected by the element temperature detector is relatively larger when a thermistor is used. Consequently, the difference in the temperature threshold of the overheat protection limit depending on the temperature of the cooling medium also becomes larger. Therefore, in a power converter configured to use a thermistor as the element temperature detector, it is possible to more effectively prevent excessive limiting of the output of the power converter by changing and setting the temperature threshold based on the temperature of the cooling medium, which is a feature of this embodiment.

[0087] <Second Example> Figure 13 is a configuration diagram of a second embodiment of the power converter according to Embodiment 1. In the power converter 100 described above, an example is shown in which a water temperature sensor 36 is provided as a means for detecting the state of the cooling medium. The state of the cooling medium is detected by the water temperature sensor 36, and a method is described in which the temperature threshold OT of the overheat protection limit is set higher as the temperature of the cooling medium increases.

[0088] In the power converter 100A shown in Figure 13, a cooler temperature sensor 37 is provided instead of a water temperature sensor 36 to detect the temperature of the cooler 351A. The cooler temperature sensor 37 is provided as a means for detecting the state of the cooling medium, and the temperature of the cooler 351A is detected by the cooler temperature sensor 37 as the state of the cooling medium. The higher the temperature of the cooler, the higher the temperature threshold OT for overheat protection limit may be set. Note that the control device 90 does not require hardware changes and can be applied only by software changes, so the reference numerals are the same as in Figure 1. The same applies to the control device 90 in the third to sixth embodiments below.

[0089] Since the temperature of the cooler 351A increases as the temperature TW of the cooling medium increases, even if a method is adopted in which the temperature threshold OT of the overheat protection limit is set higher as the temperature of the cooler 351A increases, the effect of preventing excessive restriction of the output of the power converter 100A can be obtained in the same way by setting the temperature threshold OT of the overheat protection limit higher as the temperature TW of the cooling medium increases.

[0090] Furthermore, in this embodiment, the cooling medium state detection means is configured to include a water temperature sensor 36 or a cooler temperature sensor 37. However, the power converter does not necessarily need to include a water temperature sensor 36 or a cooler temperature sensor 37. For example, the temperature information of the cooling medium may be input to the power converter by communication from an external system, such as a higher-level system (not shown).

[0091] <Third Example> Figure 14 is a configuration diagram of a third embodiment of the power converter according to Embodiment 1. In Figure 1, the semiconductor modules 61 to 66 in the power converter 100 are configured to have element temperature detectors 71 to 76 for each of the semiconductor switching elements 51 to 56. In contrast, the power converter 100B according to the third embodiment shown in Figure 14 is configured to have one element temperature detector 73 for each of the multiple semiconductor switching elements 51 to 56. Due to this change in configuration, the reference numerals of the power conversion unit 20A and the inverter circuit 25A have been changed.

[0092] In this case, the element temperature detector 73 is installed at a predetermined location that correlates with the temperature of the semiconductor switching elements 51 to 56. This makes it possible to protect multiple semiconductor switching elements 51 to 56 with a single element temperature detector 73. Overheating protection can be performed without increasing the number of components, enabling lower costs and miniaturization of the power converter.

[0093] <Fourth Example> Figure 15 is a configuration diagram of a fourth embodiment of the power converter according to Embodiment 1. In the power converter 100B according to the third embodiment, semiconductor modules 61 to 66 are composed of one semiconductor switching element and one element temperature detector.

[0094] In contrast, in the power converter 100C according to the fourth embodiment shown in Figure 15, semiconductor modules 61, 63, and 65 are composed of upper semiconductor switching elements 51, 53, and 55 and one element temperature detector 73, while semiconductor modules 62, 64, and 66 are composed of lower switching elements 52, 54, and 56 and one element temperature detector 74. Due to this change in configuration, the reference numerals of the power converter unit 20B and the inverter circuit 25B have been changed.

[0095] This allows for the installation of element temperature detectors 73 and 74 on both the upper and lower sections, enabling more precise temperature detection. Furthermore, a single element temperature detector can protect multiple semiconductor switching elements, providing overheat protection without increasing the number of components and maintaining the benefits of lower cost and miniaturization of the power converter.

[0096] <Fifth Example> Figure 16 is a configuration diagram of a fifth embodiment of the power converter according to Embodiment 1. In the power converter 100D according to the fifth embodiment, the upper switching element, the lower switching element, and one element temperature detector constitute one upper and lower arm. Due to this change in configuration, the reference numerals of the power conversion unit 20C and the inverter circuit 25C have been changed.

[0097] By providing element temperature detectors on each of the upper and lower arms, temperature can be detected with greater precision. Furthermore, a single element temperature detector can protect multiple semiconductor switching elements, enabling overheating protection without increasing the number of components, and maintaining the benefits of lower cost and miniaturization of power converters.

[0098] <Sixth Example> Figure 17 is a configuration diagram of a sixth embodiment of the power converter according to Embodiment 1. In the power converter 100 according to the first embodiment, semiconductor modules 61 to 66 are composed of one semiconductor switching element and one element temperature detector.

[0099] In contrast, in the power converter 100E according to the sixth embodiment shown in Figure 17, the semiconductor modules 61A to 66A are composed of multiple semiconductor switching elements 51a, 51b to 56a, 56b and one element temperature detector 71 to 76. Due to this change in configuration, the reference numerals of the power converter unit 20D and the inverter circuit 25D have been changed.

[0100] This allows for the protection of multiple semiconductor switching elements (51a, 51b to 56a, 56b) with a single temperature sensor, even in configurations where multiple switching elements (51a, 51b to 56a, 56b) are integrated into semiconductor modules 61A to 66A. This enables overheat protection without increasing the number of components, leading to lower costs and smaller size for power converters.

[0101] 2. Embodiment 2 <Configuration of a power converter> Figure 18 is a configuration diagram of the power converter 100F according to Embodiment 2. The power converter 100F according to Embodiment 2 differs from the power converter 100 in Figure 1 according to Embodiment 1 in the cooling medium state detection means and the control device 90A.

[0102] More specifically, the power converter 100F of the second embodiment is equipped with a flow sensor 38 in the cooler 351B that detects the flow rate of the cooling medium instead of the water temperature sensor 36 as a means for detecting the state of the cooling medium. The control device 90A receives the flow rate FW of the cooling medium detected by the flow sensor 38 as input. The control device 90A then sets a temperature threshold OT based on the flow rate FW of the cooling medium.

[0103] The configuration and operation of the power converter 100F according to Embodiment 2 will be described below, focusing on the differences from Embodiment 1, based on Figures 18 to 28. Parts identical or corresponding to those in Embodiment 1 are denoted by the same reference numerals.

[0104] The power converter 100F consists of a power conversion unit 20, a control device 90A, and a cooler 351B. The flow sensor 38 detects the flow rate FW of the cooling medium flowing inside the cooling water piping and outputs it to the control device 90A. The flow sensor 38 is placed, for example, inside the cooling water piping of the cooler 351B.

[0105] <Functional blocks of the control unit> Figure 19 is a functional block diagram of the control device 90A of the power converter 100F according to Embodiment 2. The control device 90A includes a temperature threshold setting unit 91A, an overheat protection control unit 92, a current command generation unit 93, a three-phase to two-phase conversion unit 94, a voltage command generation unit 95, a two-phase to three-phase conversion unit 96, a duty cycle conversion unit 97, and a PWM signal generation unit 98. The overheat protection control unit 92, current command generation unit 93, three-phase to two-phase conversion unit 94, voltage command generation unit 95, two-phase to three-phase conversion unit 96, duty cycle conversion unit 97, and PWM signal generation unit 98 are the same as those in Embodiment 1, so their description is omitted.

[0106] The temperature threshold setting unit 91A has a function, which is a feature of this invention, to calculate a temperature threshold for implementing overheat protection control based on the state of the cooling medium. The flow rate FW of the cooling medium is input to the temperature threshold setting unit 91A from the flow rate sensor 38. Based on this flow rate FW of the cooling medium, the temperature threshold OT for implementing overheat protection control is calculated. The calculated temperature threshold OT is then output to the overheat protection control unit 92. Details of the temperature threshold setting unit 91A will be described later.

[0107] A feature of the power converter 100F according to Embodiment 2 is that the control device 90A is equipped with a temperature threshold setting unit 91A and an overheat protection control unit 92, the temperature threshold setting unit 91A sets a temperature threshold OT based on the flow rate FW of the cooling medium, and the overheat protection control unit 92 limits the d-axis current command value and the q-axis current command value to predetermined current command values ​​based on a comparison of the temperature detection values ​​T1 to T6 with the temperature threshold OT. Another feature of the power converter 100F according to Embodiment 2 is that the temperature threshold setting unit 91B sets a higher temperature threshold OT as the flow rate FW of the cooling medium increases.

[0108] <When the temperature threshold OT is a fixed value> Here, we will explain the effect of setting the temperature threshold OT based on the flow rate FW of the cooling medium, which is a feature of the power converter 100F according to Embodiment 2. We will also explain the problems when the temperature threshold OT is set to a fixed value. Specifically, when the temperature threshold OT is set to a fixed value, we will explain using Figures 20 and 21 the case in which the output is excessively limited even though the temperature rise of the semiconductor switching element is still permissible depending on the state of the cooling medium.

[0109] Figure 20 is the first diagram illustrating the relationship between the fixed temperature threshold OT and the detected temperature TD of the power converter 100F according to Embodiment 2. Figure 21 is the second diagram illustrating the relationship between the fixed temperature threshold OT and the detected temperature TD.

[0110] The cooling medium is a liquid such as water, oil, or LLC. Figure 20 schematically shows the time chart of the junction temperature TJ of semiconductor switching elements 51 to 56 and the temperature TD detected by element temperature detectors 71 to 76 when the power converter 100F is driven from a stopped state to a constant load, when the flow rate of the cooling medium is small. Figure 21 schematically shows the time chart of the temperature of semiconductor switching elements 51 to 56 and the temperature TD detected by element temperature detectors 71 to 76 when the power converter 100F is driven from a stopped state to a constant load, when the flow rate of the cooling medium is large.

[0111] Furthermore, regarding the time charts for the element junction temperature TJ and the detected temperature TD, Figures 20 and 21 show the temperature time charts when overheat protection is not implemented, in order to clearly illustrate the difference in temperature rise due to the amount of cooling medium flow. In both Figures 20 and 21, at the starting point of the graph, both the detected temperature TD and the junction temperature TJ are equal to the cooling medium temperature TW.

[0112] In a power converter 100F equipped with a cooler 351B for cooling heat-generating elements such as semiconductor switching elements 51 to 56, the cooling performance is lower when the flow rate of the cooling medium is low compared to when the flow rate of the cooling medium is high. Therefore, as shown in Figure 20, even when the same drive operation is performed for the same loss of the semiconductor switching elements, the temperature rise of the semiconductor switching elements 51 to 56 is steeper compared to when the flow rate of the cooling medium is high.

[0113] As described in Embodiment 1, the detected temperature TD of semiconductor switching elements 51 to 56 differs from the net junction temperature TJ of semiconductor switching elements 51 to 56. Furthermore, there is a time delay (response delay) before the detected temperature TD of semiconductor switching elements 51 to 56 matches the temperature of the object being measured. Therefore, when the temperature rise of semiconductor switching elements 51 to 56 is rapid, the discrepancy between the net element junction temperature TJ of the semiconductor switching elements and the detected temperature TD by element temperature detectors 71 to 76 becomes larger compared to when the temperature rise is gradual, as shown in Figure 20.

[0114] Therefore, when the flow rate of the cooling medium is small, the temperature TD detected by the element temperature detectors 71 to 76 when the junction temperature TJ of the semiconductor switching elements 51 to 56 reaches the operating limit temperature OTJ will be lower compared to when the flow rate is large. At this point, it is necessary to set the temperature at which overheat protection is initiated as the temperature threshold OT.

[0115] Overheating failure of semiconductor switching elements 51 to 56 is prevented by reducing the output of the power converter 100F when the detected temperature TD exceeds a predetermined temperature threshold OT. In the comparative example where the temperature threshold OT is a fixed value, it is necessary to set the temperature threshold OT to match the case when the flow rate of the cooling medium is small (a state of low cooling performance). The temperature TD detected by the element temperature detectors 71 to 76 when the junction temperature TJ of the semiconductor switching elements 51 to 56 reaches the operating limit temperature OTJ is set as the temperature threshold OT.

[0116] In other words, as shown in Figure 21, when the flow rate of the cooling medium is high (high cooling performance), the junction temperature TJ of the semiconductor switching elements 51 to 56 has not yet reached the operating limit temperature OTJ, and the temperature rise is still permissible, but overheat protection is initiated. Because the temperature TD detected by the element temperature detectors 71 to 76 exceeds the temperature threshold OT, excessive overheat protection is performed.

[0117] <When the temperature threshold OT is set to a variable value> Figure 22 illustrates the relationship between the cooling medium flow rate FW and the variablely set temperature threshold OT of the power converter 100F according to Embodiment 2. In the power converter 100F, the temperature threshold setting unit 91A is configured to set the temperature threshold OT based on the flow rate FW of the cooling medium. Specifically, as shown in Figure 22, the larger the flow rate FW of the cooling medium, the higher the temperature threshold OT is set.

[0118] The operation of the temperature threshold setting unit 91A, which is a feature of the power converter 100F according to Embodiment 2, will be described below. The temperature threshold setting unit 91A takes the flow rate FW of the cooling medium from the flow sensor 38 as input and outputs a temperature threshold OT for implementing overheat protection control.

[0119] The temperature threshold setting unit 91A is equipped with a pre-defined threshold setting map for the temperature threshold OT relative to the flow rate FW of the cooling medium. The temperature threshold OT relative to the flow rate FW of the cooling medium must be set so that the temperature of the semiconductor switching elements 51 to 56 does not exceed the operating limit temperature OTJ even under the most severe operating conditions, in order to prevent thermal damage to the semiconductor switching elements 51 to 56.

[0120] Therefore, the temperature threshold OT for the flow rate FW of the cooling medium is determined when the power converter 100F is driven under the driving conditions that result in the greatest power loss in the semiconductor switching element for each state of the flow rate FW of the cooling medium. The temperature threshold OT is set to a temperature that is a predetermined margin lower than the detected temperature TD of the element temperature detectors 71 to 76 at the point when the element junction temperature TJ of the semiconductor switching elements 51 to 56 reaches the operating limit temperature OTJ.

[0121] Here, the detected temperatures TD of the element temperature detectors 71 to 76 at the point when the element junction temperature TJ of the semiconductor switching element reaches the operating limit temperature OTJ are explained using Figure 22. When the flow rate of the cooling medium is small, the temperature threshold OT is lower than when it is large. Therefore, the threshold setting map of the temperature threshold OT with respect to the flow rate FW of the cooling medium is set to be characterized by the tendency for the temperature threshold OT to increase as the flow rate FW of the cooling medium increases, as shown in Figure 22.

[0122] <Comparison of effects> Figures 23 to 28 compare the case where the temperature threshold OT is a fixed value and the case where the temperature threshold OT is a variable value. It is explained that by making the temperature threshold OT a variable value, it is possible to reliably prevent thermal damage to semiconductor switching elements while preventing excessive limiting of the power conversion device's output.

[0123] Figure 23 is a first time chart showing the temperature changes during overheat prevention using a fixed temperature threshold OT for the power converter 100F according to Embodiment 2. Figure 24 is a second time chart showing the temperature changes during overheat prevention using a fixed temperature threshold OT.

[0124] Figures 23 and 24 schematically show time charts of the junction temperature TJ of semiconductor switching elements 51 to 56 and the detected temperature TD by element temperature detectors 71 to 76 when overheat protection limiting by a fixed temperature threshold OT is applied. Figure 23 is a time chart when the power converter is driven from a stopped state to a constant load when the flow rate of the cooling medium is small. Figure 24 is a time chart when the power converter is driven from a stopped state to a constant load when the flow rate of the cooling medium is large. In both Figures 23 and 24, at the starting point of the graph, both the detected temperature TD and the junction temperature TJ are equal to the temperature TW of the cooling medium.

[0125] Figure 25 is a first time chart showing the temperature changes during overheat prevention using a variable temperature threshold OT for the power converter 100F according to Embodiment 2. Figure 26 is a second time chart showing the temperature changes during overheat prevention using a variable temperature threshold OT.

[0126] Figures 25 and 26 schematically show time charts of the junction temperature TJ of semiconductor switching elements 51 to 56 and the detected temperature TD by element temperature detectors 71 to 76 when overheat protection limiting by a variablely set temperature threshold OT is applied. Figure 25 is a time chart when the power converter 100F is driven from a stopped state to a constant load when the flow rate of the cooling medium is small. Figure 26 is a time chart when the power converter 100F is driven from a stopped state to a constant load when the flow rate of the cooling medium is large. In both Figures 25 and 26, at the starting point of the graph, both the detected temperature TD and the junction temperature TJ are equal to the temperature TW of the cooling medium.

[0127] When overheat protection is applied using a fixed temperature threshold OT, the same temperature threshold OT is used regardless of the flow rate FW of the cooling medium. Therefore, as shown in Figure 24, when the flow rate of the cooling medium is high, the overheat protection is activated even though the junction temperature TJ of the semiconductor switching elements 51 to 56 is sufficiently low compared to the operating limit temperature OTJ.

[0128] In contrast, when applying overheat protection limiting using a variable temperature threshold OT, the overheat protection limiting is implemented at a temperature threshold OT that is set to increase as the flow rate FW of the cooling medium increases. Therefore, as shown in Figure 26, even when the flow rate FW of the cooling medium is high, the overheat protection limiting will operate when the junction temperature TJ of the semiconductor switching elements 51 to 56 reaches a temperature close to the operating limit temperature OTJ.

[0129] Figure 27 shows the relationship between the cooling medium flow rate FW and the element temperature when overheating is prevented by a fixed temperature threshold OT in the power converter 100F according to Embodiment 2. Figure 28 shows the relationship between the cooling medium flow rate FW and the element temperature when overheating is prevented by a variable temperature threshold OT.

[0130] Figures 27 and 28 show the relationship between the flow rate FW of the cooling medium, the setting of the overheat protection limit threshold OT, the actual limited maximum junction temperature OTJC of semiconductor switching elements 51 to 56 when the overheat protection limit is applied, and the operating limit temperature OTJ of semiconductor switching elements 51 to 56. Figure 27 shows the overheat protection limit with a fixed temperature threshold OT, and Figure 28 shows the overheat protection limit with a variablely set temperature threshold OT.

[0131] In overheat protection limiting using a fixed temperature threshold OT, a constant overheat protection limit temperature threshold OT is applied regardless of the flow rate FW of the cooling medium, as shown in Figure 27. Therefore, when the flow rate FW of the cooling medium is large, the maximum junction temperature OTJC that is actually limited to the semiconductor switching elements 51 to 56 will be lower than the operating limit temperature OTJ. In other words, when the flow rate FW of the cooling medium is large, the system will excessively implement overheat protection limiting even though there is a margin above the operating limit temperature OTJ.

[0132] In contrast, with overheat protection limiting using a variable temperature threshold OT, as shown in Figure 28, the temperature threshold OT of the overheat protection limit is applied, which increases as the flow rate FW of the cooling medium increases. Therefore, even when the flow rate FW of the cooling medium is high, the maximum junction temperature OTJC that is actually limited to the semiconductor switching elements 51 to 56 will be close to the operating limit temperature OTJ. In other words, even when the flow rate FW of the cooling medium is high, the behavior prevents the semiconductor switching elements 51 to 56 from exceeding the operating limit temperature OTJ without excessive overheat protection limiting.

[0133] As described above, the power converter 100F according to Embodiment 2 is characterized by the ability to change and set a temperature threshold OT based on the flow rate of the cooling medium, and to limit the output of the power converter 100F when the detected temperature TD of the semiconductor switching elements 51 to 56 is higher than this temperature threshold OT. This makes it possible to more appropriately determine the overheating state of the semiconductor switching elements 51 to 56 compared to the overheating protection method of the semiconductor switching elements using a fixed temperature threshold OT, and to prevent excessive limiting of the output of the power converter 100F while reliably preventing thermal damage to the semiconductor switching elements 51 to 56.

[0134] In the power converter 100F according to Embodiment 2, a flow sensor 38 is provided as a means for detecting the state of the cooling medium. However, the power converter 100F does not necessarily need to be equipped with a flow sensor 38. For example, the flow rate FW of the cooling medium may be obtained by receiving flow rate information of the cooling medium from an external system, such as a higher-level system (not shown), via communication to the power converter.

[0135] The power converter 100F according to Embodiment 2 is characterized by setting the temperature threshold OT for overheat protection based on the flow rate FW of the cooling medium. Depending on the system in which the power converter 100F is installed, there are systems in which the water pump 353 is driven intermittently. In such systems, the flow rate FW of the cooling medium also increases and decreases intermittently. In such systems, the temperature threshold OT for overheat protection may be set based on the smallest flow rate of the cooling medium whose flow rate increases and decreases. By doing so, it is possible to reliably prevent thermal damage to semiconductor switching elements.

[0136] However, this does not apply to the setting method of the temperature threshold OT for overheat protection when the water pump 353 is driven intermittently. For example, it is also possible to set the temperature threshold OT for overheat protection based on the average flow rate of the cooling medium, which fluctuates in flow rate. This makes it possible to more appropriately suppress excessive limiting of the output of the power converter 100F.

[0137] 3. Embodiment 3 Figure 29 is a configuration diagram of the power converter 100G according to Embodiment 3. Figure 30 is a functional block diagram of the control device 90B of the power converter 100G according to Embodiment 3. Figure 31 is a diagram illustrating the method for setting the temperature threshold OT of the power converter 100G according to Embodiment 3.

[0138] The power converter 100G according to Embodiment 3 is equipped with both a water temperature sensor 36 and a flow rate sensor 38 on the cooler 351C as means for detecting the state of the cooling medium. The control device 90B receives the temperature TW of the cooling medium detected by the water temperature sensor 36 and the flow rate FW of the cooling medium detected by the flow rate sensor 38 as input. The temperature threshold setting unit 91B of the control device 90B then sets a temperature threshold OT based on the temperature TW and flow rate FW of the cooling medium.

[0139] The temperature threshold setting unit 91B is characterized by setting the temperature threshold OT higher the greater the temperature TW of the cooling medium, and setting the temperature threshold OT higher the greater the flow rate FW of the cooling medium. The temperature threshold setting unit 91B acquires the temperature TW and flow rate FW of the cooling medium. Then, it calculates the temperature gap index ITGAP between the junction temperature TJ of the semiconductor switching elements 51 to 56 and the detected temperature TD of the element temperature detectors 71 to 76 using a method described later. The temperature threshold OT is set based on the temperature gap index ITGAP. Then, the temperature threshold OT is set higher the greater the temperature TW of the cooling medium, and the temperature threshold OT is set higher the greater the flow rate FW of the cooling medium.

[0140] The temperature threshold setting unit 91B calculates the allowable temperature rise ΔT of the cooling medium from the difference between the operating limit temperature OTJ of the semiconductor switching elements 51 to 56 and the temperature TW of the cooling medium. That is, ΔT is calculated as ΔT = OTJ - TW.

[0141] As described in Embodiment 1, the larger the temperature TW of the cooling medium, that is, the smaller the allowable temperature rise ΔT, the smaller the temperature difference TGAP between the junction temperature TJ of the semiconductor switching elements 51 to 56 and the detected temperature TD of the element temperature detectors 71 to 76 becomes when the semiconductor switching elements 51 to 56 reach an overheated state. TGAP can be calculated as TGAP = TJ - TD.

[0142] Furthermore, as described in Embodiment 2, the larger the flow rate FW of the cooling medium, the smaller the temperature difference TGAP between the junction temperature TJ of the semiconductor switching elements 51 to 56 and the detected temperature TD of the element temperature detectors 71 to 76 when the semiconductor switching elements 51 to 56 reach an overheated state.

[0143] The smaller this temperature deviation TGAP is, the higher the temperature threshold OT can be set. In other words, the smaller the allowable temperature rise ΔT of the cooling medium and the larger the flow rate FW of the cooling medium, the higher the temperature threshold OT can be set.

[0144] In Embodiment 3, the temperature gap index ITGAP is calculated by dividing the allowable temperature rise ΔT by the flow rate FW of the cooling medium. That is, ITGAP is calculated as ITGAP = ΔT / FW. As shown in Figure 31, the smaller this temperature gap index ITGAP is, the higher the temperature threshold OT should be set.

[0145] This allows the temperature threshold OT to be set based on the temperature TW and flow rate FW of the cooling medium. The higher the temperature TW of the cooling medium, the higher the temperature threshold OT is set, and the higher the flow rate FW of the cooling medium, the higher the temperature threshold OT is set.

[0146] In the power converter 100G according to Embodiment 3, the temperature deviation index ITGAP is calculated by dividing the allowable temperature rise ΔT by the flow rate FW of the cooling medium, and the smaller the temperature deviation index ITGAP, the higher the temperature threshold OT is set. However, it is also possible to have a configuration in which information on the temperature threshold OT corresponding to the combination of the temperature TW of the cooling medium and the flow rate FW of the cooling medium is pre-prepared as a 3D map. In this 3D map, the temperature threshold OT is set to be higher as the temperature TW of the cooling medium increases, and the temperature threshold OT is set to be higher as the flow rate FW of the cooling medium increases.

[0147] According to the power converter 100G of Embodiment 3, overheating of the semiconductor switching elements 51 to 56 can be prevented more accurately by obtaining the temperature TW and flow rate FW of the cooling medium. This makes it possible to prevent overheating of the semiconductor switching elements 51 to 56 more appropriately while suppressing excessive limiting of the output of the power converter 100G, thereby providing an efficient power converter 100G.

[0148] In the power conversion devices according to each of the above embodiments, the current limiting method is configured to limit the current command value with respect to the d-axis current command value Id* and the q-axis current command value Iq*. However, the method of limiting the current is not limited to this, as long as it is an equivalent method of limiting the current command.

[0149] For example, one method would be to restrict the commands input from a higher-level system (not shown). More specifically, the current command value could be effectively reduced by limiting the torque command value Trq* to a predetermined torque command value. Alternatively, the current command value could be effectively reduced by limiting the torque command value Trq* to a command value obtained by multiplying it by a predetermined ratio less than 1.

[0150] Furthermore, although the power conversion device according to the above embodiment is described assuming an inverter that converts DC power to AC power, the type of power conversion device is not limited to this. Any power conversion device equipped with semiconductor switching elements that converts the output form of power is acceptable. For example, it may be an AC / DC converter that converts AC power to DC power, or a DC / DC converter that outputs DC power by changing the voltage and current levels.

[0151] 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 a particular embodiment, but can be applied individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the art disclosed herein. These include, for example, modifying, adding or omitting at least one component, or even extracting at least one component and combining it with components of other embodiments.

[0152] The various aspects of this disclosure are summarized below as an appendix.

[0153] (Note 1) A switching element that conducts and interrupts electric current. A temperature detector for detecting the temperature of the switching element, A cooler for cooling the switching element, A cooling medium state detector for detecting the state of the cooling medium passing through the cooler, and A power conversion device comprising a control device that controls the switching element to perform power conversion and also controls the switching element to prevent overheating, The control device determines a temperature threshold for determining whether overheat prevention control is necessary based on the state of the cooling medium detected by the cooling medium state detector, and performs overheat prevention control by restricting the operation of the switching element when the temperature detected by the element temperature detector is higher than the temperature threshold. (Note 2) The power conversion device described in Appendix 1, wherein the cooling medium state detector is a cooling medium temperature detector that detects the temperature of the cooling medium. (Note 3) The power conversion device described in Appendix 1, wherein the cooling medium state detector is a cooler temperature detector that detects the temperature of the cooler. (Note 4) The power conversion device according to Appendix 2 or 3, wherein the control device sets the temperature threshold higher as the temperature detected by the cooling medium state detector increases. (Note 5) The control device is a power conversion device according to any one of the appendices 1 to 4, wherein, if the temperature detected by the element temperature detector is higher than the temperature threshold, the limiting rate that restricts the operation of the switching element increases as the difference between the temperature detected by the element temperature detector and the temperature threshold increases. (Note 6) The power conversion device as described in Appendix 1, wherein the cooling medium state detector is a cooling medium flow rate detector that detects the flow rate of the cooling medium. (Note 7) The control device is a power conversion device according to Appendix 6, wherein the temperature threshold is set higher as the flow rate of the cooling medium detected by the cooling medium flow rate detector increases. (Note 8) The cooling medium state detector includes a cooling medium temperature detector for detecting the temperature of the cooling medium and a cooling medium flow rate detector for detecting the flow rate of the cooling medium. The control device is a power conversion device according to Appendix 1, which determines the temperature threshold based on the temperature of the cooling medium detected by the cooling medium temperature detector and the flow rate of the cooling medium detected by the cooling medium flow rate detector. (Note 9) The power conversion device according to Appendix 8, wherein the control device sets the temperature threshold higher as the flow rate of the cooling medium detected by the cooling medium flow rate detector increases, and sets the temperature threshold higher as the temperature detected by the cooling medium state detector increases. (Note 10) Multiple switching elements are provided in parallel. The power conversion device according to any one of the appendices 1 to 9, wherein the number of element temperature detectors is less than the number of switching elements. (Note 11) A multi-phase arm is provided with a positive-side switching element connected to the positive side of a DC power supply, a negative-side switching element connected to the negative side of the DC power supply, and an external connection point that connects the positive-side switching element and the negative-side switching element in series and supplies current to the outside. A positive electrode side element temperature detector for detecting the temperature of the positive electrode side switching element, and The system includes a negative electrode side element temperature detector for detecting the temperature of the negative electrode side switching element, The control device is a power conversion device according to Appendix 10, which limits the operation of the switching element when the temperature detected by the positive electrode side element temperature detector or the negative electrode side element temperature detector is greater than the temperature threshold. (Note 12) The power conversion device according to any one of the appendices 1 to 11, wherein the element temperature detector is a thermistor. (Note 13) The power conversion device according to any one of the appendices 1 to 12, wherein the switching element is made of a wide-bandgap semiconductor. [Explanation of Symbols]

[0154] 12 DC power supply, 36 water temperature sensor, 37 cooler temperature sensor, 38 flow sensor, 51, 51a, 51b, 52, 52a, 52b, 53, 53a, 53b, 54, 54a, 54b, 55, 55a, 55b, 56, 56a, 56b semiconductor switching elements, 71, 72, 73, 74, 75, 76 element temperature detectors, 90, 90A, 90B control devices, 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G power converters, 351, 351A, 351B coolers

Claims

1. A switching element that conducts and interrupts electric current. A temperature detector for detecting the temperature of the switching element, A cooler that cools the switching element and is also cooled by a cooling medium, and when the temperature of the cooling medium decreases, the viscosity of the cooling medium decreases and the flow rate of the cooling medium decreases, causing the cooling efficiency to decrease. A cooling medium state detector for detecting the state of the cooling medium passing through the cooler, and A power conversion device comprising a control device that controls the switching element to perform power conversion and also controls the switching element to prevent overheating, The control device is a power converter that determines a temperature threshold for determining whether overheat prevention control is necessary based on the state of the cooling medium detected by the cooling medium state detector, and restricts the operation of the switching element to perform overheat prevention control when the temperature detected by the element temperature detector is higher than the temperature threshold, The cooling medium state detector is a power conversion device which is a cooling medium flow detector that detects the flow rate of the cooling medium.

2. The power conversion device according to claim 1, wherein the cooling medium state detector further comprises a cooling medium temperature detector for detecting the temperature of the cooling medium.

3. The power conversion device according to claim 1, wherein the cooling medium state detector further comprises a cooler temperature detector for detecting the temperature of the cooler.

4. The power conversion device according to claim 2 or 3, wherein the control device sets the temperature threshold higher as the temperature detected by the cooling medium state detector increases.

5. The power conversion device according to claim 1, wherein the control device, when the temperature detected by the element temperature detector is higher than the temperature threshold, increases the limiting rate that restricts the operation of the switching element as the difference between the temperature detected by the element temperature detector and the temperature threshold increases.

6. The power conversion device according to claim 1, wherein the control device sets the temperature threshold higher as the flow rate of the cooling medium detected by the cooling medium flow rate detector increases.

7. A switching element for conducting and interrupting electric current, A temperature detector for detecting the temperature of the switching element, A cooler that cools the switching element and is also cooled by a cooling medium, and when the temperature of the cooling medium decreases, the viscosity of the cooling medium decreases and the flow rate of the cooling medium decreases, causing the cooling efficiency to decrease. A cooling medium state detector for detecting the state of the cooling medium passing through the cooler, and A power conversion device comprising a control device that controls the switching element to perform power conversion and also controls the switching element to prevent overheating, The control device is a power converter that determines a temperature threshold for determining whether overheat prevention control is necessary based on the state of the cooling medium detected by the cooling medium state detector, and restricts the operation of the switching element to perform overheat prevention control when the temperature detected by the element temperature detector is higher than the temperature threshold, The cooling medium state detector includes a cooling medium temperature detector for detecting the temperature of the cooling medium and a cooling medium flow rate detector for detecting the flow rate of the cooling medium. The control device is a power converter that determines the temperature threshold based on the temperature of the cooling medium detected by the cooling medium temperature detector and the flow rate of the cooling medium detected by the cooling medium flow rate detector.

8. The power conversion device according to claim 7, wherein the control device sets the temperature threshold higher as the flow rate of the cooling medium detected by the cooling medium flow rate detector increases, and sets the temperature threshold higher as the temperature detected by the cooling medium state detector increases.

9. Multiple switching elements are provided in parallel. The power conversion device according to claim 1 or 7, wherein the number of element temperature detectors is less than the number of switching elements.

10. A multi-phase arm is provided with a positive-side switching element connected to the positive side of a DC power supply, a negative-side switching element connected to the negative side of the DC power supply, and an external connection point that connects the positive-side switching element and the negative-side switching element in series and supplies current to the outside. A positive electrode side element temperature detector for detecting the temperature of the positive electrode side switching element, and The system includes a negative electrode side element temperature detector for detecting the temperature of the negative electrode side switching element, The power conversion device according to claim 9, wherein the control device restricts the operation of the switching element when the temperature detected by the positive electrode side element temperature detector or the negative electrode side element temperature detector is greater than the temperature threshold.

11. The power conversion device according to claim 1 or 7, wherein the element temperature detector is a thermistor.

12. The power conversion device according to claim 1 or 7, wherein the switching element is formed of a wide-bandgap semiconductor.

Images