Power conversion device

Abstract

This power conversion device (100) comprises: a power conversion circuit (25) in which positive electrode-side switching elements (51, 53, 55), negative electrode-side switching elements (52, 54, 56), and connection points at which the switching elements are connected in series are connected to a rotary electric machine (10); temperature detectors (71-76) that detect the temperatures of the switching elements (51-56); and a control unit (90), wherein the control unit (90) limits the output of the power conversion circuit (25) when the detected temperature (Ts) is higher than a limit temperature (Tlmt), performs overheat prevention control for stopping power conversion when the detected temperature (Ts) is higher than a stop temperature (Tstp), and changes the stop temperature (Tstp) on the basis of the drive state of the power conversion device (100).

Description

Power conversion device

[0001] The present disclosure relates to a power conversion device.

[0002] As a power conversion device that converts the output form of electric power, an AC / DC converter (Alternate Current Direct Current Converter) that converts alternating current power into direct current power, an inverter that converts direct current power into alternating current power, a DC / DC converter that changes the levels of the input voltage and input current, etc. are common. These power conversion devices often have a configuration including switching elements.

[0003] As a method for preventing the overheating state of the switching element of a power conversion device, a temperature detector capable of detecting the temperature of the switching element is provided, and when the detected temperature exceeds a predetermined limit temperature, the output of the power conversion device is restricted. Then, after restricting the output, when the temperature further rises and exceeds a predetermined stop temperature, the output of the power conversion device is stopped. A power conversion device having a function of protecting the switching element so as not to exceed the operating limit temperature by controlling in such a manner has been proposed. (For example, Patent Document 1).

[0004] Patent No. 6323221

[0005] In order to surely prevent the overheating state of the switching element of a power conversion device, it is necessary to protect the switching element so as not to exceed the operating limit temperature under all driving conditions and ambient environmental conditions that the power conversion device can take. In the technique disclosed in Patent Document 1, the temperature at which current limiting starts is changed according to the output of the motor control device, but the stop temperature at which current is cut off is not changed. Therefore, when the temperature difference between the detected temperature detected by the temperature detector and the element temperature of the actual switching element becomes large, there is a case where current is cut off unnecessarily early although there is a margin in the element temperature.

[0006] This disclosure provides technology to solve the above-mentioned problems. The objective is to provide a power converter that limits the output of the power converter when the detected temperature exceeds a predetermined limit temperature, which can more appropriately determine the overheating state of the switching element, reliably prevent deterioration of the switching element, and prevent the power converter from stopping its output excessively early.

[0007] The power conversion device of this disclosure includes a power conversion circuit having a leg provided with a positive-side switching element connected to the positive side of a DC power supply, a negative-side switching element connected to the negative side of a DC power supply, and a power supply line connecting the connection point where the positive-side switching element and the negative-side switching element are connected in series to a rotating electric machine; a temperature detector for detecting the temperature of the switching elements; and a control unit that controls the switching elements of the power conversion circuit to perform power conversion, limits the output of the power conversion circuit when the temperature detected by the temperature detector is higher than a predetermined limit temperature, and stops power conversion when the temperature detected by the temperature detector is higher than a stop temperature set higher than the limit temperature, wherein the control unit changes the stop temperature based on the driving state of the power conversion device.

[0008] This disclosure relates to a power converter that limits the output of the power converter when the detected temperature exceeds a predetermined limit temperature, and sets the stop temperature based on the operating state of the power converter. By doing so, it is possible to provide a power converter that can more appropriately determine the overheating state of the switching element and prevent deterioration of the switching element by cutting off the current when the detected temperature exceeds the stop temperature, while also preventing the power converter from stopping its output excessively early. This allows the power converter to continue operating up to its performance limit, and enables improved performance of the power converter.

[0009] This is a diagram showing the configuration of the power converter according to Embodiment 1. This is a hardware configuration diagram of the control unit of the power converter according to Embodiment 1. This is a functional block diagram of the control unit of the power converter according to Embodiment 1. This is a first time chart showing the changes in the detected temperature and element temperature of the power converter according to Embodiment 1. This is a second time chart showing the changes in the detected temperature and element temperature of the power converter according to Embodiment 1. This is a diagram showing the characteristics of the phase current with respect to the rotational speed at maximum torque after output limiting of the power converter according to Embodiment 1. This is a first diagram showing the setting of the stop temperature with respect to the rotational speed of the power converter according to Embodiment 1. This is a second diagram showing the setting of the stop temperature with respect to the rotational speed of the power converter according to Embodiment 1. This is a third time chart showing the changes in the detected temperature and element temperature of the power converter according to Embodiment 1. This is a first diagram showing the setting of the stop temperature with respect to the phase current of the power converter according to Embodiment 1. This is a second diagram showing the setting of the stop temperature with respect to the phase current of the power converter according to Embodiment 1. This is a first diagram showing the setting of the stop temperature with respect to the DC voltage of the power converter according to Embodiment 1. This is a second diagram showing the setting of the stop temperature with respect to the DC voltage of the power converter according to Embodiment 1. This is the first figure showing the setting of the stop temperature with respect to the carrier frequency of the power converter according to Embodiment 1. This is the second figure showing the setting of the stop temperature with respect to the carrier frequency of the power converter according to Embodiment 1. This is the first figure showing the setting of the stop temperature with respect to the gate resistance value of the power converter according to Embodiment 1. This is the second figure showing the setting of the stop temperature with respect to the gate resistance value of the power converter according to Embodiment 1. This is the first figure showing the setting of the stop temperature with respect to the dead time of the power converter according to Embodiment 1. This is the second figure showing the setting of the stop temperature with respect to the dead time of the power converter according to Embodiment 1. This is the first figure showing the setting of the stop temperature with respect to the flow rate of the power converter according to Embodiment 1. This is the second figure showing the setting of the stop temperature with respect to the flow rate of the power converter according to Embodiment 1. This is the first figure showing the setting of the stop temperature with respect to the water temperature of the power converter according to Embodiment 1. This is the second figure showing the setting of the stop temperature with respect to the water temperature of the power converter according to Embodiment 1. This is the first figure showing the setting of the stop temperature with respect to the temperature difference of the power converter according to Embodiment 1.This is a second diagram showing the setting of the stop temperature in relation to the temperature difference of the power converter according to Embodiment 1. This is a first diagram showing the setting of the stop temperature in relation to the loss of the power converter according to Embodiment 1. This is a second diagram showing the setting of the stop temperature in relation to the loss of the power converter according to Embodiment 1. This is a first flowchart showing the processing of the control unit of the power converter according to Embodiment 1. This is a second flowchart showing the processing of the control unit of the power converter according to Embodiment 1. This is a third flowchart showing the processing of the control unit of the power converter according to Embodiment 1. This is a functional block diagram of the control unit of the power converter according to Embodiment 2. This is a diagram showing the setting of the stop temperature in relation to the rotational speed of the power converter according to Embodiment 2. This is a flowchart showing the processing of the control unit of the power converter according to Embodiment 2.

[0010] Hereinafter, preferred embodiments of the rotating electric machine control device according to the present application will be described with reference to the drawings. In each figure, the same or corresponding parts will be denoted by the same reference numerals.

[0011] 1. Embodiment 1

[0012] <Configuration of the Power Converter> Figure 1 is a configuration diagram of the power converter 100 according to Embodiment 1. The power converter 100 may be used in electric vehicles such as electric vehicles and plug-in hybrid vehicles. The power converter 100 may be intended for use in driving a rotating electric machine using the power of a high-voltage battery. The power converter 100 is connected between a DC power supply 12 and a rotating electric machine 10, and converts between the DC power of the DC power supply 12 and the AC power of the rotating electric machine 10. The power converter 100 drives the rotating electric machine 10 with the power of the DC power supply 12 and charges the DC power supply 12 with regenerative power from the rotating electric machine.

[0013] A permanent magnet three-phase AC synchronous motor or a three-phase brushless motor may be used as the rotating electric machine 10. The power conversion device 100 is not limited to driving the rotating electric machine 10, and may drive other machines.

[0014] The power conversion device 100 comprises an inverter unit 20 and a control unit 90. The inverter unit 20 comprises a drive circuit 27, a capacitor 21, a power conversion circuit 25, a voltage detection unit 24, and a current detection unit 26.

[0015] The power conversion circuit 25 has positive-side switching elements 51, 53, and 55 connected to the positive-side DC bus 1a of the DC power supply 12, and negative-side switching elements 52, 54, and 56 connected to the negative-side of the DC power supply 12. The positive-side switching elements 51, 53, and 55 and the negative-side switching elements 52, 54, and 56 are connected in series at connection points, forming U-phase, V-phase, and W-phase legs. The connection points of the U-phase, V-phase, and W-phase are connected to the U-phase, V-phase, and W-phase windings of the rotating electric machine 10 by power supply lines. The power supply lines for the U-phase, V-phase, and W-phase are collectively referred to as the AC bus 2.

[0016] The control unit 90 of the power converter 100 controls the power converter circuit 25 by switching the switching elements 51 to 56 on and off via the drive circuit 27. It also acquires various information and performs drive control and overheat prevention control of the rotating electric machine 10. The drive circuit 27 is controlled based on the PWM signal input from the control unit 90.

[0017] The capacitor 21 has functions such as suppressing voltage ripple between the positive DC bus 1a and the negative DC bus 1b, reducing the power supply impedance of the inverter unit 20 to improve AC current driving capability, and absorbing surge voltage.

[0018] <Switching Elements> Generally, semiconductor elements are used for switching elements 51 to 56. Examples of switching elements include diodes that allow current to flow in only one direction, thyristors suitable for handling large currents, and power transistors capable of operating at high switching frequencies.

[0019] Among switching elements, power transistors, in particular, are used in a wide range of fields such as automobiles, refrigerators, and air conditioners. Power transistors include IGBTs (Insulated Gate Bipolar Transistors) and MOS-FETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and these power transistors are used differently depending on the application.

[0020] The power converter 100 converts input power to output power by controlling the switching operation of switching elements 51 to 56 and thereby controlling the current flowing through the switching elements 51 to 56. Power loss occurs in the switching elements 51 to 56 due to the current flowing through them, and most of this loss is converted into heat, causing the temperature of the switching elements 51 to 56 to rise.

[0021] The switching elements 51 to 56 have a defined operating limit temperature Tm, and if they continue to operate beyond this limit temperature Tm, the switching elements 51 to 56 may deteriorate. For this reason, the power converter 100 is often equipped with a cooling device such as a heat sink or water cooler to cool the heat-generating elements such as the switching elements 51 to 56.

[0022] <Temperature Detectors> Temperature detectors 71 to 76 have the function of detecting the temperature of the power conversion circuit 25. In Figure 1, the switching elements 51 to 56 are installed near the semiconductor modules 61 to 66, or are built into the semiconductor modules 61 to 66. The temperature detection values ​​T1 to T6 detected by the temperature detectors 71 to 76 are transmitted to the control unit 90.

[0023] Temperature detectors 71-76 are provided to estimate the temperature of the semiconductor junctions of the switching elements 51-56. However, since there is actually a distance between the semiconductor junctions and the temperature detectors 71-76, there is a difference between the element temperature Tj, which is the temperature of the semiconductor junction, and the detected temperature values ​​T1-T6.

[0024] The temperature sensor may be installed on the wiring board of the power conversion circuit 25 on which the semiconductor module is installed. A single temperature sensor may be provided for the entire power conversion circuit 25. Two temperature sensors may be provided, one for each of the two groups of switching elements: positive-side switching elements 51, 53, 55 and negative-side switching elements 52, 54, 56. Alternatively, three temperature sensors may be provided, one for each leg of the U-phase, V-phase, and W-phase.

[0025] The temperature detectors 71-76 are assumed to be thermistors. However, the temperature detectors 71-76 are not limited to thermistors, and the temperature may be detected by temperature sensing diodes or the like placed on the semiconductor substrate of the switching elements 51-56.

[0026] <Current Detection Unit> The current detection unit 26 functions as a phase current sensor that detects phase currents. The current detection unit 26 is composed of a U-phase current detection unit 261, a V-phase current detection unit 262, and a W-phase current detection unit 263. The U-phase current detection unit 261, the V-phase current detection unit 262, and the W-phase current detection unit 263 are configured, for example, using shunt resistors.

[0027] The U-phase current detection unit 261 outputs a U-phase current detection value corresponding to the U-phase current Iu to the control unit 90. The V-phase current detection unit 262 outputs a V-phase current detection value corresponding to the V-phase current Iv to the control unit 90. The W-phase current detection unit 263 outputs a W-phase current detection value corresponding to the W-phase current Iw to the control unit 90. In the following description, the U-phase current detection value, V-phase current detection value, and W-phase current detection value may be collectively referred to as the current detection value. The current detection unit 26 may also be a current sensor using a Hall element or the like.

[0028] <Voltage Detection Unit> The inverter unit 20 is provided with a voltage detection unit 24 that detects the voltage of the DC power supply 12. The voltage detection unit 24 is installed between the positive DC bus 1a and the negative DC bus 1b and detects the DC voltage Vpn. The voltage detection unit 24 divides the DC voltage Vpn into voltages that can be read by the control unit 90 using a voltage divider resistor or the like, and outputs the DC bus voltage information to the control unit 90.

[0029] <Rotation Angle Sensor> The rotation angle sensor 11 detects the rotor rotation angle θm of the rotating electric machine 10 using a resolver, encoder, etc. The rotor rotation angle θm detected by the rotation angle sensor 11 is output to the control unit 90. The rotor rotation angle θm is converted to an electrical angle θe based on the number of pole pairs of the rotating electric machine 10. In addition, the rotation speed ω of the rotating electric machine 10 is calculated from the rotor rotation angle θm. Therefore, the rotation angle sensor 11 functions as a rotation speed sensor that detects the rotation speed ω of the rotating electric machine 10.

[0030] <Cooler> The cooler 35 cools the switching elements 51 to 56. The cooler 35 is, for example, a water-cooled cooler. Figure 1 shows the area cooled by the cooler 35. Here, the power conversion circuit 25 and the drive circuit 27 are shown as the objects to be cooled. However, some or all of the capacitor 21, the control unit 90, the DC power supply 12, etc., may also be included as objects to be cooled.

[0031] A water-cooled cooler may be used as the cooler 35. For example, a cooling system is constructed by connecting a water-cooled cooler, a radiator, an electric motor-driven water pump, etc., with cooling water piping such as hoses. A cooling medium such as water, oil, or LLC (Long Life Coolant) is introduced into the cooler 35.

[0032] In the following explanation, the cooling medium will be described as cooling water. Cooling water flows into the cooler 35 from the cooling water inlet pipe 38 and cools the cooler 35. Then, the cooling water flows out through the cooling water outlet pipe 39 and is sent to the radiator for further cooling.

[0033] <Water Temperature Sensor> The water temperature sensor 36 functions as a cooling medium temperature sensor that detects the temperature of the cooling medium in the cooling system. The water temperature sensor 36 detects the water temperature Tw of the cooling water flowing inside the cooling water inlet pipe 38 and outputs it to the control unit 90.

[0034] The water temperature sensor 36 may, for example, be placed in the cooler 35 directly beneath the semiconductor module. The water temperature sensor 36 is not limited to being placed in the cooler 35, and may also be placed in the cooling water inlet pipe 38 or the cooling water outlet pipe 39. The water temperature sensor 36 may also be placed in the cooling water piping outside the power converter 100 to receive water temperature information from an external device.

[0035] <Flow Meter> The flow meter 37 functions as a flow sensor that detects the flow rate of the cooling medium in the cooling device. The flow meter 37 detects the flow rate Q of the cooling medium flowing inside the cooling water piping and outputs it to the control unit 90. The flow meter 37 may be placed, for example, in the cooling water inlet pipe 38.

[0036] <Carrier Frequency Sensor> The carrier frequency sensor 40 detects the carrier frequency fc, which is the switching frequency at which the switching elements 51 to 56 repeatedly switch on and off. The carrier frequency sensor 40 that detects the carrier frequency fc may also be a sensor that detects the frequency from the on / off signals of the switching elements 51 to 56. Alternatively, the carrier frequency sensor 40 may be considered as an internal counting method that calculates the frequency from the timing at which the control unit 90 switches the switching elements 51 to 56 on and off.

[0037] <Hardware Configuration of the Control Unit> Figure 2 is a hardware configuration diagram of the control unit 90 of the power converter 100 according to Embodiment 1. In this embodiment, the control unit 90 is a control device that controls the power converter 100. Each function of the control unit 90 is realized by the processing circuits provided in the control unit 90. Specifically, the control unit 90 includes, as processing circuits, a arithmetic processing unit 80 (computer) such as a CPU (Central Processing Unit), a storage device 81 that exchanges data with the arithmetic processing unit 80, an input circuit 82 that inputs external signals to the arithmetic processing unit 80, and an output circuit 83 that outputs signals from the arithmetic processing unit 80 to the outside.

[0038] The arithmetic processing unit 80 may include an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits. Furthermore, multiple arithmetic processing units 80 of the same or different types may be provided, with each processing unit being assigned to a specific task. The storage device 81 may include a RAM (Random Access Memory) configured to read and write data from the arithmetic processing unit 80, or a ROM (Read Only Memory) configured to read data from the arithmetic processing unit 80. The input circuit 82 includes a rotation angle sensor 11, a voltage detection unit 24, a current detection unit 26, temperature detectors 71-76, a water temperature sensor 36, a flow meter 37, and a carrier frequency sensor 40. Various sensors and switches are connected to the input circuit, and the input circuit includes an AD conversion unit and other interface circuits that input the output signals from these sensors and switches to the arithmetic processing unit 80. The output circuit 83 includes a drive circuit 27, to which electrical loads such as switching elements and actuators are connected, and is equipped with interface circuits such as a drive circuit and a communication circuit that convert and output the output signals from the arithmetic processing unit 80 to these electrical loads.

[0039] Each function of the control unit 90 is realized by the arithmetic processing unit 80 executing software (programs) stored in a storage device 81 such as ROM, and cooperating with other hardware of the control unit 90, such as the storage device 81, input circuit 82, and output circuit 83. The setting data such as thresholds and judgment values ​​used by the control unit 90 are stored in the storage device 81 such as ROM as part of the software (program).

[0040] Each function mounted inside the control unit 90 may be composed of a software module, or it may be composed of a combination of software and hardware.

[0041] <Overheat Prevention Control> The power conversion device 100 prevents overheating of the switching elements 51 to 56. The temperature detectors 71 to 76 detect the temperature detection values T1 to T6 of the switching elements 51 to 56 (hereinafter, collectively referred to as the detected temperature Ts). When the detected temperature Ts exceeds a predetermined limit temperature Tlmt, the output of the power conversion device is restricted. By restricting the output, overheating of the switching elements 51 to 56 is suppressed.

[0042] After restricting the output, when the temperature further rises and the detected temperature Ts exceeds a predetermined stop temperature Tstp, the power conversion device 100 stops the output. By the control unit 90 controlling in this way, it becomes possible to protect the switching elements 51 to 56 so as not to exceed the operating limit temperature Tm.

[0043] The control unit 90 changes the stop temperature Tstp based on the driving state of the power conversion device 100. The temperature difference Tdif between the element temperature Tj, which is the temperature of the semiconductor junction of the switching elements 51 to 56, and the detected temperature Ts changes according to the driving state of the power conversion device 100.

[0044] Parameters that affect the temperature difference Tdif include the rotational speed ω of the rotating electrical machine 10, the phase current Irms, the DC voltage Vpn of the DC power supply 12, the carrier frequency fc indicating the switching frequency of the switching elements 51 to 56, the gate resistance value Rg that affects the switching speed of the switching elements, the dead time Td provided to prevent the switching elements on the positive electrode side and the switching elements on the negative electrode side connected in series from short - circuiting, the flow rate Q of the cooling medium of the cooling device, the water temperature Tw of the cooling device, etc. Also, it may be possible to change the stop temperature Tstp according to the estimated value of the loss Pl of the switching elements and the estimated value of the temperature difference Tdif.

[0045] By changing the stop temperature Tstp based on the driving state of the power conversion device 100, the unnecessary stop of the output of the power conversion device 100 can be suppressed, and the driving of the power conversion device 100 can be continued. Since it is possible to prevent the output of the power conversion device from being stopped too early, the performance of the power conversion device can be improved.

[0046] <Functional Blocks of the Control Device> Fig. 3 is a functional block diagram of the control unit 90 of the power conversion device 100 according to Embodiment 1. In Fig. 3, the control unit 90 includes a temperature threshold setting unit 91, an overheat protection control unit 92, a current command generation unit 93, a three-phase / two-phase conversion unit 94, a voltage command generation unit 95, a two-phase / three-phase conversion unit 96, a duty conversion unit 97, and a PWM signal generation unit 98.

[0047] <Temperature Threshold Setting Unit> The temperature threshold setting unit 91 has a function of calculating and outputting a stop temperature Tstp for performing overheat prevention control based on input information. In Fig. 3, as input information, the rotational speed ω, the phase current Irms, the DC voltage Vpn, the carrier frequency fc, the gate resistance value Rg, the dead time Td, the flow rate Q, and the water temperature Tw are described. Any one or a plurality of these pieces of information may be input.

[0048] <Overheat Protection Control Unit> The overheat protection control unit 92 has a function of stopping the output based on the stop temperature Tstp input from the temperature threshold setting unit 91. The overheat protection control unit 92 receives a torque command Trq* from an upper system (not shown). Other control commands for controlling the rotating electrical machine 10 include a torque command, a current command, a voltage command, etc. In Fig. 3, the case of adopting the torque command Trq* as the control command is exemplified.

[0049] The overheat protection control unit 92 receives temperature detection values T1 to T6 from the temperature detectors 71 to 76 and the stop temperature Tstp from the temperature threshold setting unit 91. When the maximum value of the temperature detection values T1 to T6 is greater than a predetermined limit temperature Tlmt, the overheat protection control unit 92 generates and outputs a torque command limit value Trqc obtained by limiting the torque command value.

[0050] When the maximum value of the temperature detection values T1 to T6 exceeds the stop temperature Tstp that is higher than the limit temperature Tlmt, the overheat protection control unit 92 sets the torque command limit value Trqc to zero and outputs it. Thereby, the power conversion output can be stopped. When the maximum value of the temperature detection values T1 to T6 is smaller than the predetermined limit temperature Tlmt, the torque command Trq* is output as the torque command limit value Trqc as it is.

[0051] <Current Command Generation Unit> The torque command limit value Trqc is input to the current command generation unit 93. Based on the torque command limit value Trqc, the current command generation unit 93 generates the d-axis current command value Id* and the q-axis current command value Iq*.

[0052] Here, the d-axis represents the magnetic pole position of the rotating electric machine 10, i.e., the direction of the magnetic flux, and the q-axis represents the direction electrically perpendicular to the d-axis, thus constituting a d-q axis coordinate system. The d-q axis coordinate system is a rotating coordinate system, and when the rotor of the rotating electric machine 10, which has magnets, rotates, the d-q axis coordinate system also rotates.

[0053] <Three-phase to two-phase conversion unit> The three-phase to two-phase conversion unit 94 receives the current detection value from the current detection unit 26 and the angle detection value corresponding to the electrical angle θe detected by the rotation angle sensor 11. From the input information, the three-phase to two-phase conversion unit 94 calculates the d-axis current detection value Id and the q-axis current detection value Iq. Here, the current detection value of the current detection unit 26 is composed of the U-phase current detection value corresponding to the U-phase current Iu detected by the U-phase current detection unit 261, the V-phase current detection value corresponding to the V-phase current Iv detected by the V-phase current detection unit 262, and the W-phase current detection value corresponding to the W-phase current Iw detected by the W-phase current detection unit 263.

[0054] <Voltage Command Generation Unit> The voltage command generation unit 95 performs current feedback calculations from the d-axis current command value Id* and the q-axis current command value Iq*, and the d-axis current detection value Id and the q-axis current detection value Iq. The voltage command generation unit 95 calculates the d-axis voltage command Vdc and the q-axis voltage command Vqc from the input information.

[0055] Specifically, for example, the voltage command generation unit 95 receives a current deviation ΔId, which is the difference between the d-axis current command value Id* and the d-axis current detection value Id, and a current deviation ΔIq, which is the difference between the q-axis current command value Iq* and the q-axis current detection value Iq. The voltage command generation unit 95 calculates the d-axis voltage command Vdc and the q-axis voltage command Vqc so that the current deviation ΔId and the current deviation ΔIq converge to "0". (ΔId and ΔIq are not shown.)

[0056] <Two-phase to three-phase conversion unit> The two-phase to three-phase conversion unit 96 obtains the d-axis voltage command Vdc and the q-axis voltage command Vqc from the voltage command generation unit 95. The two-phase to three-phase conversion unit 96 obtains the electrical angle θe from the rotation angle sensor 11. Then, the two-phase to three-phase conversion unit 96 calculates the three-phase voltage commands Vuc, Vvc, and Vwc from this input information. It is preferable that the three-phase voltage commands Vuc, Vvc, and Vwc are set to be less than or equal to the DC power supply voltage input to the inverter unit 20, that is, the DC voltage Vpn detected by the voltage detection unit 24.

[0057] <Duty Cycle Conversion Unit> The duty cycle conversion unit 97 receives three-phase voltage commands Vuc, Vvc, and Vwc from the two-phase / three-phase conversion unit 96. The duty cycle conversion unit 97 also receives a DC voltage Vpn. From this input information, the duty cycle conversion unit 97 generates duty cycle commands Du, Dv, and Dw for each phase of the three-phase system. The duty cycle conversion unit 97 generates and outputs duty cycle commands Du, Dv, and Dw corresponding to the optimal correction control command.

[0058] <PWM Signal Generation Unit> The PWM signal generation unit 98 generates PWM signals. The PWM signal generation unit 98 generates PWM signals to control the switching elements 51 to 56 by switching them on and off, respectively, from the duty cycle commands Du, Dv, and Dw of each phase obtained from the duty cycle conversion unit 97.

[0059] The PWM signal generation unit 98 generates a PWM signal by comparing the duty cycle commands Du, Dv, and Dw for each phase with the carrier wave. The PWM signal generation unit 98 can, for example, employ a triangular wave comparison method using a triangular wave having the shape of an isosceles triangle with equal rising and falling speeds as the carrier. The PWM signal generation unit 98 can also employ a sawtooth wave comparison method or the like. The PWM signal generation unit 98 then generates a PWM signal.

[0060] In Figure 3, the PWM signals generated by the PWM signal generation unit 98 are shown as follows: PWM signal UH_SW applied to the switching element of the U-phase upper arm, PWM signal VH_SW applied to the switching element of the V-phase upper arm, and PWM signal WH_SW applied to the switching element of the W-phase upper arm. Additionally, the PWM signals generated by the PWM signal generation unit 98 are shown as follows: PWM signal UL_SW applied to the switching element of the U-phase lower arm, PWM signal VL_SW applied to the switching element of the V-phase lower arm, and PWM signal WL_SW applied to the switching element of the W-phase lower arm.

[0061] The PWM signal generated by the PWM signal generation unit 98 is input from the control unit 90 to the drive circuit 27 of the inverter unit 20. The drive circuit 27 turns the switching elements 51 to 56 on and off based on the PWM signal, converting DC power to AC power and supplying it to the rotating electric machine 10, and also charges the DC power supply 12 with the regenerative power generated when the rotating electric machine 10 is in a regenerative state.

[0062] <Setting the Stop Temperature> A feature of the power converter 100 is that the control unit 90 is equipped with a temperature threshold setting unit 91 and an overheat protection control unit 92, and the temperature threshold setting unit 91 sets the stop temperature Tstp based on the input information. Another feature of the power converter 100 is that the overheat protection control unit 92 sets the torque command limit value Trqc to zero and stops the output if the temperature detection values ​​T1 to T6 exceed the stop temperature Tstp.

[0063] Here, we will explain the effect of setting the stop temperature Tstp based on input information, which is a feature of Embodiment 1. Specifically, we will explain using Figures 4 and 5 the case in which the output is excessively stopped even though the temperature rise of the switching elements 51 to 56 is still acceptable.

[0064] <Changes in Detected Temperature and Element Temperature> Figure 4 is a first time chart showing the changes in the detected temperature Ts and element temperature Tj of the power converter 100 according to Embodiment 1. Figure 5 is a second time chart.

[0065] Figure 4 shows the changes in element temperature Tj of switching elements 51 to 56 and the temperature Ts detected by temperature detectors 71 to 76 when the power converter 100 is driven from a stopped state to a constant load, in the case where the switching elements 51 to 56 generate a large amount of heat. Figure 5 shows the changes in element temperature Tj of switching elements 51 to 56 and the temperature Ts detected by temperature detectors 71 to 76 when the power converter 100 is driven from a stopped state to a constant load, in the case where the switching elements 51 to 56 generate little heat.

[0066] In Figure 4, the vertical axis shows temperature and the horizontal axis shows elapsed time. The element temperature Tj, which indicates the temperature of the semiconductor junction of the switching element, is shown by a solid line. The detected temperature Ts, detected by the temperature detector, is shown by a dashed line. When the power converter 100 starts operating, the element temperature Tj and the detected temperature Ts rise.

[0067] When the rising detected temperature Ts exceeds the limit temperature Tlmt, the output is limited, and the element temperature Tj and detected temperature Ts temporarily decrease. Even after the output is limited, if there is a problem with the cooler 35, for example, the temperature will rise again. Then, when the detected temperature Ts reaches the stop temperature Tstp, the output is stopped.

[0068] As a means of detecting the temperature of the switching elements 51 to 56, as described above, temperature sensors such as thermistors and temperature-sensing diodes are placed inside or near the semiconductor module. However, it is difficult to directly measure the element temperature Tj at the semiconductor junction where the temperature of the switching elements 51 to 56 is highest. Therefore, a temperature difference Tdif occurs between the element temperature Tj of the switching elements 51 to 56 and the detected temperature Ts.

[0069] The temperature difference Tdif between the element temperature Tj and the detected temperature Ts is affected by several parameters, including the amount of heat loss that causes heat generation in the switching elements 51-56 and the cooling state of the cooler 35. To prevent overheating, it is necessary to stop the output before the element temperature Tj reaches the element's operating limit temperature Tm and the element deteriorates. For this reason, the stop temperature Tstp needs to be set low, assuming the conditions under which the temperature difference Tdif between the element temperature Tj and the detected temperature Ts is maximum when the output is limited.

[0070] In this case, as shown in Figure 5, when the heat generated by the switching elements 51 to 56 is small, the temperature difference Tdif between the temperature of the switching elements 51 to 56 and the detected temperature Ts is small. Therefore, even though the element temperature Tj of the switching elements 51 to 56 has not reached the operating limit temperature Tm and a temperature rise is still permissible, the detected temperature Ts exceeds the predetermined stop temperature Tstp, resulting in the output being stopped excessively early. To address this, the stop temperature Tstp is changed based on a parameter that affects the temperature difference Tdif between the element temperature Tj of the switching element and the detected temperature Ts.

[0071] <Setting the stop temperature according to the rotational speed> Figure 6 shows the phase current characteristics with respect to the rotational speed ω at the time of maximum torque after output limiting of the power converter 100 according to Embodiment 1. Since the phase currents Iu, Iv, and Iw of each phase fluctuate as sinusoidal waves, the effective value is indicated as the phase current Irms.

[0072] As shown in Figure 6, at low rotational speeds, the phase current is uniformly limited and losses are small, but as the rotational speed increases, the phase current increases and losses also increase. This is because, when a permanent magnet synchronous motor is used as the rotating electric machine 10, field weakening control is performed to increase the negative d-axis current in order to reduce the motor's back electromotive force at high rotational speeds.

[0073] Therefore, when the rotational speed ω is large, the phase current increases, leading to increased losses and a larger temperature difference Tdif between the element temperature Tj and the detection temperature Ts. For this reason, when the rotational speed ω is high, the stop temperature Tstp should be reduced, and conversely, when the rotational speed is low, the stop temperature Tstp should be increased.

[0074] The operation of the temperature threshold setting unit 91 and the overheat protection control unit 92 of the control unit 90 of the power converter 100 will be described below. The temperature threshold setting unit 91 takes the rotational speed ω obtained from the rotational angle sensor 11 as input and outputs a stop temperature Tstp for which overheat prevention control is performed. The temperature threshold setting unit 91 has a plurality of stop temperatures Tstp for rotational speed ω pre-configured. The stop temperature Tstp for rotational speed ω must be set so that the temperature of the switching elements 51 to 56 does not exceed the operating limit temperature Tm even under the most severe driving conditions, in order to prevent thermal damage to the switching elements 51 to 56.

[0075] Therefore, the stop temperature Tstp for a given rotational speed ω is set to a temperature that is lower by a predetermined margin temperature Tmgn from the temperature Ts detected by the temperature detectors 71-76 at the point when the element temperature Tj of the switching elements 51-56 reaches the operating limit temperature Tm, when the power converter 100 is driven under the driving conditions that result in the greatest loss in the switching elements 51-56 at each rotational speed ω.

[0076] Figure 7 is the first figure showing the setting of the stop temperature Tstp for the rotational speed ω of the power converter 100 according to Embodiment 1. The waveform of the phase current Irms for the rotational speed ω in Figure 7 is the same as in Figure 6. The temperature difference Tdif between the element temperature Tj and the detected temperature Ts at the point when the element temperature Tj of the switching elements 51 to 56 reaches the operating limit temperature Tm becomes larger as the losses of the switching elements 51 to 56 increase.

[0077] Therefore, at high rotational speeds where the current is large and losses are large, the stop temperature Tstp is set low, taking into account the operating state at the maximum rotational speed where the current is largest. Then, at low rotational speeds below a predetermined rotational speed threshold ωth, the stop temperature Tstp is set considering the operating state within the range below that rotational speed threshold ωth where the current is large and losses are largest.

[0078] The rotational speed threshold ωth and the stop temperature Tstp may be determined experimentally to find their optimal values. Alternatively, the rotational speed threshold ωth and the stop temperature Tstp may be determined through simulation to find their optimal values.

[0079] The temperature threshold setting unit 91 sets the stop temperature Tstp to a higher value when the rotational speed ω is lower than a predetermined rotational speed threshold ωth, and sets the stop temperature Tstp to a lower value when it is higher than the predetermined rotational speed threshold ωth. Here, hysteresis may be provided in the rotational speed threshold ωth. In addition, a predetermined determination time may be provided when determining when the stop temperature Tstp has been reached. This is to prevent frequent changes in the stop temperature Tstp around the rotational speed threshold ωth due to fluctuations in the detected rotational speed ω.

[0080] The overheat protection control unit 92 may generate a torque command limit value Trqc by multiplying the torque command Trq* by a ratio less than 1 (overheat prevention gain G) when the maximum value of the temperature detection values ​​T1 to T6 is greater than a predetermined limit temperature Tlmt (overheat prevention gain G is not shown). If the maximum value of the temperature detection values ​​T1 to T6 exceeds a stop temperature Tstp which is higher than the limit temperature Tlmt, the torque command limit value Trqc is set to zero and the output is stopped.

[0081] This allows the system to stop the output in order to reduce the current flowing through switching elements 51-56 if there is a risk that the element temperature Tj of switching elements 51-56 will exceed the operating limit temperature Tm after exceeding the limit temperature Tlmt. As a result, the temperature rise of switching elements 51-56 is suppressed, and deterioration of switching elements 51-56 due to exceeding the operating limit temperature Tm can be prevented.

[0082] Furthermore, if the maximum value of the temperature detection values ​​T1 to T6 exceeds the stop temperature Tstp, which is higher than the limit temperature Tlmt, the torque command limit value Trqc is set to zero in order to stop the output. However, this method is not limited to this, and the driving of the switching elements 51 to 56 may also be stopped.

[0083] It has been explained that the overheat protection control unit 92 generates a torque command limit value Trqc by multiplying the torque command Trq* by a ratio less than 1 (overheat prevention gain G) when the maximum value of the temperature detection values ​​T1 to T6 is greater than a predetermined limit temperature Tlmt. However, this is not the only way to limit the torque command Trq*. For example, the torque command Trq* may be limited to a predetermined torque command value and generated as the torque command limit value Trqc.

[0084] <Changes in detection temperature and element temperature when the stop temperature is changed> Figure 9 is a third time chart showing the changes in detection temperature Ts and element temperature Tj of the power converter 100 according to Embodiment 1. At high rotation speeds where the losses of switching elements 51 to 56 are large, the changes in detection temperature Ts and element temperature Tj of the switching elements 51 to 56 when the overheat prevention limit is applied are as shown in Figure 4 above.

[0085] In contrast, at low rotational speeds where the losses of the switching elements 51 to 56 are small, the changes in the detected temperature Ts and element temperature Tj of the switching elements 51 to 56 when the overheat prevention limit is applied are as shown in Figure 9, as described above. As shown in Figure 7, at low rotational speeds, a high value is set for the stop temperature Tstp. Therefore, the limiting operating range of the stop temperature Tstp and the limiting temperature Tlmt can be expanded to extend the operating time of the power converter 100 after the operation limit is applied.

[0086] As described above, the power converter 100 of Embodiment 1 sets the overheat prevention stop temperature Tstp based on the rotational speed ω. For this reason, at low rotational speeds where the temperature difference Tdif between the element temperature Tj of the switching elements 51 to 56 and the detected temperature Ts is small, the stop temperature Tstp is set high. At high rotational speeds where the temperature difference Tdif is large, the stop temperature Tstp is set low. This allows for a more appropriate determination of the overheating state of the switching elements 51 to 56, ensuring that the deterioration of the switching elements 51 to 56 is reliably prevented, while preventing the power converter 100 from excessively stopping its output, allowing it to continue operating up to its performance limit.

[0087] <Linear change of stop temperature according to rotational speed> Figure 8 is a second figure showing the setting of the stop temperature Tstp for the rotational speed ω of the power converter 100 according to Embodiment 1. In Figure 7, the stop temperature Tstp is switched according to the relationship between the rotational speed ω and a predetermined rotational speed threshold ωth.

[0088] However, the temperature difference Tdif between the element temperature Tj and the detection temperature Ts changes due to losses. Furthermore, the phase current Irms, which determines the magnitude of the losses, changes continuously according to the rotational speed ω, as shown in Figure 6. For this reason, the stop temperature Tstp may be changed linearly according to the rotational speed ω, as shown in Figure 8. This makes it possible to set the stop temperature Tstp more appropriately according to the losses. As a result, it is possible to prevent excessive shutdown of the output of the power converter 100 and to continue the operation of the power converter 100 up to its performance limit.

[0089] The optimal value for the stopping temperature Tstp with respect to rotational speed ω may be determined experimentally. Alternatively, the optimal value for the stopping temperature Tstp with respect to rotational speed ω may be determined through simulation.

[0090] <Setting the stop temperature Tstp according to the phase current> Figure 10 is the first figure showing the setting of the stop temperature Tstp for the phase current Irms of the power converter 100 according to Embodiment 1. Figure 11 is the second figure showing the setting of the stop temperature Tstp. In Figures 7 and 8, an example was given in which the stop temperature Tstp is set to a higher value as the rotational speed ω decreases. However, the temperature difference Tdif between the element temperature Tj and the detected temperature Ts when determining the stop temperature Tstp changes due to losses, and the magnitude of the losses also changes depending on the phase current Irms flowing through the switching elements 51 to 56.

[0091] Therefore, instead of inputting the rotational speed ω to the temperature threshold setting unit 91 of the control unit 90 of the power converter 100, the effective value of the phase current, Irms, calculated from the phase currents Iu, Iv, and Iw detected by the current detection unit 26, may be input. The temperature threshold setting unit 91 may then change the stop temperature Tstp to a higher value as the phase current Irms decreases.

[0092] Specifically, as shown in Figure 10, if the phase current Irms is greater than a predetermined current threshold Ith, a lower stop temperature Tstp is set because the temperature difference Tdif is large. If the phase current Irms is less than a predetermined current threshold Ith, a higher stop temperature Tstp is set because the temperature difference Tdif is small. This ensures that the degradation of the switching elements 51 to 56 is reliably prevented, while preventing the power converter 100 from shutting down its output excessively, and allowing the power converter 100 to continue operating up to its performance limit.

[0093] The current threshold Ith and the shutdown temperature Tstp may be determined experimentally to find their optimal values. Alternatively, the current threshold Ith and the shutdown temperature Tstp may be determined through simulation to find their optimal values.

[0094] <Continuous Change of Stop Temperature According to Phase Current> Furthermore, the temperature difference Tdif between the element temperature Tj and the detected temperature Ts changes continuously according to the magnitude of the phase current Irms. Therefore, as shown in Figure 11, the stop temperature Tstp may be continuously changed according to the phase current Irms. This makes it possible to set the stop temperature Tstp appropriately according to the phase current Irms that affects the temperature difference Tdif.

[0095] Therefore, it is possible to prevent excessive shutdown of the power converter 100's output and to continue operating the power converter 100 up to its performance limit. The characteristics of the shutdown temperature Tstp with respect to the phase current Irms may be determined experimentally to find the optimal value. Alternatively, the characteristics of the shutdown temperature Tstp with respect to the phase current Irms may be determined by simulation to find the optimal value.

[0096] <Use of Phase Current Command Values> The above describes the case in which the phase current Irms, which are the effective values ​​of the phase currents Iu, Iv, and Iw calculated from the current values ​​detected by the current detection unit 26, are input to the temperature threshold setting unit 91. However, this is not the only option, and the effective values ​​of the phase currents calculated from the current command values, namely the d-axis current command value Id* and the q-axis current command value Iq*, may also be input. This makes it possible to quickly change the stop temperature Tstp in response to changes in the current command value. This makes it possible to use the power converter 100 to its performance limit and to operate it for a longer period of time. Here, the current command value is also called the target current.

[0097] <Setting the stop temperature Tstp according to the DC voltage> Figure 12 is a first diagram showing the setting of the stop temperature Tstp for the DC voltage Vpn of the power converter 100 according to Embodiment 1. Figure 13 is a second diagram showing the setting of the stop temperature Tstp for the DC voltage Vpn. The temperature difference Tdif between the element temperature Tj and the detected temperature Ts when determining the stop temperature Tstp changes due to losses. The magnitude of the losses changes depending on the magnitude of the DC voltage Vpn applied to the switching elements 51 to 56.

[0098] Therefore, the DC voltage Vpn detected by the voltage detection unit 24 may be input to the temperature threshold setting unit 91 of the control unit 90 of the power converter 100, and the lower the DC voltage Vpn, the higher the stop temperature Tstp may be set to.

[0099] Specifically, as shown in Figure 12, if the DC voltage Vpn is greater than a predetermined voltage threshold Vth, a lower stop temperature Tstp is set because the temperature difference Tdif is large. Conversely, if the DC voltage Vpn is less than a predetermined voltage threshold Vth, a higher stop temperature Tstp is set because the temperature difference Tdif is small.

[0100] The optimal values ​​for the voltage threshold Vth and stop temperature Tstp may be determined experimentally. Alternatively, the optimal values ​​for the voltage threshold Vth and stop temperature Tstp may be determined through simulation.

[0101] This makes it possible to reliably prevent the deterioration of the switching elements 51 to 56 while preventing the power converter 100 from excessively shutting down its output. As a result, the power converter 100 can be used to its performance limit and operate continuously for a longer period of time.

[0102] <Linear change of stop temperature according to DC voltage> Furthermore, the temperature difference Tdif between the element temperature Tj and the detected temperature Ts changes depending on the magnitude of the DC voltage Vpn. Therefore, as shown in Figure 13, the stop temperature Tstp may be changed linearly according to the change in the DC voltage Vpn. This makes it possible to set the stop temperature Tstp more appropriately according to the DC voltage Vpn that affects the temperature difference Tdif.

[0103] Therefore, it becomes possible to prevent excessive shutdown of the output of the power converter 100. This makes it possible to use the power converter 100 to its performance limit and enable longer continuous operation. The characteristics of the shutdown temperature Tstp with respect to the DC voltage Vpn may be determined experimentally to find the optimal value. Alternatively, the characteristics of the shutdown temperature Tstp with respect to the DC voltage Vpn may be determined by simulation to find the optimal value.

[0104] <Setting the stop temperature Tstp according to the carrier frequency> Figure 14 is a first diagram showing the setting of the stop temperature Tstp for the carrier frequency fc of the power converter 100 according to Embodiment 1. Figure 15 is a second diagram showing the setting of the stop temperature Tstp for the carrier frequency fc. The temperature difference Tdif between the element temperature Tj and the detected temperature Ts when determining the stop temperature Tstp changes due to losses. The magnitude of the losses is affected by the carrier frequency, which is the frequency at which the switching elements 51 to 56 switch (the reciprocal of the switching period).

[0105] Therefore, the carrier frequency fc may be input to the temperature threshold setting unit 91 of the control unit 90 of the power converter 100, and the lower the carrier frequency fc, the higher the stop temperature Tstp may be set. Specifically, as shown in Figure 14, if the carrier frequency is greater than a predetermined frequency threshold fcth, a lower stop temperature Tstp is set because the temperature difference Tdif is large. Conversely, if the carrier frequency fc is smaller than a predetermined frequency threshold fcth, a higher stop temperature Tstp is set because the temperature difference Tdif is small.

[0106] The carrier frequency fc represents the switching frequency at which the switching elements 51 to 56 repeatedly switch on and off. The control unit 90 may determine the carrier frequency fc according to an external command. It is also conceivable that the carrier frequency fc may be determined by the drive circuit 27. Furthermore, it is conceivable that the control unit 90 may determine the carrier frequency fc according to the operating state of the power converter 100.

[0107] The carrier frequency fc can be detected by measuring the switching signal externally using the carrier frequency sensor 40. The carrier frequency fc may also be obtained by frequency identification using an internal counting method, which calculates the frequency from the timing at which the control unit 90 turns the switching elements 51 to 56 on and off. When the temperature threshold setting unit 91 of the control unit 90 receives the carrier frequency fc as input information, the unit that acquires the carrier frequency fc and provides the input information will be referred to as the carrier frequency sensor 40.

[0108] The optimal values ​​for the frequency threshold fcth and the stop temperature Tstp may be determined experimentally. Alternatively, the optimal values ​​for the frequency threshold fcth and the stop temperature Tstp may be determined through simulation.

[0109] This makes it possible to reliably prevent the deterioration of the switching elements 51 to 56 while preventing the power converter 100 from excessively shutting down its output. As a result, the power converter 100 can be used to its performance limit and operate continuously for a longer period of time.

[0110] <Linear change of stop temperature according to carrier frequency> Furthermore, the temperature difference Tdif between the element temperature Tj and the detected temperature Ts changes depending on the height of the carrier frequency fc. Therefore, as shown in Figure 15, the stop temperature Tstp may be changed linearly according to the change in the carrier frequency fc detected by the carrier frequency sensor 40. This makes it possible to set the stop temperature Tstp more appropriately according to the carrier frequency fc that affects the temperature difference Tdif.

[0111] Therefore, it becomes possible to prevent excessive shutdown of the output of the power converter 100. This makes it possible to use the power converter 100 to its performance limit and enable longer continuous operation. The characteristics of the shutdown temperature Tstp with respect to the carrier frequency fc may be determined experimentally to find the optimal value. Alternatively, the characteristics of the shutdown temperature Tstp with respect to the frequency threshold fcth may be determined by simulation to find the optimal value.

[0112] <Setting the stop temperature Tstp according to the gate resistance value> Figure 16 is a first diagram showing the setting of the stop temperature Tstp for the gate resistance value Rg of the power converter 100 according to Embodiment 1. Figure 17 is a second diagram showing the setting of the stop temperature Tstp for the gate resistance value Rg.

[0113] The temperature difference Tdif between the element temperature Tj and the detected temperature Ts, used to determine the stop temperature Tstp, varies depending on the loss, and the magnitude of the loss varies depending on the switching speed of the switching elements 51 to 56. In the drive circuit 27, if the gate resistors that drive the switching elements 51 to 56 are switched according to the conditions, the switching speed varies depending on the magnitude of the gate resistance value Rg.

[0114] Therefore, the gate resistance value Rg selected by the drive circuit 27 may be input to the temperature threshold setting unit 91 of the control unit 90 of the power converter 100, and the lower the gate resistance value Rg, the higher the stop temperature Tstp may be changed.

[0115] Specifically, as shown in Figure 16, if the gate resistance value Rg is greater than a predetermined gate resistance threshold Rth, a lower stop temperature Tstp is set because the temperature difference Tdif is large. Conversely, if the gate resistance value Rg is less than a predetermined gate resistance threshold Rth, a higher stop temperature Tstp is set because the temperature difference Tdif is small.

[0116] The gate resistance threshold Rth and the shutdown temperature Tstp may be determined experimentally to find their optimal values. Alternatively, the gate resistance threshold Rth and the shutdown temperature Tstp may be determined through simulation to find their optimal values.

[0117] This makes it possible to reliably prevent the deterioration of the switching elements 51 to 56 while preventing the power converter 100 from excessively shutting down its output. As a result, the power converter 100 can be used to its performance limit and operate continuously for a longer period of time.

[0118] <Linear change of stop temperature according to gate resistance value> Also, the temperature difference Tdif between the element temperature Tj and the detected temperature Ts changes depending on the magnitude of the gate resistance value Rg. Therefore, as shown in Figure 17, the stop temperature Tstp may be changed linearly according to the change in the gate resistance value Rg. This makes it possible to set the stop temperature Tstp more appropriately according to the gate resistance value Rg that affects the temperature difference Tdif.

[0119] Therefore, it becomes possible to prevent excessive shutdown of the output of the power converter 100. This makes it possible to use the power converter 100 to its performance limit and enable longer continuous operation. The characteristics of the shutdown temperature Tstp with respect to the gate resistance value Rg may be determined experimentally to find the optimal value. Alternatively, the characteristics of the shutdown temperature Tstp with respect to the gate resistance value Rg may be determined by simulation to find the optimal value.

[0120] <Setting the stop temperature Tstp according to the dead time> Figure 18 is a first diagram showing the setting of the stop temperature Tstp for the dead time Td of the power converter 100 according to Embodiment 1. Figure 19 is a second diagram showing the setting of the stop temperature Tstp for the dead time Td.

[0121] A dead time Td is provided to prevent the series-connected switching elements 51 (positive side) and 52 (negative side), 53 (positive side) and 54 (negative side), and 55 (positive side) and 56 (negative side) from simultaneously turning on and causing a short circuit. This dead time Td is used as input information.

[0122] The temperature difference Tdif between the element temperature Tj and the detected temperature Ts, which is used to determine the stop temperature Tstp, changes due to losses. The magnitude of the losses is influenced by the dead time Td when the switching elements 51-56 switch.

[0123] Therefore, the dead time Td may be input to the temperature threshold setting unit 91 of the control unit 90 of the power converter 100, and the shorter the dead time Td, the higher the value of the stop temperature Tstp may be changed.

[0124] Specifically, as shown in Figure 18, if the dead time Td is longer than a predetermined dead time threshold Tdth, a lower stop temperature Tstp is set because the temperature difference Tdif is large. Conversely, if the dead time Td is shorter than a predetermined dead time threshold Tdth, a higher stop temperature Tstp is set because the temperature difference Tdif is small.

[0125] The dead time threshold Tdth and the stop temperature Tstp may be determined experimentally to find their optimal values. Alternatively, the dead time threshold Tdth and the stop temperature Tstp may be determined through simulation to find their optimal values.

[0126] This makes it possible to reliably prevent the deterioration of the switching elements 51 to 56 while preventing the power converter 100 from excessively shutting down its output. As a result, the power converter 100 can be used to its performance limit and operate continuously for a longer period of time.

[0127] <Linear change of stop temperature according to dead time> Also, the temperature difference Tdif between the element temperature Tj and the detected temperature Ts changes according to the length of the dead time Td. Therefore, as shown in Figure 19, the stop temperature Tstp may be changed linearly according to the change in dead time Td.

[0128] This makes it possible to set the stop temperature Tstp more appropriately according to the dead time Td that affects the temperature difference Tdif. The optimal value of the characteristics of the stop temperature Tstp with respect to the dead time Td may be determined experimentally. Alternatively, the optimal value of the characteristics of the stop temperature Tstp with respect to the dead time Td may be determined by simulation.

[0129] Therefore, it becomes possible to prevent excessive shutdown of the output of the power converter 100. This makes it possible to use the power converter 100 to its performance limit and enable longer continuous operation. The characteristics of the stop temperature Tstp with respect to the dead time Td may be determined experimentally to find the optimal value. Alternatively, the characteristics of the stop temperature Tstp with respect to the dead time Td may be determined by simulation to find the optimal value.

[0130] <Setting the stop temperature Tstp according to the flow rate of the cooling water> Figure 20 is a first diagram showing the setting of the stop temperature Tstp for the flow rate Q of the power converter 100 according to Embodiment 1. Figure 21 is a second diagram showing the setting of the stop temperature Tstp for the flow rate Q.

[0131] The flow rate Q of the cooling water measured by the flow meter 37 is input, and the stop temperature Tstp may be changed to a higher value as the flow rate Q increases. Specifically, as shown in Figure 20, if the flow rate Q is greater than a predetermined flow rate threshold Qth, a high stop temperature Tstp is set because the temperature difference Tdif is small due to the high cooling performance of the cooler 35. Conversely, if the flow rate Q is less than a predetermined flow rate threshold Qth, a low stop temperature Tstp is set because the temperature difference Tdif is large.

[0132] The optimal values ​​for the flow threshold Qth and stop temperature Tstp may be determined experimentally. Alternatively, the optimal values ​​for the flow threshold Qth and stop temperature Tstp may be determined through simulation.

[0133] This ensures that the degradation of the switching elements 51-56 is reliably prevented, while also preventing the power converter 100 from excessively shutting down its output. As a result, the power converter 100 can be used to its performance limit, allowing for longer continuous operation.

[0134] <Linear change of stop temperature according to cooling water flow rate> Furthermore, the temperature difference Tdif between the element temperature Tj and the detected temperature Ts changes according to the cooling water flow rate Q. Therefore, as shown in Figure 21, the stop temperature Tstp may be changed linearly according to the change in flow rate Q. This makes it possible to set the stop temperature Tstp more appropriately according to the flow rate Q that affects the temperature difference Tdif.

[0135] Therefore, it becomes possible to prevent excessive shutdown of the power converter 100's output. This allows the power converter 100 to be used to its performance limit and to operate continuously for a longer period. The optimal value for the characteristics of the shutdown temperature Tstp with respect to the cooling water flow rate Q may be determined experimentally. Alternatively, the optimal value for the characteristics of the shutdown temperature Tstp with respect to the cooling water flow rate Q may be determined by simulation.

[0136] <Setting the stop temperature Tstp according to the cooling water temperature> Figure 22 is a first diagram showing the setting of the stop temperature Tstp for the water temperature Tw of the power converter 100 according to Embodiment 1. Figure 23 is a second diagram showing the setting of the stop temperature Tstp for the water temperature Tw of the cooling water.

[0137] The temperature difference Tdif between the element temperature Tj and the detected temperature Ts, used to determine the stop temperature Tstp, changes depending on the cooling state of the cooler 35. Therefore, the water temperature Tw of the cooling water measured by the water temperature sensor 36 can be input to the temperature threshold setting unit 91, and the stop temperature Tstp may be changed to a higher value as the water temperature Tw increases.

[0138] The higher the water temperature, the lower the viscosity of the cooling medium in the cooler 35, increasing the flow rate and improving cooling performance. Specifically, as shown in Figure 22, when the water temperature Tw is higher than a predetermined water temperature threshold Twth, a high stop temperature Tstp is set because the cooling performance is high and the temperature difference Tdif is small. Conversely, when the water temperature Tw is lower than a predetermined water temperature threshold Twth, a low stop temperature Tstp is set because the temperature difference Tdif is large.

[0139] The optimal values ​​for the water temperature threshold Twth and the stop temperature Tstp may be determined experimentally. Alternatively, the optimal values ​​for the water temperature threshold Twth and the stop temperature Tstp may be determined through simulation.

[0140] This makes it possible to reliably prevent thermal damage to the switching elements 51-56 while preventing the power converter 100 from excessively shutting down its output. As a result, the power converter 100 can be used to its performance limit and operate continuously for a longer period of time.

[0141] <Linear change of stop temperature according to cooling water temperature> Also, since the temperature difference Tdif between the element temperature Tj and the detected temperature Ts changes depending on the water temperature Tw, the stop temperature Tstp may be changed linearly according to the continuous change in water temperature Tw, as shown in Figure 23.

[0142] This allows the stop temperature Tstp to be set appropriately according to the cooling state, preventing the power converter 100 from shutting down excessively and allowing it to continue operating up to its performance limit. The characteristics of the stop temperature Tstp with respect to the water temperature Tw may be determined experimentally to find the optimal value. Alternatively, the characteristics of the stop temperature Tstp with respect to the water temperature Tw may be determined by simulation to find the optimal value.

[0143] In this embodiment, the power converter 100 is configured to include a flow meter 37 as a flow sensor for the cooling medium of the cooling device and a water temperature sensor 36 as a cooling medium temperature sensor. However, the power converter 100 does not necessarily need to include a water temperature sensor 36 and a flow meter 37.

[0144] For example, when the power converter 100 is installed in an electric vehicle, the temperature and flow rate information of the cooling medium may be input to the power converter 100 via communication from an external system, such as a higher-level system (not shown) within the electric vehicle. By acquiring information from an external system to the power converter 100, it is not necessary to install a water temperature sensor and flow meter inside the power converter 100, which can lead to a reduction in the cost of the power converter 100. At a low cost, it is possible to reliably prevent the deterioration of the switching elements 51 to 56, prevent excessive shutdown of the output of the power converter 100, and allow the power converter 100 to continue operating.

[0145] <Setting the stop temperature based on temperature difference estimation> Figure 24 is the first figure showing the setting of the stop temperature Tstp for the temperature difference Tdif of the power converter 100 according to Embodiment 1. Figure 25 is the second figure showing the setting of the stop temperature Tstp for the temperature difference Tdif.

[0146] <Functional Block of Control Device> The temperature threshold setting unit 91 receives the following inputs: the phase current Irms, which is the effective value of the phase current detected by the current detection unit 26; the DC voltage Vpn, which is detected by the voltage detection unit 24; the carrier frequency fc, which is the frequency at which the switching element switches; the gate resistance value Rg, which is selectively set by the drive circuit 27; the dead time Td, which is set to prevent arm short circuits between the positive and negative switching elements; the flow rate Q of the cooling medium; and the water temperature Tw of the cooling medium. Based on these parameters, the temperature threshold setting unit 91 calculates the stop temperature Tstp and outputs it to the overheat protection control unit 92.

[0147] The output needs to be stopped before the element temperature Tj reaches the element's operating limit temperature Tm and degrades. For this reason, the stop temperature Tstp is set to the operating limit temperature Tm minus the temperature difference Tdif between the element temperature Tj and the detected temperature Ts and a predetermined margin temperature Tmgn. The stop temperature Tstp is expressed as shown in equation (1).

[0148] Tstp = Tm - Tdif - Tmgn ... (1) The temperature difference Tdif is the difference between the element temperature Tj and the detected temperature Ts, and can be expressed as shown in equation (2).

[0149] Tdif = Tj - Ts ... (2) Detected temperature Ts: Minimum value of temperature detection values ​​T1 to T6

[0150] The element temperature Tj is affected by the heat loss Pl of the switching elements 51 to 56 and the cooling state of the cooler 35. The element temperature Tj is the sum of the cooling water temperature Tw and the temperature difference Tjw between the water temperature Tw and the element temperature Tj. The temperature difference between the water temperature Tw and the element temperature Tjw can be expressed as Tjw = f(Tw, Q, Pl) and as a function F1 with the heat loss Pl of the switching elements 51 to 56, the cooling water flow rate Q, and the cooling water temperature Tw as arguments, as shown in equation (3).

[0151] Tj = Tw + Tjw = Tw + F1(Tw, Q, Pl) ... (3) The loss Pl of the switching element can be expressed as a function F2 as shown in equation (4).

[0152] Pl = F²(Irms, Vpn, fc, Rg, Td) ... (4) Phase current Irms: Effective value of the phase current flowing through the switching element DC voltage Vpn: DC voltage applied to the switching element Carrier frequency fc: Frequency at which the switching element switches Gate resistance Rg: Resistance value that determines the switching speed of the switching element Dead time Td: Simultaneous off period during switching to avoid short circuits between the high side and low side

[0153] If the gate resistance Rg and dead time Td are not switched, the parameters in equation (4) can be omitted, and the loss Pl of the switching element can be expressed as a function F3 as in equation (5).

[0154] Pl = F3(Irms, Vpn, fc) ... (5) Phase current Irms: Effective value of the phase current flowing through the switching element DC voltage Vpn: DC voltage applied to the switching element Carrier frequency fc: Frequency at which the switching element switches

[0155] From equations (2), (3), and (5) above, the temperature difference Tdif can be expressed as shown in equation (6) below.

[0156] Tdif = Tj - Ts = Tw + F1 (Tw, Q, Pl) - Ts = Tw + F1 (Tw, Q, F3 (Irms, Vpn, fc)) ... (6)

[0157] Therefore, the temperature difference Tdif can be estimated using the phase current Irms, DC voltage Vpn, carrier frequency fc, cooling water flow rate Q, and cooling water temperature Tw as input information. Some of these parameters may be omitted as fixed values. The temperature difference Tdif may also be estimated based on at least one of these parameters. The temperature threshold setting unit 91 can switch the stop temperature Tstp based on the estimated temperature difference Tdif.

[0158] This allows a predetermined temperature difference threshold Tdifth to be established. As shown in Figure 24, if the estimated temperature difference Tdif is smaller than the predetermined temperature difference threshold Tdifth, the stop temperature Tstp can be set to a higher value. If the estimated temperature difference Tdif is larger than the temperature difference threshold Tdifth, the stop temperature Tstp can be set to a lower value.

[0159] In this way, by switching the stop temperature Tstp according to the operating state of the power converter 100, it is possible to reliably prevent deterioration of the switching elements 51 to 56, prevent excessive limiting of the output of the power converter 100 in the overheat prevention control, and allow the power converter 100 to continue operating. At this time, the optimal values ​​for the temperature difference threshold Tdifth and the stop temperature Tstp may be determined by experiment. Alternatively, the optimal values ​​for the temperature difference threshold Tdifth and the stop temperature Tstp may be determined by simulation.

[0160] <Linear change of stop temperature according to estimated temperature difference> The estimated temperature difference Tdif changes continuously. Therefore, as shown in Figure 25, the stop temperature Tstp may be continuously changed according to the estimated temperature difference Tdif. This makes it possible to set the stop temperature Tstp appropriately according to the estimated temperature difference Tdif. This prevents excessive shutdown of the output of the power converter 100 and makes it possible to continue the operation of the power converter 100 up to its performance limit. The characteristics of the stop temperature Tstp with respect to the estimated temperature difference Tdif may be determined experimentally to find the optimal value. Alternatively, the characteristics of the stop temperature Tstp with respect to the estimated temperature difference Tdif may be determined experimentally to find the optimal value.

[0161] <Setting the stop temperature for the estimated loss> Figure 26 is the first figure showing the setting of the stop temperature Tstp for the estimated loss Pl of the power converter 100 according to Embodiment 1. Figure 27 is the second figure showing the setting of the stop temperature Tstp for the estimated loss Pl.

[0162] As mentioned above, the loss Pl of the switching element can be represented by a function F3 as shown in equation (5). Therefore, the loss Pl can be estimated using the phase current Irms, DC voltage Vpn, and carrier frequency fc as input information. Some of these parameters may be omitted as fixed values. The loss Pl may also be estimated based on at least one of these parameters. By estimating the loss Pl in the temperature threshold setting unit 91, it becomes possible to switch the stop temperature Tstp.

[0163] This allows a predetermined loss threshold Plth to be established, and as shown in Figure 26, if the estimated loss Pl is smaller than the predetermined loss threshold Plth, the stop temperature Tstp can be set to a higher value. If the estimated loss Pl is greater than the loss threshold Plth, the stop temperature Tstp can be set to a lower value.

[0164] In this way, by switching the stop temperature Tstp according to the operating state of the power converter 100, it is possible to reliably prevent the deterioration of the switching elements 51 to 56, prevent excessive limiting of the output of the power converter 100 in the overheat prevention control, and allow the power converter 100 to continue operating. At this time, the loss threshold Plth and the stop temperature Tstp may be determined experimentally to find the optimal values. Alternatively, the loss threshold Plth and the stop temperature Tstp may be determined by simulation to find the optimal values.

[0165] Since the cooling water flow rate Q and water temperature Tw information are not used, there is no need to equip the power converter 100 with a water temperature sensor 36 and a flow meter 37, thus reducing costs. Furthermore, even in configurations where cooling water flow rate and water temperature information cannot be obtained from a higher-level system, the power converter 100 can continue to operate while reliably preventing deterioration of the switching elements 51-56 and suppressing excessive shutdown of the power converter 100's output.

[0166] <Linear change of stop temperature according to estimated loss> The estimated loss Pl changes continuously. Therefore, as shown in Figure 27, the stop temperature Tstp may be continuously changed according to the estimated loss Pl. This makes it possible to set the stop temperature Tstp appropriately according to the estimated loss Pl. This prevents excessive shutdown of the output of the power converter 100 and makes it possible to continue the operation of the power converter 100 up to its performance limit. The characteristics of the stop temperature Tstp with respect to the estimated loss Pl may be determined experimentally to find the optimal value. Alternatively, the characteristics of the stop temperature Tstp with respect to the estimated loss Pl may be determined by simulation to find the optimal value.

[0167] <Processing of the Control Unit> Figure 28 is a first flowchart showing the processing of the control unit 90 of the power converter 100 according to Embodiment 1. Figure 29 is a second flowchart showing the processing of the control unit 90. Figure 29 shows the processing that follows Figure 28.

[0168] The processes shown in Figures 28 and 29 are executed by the processing unit of the control unit 90 of the power converter 100. The processes shown in Figures 28 and 29 may be executed at predetermined intervals (for example, every 10 ms). Alternatively, they may be executed not at predetermined intervals, but at each event, such as each time a signal is received from the rotation angle sensor 11 of the rotating electric machine 10.

[0169] The process shown in Figure 28 is initiated, and in step S101, input information is acquired. The temperature threshold setting unit 91 and the overheat protection control unit 92 acquire various input information. In addition to the torque command Trq* and temperature detection values ​​T1 to T6 (detection temperature Ts), the input information includes one or more of the following: rotational speed ω, phase current Irms, DC voltage Vpn, carrier frequency fc, gate resistance value Rg, dead time Td, flow rate Q, and water temperature Tw, or all of these.

[0170] In step S102, parameters to be compared are selected and generated from the input information. Within the overheat protection control, information necessary to set the stop temperature Tstp is selected or generated. Estimation of the temperature difference Tdif and loss Pl may also be performed.

[0171] In step S103, it is checked whether the selected parameter is on the side that increases the temperature difference Tdif. That is, the relationship between the parameter and a predetermined threshold is determined to check whether it is on the side that increases the temperature difference Tdif.

[0172] In step S104, it is determined whether the temperature difference Tdif is increasing. If the temperature difference Tdif is increasing (determination is YES), proceed to step S105 and set the stop temperature Tstp to a value on the downward side. Then proceed to step S111.

[0173] If the temperature difference Tdif does not increase in step S104 (the determination is NO), proceed to step S106 and set the stop temperature Tstp to the value on the rising side. Then proceed to step S111.

[0174] In step S111, it is checked whether the detected temperature Ts is higher than the set stop temperature Tstp. In step S112, it is determined whether the detected temperature Ts is higher than the stop temperature Tstp. If the detected temperature Ts is higher than the stop temperature Tstp (determined as YES), the process proceeds to step S117, and power conversion is stopped. Then the process ends.

[0175] If, in step S112, the detected temperature Ts is not higher than the stop temperature Tstp (the determination is NO), proceed to step S113. In step S113, check whether the detected temperature Ts is higher than the limit temperature Tlmt.

[0176] In step S114, it is determined whether the detected temperature Ts is higher than the limit temperature Tlmt. If the detected temperature Ts is higher than the limit temperature Tlmt (determination is YES), the process proceeds to step S115 to execute power conversion limit control. This is to limit the output of the power conversion to prevent overheating of the switching element. The process then ends.

[0177] If the detected temperature Ts in step S114 is not higher than the limit temperature Tlmt (determination is NO), proceed to step S116 and continue with normal power conversion control. Then terminate the process.

[0178] The processes described in steps S104, S105, and S106 of Figure 28 correspond to the switching of the stop temperature Tstp, as explained in Figures 7, 10, 12, 14, 16, 18, 20, 22, 24, and 26.

[0179] <Processing of continuous changes in stop temperature> The setting of continuous values ​​for the stop temperature Tstp, as explained in Figures 8, 11, 13, 15, 17, 19, 21, 23, 25, and 27, will be explained in the third flowchart showing the processing of the control unit 90 in Figure 30.

[0180] Figure 29 shows the continuation of the flowchart in Figure 30. The process in Figure 30 may be executed at predetermined time intervals (for example, every 10 ms). Alternatively, it may be executed not at predetermined time intervals, but at each event, such as each time a signal is received from the rotation angle sensor 11 of the rotating electric machine 10.

[0181] The difference between Figure 30 and Figure 28 is that steps S103 through S106 are replaced with step S107. Step S107 will now be explained.

[0182] In step S107, the stop temperature Tstp is set according to the selected or generated parameters. This process corresponds to setting a continuous value for the stop temperature Tstp as explained in Figures 8, 11, 13, 15, 17, 19, 21, 23, 25, and 27.

[0183] 2. Embodiment 2 Figure 31 is a functional block diagram of the control unit 90 of the power converter 100 according to Embodiment 2. Figure 32 is a diagram showing the setting of the stop temperature Tstp with respect to the rotational speed ω of the power converter 100 according to Embodiment 2.

[0184] The power converter 100 according to Embodiment 2 differs from the power converter 100 according to Embodiment 1 only in the configuration of the control unit 90 shown in Figure 31. The configuration of the power converter 100 shown in Figure 1 and the hardware configuration of the control unit 90 shown in Figure 2 can be applied as is to Embodiment 2.

[0185] The functional block diagram of the control unit 90 in Figure 31 differs from the functional block diagram in Figure 3 in that it includes an additional stall determination unit 99 that determines whether the rotating electric machine 10 is stalled. The stall determination unit 99 changes the stop temperature Tstp when it determines that the rotating electric machine 10 is stalled. Here, stalled state refers to a state in which the rotational speed of the rotating electric machine is reduced due to overload or other reasons.

[0186] At this time, the current flowing through the switching elements 51 to 56 may increase rapidly, potentially causing a sharp rise in the element temperature Tj, which indicates the temperature of the semiconductor junction. Therefore, it is necessary to anticipate an increase in the temperature difference Tdif and lower the stop temperature Tstp to prevent damage to the switching elements 51 to 56.

[0187] <Functional Block of Control Device> As shown in the functional block diagram of the control unit 90 in Figure 31, the stall determination unit 99 receives the rotational speed ω of the rotating electric machine 10 as input information. The stall determination unit 99 determines that the machine is stalled if the rotational speed ω is less than or equal to a predetermined stall threshold ωst. If the machine is stalled, the stall determination flag S1 is set to Hi, and if the machine is not stalled, the stall determination flag S1 is set to Lo and output to the temperature threshold setting unit 91.

[0188] The temperature threshold setting unit 91 receives the rotational speed ω and the stall determination flag S1 as input information. If the stall determination flag S1 is Hi, the temperature threshold setting unit 91 sets a predetermined stop temperature Tstp, and if the stall determination flag S1 is Lo, it sets the stop temperature Tstp based on the rotational speed ω, which is a parameter indicating the operating state of the power converter 100, similar to Embodiment 1.

[0189] Figure 32 shows how the control unit 90 sets the stop temperature Tstp in relation to the rotational speed ω. As shown in Figure 32, when the rotational speed ω is less than or equal to a predetermined stall threshold ωst, the stop temperature Tstp is set to the predetermined stop temperature Tstp. At rotational speeds greater than the stall threshold, which are not stalled, the stop temperature Tstp is set to a higher value if the rotational speed ω is less than a predetermined rotational speed threshold ωth, and to a lower value if the rotational speed ω is greater than the predetermined rotational speed threshold ωth, similar to Figure 7 in Embodiment 1.

[0190] The predetermined stop temperature Tstp when a stall condition is determined will be explained. When the rotational speed ω in a stall condition is 0 rpm, the current flowing through the switching elements 51 to 56 is a DC current. The condition under which this DC current is maximum is fixed at the peak value of the AC current, resulting in a state where the current flows concentratedly through a specific phase.

[0191] When the rotational speed ω is 0 rpm, the losses of the switching elements 51-56 are greater than when the rotational speed ω is a low rotation other than 0 rpm and AC current flows through the rotating electric machine 10. When the losses are large, the temperature difference Tdif between the element temperature Tj and the detection temperature Ts of the switching elements 51-56 becomes large, so the stop temperature Tstp needs to be set low.

[0192] Therefore, the predetermined stop temperature Tstp is determined by considering the state in which the maximum current at 0 rpm flows through the switching elements 51 to 56. The temperature difference Tdif between the element temperature Tj and the detected temperature Ts is considered in the loss in the state in which a current fixed at its peak value flows through the switching elements 51 to 56.

[0193] The loss when the current flowing through switching elements 51-56 is fixed at the peak value of the maximum AC current at 0 rpm is greater than the loss at low rotation speeds above the stall threshold ωst. For this reason, the stop temperature Tstp is set to a value lower than the stop temperature Tstp at low rotation speeds above the stall threshold ωst.

[0194] <Effects of Stall Prevention> In the power converter 100 according to Embodiment 2, a stall condition in which a large current may flow through the switching elements 51 to 56 is determined, and the stop temperature Tstp is set to a predetermined lower stop temperature Tstp. This ensures that deterioration of the switching elements 51 to 56 is reliably prevented even in a stall condition, prevents excessive restriction of the output of the power converter 100, and allows the power converter 100 to continue operating.

[0195] <Processing in the control unit>

[0196] Figure 33 is a flowchart showing the processing of the control unit 90 of the power converter 100 according to Embodiment 2. Figure 33 shows the processing that follows the flowchart of Figure 28. The processing in Figures 28 and 33 may be executed at predetermined intervals (for example, every 10 ms). Alternatively, instead of at predetermined intervals, the processing may be executed at each event, such as each time a signal is received from the rotation angle sensor 11 of the rotating electric machine 10.

[0197] The difference between Figure 33, which represents Embodiment 2, and Figure 29, which represents Embodiment 1, is that steps S121 to S123 are inserted before step S111. Steps S121 to S123 will now be described.

[0198] After the stop temperature Tstp on the rising side is set in step S105 of Figure 28, or after the stop temperature Tstp on the descending side is set in step S106, the process proceeds to step S121 of Figure 33.

[0199] In step S121, the current rotational speed ω of the rotating electric machine 10 is compared with the stall threshold ωst. In step S122, it is determined whether the rotational speed ω is less than or equal to the stall threshold ωst. If the rotational speed ω is less than or equal to the stall threshold ωst (decision is YES), proceed to step S123. If the rotational speed ω is not less than or equal to the stall threshold ωst (decision is NO), proceed to step S111.

[0200] In step S123, the set stop temperature Tstp is lowered. Then, the process proceeds to step S111. The subsequent processing flow is the same as in Figure 29.

[0201] <Use of Wide Bandgap Semiconductors> In recent years, silicon carbide (SiC) and gallium nitride (GaN) have attracted attention as materials for switching elements. Switching elements formed from these materials have lower resistance in the ON state compared to conventional switching elements using silicon (Si), thus reducing power loss. In addition, they have a high electron saturation rate, allowing for quick switching between the ON and OFF states and further reducing power loss. Furthermore, compared to silicon, switching elements using silicon carbide or gallium nitride can be operated in higher temperature environments.

[0202] Switching elements constructed using wide-bandgap semiconductors have faster switching speeds compared to conventional switching elements constructed using silicon (Si). Therefore, when the losses of a switching element are divided into conduction loss and switching loss, wide-bandgap semiconductors exhibit smaller switching loss and predominantly conduction loss at high currents near the rated current compared to switching elements constructed using Si.

[0203] Therefore, in the worst-case scenario of a stall state where a DC current flows at a rotational speed of 0 rpm, the conduction loss becomes large. Consequently, the loss at 0 rpm compared to the loss at normal rotational speeds is greater when a wide-bandgap semiconductor is used than when Si is used. Thus, determining the stall state and setting the stop temperature Tstp to a predetermined stop temperature Tstp, as in Embodiment 2, is more necessary and effective when a wide-bandgap semiconductor is used.

[0204] In the power converter 100 according to the above embodiment, a configuration was described in which the torque command Trq* is limited to a predetermined torque command value or less as a method for limiting the output in overheat prevention control. However, the output limiting method is not limited to this, as long as it is a method that effectively limits the output.

[0205] For example, the current command value may be limited with respect to the d-axis current command value Id* and the q-axis current command value Iq*. More specifically, the output may be effectively reduced by limiting the current command value to predetermined d-axis current command limit values ​​and q-axis current command limit values ​​with respect to the d-axis current command value Id* and the q-axis current command value Iq*. Alternatively, the output may be effectively reduced by limiting the command value to a predetermined ratio less than 1 multiplied by the d-axis current command value Id* and the q-axis current command value Iq*.

[0206] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are envisioned within the scope of the disclosed art. For example, these include modifying, adding or omitting at least one component, or extracting at least one component and combining it with components of other embodiments.

[0207] 2 AC bus, 10 Rotating electric machine, 11 Rotation angle sensor, 12 DC power supply, 24 Voltage detection unit, 25 Power conversion circuit, 26 Current detection unit, 35 Cooler, 36 Water temperature sensor, 37 Flow meter, 40 Carrier frequency sensor, 51, 52, 53, 54, 55, 56 Switching element, 71, 72, 73, 74, 75, 76 Temperature detector, 90 Control unit, 100 Power conversion device, 261 U-phase current detection unit, 262 V-phase current detection unit, 263 W-phase current detection unit, fc Carrier frequency, fcth Frequency threshold, Irms Phase current, Ith Current threshold, Pl Loss, Plth Loss threshold, Q Flow rate, Qth Flow rate threshold, Rg Gate resistance value, Rth Gate resistance threshold, Td Dead time, Tdif Temperature difference, Tdifth; Temperature difference threshold, Tdth; Dead time threshold, Tj; Element temperature, Tlmt; Limiting temperature, Ts; Detected temperature, Tstp; Stop temperature, Tw; Water temperature, Twth; Water temperature threshold, Vpn; DC voltage, Vth; Voltage threshold, ω; Rotational speed, ωst; Stall threshold, ωth; Rotational speed threshold

Claims

1. A power conversion device comprising: a power conversion circuit having a leg provided with a positive-side switching element connected to the positive side of a DC power supply, a negative-side switching element connected to the negative side of the DC power supply, and a power supply line connecting the connection point where the positive-side switching element and the negative-side switching element are connected in series to a rotating electric machine; a temperature detector for detecting the temperature of the switching element; and a control unit that controls the switching element of the power conversion circuit to perform power conversion, limits the output of the power conversion circuit when the temperature detected by the temperature detector is higher than a predetermined limit temperature, and stops power conversion when the temperature detected by the temperature detector is higher than a stop temperature set higher than the limit temperature, wherein the control unit changes the stop temperature based on the driving state of the power conversion device.

2. The power conversion device according to claim 1, further comprising a rotation speed sensor for detecting the rotation speed of the rotating electric machine, wherein the control unit raises the stop temperature when the rotation speed of the rotating electric machine detected by the rotation speed sensor is lower than a predetermined rotation speed threshold.

3. The power conversion device according to claim 1, further comprising a rotation speed sensor for detecting the rotation speed of the rotating electric machine, wherein the control unit raises the stop temperature as the rotation speed of the rotating electric machine detected by the rotation speed sensor decreases.

4. A power conversion device according to any one of claims 1 to 3, comprising a phase current detection sensor for detecting the phase current flowing through the power supply line of the power conversion circuit, wherein the control unit raises the stop temperature when the phase current detected by the phase current detection sensor is smaller than a predetermined phase current threshold.

5. The power conversion device according to any one of claims 1 to 3, comprising a phase current detection sensor for detecting the phase current flowing through the power supply line of the power conversion circuit, wherein the control unit raises the stop temperature as the phase current detected by the phase current detection sensor decreases.

6. A power conversion device according to any one of claims 1 to 5, comprising a voltage sensor for detecting the voltage of the DC power supply, wherein the control unit raises the stop temperature when the voltage of the DC power supply detected by the voltage sensor is lower than a predetermined voltage threshold.

7. The power conversion device according to any one of claims 1 to 5, comprising a voltage sensor for detecting the voltage of the DC power supply, wherein the control unit raises the stop temperature as the voltage of the DC power supply detected by the voltage sensor decreases.

8. The power conversion device according to any one of claims 1 to 7, wherein the control unit raises the stop temperature when the carrier frequency, which is the switching frequency of the switching element, is lower than a predetermined frequency threshold.

9. The power conversion device according to any one of claims 1 to 7, wherein the control unit increases the stop temperature as the carrier frequency, which is the switching frequency of the switching element, decreases.

10. The power conversion device according to any one of claims 1 to 9, wherein the control unit increases the stop temperature as the gate resistance value for driving the switching element decreases.

11. The power conversion device according to any one of claims 1 to 10, wherein the control unit increases the stop temperature as the dead time, which is provided to prevent a short circuit between the positive-side switching element and the negative-side switching element connected in series, decreases.

12. The power converter according to any one of claims 1 to 11, further comprising a flow sensor for detecting the flow rate of a cooling medium of a cooling device that cools the power converter, wherein the control unit raises the stop temperature when the flow rate of the cooling medium detected by the flow sensor is greater than a predetermined flow rate threshold.

13. The power conversion device according to any one of claims 1 to 11, comprising a flow sensor for detecting the flow rate of a cooling medium of a cooling device that cools the power conversion device, wherein the control unit raises the stop temperature as the flow rate of the cooling medium detected by the flow sensor increases.

14. The power conversion device according to any one of claims 1 to 13, further comprising a cooling medium temperature sensor for detecting the temperature of the cooling medium of a cooling device that cools the power conversion device, wherein the control unit raises the stop temperature when the temperature of the cooling medium detected by the cooling medium temperature sensor is higher than a predetermined cooling medium temperature threshold.

15. A power conversion device according to any one of claims 1 to 13, comprising a cooling medium temperature sensor for detecting the temperature of the cooling medium of a cooling device that cools the power conversion device, wherein the stop temperature is increased as the temperature of the cooling medium detected by the cooling medium temperature sensor rises.

16. The power conversion device according to any one of claims 1 to 15, wherein the control unit raises the stop temperature when the current command value for power conversion is smaller than a predetermined current command threshold.

17. The power conversion device according to any one of claims 1 to 15, wherein the control unit raises the stop temperature as the current command value for power conversion decreases.

18. The power conversion device according to any one of claims 1 to 17, wherein the control unit estimates the loss of the switching element of the power conversion circuit, and raises the stop temperature when the estimated loss of the switching element is lower than a predetermined loss threshold.

19. The power conversion device according to any one of claims 1 to 17, wherein the control unit estimates the loss of the switching element of the power conversion circuit and increases the stop temperature as the estimated loss of the switching element decreases.

20. The power conversion device according to claim 18 or 19, comprising at least one of the following sensors: a phase current detection sensor for detecting the phase current flowing through the power supply line of the power conversion circuit; a voltage sensor for detecting the voltage of the DC power supply; and a carrier frequency sensor for detecting the carrier frequency which is the switching frequency of the switching element, wherein the control unit estimates the loss of the switching element of the power conversion circuit based on the detected values ​​detected by the provided sensors.

21. The power conversion device according to claim 18 or 19, comprising a phase current detection sensor for detecting a phase current flowing through the power supply line of the power conversion circuit, a voltage sensor for detecting the voltage of the DC power supply, and a carrier frequency sensor for detecting the carrier frequency which is the switching frequency of the switching element, wherein the control unit estimates the loss of the switching element of the power conversion circuit based on the phase current detected by the phase current detection sensor, the voltage of the DC power supply detected by the voltage sensor, and the carrier frequency detected by the carrier frequency sensor.

22. The power conversion device according to any one of claims 1 to 21, wherein the control unit estimates the junction temperature difference, which is the difference between the junction temperature of the semiconductor of the switching element of the power conversion circuit and the temperature detected by the temperature detector, and raises the stop temperature when the estimated junction temperature difference is smaller than a predetermined junction temperature difference threshold.

23. The power conversion device according to any one of claims 1 to 21, wherein the control unit estimates a junction temperature difference, which is the difference between the junction temperature of the semiconductor of the switching element of the power conversion circuit and the temperature detected by the temperature detector, and increases the stop temperature as the estimated junction temperature difference decreases.

24. The power conversion device according to claim 22 or 23, comprising at least one of the following sensors: a phase current detection sensor for detecting the phase current flowing through the power supply line of the power conversion circuit; a voltage sensor for detecting the voltage of the DC power supply; a carrier frequency sensor for detecting the carrier frequency which is the switching frequency of the switching element; a flow rate sensor for detecting the flow rate of the cooling medium of a cooling device for cooling the power conversion device; and a cooling medium temperature sensor for detecting the temperature of the cooling medium of a cooling device for cooling the power conversion device, wherein the control unit estimates the junction temperature difference based on the detected values ​​detected by the provided sensors.

25. The power conversion device according to claim 22 or 23, comprising: a phase current detection sensor for detecting a phase current flowing through the power supply line of the power conversion circuit; a voltage sensor for detecting the voltage of the DC power supply; a carrier frequency sensor for measuring the carrier frequency which is the switching frequency of the switching element; a flow rate sensor for detecting the flow rate of a cooling medium of a cooling device for cooling the power conversion device; and a cooling medium temperature sensor for detecting the temperature of the cooling medium of a cooling device for cooling the power conversion device, wherein the control unit estimates the junction temperature difference based on the phase current detected by the phase current detection sensor, the voltage of the DC power supply detected by the voltage sensor, the carrier frequency detected by the carrier frequency sensor, the flow rate of the cooling medium detected by the flow rate sensor, and the temperature of the cooling medium detected by the cooling medium temperature sensor.

26. The power conversion device according to claim 2, wherein the control unit lowers the stop temperature to a level lower than the stop temperature when the rotational speed of the rotating electric machine is equal to or greater than the stall rotational speed threshold and lower than the rotational speed threshold, if the rotational speed of the rotating electric machine detected by the rotational speed sensor is lower than a stall rotational speed threshold set to be lower than the rotational speed threshold.

27. A power conversion device according to any one of claims 1 to 25, comprising a rotation speed sensor for detecting the rotation speed of the rotating electric machine, wherein the control unit determines that the rotating electric machine is in a stalled state when the rotation speed of the rotating electric machine detected by the rotation speed sensor is lower than a predetermined stall rotation speed threshold, determines that the rotating electric machine is not in a stalled state when the rotation speed of the rotating electric machine is equal to or greater than the stall rotation speed threshold, and when the rotating electric machine is in a stalled state, the stop temperature is lowered to a level lower than when the rotating electric machine is not in a stalled state.

28. The power conversion device according to any one of claims 1 to 27, wherein the switching element of the power conversion circuit is a wide-bandgap semiconductor.

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