Power Conversion Device

Abstract

To provide a power conversion device capable of suppressing a failure of a semiconductor switching element in a case where abnormality occurs in a cooler.SOLUTION: A power conversion device comprises: a semiconductor switching element 3a; a liquid cooling type cooler 8 which cools the semiconductor switching element 3a; a thermistor 4a which detects temperature of the semiconductor switching element 3a; and a control section 6 including a gate drive circuit 6a which drives the semiconductor switching element 3a at variable switching speed. The control section 6 determines the presence / absence of abnormality in the cooler 8 based on a detected temperature Tj_sens of the thermistor 4a and controls, based on a determination result, the switching speed in turning on the semiconductor switching element 3a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device equipped with a cooler. [Background technology]

[0002] Patent Document 1 discloses a power conversion device. This power conversion device includes a power semiconductor module and a gate drive circuit that drives the power semiconductor module. The gate drive circuit includes a gate voltage threshold detection / determination circuit, a gate resistance switching circuit, and a gate resistor with a resistance variable function. The gate voltage threshold detection / determination circuit changes and controls the gate resistance value based on the element temperature of the power semiconductor element inside the power semiconductor module. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-129545 Summary of the Invention [Problem to be solved by the invention]

[0004] A power conversion device such as that described above is usually provided with a cooler. Cooling the power semiconductor elements by the cooler prevents the temperature of the power semiconductor elements from rising. However, if an abnormality occurs in the cooler, the temperature of the power semiconductor elements rises. In particular, if the cooler is a liquid-cooled type, the cooling performance of the cooler will be significantly reduced if an abnormality such as a pump failure or cooling medium leakage occurs. Therefore, if the cooler is a liquid-cooled type, the temperature of the power semiconductor elements will rise significantly if an abnormality occurs in the cooler. In this case, the surge voltage of the power semiconductor elements increases, causing the drain-source voltage to exceed the withstand voltage, which could result in a problem of the power semiconductor elements failing.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a power conversion device that can suppress failure of semiconductor switching elements when an abnormality occurs in a cooler. [Means for solving the problem]

[0006] A power conversion device according to the present disclosure includes a semiconductor switching element, a liquid-cooled cooler that cools the semiconductor switching element, a temperature sensor that detects the temperature of the semiconductor switching element, and a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed, wherein the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls the switching speed when the semiconductor switching element is turned on based on the determination result. When the control unit determines that there is no abnormality in the cooler, and when the detected temperature is equal to or lower than a threshold temperature, the control unit sets the switching speed to a first speed, and when the detected temperature exceeds the threshold temperature, the control unit sets the switching speed to a second speed lower than the first speed, and when it determines that there is an abnormality in the cooler, the control unit sets the switching speed to the second speed. do. In addition, a power conversion device according to the present disclosure includes a semiconductor switching element, a liquid-cooled cooler that cools the semiconductor switching element, a temperature sensor that detects the temperature of the semiconductor switching element, and a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed, wherein the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls the switching speed when the semiconductor switching element is turned on based on the determination result, and when the control unit determines that there is no abnormality in the cooler and the detected temperature is below a threshold temperature, the control unit sets the switching speed to a first speed, and when the detected temperature exceeds the threshold temperature, the control unit sets the switching speed to a second speed lower than the first speed, and when it determines that there is an abnormality in the cooler, the control unit sets the switching speed to the first speed when the output current of the power conversion device is below the threshold current and the detected temperature is below the threshold temperature. In addition, a power conversion device according to the present disclosure includes a semiconductor switching element, a liquid-cooled cooler that cools the semiconductor switching element, a temperature sensor that detects the temperature of the semiconductor switching element, and a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed, wherein the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls the switching speed when the semiconductor switching element is turned on based on the determination result, and when the control unit determines that there is no abnormality in the cooler and the detected temperature is equal to or lower than a threshold temperature, the control unit sets the switching speed to a first speed, and when the detected temperature exceeds the threshold temperature, the control unit sets the switching speed to a second speed lower than the first speed, and when it determines that there is an abnormality in the cooler and the detected temperature is equal to or lower than the threshold temperature, the control unit sets the switching speed to the first speed and reduces the output current of the power conversion device. In addition, the power conversion device according to the present disclosure includes a semiconductor switching element, a liquid-cooled cooler that cools the semiconductor switching element, a temperature sensor that detects the temperature of the semiconductor switching element, a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed, a current sensor circuit that detects the current flowing through the semiconductor switching element, and a voltage sensor circuit that detects the voltage applied to the semiconductor switching element, wherein the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor and controls the switching speed of the semiconductor switching element when it is turned on based on the determination result, and the control unit includes a semiconductor switching element loss calculation unit that calculates a calculated loss value of the semiconductor switching element using at least the detection value of the current sensor circuit and the detection value of the voltage sensor circuit, and a cooler state determination unit that determines whether or not there is an abnormality in the cooler based on the calculated loss value and the detected temperature. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to suppress failure of semiconductor switching elements when an abnormality occurs in a cooler. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a power conversion device according to a first embodiment. [Figure 2] 2 is a configuration diagram of one semiconductor switching element and a gate drive circuit that drives the semiconductor switching element in the power conversion device according to the first embodiment. FIG. [Figure 3] 1 is a cross-sectional view showing a configuration of a main part of a power conversion device according to a first embodiment. [Figure 4] 10A to 10C are diagrams illustrating a series of operations when a semiconductor switching element performs switching. [Figure 5] 10A to 10C are diagrams illustrating a series of operations when a semiconductor switching element performs switching. [Figure 6]10A to 10C are diagrams illustrating a series of operations when a semiconductor switching element performs switching. [Figure 7] 4 is a graph showing a current waveform of a semiconductor switching element when the semiconductor switching element is turned on. [Figure 8] 10 is a graph showing a voltage waveform of a semiconductor switching element of an opposite arm when the semiconductor switching element is turned on. [Figure 9] 10 is a graph showing a recovery current waveform of a semiconductor switching element of an opposite arm when the semiconductor switching element is turned on. [Figure 10] 10 is a graph showing a current waveform of the semiconductor switching element when the switching speed at the time of turn-on is reduced. [Figure 11] 10 is a graph showing a voltage waveform of a semiconductor switching element of an opposite arm when the switching speed at turn-on is reduced. [Figure 12] 10 is a graph showing a recovery current waveform of a semiconductor switching element of an opposite arm when the switching speed at turn-on is reduced. [Figure 13] 4 is a diagram illustrating a method for adjusting the switching speed when turning on a semiconductor switching element in the power conversion device according to the first embodiment. FIG. [Figure 14] 4 is a graph showing a current waveform of a semiconductor switching element in the power conversion device according to the first embodiment. [Figure 15] 6 is a graph showing voltage waveforms of semiconductor switching elements of an opposite arm in the power conversion device according to the first embodiment. [Figure 16] 6 is a graph showing a recovery current waveform of a semiconductor switching element of an opposite arm in the power conversion device according to the first embodiment. [Figure 17] 6 is a graph showing an example of changes in the junction temperature of a semiconductor switching element and the temperature detected by a thermistor in a power conversion device according to a comparative example of the first embodiment. [Figure 18]4 is a graph showing an example of changes in the junction temperature of a semiconductor switching element, the temperature detected by a thermistor, and the rate of temperature rise in the power conversion device according to the first embodiment. [Figure 19] 4 is a graph showing an example of changes in the junction temperature of a semiconductor switching element, the temperature detected by a thermistor, and the rate of temperature rise in the power conversion device according to the first embodiment. [Figure 20] 10 is a configuration diagram of a semiconductor switching element and a gate drive circuit in a power conversion device according to a first modification of the first embodiment. FIG. [Figure 21] 10 is a graph showing an example of waveforms of a gate voltage, a gate-source voltage, and a drain current of a semiconductor switching element in a power conversion device according to a first modification of the first embodiment. [Figure 22] 10 is a graph showing an example of waveforms of a gate voltage, a gate-source voltage, and a drain current of a semiconductor switching element in a power conversion device according to a first modification of the first embodiment. [Figure 23] FIG. 10 is a configuration diagram of a semiconductor switching element and a gate drive circuit in a power conversion device according to a second modification of the first embodiment. [Figure 24] 10 is a diagram illustrating the operation of the gate drive circuit in the power conversion device according to the second modification of the first embodiment. FIG. [Figure 25] 10 is a diagram illustrating the operation of the gate drive circuit in the power conversion device according to the second modification of the first embodiment. FIG. [Figure 26] 10 is a graph showing an example of the operation of a switching element of a gate drive circuit in a power conversion device according to a second modification of the first embodiment, and examples of waveforms of a Zener diode voltage, a gate-source voltage, and a drain current. [Figure 27] 10 is a graph showing an example of the operation of a switching element of a gate drive circuit in a power conversion device according to a second modification of the first embodiment, and examples of waveforms of a Zener diode voltage, a gate-source voltage, and a drain current. [Figure 28] 4 is a flowchart showing an example of processing executed by a control unit in the power conversion device according to the first embodiment. [Figure 29] FIG. 10 is a block diagram showing the configuration of a control unit in a power conversion device according to a second embodiment. [Figure 30] FIG. 10 is a block diagram showing the configuration of a cooler state determination unit in the power conversion device according to the second embodiment. [Figure 31] FIG. 10 is a block diagram showing a configuration of a control unit in a power conversion device according to a modification of the second embodiment. [Figure 32] FIG. 10 is a block diagram showing a configuration of a junction temperature calculation unit in a power conversion device according to a modification of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiment 1 A power conversion device according to embodiment 1 will be described. Fig. 1 is a schematic configuration diagram of the power conversion device according to this embodiment. As shown in Fig. 1, the power conversion device of this embodiment has a three-phase inverter.

[0010] A DC input power supply 1 is connected to the input section of the inverter. The DC input power supply 1 is a battery that outputs a DC voltage. When the power conversion device of this embodiment is applied to an electric vehicle or a hybrid vehicle, a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery is usually used as the DC input power supply 1. A motor 7, which is a load of the inverter, is connected to the output section of the inverter. The motor 7 may be a generator motor. For convenience, the phases of the motor 7 are referred to as a U phase, a V phase, and a W phase.

[0011] The input stage of the inverter is provided with a smoothing capacitor 2 and a plurality of semiconductor switching elements 3a to 3f. The smoothing capacitor 2 is provided to remove voltage ripple and noise.

[0012] Each of the semiconductor switching elements 3a to 3f is a power semiconductor element for power conversion. Each of the semiconductor switching elements 3a to 3f is configured by a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Each of the semiconductor switching elements 3a to 3f has an internal body diode. Each of the semiconductor switching elements 3a to 3f is formed of a wide bandgap semiconductor such as silicon carbide (SiC).

[0013] The output voltage of smoothing capacitor 2 is converted into a three-phase AC voltage by the switching operations of semiconductor switching elements 3a to 3f, and the three-phase AC voltage is output to motor 7 via three-phase output terminals Vu, Vv, and Vw.

[0014] The power conversion device is provided with a cooler 8. The cooler 8 is configured to cool electronic components such as a semiconductor module including each of the semiconductor switching elements 3a to 3f, and a smoothing capacitor 2. In FIG. 1, the long dashed line marked with the reference numeral 8 indicates the range cooled by the cooler 8.

[0015] The cooler 8 is a liquid-cooled cooler. Liquid-cooled coolers include water-cooled coolers and oil-cooled coolers. A liquid coolant such as water, oil, or LLC is used as the coolant for the cooler 8. The cooler 8, together with a hose, an electric pump, a radiator, and the like, constitutes a coolant circuit. When the electric pump is driven, the coolant circulates through the coolant circuit. This allows the coolant to flow through the cooler 8.

[0016] The control unit 6 includes a processor, a storage device, an input / output interface circuit, and other hardware components. The control unit 6 controls the on / off states of the semiconductor switching elements 3a to 3f, with dead time in between. The control unit 6 outputs a control signal to the semiconductor switching element 3a via a control line 32a. The semiconductor switching element 3a performs switching operations based on the control signal input from the control unit 6.

[0017] Similarly, semiconductor switching element 3b performs a switching operation based on a control signal input from control unit 6 via control line 32b. Semiconductor switching element 3c performs a switching operation based on a control signal input from control unit 6 via control line 32c. Semiconductor switching element 3d performs a switching operation based on a control signal input from control unit 6 via control line 32d. Semiconductor switching element 3e performs a switching operation based on a control signal input from control unit 6 via control line 32e. Semiconductor switching element 3f performs a switching operation based on a control signal input from control unit 6 via control line 32f.

[0018] At the input stage of the inverter, a voltage sensor circuit 20 is provided in parallel with the smoothing capacitor 2. The voltage sensor circuit 20 is connected to the control unit 6 via a signal line 31a. The control unit 6 acquires information about the input voltage of the inverter based on the signal from the voltage sensor circuit 20.

[0019] Current sensor circuits 21a, 21b, and 21c are provided in the output stage of the inverter. Current sensor circuit 21a is provided between the three-phase output terminal Vu and the motor 7, i.e., in the U-phase of the inverter output stage. Current sensor circuit 21a is connected to the control unit 6 via signal line 31b. Current sensor circuit 21b is provided between the three-phase output terminal Vv and the motor 7, i.e., in the V-phase of the inverter output stage. Current sensor circuit 21b is connected to the control unit 6 via signal line 31c. Current sensor circuit 21c is provided between the three-phase output terminal Vw and the motor 7, i.e., in the W-phase of the inverter output stage. Current sensor circuit 21c is connected to the control unit 6 via signal line 31d.

[0020] The current sensor circuits 21a, 21b, and 21c detect three-phase currents Iu, Iv, and Iw between the three-phase output terminals Vu, Vv, and Vw and the motor 7. The control unit 6 acquires information about the output currents output from the inverter based on signals from the current sensor circuits 21a, 21b, and 21c.

[0021] The semiconductor switching element 3a is provided inside the semiconductor module 5a. A thermistor 4a is also provided inside the semiconductor module 5a. The thermistor 4a is a temperature sensor that detects the temperature of the semiconductor switching element 3a. The thermistor 4a is arranged in close proximity to the semiconductor switching element 3a. The thermistor 4a is connected to the control unit 6 via a signal line 33a. The control unit 6 obtains information about the temperature of the semiconductor switching element 3a based on the signal from the thermistor 4a.

[0022] The semiconductor switching element 3b is provided inside the semiconductor module 5b. A thermistor 4b is also provided inside the semiconductor module 5b. The thermistor 4b is a temperature sensor that detects the temperature of the semiconductor switching element 3b. The thermistor 4b is arranged in close proximity to the semiconductor switching element 3b. The thermistor 4b is connected to the control unit 6 via a signal line 33b. The control unit 6 obtains information about the temperature of the semiconductor switching element 3b based on a signal from the thermistor 4b.

[0023] The semiconductor switching element 3c is provided inside a semiconductor module 5c. A thermistor 4c is also provided inside the semiconductor module 5c. The thermistor 4c is a temperature sensor that detects the temperature of the semiconductor switching element 3c. The thermistor 4c is arranged in close proximity to the semiconductor switching element 3c. The thermistor 4c is connected to the control unit 6 via a signal line 33c. The control unit 6 obtains information about the temperature of the semiconductor switching element 3c based on a signal from the thermistor 4c.

[0024] The semiconductor switching element 3d is provided inside a semiconductor module 5d. A thermistor 4d is also provided inside the semiconductor module 5d. The thermistor 4d is a temperature sensor that detects the temperature of the semiconductor switching element 3d. The thermistor 4d is arranged in close proximity to the semiconductor switching element 3d. The thermistor 4d is connected to a control unit 6 via a signal line 33d. The control unit 6 obtains information about the temperature of the semiconductor switching element 3d based on a signal from the thermistor 4d.

[0025] The semiconductor switching element 3e is provided inside the semiconductor module 5e. A thermistor 4e is also provided inside the semiconductor module 5e. The thermistor 4e is a temperature sensor that detects the temperature of the semiconductor switching element 3e. The thermistor 4e is arranged in close proximity to the semiconductor switching element 3e. The thermistor 4e is connected to the control unit 6 via a signal line 33e. The control unit 6 obtains information about the temperature of the semiconductor switching element 3e based on a signal from the thermistor 4e.

[0026] The semiconductor switching element 3f is provided inside the semiconductor module 5f. A thermistor 4f is also provided inside the semiconductor module 5f. The thermistor 4f is a temperature sensor that detects the temperature of the semiconductor switching element 3f. The thermistor 4f is arranged in close proximity to the semiconductor switching element 3f. The thermistor 4f is connected to the control unit 6 via a signal line 33f. The control unit 6 obtains information about the temperature of the semiconductor switching element 3f based on a signal from the thermistor 4f.

[0027] A rotation angle sensor (not shown) detects the rotation angle θm of the motor 7. The control unit 6 acquires information about the rotation angle θm of the motor 7 based on a signal from the rotation angle sensor. Information about the torque command value Trq* and information about the DC voltage command value V2* of the motor 7 are input to the control unit 6 from outside the power conversion device.

[0028] Fig. 2 is a configuration diagram of one semiconductor switching element and a gate drive circuit that drives it in a power conversion device according to this embodiment. As shown in Fig. 2, the control unit 6 has a gate drive circuit 6a that drives the semiconductor switching element 3a. Although Fig. 2 only shows the gate drive circuit 6a, the control unit 6 has a plurality of gate drive circuits that drive the plurality of semiconductor switching elements 3a to 3f, respectively. The gate drive circuits other than the gate drive circuit 6a have the same configuration as the gate drive circuit 6a.

[0029] The gate drive circuit 6a includes a drive circuit main body 6b and a gate resistance switching circuit 6c. The drive circuit main body 6b is connected to the gate G of the semiconductor switching element 3a via the gate resistance switching circuit 6c. The gate resistance switching circuit 6c is provided with separate circuits for turn-on (Ton) and turn-off (Toff).

[0030] The turn-on circuit includes a resistor Rgon1 and a bypass circuit 6d connected in parallel to the resistor Rgon1. The bypass circuit 6d includes a switching element SW and a resistor Rgon2 connected in series.

[0031] For example, under normal circumstances, the switching element SW is in the OFF state. When the switching element SW is in the OFF state, the gate resistance of the semiconductor switching element 3a when it is turned on is Rgon1.

[0032] When the switching element SW is turned on, the gate resistance of the semiconductor switching element 3a decreases from Rgon1 to a combined resistance Rgon1 / / Rgon2, where Rgon1 / / Rgon2 represents the combined resistance when the resistors Rgon1 and Rgon2 are connected in parallel.

[0033] That is, to increase the switching speed of the semiconductor switching element 3a when it is turned on, the control unit 6 turns on the switching element SW. This reduces the gate resistance, and therefore increases the switching speed of the semiconductor switching element 3a when it is turned on. In this embodiment, the control unit 6 controls the switching element SW based on the temperature of the semiconductor switching element 3a, etc.

[0034] The turn-off circuit is provided with a resistor Rgoff. When the semiconductor switching element 3a is turned off, it is switched via the resistor Rgoff.

[0035] 2, the resistor Rgon1, the switching element SW, and the resistor Rgon2 are connected in parallel, but this is not limited to this. The gate resistance at turn-on may be configured to be switchable between the resistor Rgon1 and a lower resistor Rgon2 by a relay in the gate drive circuit 6a (Rgon1>Rgon2). The control unit 6 normally sets the gate resistance at turn-on to the resistor Rgon1. When increasing the switching speed at turn-on of the semiconductor switching element 3a, the control unit 6 switches the gate resistance at turn-on from the resistor Rgon1 to the resistor Rgon2.

[0036] Next, the physical configuration of the power conversion device according to this embodiment will be described. Fig. 3 is a cross-sectional view showing the configuration of the main part of the power conversion device according to this embodiment. Fig. 3 shows the cross-sectional configuration of semiconductor module 5a. The following description will be given taking semiconductor module 5a as an example, but semiconductor modules 5b to 5f have the same configuration as semiconductor module 5a.

[0037] 3, the semiconductor module 5a is mounted on the outer surface 8a of the cooler 8. The semiconductor module 5a has a substrate 43, a semiconductor switching element 3a, a thermistor 4a, a bus bar 41, and a resin molded body 44. The semiconductor switching element 3a and thermistor 4a are mounted on one surface 43a of the substrate 43. The bus bar 41 is connected to the semiconductor switching element 3a via a solder layer 42.

[0038] The thermistor 4a is disposed in proximity to the semiconductor switching element 3a on the surface 43a of the substrate 43. However, the thermistor 4a is not in direct contact with the semiconductor switching element 3a.

[0039] The thermistor 4a is provided outside the semiconductor switching element 3a, not inside it. In other words, the thermistor 4a is different from a temperature measuring diode, which is provided in the same semiconductor chip as the semiconductor switching element to detect the temperature of the semiconductor switching element.

[0040] The thermistor 4a is indirectly connected to the semiconductor switching element 3a via a thermal network, which will be described later. Heat from the semiconductor switching element 3a is transferred to the thermistor 4a via the thermal network. This allows the thermistor 4a to indirectly detect the temperature of the semiconductor switching element 3a.

[0041] The resin molded body 44 covers the substrate 43, the semiconductor switching elements 3a, thermistor 4a, and a portion of the bus bar 41. The resin molded body 44 is integrally molded with the substrate 43, the semiconductor switching elements 3a, thermistor 4a, and bus bar 41. The other surface 43b of the substrate 43 is exposed from the resin molded body 44. The surface 43b of the substrate 43 is fixed to the surface 8a of the cooler 8 via an insulating member 45.

[0042] A cooling medium flow path 8b is formed inside the cooler 8. A cooling medium flows through the cooling medium flow path 8b. The heat generated in the semiconductor module 5a is absorbed by the cooling medium, thereby cooling the semiconductor module 5a.

[0043] Next, a recovery surge caused by the recovery of a diode in a semiconductor switching element will be described. Figures 4 to 6 are diagrams illustrating a series of operations when a semiconductor switching element switches on. The dashed arrows in Figures 4 to 6 indicate the flow of current.

[0044] 4, both semiconductor switching elements 3a and 3b are in the OFF state, and current flows from the three-phase output terminal Vu to the motor 7. At this time, semiconductor switching element 3d is in the ON state, and current flowing from the V-phase of the motor 7 to the power conversion device passes through semiconductor switching element 3d. The current also passes through the internal diode of semiconductor switching element 3b and flows to the U-phase of the motor 7.

[0045] Next, in the operating mode shown in Figure 5, semiconductor switching element 3a is turned on. This causes current to begin flowing from semiconductor switching element 3a to the U-phase of motor 7, increasing the current through semiconductor switching element 3a. Meanwhile, the current through semiconductor switching element 3b on the opposite arm decreases. Because the inductance component of the internal coil of motor 7 is large, the current flowing through the U-phase of motor 7 is almost constant.

[0046] Next, in the operating mode shown in Figure 6, the current passing through semiconductor switching element 3a becomes equal to the current flowing through the U-phase of motor 7, and the current passing through semiconductor switching element 3b in the opposite arm disappears. When the current passing through semiconductor switching element 3b disappears, the state of the internal diode of semiconductor switching element 3b changes from forward bias to reverse bias. As a result, a recovery current flows through semiconductor switching elements 3a and 3b, as indicated by the dotted arrows in Figure 6.

[0047] After that, in the internal diode of semiconductor switching element 3b, the depletion layer expands due to the external voltage, and the depletion layer is charged by the recovery current. As a result, the internal diode voltage of the internal diode of semiconductor switching element 3b rises. At this time, a recovery surge voltage ΔV is generated due to the time change (dirr / dt) of the recovery current and the path inductance Ls (ΔV = Ls × dirr / dt). The recovery surge voltage ΔV is added to the drain-source voltage Vds of semiconductor switching element 3b.

[0048] Next, we will explain how the recovery characteristics described above are affected by temperature. Fig. 7 is a graph showing the current waveform of a semiconductor switching element when the semiconductor switching element is turned on. Fig. 8 is a graph showing the voltage waveform of a semiconductor switching element of an opposite arm when the semiconductor switching element is turned on. Fig. 9 is a graph showing the recovery current waveform of a semiconductor switching element of an opposite arm when the semiconductor switching element is turned on.

[0049] The vertical axis in Fig. 7 represents the drain-source current Ids of semiconductor switching element 3a. The vertical axis in Fig. 8 represents the drain-source voltage Vds of semiconductor switching element 3b. The vertical axis in Fig. 9 represents the internal diode current of semiconductor switching element 3b. The horizontal axis in Figs. 7 to 9 represents time. In each graph in Figs. 7 to 9, the dashed line represents the waveform at room temperature, and the solid line represents the waveform at high temperature.

[0050] Generally, the recovery current of a diode has a negative peak, as shown in Figure 9. The higher the temperature, the deeper the negative peak becomes. In other words, the higher the temperature, the smaller the negative peak value becomes. After the recovery current reaches its negative peak, it attempts to return to 0 A. Therefore, at high temperatures, the recovery current returns faster. In Figure 9, the recovery current return speed is represented as dirr / dt. As a result, as shown in Figure 8, the recovery surge voltage ΔV increases at high temperatures, which may cause the voltage Vds to exceed the withstand voltage of the semiconductor switching element 3b.

[0051] Therefore, the switching speed (di / dt) at turn-on is adjusted so that the voltage Vds does not exceed the breakdown voltage of the semiconductor switching element 3b at high temperatures. The switching speed at turn-on is adjusted by the gate resistance at turn-on. The higher the gate resistance at turn-on, the slower the switching speed at turn-on.

[0052] Fig. 10 is a graph showing the current waveform of the semiconductor switching element when the switching speed at turn-on is reduced. Fig. 11 is a graph showing the voltage waveform of the semiconductor switching element of the opposite arm when the switching speed at turn-on is reduced. Fig. 12 is a graph showing the recovery current waveform of the semiconductor switching element of the opposite arm when the switching speed at turn-on is reduced. The vertical and horizontal axes in Figs. 10 to 12 are the same as the vertical and horizontal axes in Figs. 7 to 9, respectively. In each of the graphs in Figs. 10 to 12, the thick lines represent the waveform when the switching speed at turn-on is reduced.

[0053] 10 to 12, when the switching speed (di / dt) at turn-on decreases, the negative peak of the recovery current becomes shallower. As a result, the return speed (dirr / dt) of the recovery current decreases, and the recovery surge voltage ΔV decreases. This prevents the voltage Vds from exceeding the withstand voltage of the semiconductor switching element 3b.

[0054] On the other hand, if the turn-on switching speed is reduced only by considering the breakdown voltage at high temperatures, the switching speed will remain low even at room temperature when the recovery surge is relatively small, resulting in increased switching loss.

[0055] In commercial driving of electric vehicles, hybrid vehicles, etc., the motor output used by users is generally less than half of the rated output. The fuel economy measurement conditions for the WLTC (World Wide-Harmonized Light Vehicles Test Cycle) mode, which is representative of catalog fuel economy, are set based on commercial driving. Therefore, even under the fuel economy measurement conditions for the WLTC mode, the motor output is generally less than half of the rated output. For this reason, when considering commercial driving and the fuel economy measurement conditions for the WLTC mode, the current flowing from the inverter to the motor is relatively small.

[0056] Losses in semiconductor switching elements account for almost all inverter losses. In addition to the switching losses mentioned above, losses in semiconductor switching elements also include conduction losses. Conduction losses are proportional to the square of the current. Therefore, when the current flowing from the inverter to the motor is small, the proportion of conduction losses in semiconductor switching element losses decreases, and the proportion of switching losses increases.

[0057] Furthermore, when the motor output is low, that is, when the load on the inverter is low, the loss in the semiconductor switching elements is small, so the temperature of the semiconductor switching elements does not rise very high.

[0058] For these reasons, under measurement conditions in the normal operating range that general users care about, if the switching speed at turn-on is slow, inverter loss increases and power consumption or fuel economy decreases. The worse the recovery characteristics of a semiconductor switching element at high temperatures, the more it is necessary to prevent the voltage Vds from exceeding the breakdown voltage due to a recovery surge at high temperatures, so the switching speed at turn-on must be slowed down. For this reason, the worse the recovery characteristics of a semiconductor switching element at high temperatures, the more likely it is that power consumption or fuel economy will decrease.

[0059] To solve this problem, in this embodiment, the switching speed of the semiconductor switching element when it is turned on is adjusted based on the temperature of the semiconductor switching element. Specifically, when the temperature of the semiconductor switching element is not high, the recovery surge is relatively small, so the switching speed of the semiconductor switching element when it is turned on is increased. This makes it possible to reduce inverter loss in the normal operating range where the inverter load is relatively low.

[0060] 13 is a diagram illustrating a method for adjusting the switching speed of a semiconductor switching element when it is turned on in a power conversion device according to this embodiment. In the following description, semiconductor switching element 3a is mainly used as an example, but the same applies to other semiconductor switching elements.

[0061] First, the control unit 6 acquires information about the temperature of the semiconductor switching element 3a based on a signal from the thermistor 4a. If the temperature of the semiconductor switching element 3a is equal to or lower than a threshold temperature, the control unit 6 determines that the temperature of the semiconductor switching element 3a is room temperature. If the temperature of the semiconductor switching element 3a is higher than the threshold temperature, the control unit 6 determines that the temperature of the semiconductor switching element 3a is high. Information about the threshold temperature is stored in a storage device provided in the control unit 6.

[0062] When the control unit 6 determines that the temperature of the semiconductor switching element 3a is room temperature, it turns on the switching element SW of the gate drive circuit 6a. When the switching element SW is turned on, the gate current flows not only through the path indicated by the solid arrow passing through the resistor Rgon1 but also through the path indicated by the dashed arrow passing through the resistor Rgon2. This reduces the gate resistance, and the rise speed of the gate voltage of the semiconductor switching element 3a increases. Therefore, the switching speed of the semiconductor switching element 3a increases when it is turned on.

[0063] Fig. 14 is a graph showing a current waveform of a semiconductor switching element in a power conversion device according to this embodiment. Fig. 15 is a graph showing a voltage waveform of a semiconductor switching element in an opposite arm in a power conversion device according to this embodiment. Fig. 16 is a graph showing a recovery current waveform of a semiconductor switching element in an opposite arm in a power conversion device according to this embodiment.

[0064] The vertical and horizontal axes in Figures 14 to 16 are the same as those in Figures 7 to 9. In each graph in Figures 14 to 16, the thin lines represent the waveform before the switching speed is adjusted. The thick lines represent the waveform after the switching speed is adjusted, i.e., after the switching speed has increased. As described above, the switching speed is adjusted when the temperature of the semiconductor switching element 3a is at room temperature.

[0065] 14 to 16, because the temperature of semiconductor switching element 3a is room temperature, increasing the switching speed (di / dt) of semiconductor switching element 3a when it is turned on only slightly affects the recovery current of semiconductor switching element 3b. Therefore, the increase in voltage Vds due to the recovery surge is only slight, and it is possible to prevent voltage Vds from exceeding the withstand voltage of semiconductor switching element 3b.

[0066] On the other hand, increasing the switching speed reduces switching loss. Therefore, by increasing the switching speed at room temperature, switching loss at room temperature can be reduced, and inverter loss can be reduced.

[0067] In the gate drive circuit 6a of this embodiment, the value of the resistor Rgon2 is set so that the voltage Vds does not exceed the withstand voltage of the semiconductor switching element even if the gate resistance decreases from the resistor Rgon1 to the combined resistor Rgon1 / / Rgon2 when the temperature of the semiconductor switching element is at room temperature.

[0068] Generally, the lower the switching loss of a semiconductor switching element, the greater the effect of the switching speed at turn-on on the switching loss. Therefore, when this embodiment is applied to a semiconductor switching element with low switching loss, such as a wide bandgap semiconductor, a particularly large loss reduction effect can be achieved.

[0069] Next, the responsiveness of the thermistor will be explained using thermistor 4a as an example. Thermistor 4a is installed to detect the junction temperature of semiconductor switching element 3a. However, because the junction is located in the center of the chip, thermistor 4a cannot be installed directly on the junction due to its structure. For this reason, thermistor 4a is placed in close proximity to semiconductor switching element 3a.

[0070] As shown in Figure 3, the thermal circuit network between the semiconductor switching element 3a and thermistor 4a is composed of thermal resistors 50a, 50b, 51a, 51b, 52a, 52b, 52c, 53a, 53b, 54a, 54b, and 54c. Thermal resistors 50a, 51a, 51b, and 50b are formed in the direct heat transfer path from the junction of the semiconductor switching element 3a to thermistor 4a. Thermal resistors 52a, 52b, 52c, 53a, and 53b are formed in the heat transfer path from the junction of the semiconductor switching element 3a to thermistor 4a via the cooler 8. Thermal resistors 54a, 54b, and 54c are formed in the heat dissipation path from the heat transfer path via the cooler 8 to the cooling medium flowing through the cooling medium flow path 8b.

[0071] When there is no abnormality in the cooler 8, the temperature of each part of the semiconductor module 5a rises based on the temperature of the cooling medium in the cooling medium flow path 8b, depending on the loss generated in the semiconductor switching element 3a and the thermal resistance of each part of the thermal circuit network. As a result, the junction temperature of the semiconductor switching element 3a, the temperature detected by the thermistor 4a, and the temperature of the cooling medium in the cooling medium flow path 8b are uniquely determined. Therefore, by knowing the thermal resistances of each part of the thermal circuit network, the junction temperature of the semiconductor switching element 3a can be estimated from the temperature detected by the thermistor 4a.

[0072] However, if the state of the cooler 8 changes, for example, if the coolant no longer exists in the coolant flow path 8b due to a coolant leak, the heat dissipation path to the coolant is lost, and the thermal resistances 54a, 54b, and 54c in the thermal network disappear. While the thermal network shown in Figure 3 is represented only by multiple thermal resistors, an actual thermal network has a heat capacity in parallel with each thermal resistance. As a result, the junction temperature of the semiconductor switching element 3a and the temperature detected by the thermistor 4a are initially determined by the temperature distribution when the coolant disappears, and then undergo a transient temperature transition in which the heat capacity becomes dominant. Thus, if the state of the cooler 8 changes, the thermal network changes, and the relationship between the junction temperature of the semiconductor switching element 3a and the temperature detected by the thermistor 4a changes. Therefore, it becomes difficult to estimate the junction temperature of the semiconductor switching element 3a from the temperature detected by the thermistor 4a.

[0073] Fig. 17 is a graph showing an example of changes in the junction temperature of the semiconductor switching element and the detected temperature of the thermistor in a power conversion device according to a comparative example of this embodiment. The horizontal axis represents time, and the vertical axis represents temperature. The solid line represents changes in the junction temperature Tj of semiconductor switching element 3a. The dashed line represents changes in the detected temperature Tj_sens of the thermistor 4a. Note that while Fig. 17 shows changes in the temperature of semiconductor switching element 3a, the temperatures of the other semiconductor switching elements 3b to 3f also change in the same way as the temperature of semiconductor switching element 3a.

[0074] In this example, the inverter starts operating at time t0. After that, the inverter operates at a constant output. After a sufficiently long time has passed since the inverter output became constant, the cooling medium in the cooler 8 disappears at time t1. Before time t1, the cooler 8 is in a normal cooler state, with no abnormalities. After time t1, the cooler 8 is in an abnormal cooler state, with an abnormality occurring.

[0075] If there is no abnormality in the cooler 8, the junction temperature Tj and the detected temperature Tj_sens will each settle to a constant temperature after a sufficiently long time has passed since the inverter output became constant. The settling temperature of the junction temperature Tj is determined by the heat generated by losses in the semiconductor switching element 3a and the cooling performance of the cooler 8. The detected temperature Tj_sens is a temperature obtained by indirectly measuring the junction temperature Tj. For this reason, the time constant of the detected temperature Tj_sens is longer than the time constant of the junction temperature Tj, and the settling temperature of the detected temperature Tj_sens will be lower than the settling temperature of the junction temperature Tj. The temperature difference between the settling temperature of the junction temperature Tj and the settling temperature of the detected temperature Tj_sens is ΔT1.

[0076] When the cooling medium of the cooler 8 is lost and the cooler 8 enters an abnormal state, the cooling performance of the cooler 8 decreases. As a result, the heat generated by the semiconductor switching element 3a causes a large rise in the junction temperature Tj of the semiconductor switching element 3a. The detected temperature Tj_sens of the thermistor 4a rises with a delay from the junction temperature Tj.

[0077] When the detected temperature Tj_sens reaches the threshold temperature Tth at time t2, the gate resistance is switched from a low resistance to a high resistance, and the switching speed at the time of turning on the semiconductor switching element 3a decreases.

[0078] The threshold temperature Tth is set to a higher temperature than the settling temperature of the detected temperature Tj_sens. This is because, when the operating conditions and installation environment are normal, it is desirable to increase the switching speed as much as possible in the normal operating range where the loss of the semiconductor switching element 3a is relatively low, while taking into account the detection error of the thermistor 4a, variations in the amount of heat generated by the semiconductor switching element 3a, and variations in the flow rate of the cooling medium. For this reason, the time (t2-t1) from time t1 when the cooling medium is lost to time t2 when the detected temperature Tj_sens reaches the threshold temperature Tth is relatively long.

[0079] After the cooling medium in the cooler 8 is lost, the temperature difference ΔT2 between the junction temperature Tj and the detected temperature Tj_sens becomes larger than ΔT1. Furthermore, the temperature difference ΔT2 increases as the time elapsed from time t1 becomes longer. Therefore, as the time (t2-t1) becomes longer, the junction temperature Tj reaches the high temperature T1 when the detected temperature Tj_sens reaches the threshold temperature Tth.

[0080] The switching element SW of the gate drive circuit 6a remains on until the detected temperature Tj_sens reaches the threshold temperature Tth. Therefore, the switching speed of the semiconductor switching element 3a when it is turned on remains high until the detected temperature Tj_sens reaches the threshold temperature Tth. Therefore, if the junction temperature Tj becomes high, the semiconductor switching element 3a may break down due to a recovery surge exceeding the breakdown voltage.

[0081] To prevent the semiconductor switching element 3a from failing due to an excess of withstand voltage, it is possible to set the threshold temperature Tth at a lower value, i.e., a value close to the settling temperature of the detected temperature Tj_sens, taking into account the increase in the temperature difference ΔT2 when the cooler 8 malfunctions. However, if the threshold temperature Tth is set low, the gate resistance may be switched from low to high even when the cooler 8 is normal and the inverter load is relatively low due to detection errors of the thermistor 4a, variations in the heat generation amount of the semiconductor switching element 3a, variations in the flow rate of the cooling medium, etc. As a result, the switching speed of the semiconductor switching element 3a when turned on in the normal operating range does not necessarily increase, resulting in little improvement in power consumption or fuel economy.

[0082] To solve these problems, the control unit 6 of this embodiment determines whether or not there is an abnormality in the cooler 8 based on the temperature Tj_sens detected by the thermistor 4a, and adjusts the switching speed of the semiconductor switching element 3a when it is turned on based on the determination result. In this embodiment, whether or not there is an abnormality in the cooler 8 is determined by comparing the temperature rise rate of the detected temperature Tj_sens with a preset threshold rise rate TRth1. The temperature rise rate is the rate of increase of the detected temperature Tj_sens per hour. The temperature rise rate is calculated based on the detected temperature Tj_sens. Information about the threshold rise rate TRth1 is stored in a storage device provided in the control unit 6.

[0083] 18 is a graph showing an example of changes in the junction temperature of the semiconductor switching element, the detected temperature of the thermistor, and the rate of temperature rise in the power conversion device according to this embodiment. The upper part of the graph shows changes in the junction temperature Tj of the semiconductor switching element 3a and the detected temperature Tj_sens of the thermistor 4a. The horizontal axis of the upper part represents time. The vertical axis of the upper part represents temperature. The lower part of the graph shows changes in the rate of temperature rise of the detected temperature Tj_sens. The horizontal axis of the lower part is the same time axis as the horizontal axis of the upper part. The vertical axis of the lower part represents the rate of temperature rise.

[0084] As shown in FIG. 18, if there is no abnormality in the cooler 8, when the inverter starts operating at time t0, the detected temperature Tj_sens rises. As a result, the temperature rise rate of the detected temperature Tj_sens rises rapidly and reaches temperature rise rate TR1. Temperature rise rate TR1 is the maximum value of the temperature rise rate when there is no abnormality in the cooler 8. Thereafter, the temperature rise rate gradually decreases from temperature rise rate TR1. When a sufficiently long time has passed since the inverter output became constant, the detected temperature Tj_sens settles at a constant temperature, and the temperature rise rate becomes 0.

[0085] The threshold increase rate TRth1 is set in advance as a threshold for the temperature increase rate. The threshold increase rate TRth1 is set to a value higher than the temperature increase rate TR1, taking into account the detection error of the thermistor 4a, variations in the heat generation amount of the semiconductor switching element 3a, variations in the flow rate of the cooling medium, etc. In other words, when there is no abnormality in the cooler 8, the temperature increase rate does not reach the threshold increase rate TRth1.

[0086] At time t1, the cooling medium in the cooler 8 disappears, causing the cooler 8 to enter an abnormal state, and the temperature rise rate rises rapidly from 0 to a value higher than the temperature rise rate TR1. At time t3, the temperature rise rate exceeds the threshold rise rate TRth1. When the temperature rise rate exceeds the threshold rise rate TRth1, the control unit 6 determines that the cooler 8 is abnormal.

[0087] When an abnormality occurs in the cooler 8, the detected temperature Tj_sens starts to rise from a constant settling temperature. Therefore, when an abnormality occurs in the cooler 8, the rate of temperature rise rises more rapidly than the rise in the detected temperature Tj_sens. Therefore, by determining an abnormality in the cooler 8 based on the rate of temperature rise, the time (t3-t1) from when an abnormality occurs in the cooler 8 to when the abnormality is detected can be shortened. The time (t3-t1) is shorter than the time (t2-t1) in FIG. 17.

[0088] When the control unit 6 determines that there is an abnormality in the cooler 8, it performs a process of switching the gate resistance from low resistance to high resistance as a protective operation to protect the semiconductor switching element 3a. Specifically, the control unit 6 sets the switching element SW of the gate drive circuit 6a shown in Figure 2 to OFF. As a result, the gate resistance increases from Rgon1 / / Rgon2 to Rgon1, and the switching speed when the semiconductor switching element 3a is turned on decreases.

[0089] In this embodiment, the time (t3-t1) from when an abnormality occurs in the cooler 8 until the abnormality is detected is short, so the junction temperature Tj when the gate resistance is switched is suppressed to temperature T2, which is lower than temperature T1 in Fig. 17. Therefore, it is possible to suppress the withstand voltage from being exceeded due to a recovery surge, and therefore it is possible to suppress the semiconductor switching element 3a from breaking down.

[0090] Furthermore, when the detected temperature Tj_sens exceeds the threshold temperature Tth, the control unit 6 sets the switching element SW of the gate drive circuit 6a to OFF in the same manner as above. As a result, the gate resistance increases from Rgon1 / / Rgon2 to Rgon1, and the switching speed of the semiconductor switching element 3a when it is turned on decreases.

[0091] In this embodiment, the switching speed of the semiconductor switching element 3a when it is turned on when the detected temperature Tj_sens exceeds the threshold temperature Tth is the same as the switching speed of the semiconductor switching element 3a when it is turned on when an abnormality occurs in the cooler 8.

[0092] If an abnormality occurs in the cooler 8, the temperature increase rate is sufficiently higher than the increase rate of the detected temperature Tj_sens. Therefore, the temperature increase rate reaches the threshold increase rate TRth1 before the detected temperature Tj_sens reaches the threshold temperature Tth. Consequently, the threshold temperature Tth does not function when an abnormality occurs in the cooler 8, and functions only when the cooler 8 is not abnormal.

[0093] On the other hand, the threshold increase rate TRth1 is set to a value higher than the value that the temperature increase rate reaches when there is no abnormality in the cooler 8. For example, even if an abnormality occurs in a power conversion device other than the cooler 8 or an overoutput occurs in the power conversion device, the temperature increase rate does not reach the threshold increase rate TRth1 when there is no abnormality in the cooler 8. For this reason, the threshold increase rate TRth1 does not function when there is no abnormality in the cooler 8, and functions only when there is an abnormality in the cooler 8.

[0094] The temperature rise rate shown in Fig. 18 is expressed by a ramp function with a relatively long unit time to avoid the influence of noise. However, in order to shorten the time (t3-t1) from when an abnormality occurs in the cooler 8 until the abnormality is detected, it is more effective to set the unit time to be shorter.

[0095] Fig. 19 is a graph showing an example of changes in the junction temperature of the semiconductor switching element, the detected temperature of the thermistor, and the temperature rise rate in the power conversion device according to this embodiment. Fig. 19 shows in more detail the changes in the junction temperature Tj, the detected temperature Tj_sens, and the temperature rise rate after time t3 in Fig. 18.

[0096] 19, two threshold increase rates TRth1 and TRth2 are set for the temperature increase rate. The threshold increase rate TRth2 is higher than the threshold increase rate TRth1 (TRth2>TRth1). Information on the threshold increase rate TRth1 and the threshold increase rate TRth2 is stored in a storage device provided in the control unit 6.

[0097] After the gate resistance is switched from low to high at time t3, the temperature rise rate of the detection temperature Tj_sens continues to rise and exceeds the threshold rise rate TRth2 at time t4. When the temperature rise rate exceeds the threshold rise rate TRth2, the control unit 6 reduces the output of the inverter for a preset threshold time Δt10. As the inverter output decreases, the rise in the junction temperature Tj slows after time t4, and the temperature rise rate of the detection temperature Tj_sens gradually decreases.

[0098] The temperature rise rate falls below the threshold rise rate TRth2 at time t5. However, the time elapsed since the temperature rise rate exceeded the threshold rise rate TRth2 has not yet reached the threshold time Δt10. Therefore, the control unit 6 continues to reduce the inverter output.

[0099] The temperature rise rate falls below the threshold rise rate TRth1 at time t6. When the temperature rise rate falls below the threshold rise rate TRth1, the control unit 6 may perform a process of switching the gate resistance from high resistance to low resistance.

[0100] At time t7, the time elapsed since the temperature rise rate exceeded the threshold rise rate TRth2 reaches the threshold time Δt10. When the time elapsed since the temperature rise rate exceeded the threshold rise rate TRth2 reaches the threshold time Δt10, the control unit 6 stops the inverter. As a result, the output of the inverter becomes 0. As the inverter stops, the rise in the junction temperature Tj stops. The junction temperature Tj gradually decreases after time t7. This prevents the junction temperature Tj from reaching the failure temperature of the element.

[0101] As described above, in this embodiment, a gate drive circuit 6a is provided that changes the switching speed of the semiconductor switching element 3a when it is turned on. If there is no abnormality in the cooler 8 and the semiconductor switching element 3a is at room temperature, the control unit 6 increases the switching speed of the semiconductor switching element 3a when it is turned on. This reduces switching loss and improves power consumption or fuel economy during on-road driving.

[0102] By monitoring the rate of temperature rise, the control unit 6 can detect abnormalities in the cooler 8, such as the interruption of the flow of the cooling medium or the loss of the cooling medium, at an early stage. This allows the drive conditions of the power conversion device to be devised and controlled while suppressing an excess of the withstand voltage due to a recovery surge. This allows the power conversion device to continue operating while preventing the semiconductor switching element 3a from breaking down due to high temperatures.

[0103] In this embodiment, a thermistor 4a provided outside the semiconductor switching element 3a is used as the temperature sensor, rather than a temperature measuring diode provided on the same semiconductor chip as the semiconductor switching element 3a. This allows the element area of ​​the semiconductor switching element 3a to be reduced, thereby reducing the cost of the power conversion device.

[0104] When the thermistor 4a external to the semiconductor switching element 3a is used, the difference between the junction temperature Tj and the detected temperature Tj_sens tends to become large. Therefore, if an abnormality occurs in the cooler 8 and the junction temperature Tj rises suddenly, the protective action executed based on the detected temperature Tj_sens may not be able to be performed in time, which may result in a breakdown of the semiconductor switching element 3a.

[0105] In contrast, in the present embodiment, an abnormality in the cooler 8 can be detected early based on the rate of temperature rise, so that a protective operation can be performed according to the state of the cooler 8 and the temperature that the junction temperature Tj reaches can be reduced. As a result, even when a thermistor 4a external to the semiconductor switching element 3a is used, failure of the semiconductor switching element 3a can be suppressed without increasing costs.

[0106] Therefore, according to this embodiment, by reducing the element area of ​​the semiconductor switching element 3 a, it is possible to reduce costs while suppressing failures in the semiconductor switching element 3 a. Since the chip cost of wide bandgap semiconductors such as SiC elements and GaN elements is high, the cost reduction effect is particularly significant when a wide bandgap semiconductor is used for the semiconductor switching element 3 a.

[0107] Next, a modification of this embodiment will be described. In the configuration shown in Fig. 2, the switching speed is changed by switching the gate resistance value, but this is not limiting. Fig. 20 is a configuration diagram of semiconductor switching elements and gate drive circuits in a power conversion device according to a first modification of this embodiment.

[0108] As shown in FIG. 20, the gate drive circuit 6a of this modification has a variable voltage source Vg. This allows the gate drive circuit 6a to change the gate voltage value applied to the gate G of the semiconductor switching element 3a. The switching speed of the semiconductor switching element 3a increases as the gate voltage value increases. Therefore, the gate drive circuit 6a can change the switching speed of the semiconductor switching element 3a when it is turned on by switching the gate voltage value. In this way, the switching speed of the semiconductor switching element 3a when it is turned on may be changed by switching the gate voltage value.

[0109] 21 and 22 are graphs showing examples of waveforms of the gate voltage, gate-source voltage, and drain current of the semiconductor switching element in the power conversion device according to this modification. Fig. 21 shows the waveforms when the temperature of the semiconductor switching element is at room temperature. Fig. 22 shows the waveforms when the temperature of the semiconductor switching element is high or when there is an abnormality in the cooler.

[0110] As shown in FIG. 21, when the control unit 6 determines that the temperature of the semiconductor switching element 3a is at room temperature, it keeps the gate voltage at a relatively high voltage.

[0111] On the other hand, if the control unit 6 determines that the temperature of the semiconductor switching element 3a is high or that there is an abnormality in the cooler 8, as shown in FIG. 22, the control unit 6 maintains the gate voltage at a voltage lower than the rated voltage from the time of turn-on until the drain current rises. This reduces the switching speed of the semiconductor switching element 3a when it is turned on. After a sufficient amount of time has passed, the control unit 6 increases the gate voltage to the normal gate voltage. This keeps the gate voltage at the normal voltage for most of the time when the element is conducting, thereby suppressing an increase in conduction loss due to an increase in on-resistance.

[0112] Fig. 23 is a configuration diagram of a semiconductor switching element and a gate drive circuit in a power conversion device according to a second modification of the present embodiment. As shown in Fig. 23, resistors Rgon1, Rgon2, Zener diode Zdiode, and switching element SW are provided between drive circuit body 6b and semiconductor switching element 3a in the turn-on circuit. Resistor Rgon2, Zener diode Zdiode, and switching element SW are connected in parallel with each other. Resistor Rgon1 is connected in series with resistor Rgon2, Zener diode Zdiode, and switching element SW.

[0113] Figures 24 and 25 are diagrams illustrating the operation of the gate drive circuit in the power conversion device according to this modification when it is turned on. Figures 26 and 27 are graphs illustrating the operation of the switching elements of the gate drive circuit in the power conversion device according to this modification, as well as example waveforms of the Zener diode voltage, gate-source voltage, and drain current.

[0114] As shown in Fig. 24, when the control unit 6 determines that the temperature of the semiconductor switching element 3a is room temperature, it turns on the switching element SW of the gate drive circuit 6a. As a result, no voltage is applied across the Zener diode Zdiode, as shown in Fig. 26. The gate current flows through the switching element SW to the gate G of the semiconductor switching element 3a.

[0115] On the other hand, if the control unit 6 determines that the temperature of the semiconductor switching element 3a is high or that there is an abnormality in the cooler 8, it turns off the switching element SW of the gate drive circuit 6a, as shown in Fig. 25. As a result, a voltage is applied across the Zener diode Zdiode, as shown in Fig. 27. This reduces the voltage applied to the gate G of the semiconductor switching element 3a, and the switching speed when the semiconductor switching element 3a is turned on decreases.

[0116] The voltage across Zener diode Zdiode continues to be applied until the gate-source voltage rises to a certain level. Once the gate-source voltage has risen to a certain level, the difference between the gate power supply voltage of gate drive circuit 6a and the gate-source voltage decreases, causing the voltage across Zener diode Zdiode to drop.

[0117] Here, the resistor Rgon2 connected in parallel with the Zener diode Zdiode is a resistor required to raise the gate-source voltage to the gate power supply voltage. It is desirable that the resistance value of the resistor Rgon2 is sufficiently larger than that of the resistor Rgon1.

[0118] According to the first and second modifications, the gate voltage applied to the semiconductor switching element 3a is controlled, thereby adjusting the switching speed of the semiconductor switching element 3a when it is turned on. The first and second modifications also achieve the same effects as the configuration shown in FIG.

[0119] Next, an overview of the processing executed by the control unit 6 in the power conversion device according to this embodiment will be described. Fig. 28 is a flowchart showing an example of the processing executed by the control unit in the power conversion device according to this embodiment. The following describes semiconductor switching element 3a, but similar processing is also executed for other semiconductor switching elements.

[0120] In step S1 of FIG. 28, the control unit 6 acquires the detected temperature Tj_sens from the thermistor 4a.

[0121] Next, in step S2, the control unit 6 calculates the temperature rise rate of the detected temperature Tj_sens based on the detected temperature Tj_sens.

[0122] Next, in steps S3 and S4, the control unit 6 determines whether or not there is an abnormality in the cooler 8 based on the rate of temperature rise. In this embodiment, the cooler 8 is a liquid-cooled cooler. In this embodiment, the state of the cooler 8 determined by the control unit 6 is either a normal state in which the cooler 8 is not abnormal, or an abnormal state in which the coolant is leaking.

[0123] If it is determined that there is no abnormality in the cooler 8, the process of the control unit 6 returns to step S1. If it is determined that there is an abnormality in the cooler 8, the process of the control unit 6 proceeds to step S5.

[0124] In step S5, the control unit 6 reduces the switching speed of the semiconductor switching element 3a when it is turned on.

[0125] As described above, the power conversion device according to this embodiment includes the semiconductor switching element 3a, the liquid-cooling type cooler 8, the temperature sensor, and the control unit 6. The cooler 8 is configured to cool the semiconductor switching element 3a. The temperature sensor is configured to detect the temperature of the semiconductor switching element 3a. The control unit 6 has a gate drive circuit 6a. The gate drive circuit 6a is configured to drive the semiconductor switching element 3a at a variable switching speed.

[0126] The control unit 6 is configured to determine whether or not there is an abnormality in the cooler 8 based on the temperature Tj_sens detected by the temperature sensor, and to control the switching speed of the semiconductor switching element 3a when it is turned on based on the determination result. In this embodiment, the control unit 6 is configured to reduce the switching speed of the semiconductor switching element 3a when it is turned on if it is determined that there is an abnormality in the cooler 8.

[0127] If an abnormality occurs in the liquid-cooled cooler 8, the temperature of the semiconductor switching element 3a rises significantly, and an increase in the recovery surge voltage ΔV may cause the voltage Vds to exceed the withstand voltage of the semiconductor switching element 3a. With the above configuration, an abnormality in the cooler 8 can be detected earlier based on the detected temperature Tj_sens. Therefore, if an abnormality occurs in the cooler 8, the switching speed of the semiconductor switching element 3a when it is turned on can be reduced to prevent the voltage Vds from exceeding the withstand voltage of the semiconductor switching element 3a. Therefore, with the above configuration, it is possible to prevent failure of the semiconductor switching element 3a when an abnormality occurs in the cooler 8.

[0128] In the power conversion device according to this embodiment, the temperature sensor is a thermistor 4a provided outside the semiconductor switching element 3a.

[0129] This configuration allows the number of temperature measuring diodes provided in the same semiconductor chip as the semiconductor switching element 3a to be reduced, thereby reducing the element area of ​​the semiconductor switching element 3a and reducing the cost of the power conversion device.

[0130] In this embodiment, since an abnormality in the cooler 8 can be detected early based on the rate of temperature rise, even if there is a large difference between the junction temperature Tj and the detected temperature Tj_sens, protection operation for the semiconductor switching element 3a can be performed early. Therefore, even when a thermistor 4a is used as a temperature sensor, failure of the semiconductor switching element 3a can be suppressed.

[0131] In the power conversion device according to this embodiment, when the control unit 6 determines that there is no abnormality in the cooler 8 and the detected temperature Tj_sens is equal to or lower than the threshold temperature Tth, the control unit 6 sets the switching speed of the semiconductor switching element 3a when it is turned on to a first speed. When the control unit 6 determines that there is no abnormality in the cooler 8 and the detected temperature Tj_sens exceeds the threshold temperature Tth, the control unit 6 sets the switching speed of the semiconductor switching element 3a when it is turned on to a second speed that is lower than the first speed. When the control unit 6 determines that there is an abnormality in the cooler 8, the control unit 6 sets the switching speed of the semiconductor switching element 3a when it is turned on to the second speed.

[0132] According to this configuration, when the temperature of the semiconductor switching element 3a is high, the switching speed at which the semiconductor switching element 3a is turned on is reduced, thereby preventing the voltage Vds from exceeding the withstand voltage of the semiconductor switching element 3a. Furthermore, because the switching speed when the detected temperature Tj_sens is equal to or lower than the threshold temperature Tth is the same as the switching speed when an abnormality occurs in the cooler 8, the configuration of the gate drive circuit 6a can be simplified.

[0133] In the power conversion device according to this embodiment, the control unit 6 controls the switching speed by adjusting the gate resistance of the semiconductor switching element 3 a. As a result, the gate resistance of the semiconductor switching element 3 a when the switching speed is set to the first speed is lower than the gate resistance of the semiconductor switching element 3 a when the switching speed is set to the second speed.

[0134] According to this configuration, the switching speed of the semiconductor switching element 3a can be changed by switching the gate resistance of the semiconductor switching element 3a.

[0135] In the power conversion device according to this embodiment, the control unit 6 controls the switching speed by adjusting the gate voltage of the semiconductor switching element 3a. As a result, the gate voltage of the semiconductor switching element 3a when the switching speed is set to the first speed is higher than the gate voltage of the semiconductor switching element 3a when the switching speed is set to the second speed.

[0136] According to this configuration, the switching speed of the semiconductor switching element 3a can be changed by switching the gate voltage of the semiconductor switching element 3a.

[0137] In the power conversion device according to this embodiment, the control unit 6 determines that the cooler 8 has an abnormality when the temperature increase rate, which is the increase rate per hour of the detected temperature Tj_sens, exceeds the threshold increase rate TRth1.

[0138] When an abnormality occurs in the cooler 8, the rate of increase in the detected temperature Tj_sens increases more rapidly than the increase in the detected temperature Tj_sens. Therefore, with this configuration, an abnormality in the cooler 8 can be detected at an earlier stage.

[0139] In the power conversion device according to this embodiment, the threshold increase rate is set to a value higher than the temperature increase rate when the cooler 8 is not abnormal.

[0140] This configuration makes it difficult for erroneous detection of an abnormality in the cooler 8 to occur. Here, erroneous detection of an abnormality in the cooler 8 means that it is determined that there is an abnormality in the cooler 8 even though there is no abnormality in the cooler 8.

[0141] In the power conversion device according to this embodiment, the semiconductor switching element 3a is formed of a wide bandgap semiconductor.

[0142] When this embodiment is applied to a semiconductor switching element with low switching loss, such as a wide bandgap semiconductor element, a particularly high loss reduction effect can be obtained.

[0143] Embodiment 2 A description will be given of a power conversion device according to embodiment 2. The substantial circuit configuration of the power conversion device of this embodiment is the same as that of embodiment 1.

[0144] In the first embodiment, the presence or absence of an abnormality in the cooler 8 is determined based on the rate of temperature rise of the detected temperature Tj_sens, but in the present embodiment, the presence or absence of an abnormality in the cooler 8 is determined based on the detected temperature Tj_sens and the loss of the semiconductor switching element. In the present embodiment, similar to the first embodiment, the switching speed at the time of turn-on of the semiconductor switching element is adjusted based on the presence or absence of an abnormality in the cooler 8.

[0145] Furthermore, in this embodiment, the method of estimating the junction temperature Tj of the semiconductor switching element is switched depending on the state of the cooler 8. Therefore, even if the state of the cooler 8 changes, the junction temperature Tj can be accurately estimated, and the power conversion operation of the power conversion device can be safely continued.

[0146] Fig. 29 is a block diagram showing the configuration of a control unit in a power conversion device according to this embodiment. As shown in Fig. 29, the control unit 6 of this embodiment has a semiconductor switching element loss calculation unit 61, a cooler state determination unit 62, an inverter operation control unit 63, and a gate drive circuit 64. The semiconductor switching element loss calculation unit 61, the cooler state determination unit 62, and the inverter operation control unit 63 are functional blocks realized by, for example, a processor executing a program stored in a storage device.

[0147] The semiconductor switching element loss calculation unit 61 calculates the loss of each semiconductor switching element based on information such as the semiconductor switching element loss information 69. The semiconductor switching element loss calculation unit 61 outputs the loss of each semiconductor switching element obtained by calculation as a loss calculation value 65 of each semiconductor switching element.

[0148] The cooler state determination unit 62 estimates the state of the cooler 8 based on the loss calculation value 65 of each semiconductor switching element and the temperature detection values ​​of each thermistor 4a to 4f. The cooler state determination unit 62 outputs the estimated state of the cooler 8 as cooler state information 66.

[0149] The inverter operation control unit 63 generates gate control signals 67 that control the on / off of each semiconductor switching element based on the cooler state information 66. The inverter operation control unit 63 outputs the generated gate control signals 67 to the gate drive circuit 64. The inverter operation control unit 63 also outputs semiconductor switching element loss information 69 to the semiconductor switching element loss calculation unit 61.

[0150] The gate drive circuit 64 generates a gate drive signal 68 based on the gate control signal 67. The gate drive circuit 64 outputs the gate drive signal 68 to each semiconductor switching element.

[0151] Next, we will explain a method for estimating the state of the cooler 8. The cooler state determination unit 62 determines whether or not there is an abnormality in the cooler 8 based on the loss calculation value 65 of each semiconductor switching element and the temperature detection values ​​of each thermistor 4a to 4f.

[0152] The loss calculation value 65 is calculated by the semiconductor switching element loss calculation unit 61 based on semiconductor switching element loss information 69. The semiconductor switching element loss information 69 includes information such as the carrier frequency, switching-on time, current detection values ​​of the current sensor circuits 21a to 21c, voltage detection value of the voltage sensor circuit 20, and dead time value. The semiconductor switching element loss calculation unit 61 also stores in advance information on the loss characteristics of each semiconductor switching element and the loss characteristics of the body diode inside each semiconductor switching element. Based on this information, the semiconductor switching element loss calculation unit 61 calculates the conduction loss and switching loss for each semiconductor switching element and body diode. The semiconductor switching element loss calculation unit 61 outputs the sum of these conduction losses and switching losses as the loss calculation value 65.

[0153] Fig. 30 is a block diagram showing the configuration of a cooler state determination unit in the power conversion device according to this embodiment. As shown in Fig. 30, the cooler state determination unit 62 includes a temperature detection value holding unit 62A, a temperature detection value estimation unit 62B, an addition / subtraction method 62C, and a comparison determination unit 62D.

[0154] The temperature detection value holding unit 62A holds past temperature detection values. The temperature detection value estimation unit 62B estimates the current temperature detection value based on the past temperature detection value and the loss calculation value 65. The addition / subtraction method 62C calculates the difference between the estimated value of the current temperature detection value and the temperature detection values ​​of the thermistors 4a to 4f. The comparison / determination unit 62D determines the state of the cooler 8 based on the difference between the estimated value of the current temperature detection value and the temperature detection values ​​of the thermistors 4a to 4f.

[0155] Here, the cooler 8 in this embodiment is a liquid-cooled cooler. The state of the cooler 8 determined by the comparison and determination unit 62D is either a normal state in which the cooler 8 is not abnormal, or an abnormal state in which the cooler 8 is leaking the cooling medium.

[0156] The detected temperature value estimation unit 62B stores in advance the correlation between the detected temperature values ​​of the thermistors 4a-4f and the losses of the corresponding semiconductor switching elements 3a-3f. This correlation is for when the cooler 8 is in a normal state. The detected temperature value estimation unit 62B estimates the current detected temperature value that should be detected using the past detected temperature values ​​stored in the detected temperature value storage unit 62A, the current calculated loss value 65, and the above correlation. The detected temperature value that should be detected is the detected temperature value when the cooler 8 is in a normal state.

[0157] The comparison and determination unit 62D is set with a threshold value for the difference between the estimated value of the current temperature detection value and the temperature detection values ​​of the thermistors 4a to 4f. If the difference is equal to or less than the threshold value, the comparison and determination unit 62D determines that there is no abnormality in the cooler 8. If the difference exceeds the threshold value, the comparison and determination unit 62D determines that there is an abnormality in the cooler 8. Based on the result of the determination, the comparison and determination unit 62D outputs information indicating whether or not there is an abnormality in the cooler 8 as cooler status information 66.

[0158] The correlation between the temperature detection values ​​of the thermistors 4a to 4f and the losses of the corresponding semiconductor switching elements 3a to 3f is approximated by a lag element of zeroth order or higher. When the purpose is protection during steady-state operation, where time factors do not need to be considered, a zeroth order approximation, i.e., an approximation using only thermal resistance, is sufficient, thereby reducing the processing load on the control unit 6. When the inverter output fluctuations are large and time factors need to be considered, an approximation using a lag element of first order or higher, i.e., an approximation using thermal resistance and heat capacity, is desirable. The higher the order of the lag element, the more accurately the correlation can be approximated, but the greater the processing load on the control unit 6. For this reason, it is desirable to appropriately set the order of the lag element, taking into account the accuracy of the correlation and the processing load on the control unit 6.

[0159] This allows the control unit 6 to estimate the state of the cooler 8 so as to accurately follow the time-dependent output change of the inverter while suppressing the processing load.

[0160] Next, a method for adjusting the switching speed of a semiconductor switching element when it is turned on in this embodiment will be described using the semiconductor switching element 3a as an example. If there is no abnormality in the cooler 8, the control unit 6 determines that the temperature of the semiconductor switching element 3a is high when the temperature detection value of the thermistor 4a exceeds a preset threshold. In this case, the control unit 6 switches the gate resistance of the gate drive circuit 6a so that the switching speed of the semiconductor switching element 3a when it is turned on decreases. This threshold is set for the purposes of protective operation when a predetermined operating range is exceeded and improving inverter efficiency, assuming that there is no abnormality in the cooler 8.

[0161] If it is determined based on the cooler status information 66 that there is an abnormality in the cooler 8, the control unit 6 switches the gate resistance of the gate drive circuit 6a so as to reduce the switching speed of the semiconductor switching element 3a when it is turned on. This process is the same as the process performed when it is determined that the temperature of the semiconductor switching element 3a is high. Thereafter, the control unit 6 performs protective operations such as reducing the output of the inverter and stopping the inverter, as in the case after time t3 in FIG. 19 .

[0162] Next, a modified example of this embodiment will be described. This modified example differs from the configuration shown in Figures 29 and 30 in that a junction temperature calculation unit is added to the control unit 6, and that the control unit 6 performs a protection operation based on the calculated junction temperature value. The following description will focus on the differences from the configurations shown in Figures 29 and 30.

[0163] Fig. 31 is a block diagram showing the configuration of a control unit in a power conversion device according to this modification. Fig. 32 is a block diagram showing the configuration of a junction temperature calculation unit in a power conversion device according to this modification.

[0164] As shown in FIG. 31, the control unit 6 of this modified example further includes a junction temperature calculation unit 70 in addition to a semiconductor switching element loss calculation unit 61, a cooler state determination unit 62, an inverter operation control unit 63, and a gate drive circuit 64.

[0165] As shown in FIG. 32, the junction temperature calculation section 70 includes a junction temperature rise characteristics selection section 70A, a junction temperature rise calculation section 70B, and an adder / subtractor 70C.

[0166] Before describing the function and operation of the control unit 6, the information added in this modification will be described. The output signal of the junction temperature calculation unit 70 is a junction temperature calculation value 71. The output signal of the junction temperature rise characteristic selection unit 70A is a junction temperature rise characteristic 71A. The output signal of the junction temperature rise calculation unit 70B is a junction temperature rise value 71B.

[0167] The semiconductor switching element loss calculation unit 61 calculates the loss of each semiconductor switching element based on information such as semiconductor switching element loss information 69 from the inverter operation control unit 63. The semiconductor switching element loss calculation unit 61 outputs the loss of each semiconductor switching element obtained by calculation as a loss calculation value 65 of each semiconductor switching element.

[0168] The cooler state determination unit 62 estimates the state of the cooler 8 based on the loss calculation value 65 of each semiconductor switching element and the temperature detection values ​​of each thermistor 4a to 4f. The cooler state determination unit 62 outputs the estimated state of the cooler 8 as cooler state information 66.

[0169] Inputs to the inverter operation control unit 63 are cooler state information 66 from the cooler state determination unit 62, voltage information from the voltage sensor circuit 20, current information from the current sensor circuits 21a to 21c, and a junction temperature calculation value 71 from a junction temperature calculation unit 70. Based on these inputs, the inverter operation control unit 63 generates gate control signals 67 that control the on / off of each semiconductor switching element. The inverter operation control unit 63 outputs the generated gate control signals 67 to a gate drive circuit 64. Furthermore, the inverter operation control unit 63 outputs semiconductor switching element loss information 69 to the semiconductor switching element loss calculation unit 61.

[0170] The gate drive circuit 64 converts the gate control signal 67 into a gate drive signal 68. The gate drive circuit 64 outputs the gate drive signal 68 to each semiconductor switching element.

[0171] The inputs to the junction temperature calculation unit 70 are cooler state information 66 from the cooler state determination unit 62, loss calculation values ​​65 of each semiconductor switching element from the semiconductor switching element loss calculation unit 61, and temperature detection values ​​of each thermistor 4a to 4f. Based on these inputs, the junction temperature calculation unit 70 outputs a junction temperature calculation value 71.

[0172] A description will now be given of a method for calculating the junction temperature in the junction temperature calculation unit 70. The junction temperature calculation unit 70 calculates the junction temperature of each semiconductor switching element based on the above inputs.

[0173] Here, the junction temperature calculation value 71 output by the junction temperature calculation unit 70 can be fed back and input to the semiconductor switching element loss calculation unit 61. By inputting the junction temperature calculation value 71 to the semiconductor switching element loss calculation unit 61, it is possible to add junction temperature dependency to the loss characteristics of the semiconductor switching elements and diodes that are stored in advance in the semiconductor switching element loss calculation unit 61. This allows the semiconductor switching element loss calculation unit 61 to calculate the loss of each semiconductor switching element more accurately.

[0174] Next, the function of the junction temperature calculation unit 70 will be described with reference to Fig. 32. Cooler state information 66 is input to the junction temperature rise characteristic selection unit 70A from the cooler state determination unit 62. Based on the cooler state information 66, the junction temperature rise characteristic selection unit 70A selects a junction temperature rise characteristic 71A that corresponds to the state of the cooler 8.

[0175] Junction temperature rise calculation unit 70B receives junction temperature rise characteristic 71A from junction temperature rise characteristic selection unit 70A and loss calculation value 65 of each semiconductor switching element from semiconductor switching element loss calculation unit 61. Junction temperature rise calculation unit 70B calculates junction temperature rise value 71B based on junction temperature rise characteristic 71A and loss calculation value 65 of each semiconductor switching element.

[0176] Adder-subtractor 70C adds junction temperature rise value 71B from junction temperature rise calculation unit 70B and the temperature detection values ​​of each of the thermistors 4a to 4f, thereby obtaining calculated junction temperatures 71 for each of thermistors 4a to 4f.

[0177] Here, the cooler 8 in this modified example is a liquid-cooled cooler. The state of the cooler 8 determined by the comparison / determination unit 62D is either a normal state in which the cooler 8 is not abnormal, or an abnormal state in which the coolant is leaking. Furthermore, the junction temperature rise characteristic 71A selected by the junction temperature rise characteristic selection unit 70A is either a temperature rise characteristic when the cooler 8 is in a normal state, or a temperature rise characteristic when the cooler 8 is in an abnormal state.

[0178] The junction temperature rise characteristics selection unit 70A stores in advance the correlation between the temperature difference between the temperature detection value of each thermistor 4a-4f and the junction temperature of the corresponding semiconductor switching element 3a-3f, and the loss of the corresponding semiconductor switching element 3a-3f, for each state of the cooler 8. Based on the cooler state information 66, the junction temperature rise characteristics selection unit 70A selects and outputs an appropriate correlation.

[0179] The above correlation is approximated by a delay element of zeroth order or higher for the same reason as the correlation between the temperature detection values ​​of the thermistors 4a to 4f and the losses of the corresponding semiconductor switching elements 3a to 3f.

[0180] As described above, in this modification, the junction temperature of each of the semiconductor switching elements 3a to 3f can be estimated more accurately even if the state of the cooler 8 changes. Therefore, even if the cooler 8 goes into an abnormal state, by monitoring the junction temperature of each of the semiconductor switching elements 3a to 3f, it is possible to reliably perform protection operations for each of the semiconductor switching elements 3a to 3f.

[0181] As described above, the power conversion device according to this embodiment further includes current sensor circuits 21a to 21c and voltage sensor circuit 20. Current sensor circuits 21a to 21c detect the current flowing through semiconductor switching element 3a. Voltage sensor circuit 20 detects the voltage applied to semiconductor switching element 3a.

[0182] The control unit 6 has a semiconductor switching element loss calculation unit 61 and a cooler state determination unit 62. The semiconductor switching element loss calculation unit 61 calculates a loss calculation value 65 of the semiconductor switching element 3a using at least the detection values ​​of the current sensor circuits 21a to 21c and the detection value of the voltage sensor circuit 20. The cooler state determination unit 62 determines whether or not there is an abnormality in the cooler 8 based on the loss calculation value 65 and the detected temperature.

[0183] According to this configuration, it is possible to determine whether or not there is an abnormality in the cooler 8 based on the loss calculation value 65 and the detected temperature, so that even if an abnormality occurs in the cooler 8, the protection operation for the semiconductor switching element 3a can be performed more reliably.

[0184] In the power conversion device according to this embodiment, cooler state determination unit 62 includes detected temperature value estimation unit 62B and comparison / determination unit 62D. Detected temperature value estimation unit 62B calculates a detected temperature estimated value, which is an estimated value of the detected temperature, based on past detected temperatures and calculated loss value 65. Comparison / determination unit 62D compares the estimated detected temperature value with the detected temperature detected by the thermistor to determine whether or not there is an abnormality in cooler 8.

[0185] According to this configuration, it is possible to more appropriately determine whether or not the cooler 8 has an abnormality.

[0186] In the power conversion device according to this embodiment, the control unit 6 further includes a junction temperature calculation unit 70 that estimates the junction temperature of the semiconductor switching element 3a based on the loss calculation value 65, the state of the cooler 8, and the temperature detected by the thermistor.

[0187] According to this configuration, the junction temperature of the semiconductor switching element 3a can be estimated more accurately, so that even if an abnormality occurs in the cooler 8, the protection operation for the semiconductor switching element 3a can be reliably performed based on the junction temperature.

[0188] Embodiment 3 A description will be given of a power conversion device according to embodiment 3. The substantial circuit configuration of the power conversion device of this embodiment is the same as that of embodiment 1.

[0189] In the first and second embodiments, when an abnormality occurs in the cooler 8, the switching speed is suppressed so that a recovery surge does not cause the voltage Vds to exceed the breakdown voltage of the element. In contrast, in the present embodiment, even when an abnormality occurs in the cooler 8, a protective operation is performed that takes into consideration reducing the loss of the inverter as much as possible.

[0190] In this embodiment, when the control unit 6 determines that there is an abnormality in the cooler 8, the inverter output current is reduced to a predetermined load or less, while continuing high-speed switching without reducing the switching speed of the semiconductor switching elements. Because the temperature difference between the junction temperature Tj and the detected temperature Tj_sens is uniquely determined by reducing the output current, the control unit 6 can more accurately estimate the junction temperature Tj based on the detected temperature Tj_sens. This allows the switching speed of the semiconductor switching elements to be maintained at a high speed until the junction temperature Tj reaches a high temperature.

[0191] By maintaining a high switching speed, the loss of the semiconductor switching elements is reduced, and the temperature of the semiconductor switching elements is less likely to become high. As a result, even if there is an abnormality in the cooler 8, low loss in the power conversion device can be achieved.

[0192] However, when the detected temperature Tj_sens of the thermistor exceeds the threshold temperature Tth, the control unit 6 reduces the switching speed at the time of turning on the semiconductor switching element by switching the gate resistor, etc. Thereafter, the control unit 6 performs protective operations such as reducing the output of the inverter and stopping the inverter, similar to the operations after time t3 in FIG.

[0193] For example, when the control unit 6 determines that the cooler 8 has an abnormality and the detected temperature Tj_sens is equal to or lower than the threshold temperature Tth, the control unit 6 sets the switching speed of the semiconductor switching elements when they are turned on to a relatively high value and reduces the output current of the inverter. When the control unit 6 determines that the cooler 8 has an abnormality and the detected temperature Tj_sens exceeds the threshold temperature Tth, the control unit 6 sets the switching speed of the semiconductor switching elements when they are turned on to a relatively low value.

[0194] As described above, in this embodiment, when an abnormality occurs in the cooler 8, the output current of the inverter is reduced while the switching speed of the semiconductor switching elements is maintained at a high value. However, there are cases where a reduction in the output current of the inverter is not permitted due to requirements from the vehicle. In such cases, the control unit 6 may control the switching speed based on the output current of the inverter.

[0195] For example, when the control unit 6 determines that the cooler 8 has an abnormality, and the output current is equal to or lower than a preset threshold current and the detected temperature Tj_sens is equal to or lower than the threshold temperature Tth, the control unit 6 sets the switching speed of the semiconductor switching element at turn-on to a relatively high value. When the control unit 6 determines that the cooler 8 has an abnormality, and the output current is higher than the threshold current or the detected temperature Tj_sens is higher than the threshold temperature Tth, the control unit 6 sets the switching speed of the semiconductor switching element at turn-on to a relatively low value.

[0196] As described above, in the power conversion device according to this embodiment, when the control unit 6 determines that there is no abnormality in the cooler 8 and the detected temperature Tj_sens is equal to or lower than the threshold temperature Tth, the control unit 6 sets the switching speed at turn-on of the semiconductor switching element 3a to the first speed. When the control unit 6 determines that there is no abnormality in the cooler 8 and the detected temperature Tj_sens exceeds the threshold temperature Tth, the control unit 6 sets the switching speed at turn-on of the semiconductor switching element 3a to the second speed, which is lower than the first speed.

[0197] When the control unit 6 determines that there is an abnormality in the cooler 8, if the detected temperature Tj_sens is equal to or lower than the threshold temperature Tth, it sets the switching speed of the semiconductor switching element 3a when it is turned on to the first speed and reduces the output current of the power conversion device.

[0198] According to this configuration, even if there is an abnormality in the cooler 8, the loss in the power conversion device can be reduced as much as possible, and therefore the electricity cost or fuel efficiency can be improved.

[0199] In the power conversion device according to this embodiment, when the control unit 6 determines that there is no abnormality in the cooler 8 and the detected temperature Tj_sens is equal to or lower than the threshold temperature Tth, the control unit 6 sets the switching speed at turn-on of the semiconductor switching element 3a to a first speed. When the control unit 6 determines that there is no abnormality in the cooler 8 and the detected temperature Tj_sens exceeds the threshold temperature Tth, the control unit 6 sets the switching speed at turn-on of the semiconductor switching element 3a to a second speed lower than the first speed.

[0200] When the control unit 6 determines that there is an abnormality in the cooler 8, if the output current of the power conversion device is equal to or less than the threshold current and the detected temperature Tj_sens is equal to or less than the threshold temperature Tth, the control unit 6 sets the switching speed at the time of turning on the semiconductor switching element 3a to the above-mentioned first speed.

[0201] According to this configuration, even if there is an abnormality in the cooler 8, the loss in the power conversion device can be reduced as much as possible, and therefore the electricity cost or fuel efficiency can be improved.

[0202] In the above embodiment, the power conversion device is described as an inverter circuit, but the power conversion device may be a converter circuit.

[0203] In the above embodiment, a liquid-cooled cooler is used as the cooler 8, but the cooler 8 is not limited to a liquid-cooled type. The cooler 8 may be an air-cooled cooler. For example, if the fan of an air-cooled cooler breaks down, the cooling performance will decrease and the element temperature will rise. Therefore, the same effect can be obtained even if the above embodiment is applied to a power conversion device equipped with an air-cooled cooler.

[0204] In the above embodiment, a state in which the cooling medium in the cooler 8 has disappeared has been given as an example of a state in which the cooler 8 is abnormal, but this is not limiting. States in which the cooler 8 is abnormal also include a state in which a portion of the cooling medium has disappeared, a state in which the electric pump has broken down and the circulation of the cooling medium has stopped, etc.

[0205] In the above-described first embodiment, the presence or absence of an abnormality in the cooler 8 is determined based on the rate of temperature rise of the detected temperature Tj_sens. In the above-described second embodiment, the presence or absence of an abnormality in the cooler 8 is determined based on the detected temperature Tj_sens and the loss of the semiconductor switching element. Which of the first and second embodiments is better depends on the load processing status of the microcomputer, the load on the vehicle, etc. Therefore, the control unit 6 may be configured to switch what is used to determine the presence or absence of an abnormality in the cooler 8.

[0206] For example, if any of the voltage sensor circuit 20 and the current sensor circuits 21a to 21c is faulty, the loss of the semiconductor switching element cannot be calculated. Therefore, the control unit 6 cannot determine whether or not there is an abnormality in the cooler 8 based on the detected temperature Tj_sens and the loss of the semiconductor switching element. Therefore, in this case, the control unit 6 determines whether or not there is an abnormality in the cooler 8 based on the rate of temperature rise of the detected temperature Tj_sens.

[0207] In the above embodiment, the number of chips inside each of the semiconductor modules 5a to 5f may be one or more than two, and the number of semiconductor modules may be one or more than two.

[0208] In the above embodiment, each of the semiconductor switching elements 3a to 3f has an internal diode, but this is not limiting. A diode provided separately from each of the semiconductor switching elements 3a to 3f may be connected in parallel to each of the semiconductor switching elements 3a to 3f.

[0209] In the above embodiment, each of the semiconductor switching elements 3a to 3f is configured by a MOSFET, but each of the semiconductor switching elements 3a to 3f may be configured by an IGBT (Insulated Gate Bipolar Transistor) and a diode.

[0210] In the above embodiment, a thermistor provided outside the semiconductor switching element is used as an example of a temperature sensor, but the temperature sensor may also be a temperature measuring diode provided within the same semiconductor chip as the semiconductor switching element.

[0211] The above-described embodiments can be implemented in combination with each other.

[0212] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0213] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) a semiconductor switching element; a liquid-cooling type cooler that cools the semiconductor switching element; a temperature sensor for detecting the temperature of the semiconductor switching element; a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed; Equipped with The control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls the switching speed of the semiconductor switching element when it is turned on based on the determination result. (Appendix 2) 2. The power conversion device according to claim 1, wherein the temperature sensor is a thermistor provided outside the semiconductor switching element. (Appendix 3) 3. The power conversion device according to claim 1, wherein the control unit reduces the switching speed when it determines that an abnormality has occurred in the cooler. (Appendix 4) The control unit When it is determined that there is no abnormality in the cooler, if the detected temperature is equal to or lower than a threshold temperature, the switching speed is set to a first speed, and if the detected temperature exceeds the threshold temperature, the switching speed is set to a second speed lower than the first speed; 4. The power conversion device according to claim 1, wherein the switching speed is set to the second speed when it is determined that an abnormality occurs in the cooler. (Appendix 5) 5. The power conversion device according to claim 4, wherein the control unit controls the switching speed by adjusting a gate resistance of the semiconductor switching element. (Appendix 6) 5. The power conversion device according to claim 4, wherein the control unit controls the switching speed by adjusting a gate voltage of the semiconductor switching element. (Appendix 7) The power conversion device according to any one of Supplementary Note 1 to Supplementary Note 6, wherein the control unit determines that there is an abnormality in the cooler when a temperature rise rate, which is a rate of rise per unit time of the detected temperature, exceeds a threshold rise rate. (Appendix 8) 8. The power conversion device according to claim 7, wherein the threshold increase rate is set to a value higher than a temperature increase rate when the cooler is normal. (Appendix 9) a current sensor circuit for detecting a current flowing through the semiconductor switching element; a voltage sensor circuit for detecting a voltage applied to the semiconductor switching element; Furthermore, The control unit a semiconductor switching element loss calculation unit that calculates a loss calculation value of the semiconductor switching element using at least the detection value of the current sensor circuit and the detection value of the voltage sensor circuit; The power conversion device according to any one of Supplementary Note 1 to Supplementary Note 8, further comprising: a cooler state determination unit that determines whether or not the cooler is abnormal based on the loss calculation value and the detected temperature. (Appendix 10) The cooler state determination unit a detected temperature value estimation unit that calculates an estimated detected temperature value that is an estimated value of the detected temperature based on the past detected temperature and the calculated loss value; 10. The power conversion device according to claim 9, further comprising a comparison and determination unit that compares the estimated detected temperature value with the detected temperature detected by the temperature sensor to determine whether or not there is an abnormality in the cooler. (Appendix 11) The control unit 11. The power conversion device according to claim 9 or 10, further comprising a junction temperature calculation unit that estimates a junction temperature of the semiconductor switching element based on the loss calculation value, a state of the cooler, and the detected temperature. (Appendix 12) The control unit When it is determined that there is no abnormality in the cooler, if the detected temperature is equal to or lower than a threshold temperature, the switching speed is set to a first speed, and if the detected temperature exceeds the threshold temperature, the switching speed is set to a second speed lower than the first speed; 3. The power conversion device according to claim 1, wherein when it is determined that there is an abnormality in the cooler, if the output current of the power conversion device is equal to or less than a threshold current and the detected temperature is equal to or less than the threshold temperature, the switching speed is set to the first speed. (Appendix 13) The control unit When it is determined that there is no abnormality in the cooler, if the detected temperature is equal to or lower than a threshold temperature, the switching speed is set to a first speed, and if the detected temperature exceeds the threshold temperature, the switching speed is set to a second speed lower than the first speed; 3. The power conversion device according to claim 1, wherein, when it is determined that there is an abnormality in the cooler, if the detected temperature is equal to or lower than the threshold temperature, the switching speed is set to the first speed and the output current of the power conversion device is reduced. (Appendix 14) 14. The power conversion device according to any one of claims 1 to 13, wherein the semiconductor switching elements are formed of wide bandgap semiconductors. [Explanation of symbols]

[0214] 1 DC input power supply, 2 smoothing capacitor, 3a, 3b, 3c, 3d, 3e, 3f semiconductor switching element, 4a, 4b, 4c, 4d, 4e, 4f thermistor, 5a, 5b, 5c, 5d, 5e, 5f semiconductor module, 6 control unit, 6a gate drive circuit, 6b drive circuit main body, 6c gate resistance switching circuit, 6d bypass circuit, 7 motor, 8 cooler, 8a surface, 8b cooling medium flow path, 20 voltage sensor circuit, 21a, 21b, 21c current sensor circuit, 31a, 31b, 31c, 31d signal line, 32a, 32b, 32c, 32d, 32e, 32f control line, 33a, 33b, 33c, 33d, 33e, 33f signal line, 41 bus bar, 42 solder layer, 43 Substrate, 43a, 43b surface, 44 resin molded body, 45 insulating member, 50a, 50b, 51a, 51b, 52a, 52b, 52c, 53a, 53b, 54a, 54b, 54c thermal resistance, 61 semiconductor switching element loss calculation unit, 62 cooler state determination unit, 62A temperature detection value holding unit, 62B temperature detection value estimation unit, 62C addition and subtraction method, 62D comparison determination unit, 63 inverter operation control unit, 64 gate drive circuit, 65 loss calculation value, 66 cooler state information, 67 gate control signal, 68 gate drive signal, 69 semiconductor switching element loss information, 70 junction temperature calculation unit, 70A junction temperature rise characteristics selection unit, 70B junction temperature rise calculation unit, 70C adder / subtractor, 71 junction temperature calculation value, 71A Junction temperature rise characteristics, 71B junction temperature rise value, G gate section, Ids current, Rgoff resistance, Rgon1 resistance, Rgon2 resistance, SW switching element, T1 temperature, T2 temperature, Tj junction temperature, Tj_sens detection temperature, Tth threshold temperature, TR1 temperature rise rate, TRth1 threshold rise rate, TRth2 threshold rise rate, Vds voltage, Vg variable voltage source, Vu, Vv, Vw 3-phase output terminals, t0, t1, t2, t3, t4, t5, t6, t7 times, Zdiode Zener diode, Δt10 threshold time, ΔT2 temperature difference, ΔV recovery surge voltage.

Claims

1. a semiconductor switching element; a liquid-cooling type cooler that cools the semiconductor switching element; a temperature sensor for detecting the temperature of the semiconductor switching element; a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed; Equipped with the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls a switching speed at the time of turning on the semiconductor switching element based on the determination result; The control unit When it is determined that there is no abnormality in the cooler, if the detected temperature is equal to or lower than a threshold temperature, the switching speed is set to a first speed, and if the detected temperature exceeds the threshold temperature, the switching speed is set to a second speed lower than the first speed; The power conversion device sets the switching speed to the second speed when it is determined that an abnormality has occurred in the cooler.

2. 2. The power conversion device according to claim 1, wherein the temperature sensor is a thermistor provided outside the semiconductor switching element.

3. The power conversion device according to claim 1 , wherein the control unit reduces the switching speed when it determines that the cooler has an abnormality.

4. 4. The power conversion device according to claim 1, wherein the control unit controls the switching speed by adjusting a gate resistance of the semiconductor switching element.

5. 4. The power conversion device according to claim 1, wherein the control unit controls the switching speed by adjusting a gate voltage of the semiconductor switching element.

6. The power conversion device according to any one of claims 1 to 3, wherein the control unit determines that there is an abnormality in the cooler when a temperature rise rate, which is the rate of rise per unit time of the detected temperature, exceeds a threshold rise rate.

7. The power conversion device according to claim 6 , wherein the threshold increase rate is set to a value higher than a temperature increase rate when the cooler is normal.

8. a current sensor circuit for detecting a current flowing through the semiconductor switching element; a voltage sensor circuit for detecting a voltage applied to the semiconductor switching element; Furthermore, The control unit a semiconductor switching element loss calculation unit that calculates a loss calculation value of the semiconductor switching element using at least the detection value of the current sensor circuit and the detection value of the voltage sensor circuit; The power conversion device according to any one of claims 1 to 3, further comprising a cooler state determination unit that determines whether or not the cooler is abnormal based on the loss calculation value and the detected temperature.

9. The cooler state determination unit a detected temperature value estimation unit that calculates an estimated detected temperature value that is an estimated value of the detected temperature based on the past detected temperature and the calculated loss value; The power conversion device according to claim 8 , further comprising a comparison and determination unit that compares the estimated detected temperature value with the detected temperature detected by the temperature sensor to determine whether or not the cooler is abnormal.

10. The control unit 9. The power conversion device according to claim 8, further comprising a junction temperature calculation unit that estimates a junction temperature of the semiconductor switching element based on the calculated loss value, a state of the cooler, and the detected temperature.

11. a semiconductor switching element; a liquid-cooling type cooler that cools the semiconductor switching element; a temperature sensor for detecting the temperature of the semiconductor switching element; a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed; Equipped with the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls a switching speed at the time of turning on the semiconductor switching element based on the determination result; The control unit When it is determined that there is no abnormality in the cooler, if the detected temperature is equal to or lower than a threshold temperature, the switching speed is set to a first speed, and if the detected temperature exceeds the threshold temperature, the switching speed is set to a second speed lower than the first speed; When it is determined that there is an abnormality in the cooler, if the output current of the power conversion device is equal to or less than a threshold current and the detected temperature is equal to or less than the threshold temperature, the power conversion device sets the switching speed to the first speed.

12. a semiconductor switching element; a liquid-cooling type cooler that cools the semiconductor switching element; a temperature sensor for detecting the temperature of the semiconductor switching element; a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed; Equipped with the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls a switching speed at the time of turning on the semiconductor switching element based on the determination result; The control unit When it is determined that there is no abnormality in the cooler, if the detected temperature is equal to or lower than a threshold temperature, the switching speed is set to a first speed, and if the detected temperature exceeds the threshold temperature, the switching speed is set to a second speed lower than the first speed; When it is determined that there is an abnormality in the cooler, if the detected temperature is equal to or lower than the threshold temperature, the power conversion device sets the switching speed to the first speed and reduces the output current of the power conversion device.

13. The power conversion device according to any one of claims 1 to 3, wherein the semiconductor switching elements are formed of wide bandgap semiconductors.

14. a semiconductor switching element; a liquid-cooling type cooler that cools the semiconductor switching element; a temperature sensor for detecting the temperature of the semiconductor switching element; a control unit having a gate drive circuit that drives the semiconductor switching element at a variable switching speed; a current sensor circuit for detecting a current flowing through the semiconductor switching element; a voltage sensor circuit for detecting a voltage applied to the semiconductor switching element; Equipped with the control unit determines whether or not there is an abnormality in the cooler based on the temperature detected by the temperature sensor, and controls a switching speed at the time of turning on the semiconductor switching element based on the determination result; The control unit a semiconductor switching element loss calculation unit that calculates a loss calculation value of the semiconductor switching element using at least the detection value of the current sensor circuit and the detection value of the voltage sensor circuit; a cooler state determination unit that determines whether or not the cooler is abnormal based on the loss calculation value and the detected temperature.

Images