Power conversion device

Abstract

The present application aims to realize a small power conversion device capable of preventing a sharp temperature rise. A power conversion device (1) includes a control operation section (3) that generates a first drive signal, a stall determination section (27) that determines a stall state of a motor (2), a duty ratio control section (23) that outputs a second drive signal, a power conversion circuit (4) that drives the motor based on the second drive signal, and a loss reduction section (26) that reduces the heat generation amount of a switching element (5) of the circuit (4) in the case where the stall state is determined. The duty ratio control section (23) outputs a second drive signal obtained by changing the on-time of a switching element in the first drive signal in order to distribute current to a switching element connected in series with a freewheel diode (6) of the circuit (4) having the maximum temperature information, in the case where the stall state is determined and the first temperature information of the switching element (5) connected in series with the freewheel diode is reduced.

Description

Technical Field

[0001] This application relates to power conversion devices. Background Technology

[0002] Power conversion devices are used in devices such as those with electric motors as loads, hybrid vehicles equipped with both electric motors and engines, and electric vehicles. In these vehicles, situations such as driving onto a curb with the tires locked, insufficient throttle input on a steep slope, or stopping the vehicle and locking the motor can occur. Furthermore, in vehicles climbing hills at extremely low speeds, the rotor may sometimes fail to keep up, causing the motor to stall. When the motor locks up or stalls, measures must be taken to prevent prolonged and high-current energization of the multiple power conversion elements constituting the power conversion device—such as switching elements and return diodes—or specific power conversion elements, which could lead to thermal damage.

[0003] Patent Document 1 discloses a power conversion device that includes a heat generation measurement unit for measuring the heat loss of each of the multiple power conversion elements constituting the power conversion device, and pre-stores the thermal resistance value of each power conversion element. The power conversion device of Patent Document 1 calculates the temperature rise in each power conversion element based on the thermal resistance value and the heat loss measured by the heat generation measurement unit. In order to distribute the current flowing through the power conversion element with the largest calculated temperature rise to the other elements, the on / off timing of the drive signals generated by the control arithmetic unit for each power conversion element is modified.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 3638265 ( Figure 1 , Figure 12 ) Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] In power conversion devices installed in vehicles, etc., the conduction rate of switching elements is higher than that of return diodes during stable operation. Furthermore, the size of the power conversion elements is one of the factors determining the size of the power conversion device. Therefore, from the viewpoint of conduction rate during stable operation, the size of the power conversion elements constituting the power conversion device is generally designed so that the return diode is smaller than the switching element. Therefore, in the power conversion device of Patent Document 1, when the return diode is designed to be smaller than the switching element, if a large current flows through the return diode when the motor locks up or stalls, the temperature rises sharply, and the current distribution sometimes reaches its limit. To avoid a sharp temperature rise, there is a problem of increasing the size of the return diode.

[0009] The purpose of the technology disclosed in this application is to realize a small power conversion device that can prevent a rapid rise in temperature.

[0010] Technical means for solving technical problems

[0011] An example power conversion device disclosed in this application provides alternating current converted from direct current to drive a motor. The power conversion device includes: a power conversion circuit having multiple switching elements and return diodes, and multiple temperature monitors that output temperature information (i.e., first temperature information) of each switching element, and providing the alternating current to drive the motor; a control calculation unit that determines the switching timing of the multiple switching elements in the power conversion circuit and generates a first drive signal; and a rotation detector that detects the rotor position of the motor. The power conversion device further includes: a component temperature estimation unit that estimates the temperature information of the return diode, i.e., the second temperature information, based on the first temperature information; a stall determination unit that determines the stall state of the motor based on the rotor position of the motor; a loss reduction unit that reduces the heat generation of the switching elements when the stall determination unit determines that the motor is in a stall state; a duty cycle control unit that outputs the first drive signal as a second drive signal without changing the first drive signal, or outputs a second drive signal obtained by changing the on-time of the switching elements in the first drive signal; and a gate drive circuit that outputs a third drive signal that causes multiple switching elements to switch according to the second drive signal to the power conversion circuit. When the stall determination unit determines that the stall state has occurred, and the first temperature information of the switching element connected in series with the return diode with the maximum second temperature information has been reduced by the operation of the loss reduction unit, the duty cycle control unit outputs a second drive signal obtained by changing the on-time of the switching element in the first drive signal to the gate drive circuit, so as to distribute the current flowing through the return diode with the maximum second temperature information to the switching element connected in series with the return diode.

[0012] Invention Effects

[0013] In an example power conversion device disclosed in this application, when the first temperature information of the switching element connected in series with the return diode, which is determined to be in a stall state, is reduced by the operation of the loss reduction section, the current flowing through the return diode is distributed to the series-connected switching element. Therefore, it can be miniaturized and prevents a sharp rise in temperature. Attached Figure Description

[0014] Figure 1This is a diagram showing the structure of the power conversion device according to Embodiment 1.

[0015] Figure 2 It is shown Figure 1 A diagram showing the structure of a power conversion circuit.

[0016] Figure 3 It is shown Figure 1 A diagram showing the structure of the control and arithmetic unit.

[0017] Figure 4 This is a diagram illustrating an example of loss calculation for the power conversion device according to Embodiment 1.

[0018] Figure 5 This is a diagram illustrating an example of the power-on time allocation of a power conversion device before the loss reduction operation.

[0019] Figure 6 This is a diagram showing an example of the power-on time allocation of the power conversion device according to Embodiment 1.

[0020] Figure 7 This is a diagram showing an example of the maximum loss of a power conversion device before the loss reduction operation.

[0021] Figure 8 This is a diagram illustrating an example of the maximum loss of the power conversion device according to Embodiment 1.

[0022] Figure 9 This is a diagram illustrating the hardware structure for implementing the power conversion device according to Embodiment 1.

[0023] Figure 10 This is a diagram showing the structure of the first power conversion device according to Embodiment 2.

[0024] Figure 11 This is a diagram showing the structure of the second power conversion device according to Embodiment 2.

[0025] Figure 12 This is a diagram showing the structure of the first power conversion device according to Embodiment 3.

[0026] Figure 13 This is a diagram showing the structure of the second power conversion device according to Embodiment 3.

[0027] Figure 14 This is a diagram showing the structure of the power conversion device according to Embodiment 4.

[0028] Figure 15 This is a diagram showing the structure of the power conversion device according to Embodiment 5.

[0029] Figure 16This is a diagram showing the structure of the power conversion device according to Embodiment 6. Detailed Implementation

[0030] Implementation method 1.

[0031] Figure 1 This is a diagram showing the structure of the power conversion device according to Embodiment 1. Figure 2 It is shown Figure 1 A diagram showing the structure of the power conversion circuit. Figure 3 It is shown Figure 1 A diagram showing the structure of the control and arithmetic unit. Figure 4 This is a diagram illustrating an example of loss calculation for the power conversion device according to Embodiment 1. Figure 5 This is a diagram illustrating an example of the power-on time allocation of the power conversion device before the loss reduction operation. Figure 6 This is a diagram showing an example of the power-on time allocation of the power conversion device according to Embodiment 1. Figure 7 This is a diagram showing an example of the maximum loss of the power conversion device before the loss reduction operation. Figure 8 This is a diagram illustrating an example of the maximum loss of the power conversion device according to Embodiment 1. Figure 9 This diagram illustrates the hardware structure for implementing the power conversion device according to Embodiment 1. The power conversion device 1 includes a power conversion circuit 4, a current detector 7, a rotation detector 9 for detecting rotor position θ, a gate drive circuit 8, a duty cycle control unit 23, a control calculation unit 3, a loss reduction unit 26, a stall determination unit 27, and a component temperature estimation unit 25. The power conversion device 1 drives, for example, a three-phase AC motor 2 as a load. Figure 1 , Figure 2 The diagram illustrates an example where the load of the power conversion device 1 is a three-phase AC motor 2. In this case, the power conversion circuit 4 converts direct current (DC) to alternating current (AC) and supplies the AC power obtained from the DC to the motor 2. The current detector 7 detects the values ​​of the output current from the power conversion circuit 4 to the motor 2, namely the output current values ​​iu, iv, and iw.

[0032] In the power conversion circuit 4, for example, an arm is formed by two power conversion elements: a switching element 5a such as an IGBT (Insulated Gate Bipolar Transistor) and a return diode 6a connected in reverse parallel to the switching element 5a. Figure 2The power conversion circuit 4 shown has six arms. A branch formed by connecting the first arm, containing a switching element 5a and a return diode 6a, and the second arm, containing a switching element 5b and a return diode 6b, in series has an output terminal 51u connected to the load between these two arms. A branch formed by connecting the third arm, containing a switching element 5c and a return diode 6c, and the fourth arm, containing a switching element 5d and a return diode 6d, in series has an output terminal 51v connected to the load between these two arms. A branch formed by connecting the fifth arm, containing a switching element 5e and a return diode 6e, and the sixth arm, containing a switching element 5f and a return diode 6f, in series has an output terminal 51w connected to the load between these two arms. Appropriately, the switching elements are uniformly designated as 5, and 5a to 5f are used in distinguishing cases. The return diodes are uniformly designated as 6, and 6a to 6f are used in distinguishing cases.

[0033] One end of each of the three branches is connected to the high-potential side wiring 52p, and the other end of each branch is connected to the low-potential side wiring 52n. A DC power supply device 10 and a filter capacitor 11 are connected between the input terminal 50p connected to the high-potential side wiring 52p and the input terminal 50n connected to the low-potential side wiring 52n. The DC power supply device 10 supplies power to the power conversion device 1 via the filter capacitor 11.

[0034] like Figure 1 , Figure 2 As shown, when the load is a three-phase AC motor 2, the power conversion circuit 4 has three branches. The output terminals 51u, 51v, and 51w of each branch are connected to the U-phase, V-phase, and W-phase of the motor 2, respectively. Appropriately, the branch connected to the U-phase is referred to as the U-phase branch, the component connected to the P-side (high potential side) of the DC power supply device 10 in the U-phase branch is called the UP-phase power conversion element, and the component connected to the N-side (low potential side) of the DC power supply device 10 is called the UN-phase power conversion element. The branches and arms of the V-phase and W-phase are also represented in the same way as the U-phase branch and the U-phase arms. Switching element 5a and return diode 6a are UP-phase power conversion elements, switching element 5b and return diode 6b are UN-phase power conversion elements, switching element 5c and return diode 6c are VP-phase power conversion elements, and switching element 5d and return diode 6d are VN-phase power conversion elements. Switching element 5e and return diode 6e are WP phase power conversion elements, while switching element 5f and return diode 6f are WN phase power conversion elements.

[0035] The power conversion circuit 4 includes gate terminals 53a to 53f that receive a gate drive signal sg4 output from the gate drive circuit 8. Gate terminal 53a is connected to the gate of switching element 5a, and gate terminal 53b is connected to the gate of switching element 5b. Similarly, gate terminals 53c and 53d are connected to the gates of switching elements 5c and 5d, respectively, and gate terminals 53e and 53f are connected to the gates of switching elements 5e and 5f, respectively. Furthermore, the power conversion circuit 4 includes temperature monitors 24a to 24f that detect the temperature information of switching elements 5a to 5f, i.e., the temperature rise ΔTsw. The temperature rise ΔTswb of switching element 5a detected by temperature monitor 24a is output from monitor terminal 54a, and the temperature rise ΔTswb of switching element 5b detected by temperature monitor 24b is output from monitor terminal 54b. Similarly, the temperature rise ΔTswc of switching element 5c detected by temperature monitor 24c is output from monitor terminal 54c, and the temperature rise ΔTswd of switching element 5d detected by temperature monitor 24d is output from monitor terminal 54d. The temperature rise ΔTswe of switching element 5e detected by temperature monitor 24e is output from monitor terminal 54e, and the temperature rise ΔTswf of switching element 5f detected by temperature monitor 24f is output from monitor terminal 54f. Temperature rise ΔTsw is a collective term for the six temperature rises ΔTswa to ΔTswf. When not distinguishing between the six temperature rises ΔTswa to ΔTswf, it is appropriate to represent it as temperature rise ΔTsw.

[0036] The component temperature estimation unit 25 estimates the temperature information, i.e., the temperature rise ΔTdi, of each return current diode 6a to 6f. More specifically, the component temperature estimation unit 25 estimates the temperature rises ΔTdia to ΔTdif of each return current diode 6a to 6f based on the temperature rises ΔTswa to ΔTswf output from the temperature monitors 24a to 24f of each switching element 5a to 5f. Appropriately, the temperature rise ΔTsw of the switching element 5 is represented as the first temperature information, and the temperature rise ΔTdi of the return current diode 6 is represented as the second temperature information. The temperature rise ΔTdia of the return current diode 6a is estimated based on the temperature rise ΔTswa of the switching element 5a, and the temperature rise ΔTdib of the return current diode 6b is estimated based on the temperature rise ΔTswb of the switching element 5b. The temperature rise ΔTdic of the return current diode 6c is estimated based on the temperature rise ΔTswc of the switching element 5c, and the temperature rise ΔTdid of the return current diode 6d is estimated based on the temperature rise ΔTswd of the switching element 5d. The temperature rise ΔTdie of the return diode 6e is estimated based on the temperature rise ΔTswe of the switching element 5e, and the temperature rise ΔTdif of the return diode 6f is estimated based on the temperature rise ΔTswf of the switching element 5f. Temperature rise ΔTdi is a collective term for the six temperature rises ΔTdia to ΔTdif. When not distinguishing between the six temperature rises ΔTdia to ΔTdif, it is appropriate to represent it as temperature rise ΔTdi.

[0037] Current detector 7 exists in each of phases U, V, and W. The current detector 7a for phase U, the current detector 7b for phase V, and the current detector 7c for phase W detect the output current values ​​iu, iv, and iw of each phase output from the output terminals 51u, 51v, and 51w to the motor 2, respectively. Current detector 7 is a collective term for the three current detectors 7a, 7b, and 7c. When not distinguishing between the three current detectors 7a, 7b, and 7c, it is appropriately referred to as current detector 7.

[0038] The control calculation unit 3 determines the switching timing of the switching elements 5a to 5f to enable the motor 2 to perform the desired operation and controls the output power from the power conversion circuit 4 to the motor 2. The control calculation unit 3 outputs the gate drive signal sg2 and the normal voltage command values ​​vu0*, vv0*, and vw0* to the duty cycle control unit 23. Based on the gate drive signal sg2, the duty cycle control unit 23 generates a gate drive signal sg3 with an adjusted duty cycle, and based on the gate drive signal sg3, the gate drive circuit 8 generates a gate drive signal sg4 to drive the switching elements 5a to 5f. The gate drive signal sg2 has six gate drive signals up0, un0, vp0, vn0, wp0, and wn0 corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e, and 5f. Gate drive signal sg3 has six gate drive signals up1, un1, vp1, vn1, wp1, and wn1 corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e, and 5f. Gate drive signal sg4 has six gate drive signals up, un, vp, vn, wp, and wn corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e, and 5f.

[0039] The stall determination unit 27 calculates the rotational speed Nm of the motor 2 based on the rotor position θ output from the rotation detector 9, and determines whether the motor 2 is in a stall state. A stall state is when the motor 2 is in an extremely low rotational speed state, and the rotor cannot follow the rotating magnetic field on the stator side of the motor 2. The stall determination unit 27 determines a stall state when the rotational speed Nm is, for example, 10 rpm. When the stall determination unit 27 determines that the motor 2 is in a stall state, it outputs a stall determination signal sig1 indicating the stall state. For example, the stall determination signal sig1 is at level H when indicating a stall state, and at level L when indicating a non-stall state. Here, the method for converting the rotor position θ into the rotational speed Nm of the motor 2 is known, and therefore its description is omitted.

[0040] The stall determination unit 27 outputs a stall determination signal sig1 to the duty cycle control unit 23 and the loss reduction unit 26. The duty cycle control unit 23 receives the stall determination signal sig1, indicating a stall state, and begins increasing the current allocation to the switching element through the return diode. The stall determination signal sig1, indicating a stall state, becomes an instruction to change the current allocation to the duty cycle control unit 23. The loss reduction unit 26 receives the stall determination signal sig1, indicating a stall state, and begins reducing the loss of the switching element 5. The stall determination signal sig1, indicating a stall state, becomes an instruction to perform the loss reduction operation of the switching element 5 for the loss reduction unit 26.

[0041] The loss reduction unit 26 receives a stall determination signal sig1 indicating a stall state and outputs a frequency change signal sig2 indicating a change to the control calculation unit 3. For example, the frequency change signal sig2 is at level H when indicating a change and at level L when indicating no change. The control calculation unit 3 receives the frequency change signal sig2 indicating a change and generates a gate drive signal sg2 at a lower frequency than before the stall state determination, i.e., lower than usual. Because the frequency of the gate drive signal sg2 is reduced, the loss of the switching element 5 is reduced. Because the loss of the switching element 5 is reduced, the heat generated by the switching element 5 is reduced. The loss reduction unit 26 is a function block that indicates the start of the operation to reduce the loss of the switching element 5 or the operation to reduce the heat generated by the switching element 5. The frequency change signal sig2 is an example of a loss reduction signal that reduces the loss of the switching element 5.

[0042] Upon receiving a stall determination signal sig1 indicating a stall state and when the loss of switching element 5 decreases, the duty cycle control unit 23 outputs voltage command values ​​vua*, vva*, and vwa* obtained by modifying the normal voltage command values ​​vu0*, vv0*, and vw0* output from the control calculation unit 3, and a voltage command modification signal sig3 that generates a gate drive signal sg2 based on these voltage command values ​​vua*, vva*, and vwa*, i.e., a modified voltage command modification signal sig3, to the control calculation unit 3. When the first temperature information, i.e., the temperature rise ΔTsw, of switching element 5 connected in series with the return diode 6 where the second temperature information, i.e., the temperature rise ΔTdi, is maximum, decreases due to the operation of the loss reduction unit 26, the duty cycle control unit 23 outputs voltage command values ​​vua*, vva*, vwa*, and the modified voltage command modification signal sig3 to the control calculation unit 3. For example, the voltage command change signal sig3 is at level H when indicating a change, and at level L when indicating no change.

[0043] The gate drive circuit 8 outputs a gate drive signal sg4 to control the on / off operation of the switching elements 5a to 5f based on the gate drive signal sg3 generated from the duty cycle control unit 23. The gate drive signal sg4 changes at the same timing as the gate drive signal sg3, but its voltage value is different from that of the gate drive signal sg3.

[0044] The control calculation unit 3 will be described below. The control calculation unit 3 includes: a vector control unit 12 that generates voltage command values ​​vu0*, vv0*, and vw0* for phases U, V, and W; a selector 41 that selects any one of the voltage command values ​​vu0*, vv0*, and vw0* generated by the voltage command values ​​vua*, vva*, and vwa* generated by the duty cycle control unit 23 and outputs the voltage command values ​​vu*, vv*, and vw*; and a PWM control unit 18 that generates a gate drive signal sg2 for PWM (Pulse Width Modulation) control of the power conversion circuit 4 based on the voltage command values ​​vu*, vv*, and vw*. Various methods exist for generating the gate drive signal sg2. Here, the following method is explained: the voltage command values ​​vu0*, vv0*, and vw0* of each phase are calculated using known vector control, V / F (Voltage / Frequency) control, etc., and the gate drive signal sg2 is generated based on the voltage command values ​​vu0*, vv0*, and vw0* of each phase and using the known triangular wave comparison sine wave PWM method.

[0045] like Figure 3 As shown, the vector control unit 12 includes a torque control unit 13, a current control unit 14, a voltage coordinate conversion unit 15, a coordinate conversion unit 16, and an angular velocity conversion unit 17. The PWM control unit 18 includes a triangular wave oscillator 19, comparators 20a, 20b, and 20c, inverters 21a, 21b, and 21c, and a dead-time circuit 22. Comparator 20a and inverter 21a are the U-phase comparator and inverter, comparator 20b and inverter 21b are the V-phase comparator and inverter, and comparator 20c and inverter 21c are the W-phase comparator and inverter.

[0046] First, the operation of the vector control unit 12 will be explained. The angular velocity conversion unit 17 converts the rotor position θ detected by the rotation detector 9 into an angular velocity ω. The torque control unit 13 calculates the d-axis current target value id* and the q-axis current target value iq* based on the angular velocity ω of the motor 2 obtained by the angular velocity conversion unit 17 and the torque command value T*. The torque command value T* is output from, for example, a higher-level control device. The coordinate conversion unit 16 generates the d-axis current value id and the q-axis current value iq based on the output current values ​​iu, iv, and iw detected by the current detector 7. The current control unit 14 controls the d-axis current value id and the q-axis current value iq, corresponding to the angular velocity ω of the motor 2, to follow the d-axis current target value id* and the q-axis current target value iq*, and outputs the d-axis voltage target value vd* and the q-axis voltage target value vq*. The voltage coordinate conversion unit 15 converts the d-axis voltage target value vd* and the q-axis voltage target value vq* into voltage command values ​​vu0*, vv0*, and vw0* for each phase.

[0047] For selector 41, selectors 41a, 41b, and 41c exist in each of the U-phase, V-phase, and W-phase. Selector 41 is a collective term for the three selectors 41a, 41b, and 41c. When not distinguishing between the three selectors 41a, 41b, and 41c, it is appropriately referred to as selector 41. The voltage command values ​​vu0*, vv0*, and vw0* generated by the vector control unit 12 are the voltage command values ​​when the stall determination unit 27 does not perform stall determination, i.e., the normal voltage command values. When the voltage command change signal sig3 output from the duty cycle control unit 23 indicates no change (e.g., L level), selector 41 outputs the voltage command values ​​vu0*, vv0*, and vw0* output from the duty cycle control unit 23 as voltage command values ​​vu*, vv*, and vw*. When the voltage command change signal sig3 output from the duty cycle control unit 23 indicates a change (e.g., H level), the selector 41 outputs the voltage command values ​​vua*, vva*, and vwa* output from the duty cycle control unit 23 as voltage command values ​​vu*, vv*, and vw*.

[0048] Selector 41a outputs the voltage command value vu0* as the voltage command value vu* when the voltage command change signal sig3 indicates no change, and outputs the voltage command value vua* as the voltage command value vu* when the voltage command change signal sig3 indicates a change. Similarly, selector 41b outputs the voltage command value vv0* as the voltage command value vv* when the voltage command change signal sig3 indicates no change, and outputs the voltage command value vva* as the voltage command value vv* when the voltage command change signal sig3 indicates a change. Selector 41c outputs the voltage command value vw0* as the voltage command value vw* when the voltage command change signal sig3 indicates no change, and outputs the voltage command value vwa* as the voltage command value vw* when the voltage command change signal sig3 indicates a change.

[0049] The operation of the PWM control unit 18 will be explained. The PWM control unit 18 includes a triangular wave oscillator 19 with an output carrier VC, comparators 20a, 20b, 20c, inverters 21a, 21b, 21c, and a dead-time circuit 22. The carrier VC is used to generate the gate drive signal sg1. The PWM control unit 18 generates the gate drive signal sg1 based on the voltage command values ​​vu*, vv*, and vw* of each phase, and generates a gate drive signal sg2 after adjusting the dead time of the gate drive signal sg1. The gate drive signal sg1 has six gate drive signals up*, un*, vp*, vn*, wp*, and wn* corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e, and 5f. The comparator 20a compares the voltage command value vu* with the output of the triangular wave oscillator 19, i.e., the carrier VC, and generates the gate drive signal up* for the switching element 5a on the P side. Inverter 21a generates a gate drive signal un* obtained by inverting the gate drive signal up*, for use in the N-side switching element 5b. Comparators 20b and 20c perform the same operation as inverters 21b and 21c. Comparator 20b compares the voltage command value vv* with the output of the triangular wave oscillator 19, i.e., the carrier wave vc, and generates a gate drive signal vp* for the P-side switching element 5c. Inverter 21b generates a gate drive signal vn* obtained by inverting the gate drive signal vp*, for use in the N-side switching element 5d. Comparator 20c compares the voltage command value vw* with the output of the triangular wave oscillator 19, i.e., the carrier wave vc, and generates a gate drive signal wp* for the P-side switching element 5e. Inverter 21c generates a gate drive signal wn* obtained by inverting the gate drive signal wp*, for use in the N-side switching element 5f.

[0050] When the turn-off action of switching element 5 is delayed, in order to prevent a power supply short circuit caused by the simultaneous conduction of switching elements 5a, 5c, 5e on the P side and switching elements 5b, 5d, 5f on the N side, the dead-time circuit 22 adds a dead-time tdd to delay the conduction period of the gate drive signal sg1. The dead-time circuit 22 outputs the gate drive signal sg2 obtained by adding the dead-time tdd to the gate drive signal sg1. The dead-time circuit 22 generates the gate drive signal up0 obtained by adding the dead-time tdd to the gate drive signal up*, and generates the gate drive signal un0 obtained by adding the dead-time tdd to the gate drive signal un*. Similarly, the dead-time circuit 22 generates a gate drive signal vp0 obtained by adding a dead time tdd to the gate drive signal vp*, generates a gate drive signal vn0 obtained by adding a dead time tdd to the gate drive signal vn*, generates a gate drive signal wp0 obtained by adding a dead time tdd to the gate drive signal wp*, and generates a gate drive signal wn0 obtained by adding a dead time tdd to the gate drive signal wn*.

[0051] The PWM control unit 18 compares the output of the selector 41, i.e., the voltage command values ​​vu*, vv*, and vw* for each of the three phases, with the output of the triangular wave oscillator 19, i.e., the carrier wave vc. As a result, when the amplitude of the voltage command values ​​vu*, vv*, and vw* for each phase is greater than the amplitude of the carrier wave vc, a gate drive signal is output to turn on the switching element on the P-side of that phase. Conversely, when the amplitude of the voltage command values ​​vu*, vv*, and vw* for each phase is less than the amplitude of the carrier wave vc, a gate drive signal is output to turn off the switching element on the P-side of that phase.

[0052] The PWM control unit 18 generates gate drive signals up*, vp*, and wp* for the P-side switching elements 5a, 5c, and 5e of each phase. Additionally, the gate drive signals un*, vn*, and wn* for the N-side switching elements 5b, 5d, and 5f are obtained by inverting the gate drive signals up*, vp*, and wp* for the P-side switching elements 5a, 5c, and 5e using inverters 21a, 21b, and 21c. The gate drive signals sg1 and sg2 are pulse-shaped signals.

[0053] As described above, the gate drive signal sg2 generated by the control calculation unit 3 is converted into the gate drive signal sg4 via the duty cycle control unit 23 and the gate drive circuit 8, and the gate drive signal sg4 is output to the power conversion circuit 4. The duty cycle control unit 23 includes a target voltage change unit 29 and a mode generation unit 30. The target voltage change unit 29 outputs the voltage command change signal sig3 to the control calculation unit 3 to change the normal voltage command values ​​vu0*, vv0*, and vw0* of each phase into voltage command values ​​vua*, vva*, and vwa* using the method described later, and further generates the gate drive signal sg2 based on the voltage command values ​​vua*, vva*, and vwa*. The mode generation unit 30 takes into account the component characteristics and the generation of higher harmonics to generate a mode, i.e., a pulsed gate drive signal sg3. The gate drive signals sg3 and sg4, like the gate drive signals sg1 and sg2, are also pulsed signals. The generation methods of the gate drive signal sg3 based on the duty cycle control unit 23 and the gate drive signal sg4 based on the gate drive circuit 8 will be described.

[0054] The power conversion circuit 4 controls the on / off state of the six switching elements 5 through the pulsed gate drive signal sg4, and provides a sinusoidal line-to-line voltage to the motor 2. At this time, the power conversion elements constituting the six arms of the power conversion circuit 4, namely the six switching elements 5 and the six return diodes 6, generate losses. The loss of each arm, namely the arm loss Pla, is represented by the sum of the loss of the switching element 5, namely the switching element loss Pls, and the loss of the return diode 6, namely the diode loss Pld. The switching element loss Pls is represented by the sum of the steady-state loss Psat of the switching element 5 and the switching loss Psw of the switching element 5. The diode loss Pld is represented by the sum of the steady-state loss Pf of the return diode 6 and the recovery loss Pr of the return diode 6. Therefore, the arm loss Pla is represented as shown in equation (1).

[0055] Pla=Psat+Psw+Pf+Pr···(1)

[0056] If the saturation voltage of the switching element 5 is set to Vsat, the current flowing through the switching element 5, i.e. the switching element current, is set to Imot, and the pass rate of the gate drive signal of the switching elements 5a, 5c, and 5e on the P side is set to Dt, then the steady-state loss Psat of the switching element 5 can be expressed as in equation (2).

[0057] Psat=Vsat×Imot×Dt···(2)

[0058] If the time for switching element 5 to be turned on is defined as the on-time, and the time for switching element 5 to be turned off is defined as the off-time, then the energizing rate Dt is expressed as on-time / (on-time + off-time).

[0059] If the turn-on loss of switching element 5 is set to Pon, the turn-off loss of switching element 5 is set to Poff, the frequency of carrier vc is set to fc, the energy of the switch-on state of each pulse is set to Eon, and the energy of the switch-off state of each pulse is set to Eoff, then the switching loss Psw of switching element 5 is expressed as in equation (3).

[0060] Psw=Pon+Poff=fc×(Eon+Eoff)···(3)

[0061] If the saturation voltage of the return diode 6 is set to Vfsat, and the current carrying capacity Dt and the switching element current Imot are used, the steady-state loss Pf of the return diode 6 is expressed as in equation (4). If the voltage of the DC power supply device 10 is set to Vdc, the recovery current of the return diode 6 is set to Irr, and the recovery time is set to trr, the recovery loss Pr of the return diode 6 is expressed as in equation (5).

[0062] Pf=(1-Dt)×Vfsat×Imot···(4)

[0063] Pr=Vdc×Irr×trr / 4···(5)

[0064] The switching element current Imot flowing through switching element 5 is expressed by equation (6) using amplitude I0 and phase ωt. If the modulation rate and power factor angle in the triangular wave compared to the sine wave PWM are set as MR and θp respectively, then the conductivity Dt can be expressed by equation (7).

[0065] Imot=I0sinωt···(6)

[0066] Dt=1 / 2+MR×sin(ωt+θp) / 2···(7)

[0067] If we use equations (1) to (7) above to calculate the losses of the six switching elements 5 and the six return diodes 6 under stall conditions, we get Figure 4 The losses are shown. The losses of the power conversion elements in each phase are as follows: Figure 4Thus, it exhibits periodicity. The horizontal axis represents the electrical angle [rad] of motor 2, and the vertical axis represents the current of the switching element Imot. The vertical axis represents the losses of the switching element Plsp on the P side, the diode loss Pldp on the P side, the switching element loss Plsn on the N side, and the diode loss Pldn on the N side. Taking phase U as an example, when the switching element current Imot in phase U is positive, i.e., when the electrical angle of motor 2 is 0 to π, the current only flows through the switching element 5a on the P side of phase U and the return diode 6b on the N side of phase U, and the current does not flow through the switching element 5b on the N side of phase U and the return diode 6a on the P side of phase U. Therefore, these two power conversion elements, namely the switching element 5a and the return diode 6b, generate losses, while the switching element 5b on the N side of phase U and the return diode 6a on the P side of phase U, which do not carry current, do not generate losses.

[0068] When the current Imot of the switching element in phase U is negative, that is, when the electrical angle of motor 2 is π to 2π, the current only flows through the switching element 5b on the N side of phase U and the return diode 6a on the P side of phase U, and the current does not flow through the switching element 5a on the P side of phase U and the return diode 6b on the N side of phase U. Therefore, these two power conversion elements, namely the switching element 5b and the return diode 6a, generate losses, while the switching element 5a on the P side of phase U and the return diode 6b on the N side of phase U, which do not carry current, do not generate losses.

[0069] Furthermore, the differences in component characteristics and current-carrying time between the switching element 5a on the P side of phase U and the return current diode 6b on the N side of phase U, due to differences in component size, sometimes result in significant differences in losses. Similarly, the differences in component characteristics and current-carrying time between the switching element 5b on the N side of phase U and the return current diode 6a on the P side of phase U, due to differences in component size, sometimes result in significant differences in losses. These differences in losses can be attributed to factors such as differences in component characteristics, etc. Figure 5 As shown, this can also be caused by the difference in the energizing time of each component. Figure 5 This diagram illustrates a typical example of the power-on time allocation for a power conversion device. Additionally, it illustrates an example of the power-on time allocation for a power conversion device before changing the voltage command values ​​vu*, vv*, and vw* in a stall state, i.e., before the loss reduction operation. Figure 5The diagram shows the following waveforms: carrier waveform 61 (carrier VC), voltage command waveform 62 (target voltage command values ​​vu*, vv*, vw*), power conversion mode 63a (P-side power conversion mode), power conversion mode 63b (N-side power conversion mode), characteristics of P-side switching element loss Plsp (P-side switching element loss characteristic 68a), characteristics of P-side diode loss Pldp (P-side diode loss characteristic 68c), characteristics of N-side switching element loss Plsn (N-side switching element loss characteristic 68b), and characteristics of N-side diode loss Pldn (N-side diode loss characteristic 68d). The horizontal axis represents the electrical angle [rad] of motor 2. The vertical axis represents voltage for carrier waveform 61, voltage command waveform 62, P-side power conversion mode 63a, and N-side power conversion mode 63b. The vertical axis of the loss characteristics of P-side switching elements 68a, P-side diodes 68c, N-side switching elements 68b, and N-side diodes 68d represents losses. Figure 5 The diagram also shows the on-time Tsp of the P-side switching element, the on-time Tsn of the N-side switching element, the on-time Tdp of the P-side return diode, and the on-time Tdn of the N-side return diode.

[0070] exist Figure 7 The figure shows the maximum loss when the allowable losses of the power conversion element, namely the allowable losses of the switching element 5 and the return diode 6, are 200W and 100W, respectively. Figure 7 The maximum loss is represented by a bar graph. SW represents the switching element, and D represents the return diode. The vertical axis represents the loss [W]. The maximum loss of switching element 5, i.e., the maximum loss of switching element 71a, is 185W. The maximum loss of switching element 71a relative to the allowable loss of 200W has a margin Pm1 of only 7.5%, which is zero. The maximum loss of return diode 6, i.e., the maximum loss of return diode 71b, is 95W. The maximum loss of return diode 71b relative to the allowable loss of 100W has a margin Pm2 of only 5%, which is even less than that of switching element 5.

[0071] In the power conversion device of Patent Document 1, the energizing time of the power conversion elements is allocated, and the losses generated are distributed between the P-side power conversion elements and the N-side power conversion elements, but if... Figure 7 As shown, neither the switching element 5 nor the return diode 6 has any margin. Therefore, even if the loss of the return diode 6 is allocated to the switching element 5, the loss of the return diode 6 can only decrease from, for example, 95W to 90W. Compared to the allowable loss of 100W, the margin is improved from 5% to 10%, but the improvement is small.

[0072] Furthermore, to further reduce the losses of the return diode 6, the steady-state loss Pf accounts for the majority of the losses generated during stall, necessitating a reduction in Pf. However, the saturation voltage Vfsat in equation (4) is inversely proportional to the size of the return diode 6. Therefore, reducing the saturation voltage Vfsat increases the size of the return diode 6. This increased size leads to a larger power conversion device, resulting in higher costs.

[0073] Therefore, in order to realize a small power conversion device 1 that can prevent a rapid rise in temperature, the focus is on the switching element 5, which is easier to control in terms of loss generation than the return diode 6. In the proportion of losses generated by the switching element 5, the steady-state loss Psat is approximately equal to the switching loss Psw. In Embodiment 1, an example is described as follows: the loss reduction unit 26 is used to make the carrier frequency fc of the triangular wave oscillator 19, which switches the switching element 5, lower than usual, thereby reducing the loss of the switching element 5. The carrier frequency is appropriately labeled fc.

[0074] The stall determination unit 27 outputs a stall determination signal sig1, indicating the stall state, to the loss reduction unit 26 after determining that a stall state has been detected. The loss reduction unit 26 receives the trigger signal and outputs a frequency change signal sig2, indicating the change, to the triangular wave oscillator 19 of the PWM control unit. The triangular wave oscillator 19 receives the frequency change signal sig2 and outputs a carrier wave vc with a frequency fc lower than usual to the comparators 20a to 20c. As a result, the frequency fc of equation (3) decreases, that is, the switching loss Psw decreases, and the maximum loss of the switching element 5 changes, for example, from 185W to 160W. The duty cycle control unit 23 determines the loss reduction of the switching element 5, which is connected in series with the return diode 6, which is connected to the second temperature information, i.e., the temperature rise ΔTsw, based on the decrease in the first temperature information, i.e., the temperature rise ΔTdi.

[0075] Subsequently, the duty cycle control unit 23 determines the conduction rate Dt of the power conversion element, i.e., the switching element 5 and the return current diode 6, based on the temperature rise ΔTdi of each return current diode 6 output from the element temperature estimation unit 25. In other words, the duty cycle control unit 23 outputs the gate drive signal sg3, obtained by changing the on-time of the switching element 5 in the gate drive signal sg2, to the gate drive circuit 8 to distribute the current flowing through the return current diode 6, which has the largest second temperature information, to the switching element 5 connected in series with the return current diode 6. As described above, the element temperature estimation unit 25 estimates the temperature rise ΔTdi of the return current diode 6 based on the temperature rise ΔTsw of each switching element 5 output from the temperature monitors 24a-24f of each switching element 5a-5f, and sends the estimated temperature rise ΔTdi to the duty cycle control unit 23.

[0076] exist Figure 6 The diagram shows an example of the power conversion device 1's on-time allocation when reducing the loss of the return diode 6. The target voltage change unit 29 generates target voltage command values ​​vua*, vva*, and vwa*. Figure 5 The voltage command waveform 62 shown is changed to voltage command waveform 67. Figure 6 The horizontal axis and the vertical axis are Figure 5 The horizontal and vertical axes are the same. Figure 6 The diagram shows the power conversion element's energizing mode on the P side (P-side energizing mode 64a), the power conversion element's energizing mode on the N side (N-side energizing mode 64b), the characteristics of the P-side switching element loss Plsp (P-side switching element loss characteristic 69a), the characteristics of the P-side diode loss Pldp (P-side diode loss characteristic 69c), the characteristics of the N-side switching element loss Plsn (N-side switching element loss characteristic 69b), and the characteristics of the N-side diode loss Pldn (N-side diode loss characteristic 69d).

[0077] Figure 6The voltage command waveform 67 shown is an example as follows: In the range of electrical angle 0 to π, 0.4 times the voltage amplitude of voltage command waveform 62 is added to the voltage amplitude of voltage command waveform 62; in the range of electrical angle π to 2π, 0.4 times the voltage amplitude of voltage command waveform 62 is subtracted from the voltage amplitude of voltage command waveform 62. The target voltage change unit 29 generates the voltage command value vua* for phase U as follows: In the range of electrical angle 0 to π, the target voltage change unit 29 adds 0.4 times the voltage command value vu0* to the normal voltage command value vu0*; in the range of electrical angle π to 2π, it subtracts 0.4 times the voltage command value vu0* from the normal voltage command value vu0* to generate the new target voltage command value vua*. The target voltage change unit 29 similarly generates the voltage command values ​​vva* and vwa* for phase V and phase W. The target voltage modification unit 29 adds 0.4 times the voltage command value vv0* to the normal voltage command value vv0* in the range of electrical angle 0 to π, and subtracts 0.4 times the voltage command value vv0* from the normal voltage command value vv0* in the range of electrical angle π to 2π, to generate a new target voltage command value vva*. The target voltage modification unit 29 adds 0.4 times the voltage command value vw0* to the normal voltage command value vw0* in the range of electrical angle 0 to π, and subtracts 0.4 times the voltage command value vw0* from the normal voltage command value vw0* in the range of electrical angle π to 2π, to generate a new target voltage command value vwa*.

[0078] Figure 8 The diagram shows that after the loss reduction unit 26 reduces the loss of the switching element 5, as shown in the diagram... Figure 6 That would change the maximum loss when the power conversion element is powered on. Figure 8 The horizontal axis and the vertical axis are Figure 7 The horizontal and vertical axes are the same. The maximum loss of switching element 5 is the maximum loss of switching element 72a, and the maximum loss of return diode 6 is the maximum loss of return diode 72b. Figure 8 In the middle, it is shown by dashed lines. Figure 7 The maximum loss of the switching element 71a and the maximum loss of the return diode 71b before loss distribution are shown. As described above, through the operation of the loss reduction unit 26, the maximum loss of the switching element 5 decreases from 185W to 160W, becoming the maximum loss of the switching element 73. Afterwards, as... Figure 6 By changing the power conversion element's operating mode, the maximum loss of the return diode 6 can be reduced from 95W to 65W. Specifically, the 30W increase in loss 74 for the switching element 5 is added to the maximum switching element loss 73, resulting in a maximum switching element loss 72a of 190W.

[0079] The combined loss of the maximum loss of the switching element 72a and the maximum loss of the return diode 72b in the same phase is simply that the loss of the return diode 6 is distributed to the switching element 5. Therefore, the overall generation loss of the power conversion element in this phase remains unchanged before and after the distribution. However, the loss of the return diode 6 is greatly reduced, and the margin Pm4 when the allowable loss is set to 100W is significantly improved from a margin of 5% Pm2 to 35%. On the other hand, the loss of the switching element 5 increases by 30W, and the margin Pm3 when the allowable loss is set to 200W is changed from a margin of 7.5% Pm1 to 5%.

[0080] Taking phase U as an example, for Figure 8 The following explanation is provided. Through the operation of the loss reduction unit 26, the maximum loss of the switching elements 5a and 5b in phase U decreases from 185W to 160W, becoming a maximum switching element loss of 73W. Afterwards, as... Figure 6 By changing the energizing mode of the power conversion elements in phase U, the maximum loss of return diodes 6a and 6b can be reduced from 95W to 65W. Specifically, the maximum loss of switching elements 5a and 5b is increased by 30W, which, when added to the maximum loss of switching element 73, becomes a maximum loss of 190W for switching element 72a. The total loss of the maximum loss of switching element 72a and the maximum loss of return diode 72b in electrical angles from 0 to π is simply the result of distributing the loss of return diode 6b on the N side of phase U to the switching element 5a on the P side of phase U. Therefore, the overall loss of the power conversion elements in phase U remains unchanged before and after the distribution. Furthermore, the total loss of the maximum loss of switching element 72a and the maximum loss of return diode 72b in electrical angles from π to 2π is simply the result of distributing the loss of return diode 6a on the P side of phase U to the switching element 5b on the N side of phase U. Therefore, the overall loss of the power conversion elements in phase U remains unchanged before and after the distribution. However, the losses of return diodes 6a and 6b are greatly reduced, and the margin Pm4 when the allowable loss is set to 100W is significantly improved from 5% margin Pm2 to 35%. On the other hand, the losses of switching elements 5a and 5b increase by 30W, and the margin Pm3 when the allowable loss is set to 200W is changed from 7.5% margin Pm1 to 5%.

[0081] like Figure 6As shown, when the overall losses of the power conversion elements are distributed in phase U, the phase voltage of phase U drops significantly from a sinusoidal shape, and the line-to-line voltage between the output terminals is obtained as the output of the power conversion device. Therefore, in the mode generation unit 30 that generates the power distribution mode, namely the P-side power-on mode 64a and the N-side power-on mode 64b, the same loss distribution is performed for the other phases (V phase and W phase), generating a power distribution mode in which the line-to-line voltage becomes sinusoidal, and controlling it so that there is no difference in the line-to-line voltage before and after loss distribution. Setting phases U, V, and W to have the same loss distribution is the same as the control in Patent Document 1. In addition to maintaining the line-to-line voltage, the duty cycle control unit 23 also considers the element characteristics, the generation of higher harmonics, etc., to generate the gate drive signal sg3.

[0082] In Embodiment 1, when the power conversion device 1 determines that the motor 2 is in a stall state, the loss reduction unit 26 reduces the loss of the switching element 5. Then, the duty cycle control unit 23 changes the energizing time of the power conversion elements in each phase, namely the switching element 5 and the return diode 6, and distributes the losses between the P-side and N-side power conversion elements. Therefore, Embodiment 1, by using a larger and temperature-balanced switching element 5 to bear the losses of a smaller and temperature-balanced return diode 6, avoids the need for a large-scale return diode 6 and prevents a rapid temperature rise. Thus, Embodiment 1 is more compact and prevents a rapid temperature rise. The power conversion device 1 of Embodiment 1 is miniaturized, thus enabling a low-cost power conversion device.

[0083] in addition, Figure 1 The control calculation unit 3, duty cycle control unit 23, component temperature estimation unit 25, loss reduction unit 26, and stall determination unit 27 can be controlled by... Figure 9 The processor 120 and memory 121 shown implement the functions. In this case, the control calculation unit 3, duty cycle control unit 23, component temperature estimation unit 25, loss reduction unit 26, and stall determination unit 27 are implemented by the processor 120 executing the program stored in the memory 121. Alternatively, multiple processors 120 and multiple memories 121 can also cooperate to execute each function.

[0084] As described above, the power conversion device 1 of Embodiment 1 provides alternating current converted from direct current to drive the motor 2. The power conversion device 1 includes: a power conversion circuit 4, which has multiple switching elements 5 and a return diode 6, and multiple temperature monitors 24a, 24b, 24c, 24d, 24e, and 24f that output the temperature information of each switching element 5, i.e., first temperature information (ΔTsw), and provides the alternating current to drive the motor 2; a control calculation unit 3, which determines the switching timing of the multiple switching elements 5 in the power conversion circuit 4 and generates a first drive signal (gate drive signal sg2); and a rotation detector 9, which detects the rotor position θ of the motor 2. The power conversion device 1 further includes: a component temperature estimation unit 25, which estimates the temperature information of the return diode 6, i.e., the second temperature information (ΔTdi), based on the first temperature information (ΔTsw); a stall determination unit 27, which determines the stall state of the motor 2 based on the rotor position θ of the motor 2; a loss reduction unit 26, which reduces the heat generation of the switching element 5 when the stall determination unit 27 determines that the motor 2 is in a stall state; and a duty cycle control unit 23, which reduces the heat generation of the switching element 5 without... When the first drive signal (gate drive signal sg2) is changed, it is output as the second drive signal (gate drive signal sg3), or the second drive signal (gate drive signal sg3) obtained by changing the on-time of the switching element in the first drive signal (gate drive signal sg2) is output; and the gate drive circuit 8 outputs a third drive signal (gate drive signal sg4) that causes the plurality of switching elements 5 to switch according to the second drive signal (gate drive signal sg3) to the power conversion circuit 4. When the stall determination unit 27 determines that a stall state has occurred, and the first temperature information (ΔTsw) of the switching element 5 connected in series with the return current diode 6, which has the maximum second temperature information (ΔTdi), has decreased due to the operation of the loss reduction unit 26, the duty cycle control unit 23 outputs a second drive signal (gate drive signal sg3) obtained by changing the on-time of the switching element 5 in the first drive signal (gate drive signal sg2) to the gate drive circuit 8. This distributes the current flowing through the return current diode 6, which has the maximum second temperature information (ΔTdi), to the switching element 5 connected in series with the return current diode 6. With this structure, the power conversion device 1 of Embodiment 1, when a stall state is determined and the first temperature information (ΔTsw) of the switching element 5 connected in series with the return current diode 6, which has the maximum second temperature information (ΔTdi), has decreased due to the operation of the loss reduction unit 26, distributes the current flowing through the return current diode 6 to the switching element 5 connected in series. Therefore, it can be miniaturized and prevents a rapid temperature rise.

[0085] Implementation method 2.

[0086] Figure 10 This is a diagram showing the structure of the first power conversion device according to Embodiment 2. Figure 11 This is a diagram showing the structure of the second power conversion device according to Embodiment 2. It is explained that the power conversion device 1 of Embodiment 1 can reduce the loss of the switching element 5 by decreasing the carrier frequency fc. However, depending on the value of the carrier frequency fc, current ripple and noise sometimes increase due to the decrease in carrier frequency fc. For the power conversion device 1 mounted in a vehicle, it is preferable to have as little current ripple and noise as possible. Therefore, in Embodiment 2, the following example is described: the loss reduction unit 26 increases the rate of change of the gate drive signal sg4 of the gate drive circuit 8, i.e., the switching speed.

[0087] One method to accelerate switching speed is to reduce the resistance value of the gate resistor in the gate drive circuit 8, but since this is known technology, detailed explanation is omitted here. The loss distribution method is the same as in Embodiment 1. Figure 10 The first power conversion device 1 involved in Embodiment 2 shown herein and Figure 1 The difference in the power conversion device 1 shown is that the loss reduction unit 26 generates a switching speed change signal sig4 instead of a frequency change signal sig2. The main difference from the power conversion device 1 of Embodiment 1 will be explained. In the first power conversion device 1 of Embodiment 2, the frequency change signal sig2 is not input to... Figure 3 The triangular wave oscillator 19 is shown. The loss reduction unit 26 receives the stall determination signal sig1, which indicates a stall state, and outputs the switching speed change signal sig4, which indicates a high-speed command to make the switching speed faster than before the stall state determination, to the gate drive circuit 8. For example, the switching speed change signal sig4 is at level H when indicating a high-speed command, and at level L when indicating a low-speed command. The gate drive circuit 8 receives the switching speed change signal sig4, which indicates a high-speed command, and increases the switching speed of the gate drive signal sg4. By increasing the switching speed of the gate drive signal sg4, the energy Eon of the switch on state and the energy Eoff of the switch off state in equation (3) are reduced, that is, the loss of the switching element 5 is reduced. Since the loss of the switching element 5 is reduced, the heat generated by the switching element 5 is reduced. The switching speed change signal sig4 is an example of a loss reduction signal that reduces the loss of the switching element 5.

[0088] The first power conversion device 1 of Embodiment 2, like the power conversion device 1 of Embodiment 1, can be miniaturized and prevents a rapid rise in temperature. The first power conversion device 1 of Embodiment 2 can be miniaturized, thus enabling a low-cost power conversion device. By accelerating the switching speed of the gate drive signal sg4, the first power conversion device 1 of Embodiment 2 can avoid increased current ripple and noise, making it suitable for vehicles.

[0089] A method for accelerating the switching speed of the gate drive signal sg4 of the gate drive circuit 8 can be added to the power conversion device 1 of Embodiment 1. Figure 11 The second power conversion device 1 involved in Embodiment 2 shown herein and Figure 1 The difference between the power conversion device 1 shown and the one described is that the loss reduction unit 26 generates a frequency change signal sig2 and a switching speed change signal sig4. The main difference from the power conversion device 1 of Embodiment 1 will be explained. The loss reduction unit 26 receives a stall determination signal sig1 indicating a stall state, outputs a frequency change signal sig2 indicating a change to the control calculation unit 3, and outputs a switching speed change signal sig4 indicating a high-speed command to the gate drive circuit 8. The operation of the loss reduction unit 26 and the gate drive circuit 8 related to the added switching speed change signal sig4 is the same as that of the first power conversion device 1 of Embodiment 2.

[0090] The second power conversion device 1 of Embodiment 2, like the power conversion device 1 of Embodiment 1, can be miniaturized and prevents a rapid rise in temperature. The miniaturization of the second power conversion device 1 of Embodiment 2 enables a low-cost power conversion device. By accelerating the switching speed of the gate drive signal sg4, the second power conversion device 1 of Embodiment 2 avoids increased current ripple and noise, thus enabling a power conversion device suitable for vehicles.

[0091] Furthermore, the loss reduction unit 26 in the power conversion device 1 of Embodiment 2 can of course be applied to all embodiments described below. Moreover, the same effect as in Embodiment 2 can be obtained in this case.

[0092] Implementation method 3.

[0093] Figure 12 This is a diagram showing the structure of the first power conversion device according to Embodiment 3. Figure 13 This is a diagram showing the structure of the second power conversion device according to Embodiment 3. Embodiment 3 illustrates the following example: the loss reduction unit 26 increases the voltage value of the gate drive signal sg4 of the gate drive circuit 8. Figure 13 The first power conversion device 1 involved in Embodiment 3 shown is... Figure 1The difference between the power conversion device 1 shown and the one described is that the gate drive circuit 8 includes a boost converter 31, and the loss reduction section 26 generates a gate voltage change signal sig5 instead of a frequency change signal sig2. The main differences from the power conversion device 1 of Embodiment 1 will be explained.

[0094] In the first power conversion device 1 according to embodiment 3, the frequency change signal sig2 is not input to... Figure 3 The triangular wave oscillator 19 is shown. The loss reduction unit 26 receives the stall determination signal sig1 indicating a stall state and outputs the gate voltage change signal sig5, which indicates that the voltage value of the gate drive signal sg4 is larger than that before the stall state determination, to the gate drive circuit 8. For example, the gate voltage change signal sig5 is at level H when indicating a change and at level L when indicating no change. The gate drive circuit 8 receives the gate voltage change signal sig5 indicating a change and increases the voltage value of the gate drive signal sg4. Since the voltage value of the gate drive signal sg4 increases, the saturation voltage Vsat of equation (2) decreases, which can reduce the steady-state loss Psat of the switching element 5. By reducing the steady-state loss Psat of the switching element 5, the loss of the switching element 5 can be reduced. Since the loss of the switching element 5 is reduced, the heat generated by the switching element 5 is reduced. The gate voltage change signal sig5 is an example of a loss reduction signal that reduces the loss of the switching element 5.

[0095] The first power conversion device 1 in Embodiment 3, like the power conversion device 1 in Embodiment 1, can be miniaturized and prevents a rapid temperature rise. The first power conversion device 1 in Embodiment 3 reduces steady-state losses Psat; therefore, in power conversion devices using motor control methods with low PWM-controlled carrier frequencies fc, the temperature rise of the switching element 5 can also be reduced. This allows the switching element 5, which has a temperature margin, to bear the losses of the return diode 6, which lacks a temperature margin, thus preventing the return diode 6 from becoming too large. The first power conversion device 1 in Embodiment 3 can be miniaturized, thus enabling a low-cost power conversion device.

[0096] A method for increasing the voltage value of the gate drive signal sg4 of the gate drive circuit 8 can be added to the power conversion device 1 of Embodiment 1. Figure 13 The second power conversion device 1 involved in Embodiment 3 shown is... Figure 1The power conversion device 1 shown differs from that of Embodiment 1 in that the loss reduction unit 26 generates a frequency change signal sig2 and a gate voltage change signal sig5. The main differences from the power conversion device 1 of Embodiment 1 will be explained. The loss reduction unit 26 receives a stall determination signal sig1 indicating a stall state, outputs a frequency change signal sig2 indicating a change to the control calculation unit 3, and outputs a gate voltage change signal sig5 indicating a change to the gate drive circuit 8. The operation of the loss reduction unit 26 and the gate drive circuit 8 related to the added gate voltage change signal sig5 is the same as that of the first power conversion device 1 of Embodiment 3.

[0097] The second power conversion device 1 in Embodiment 3, like the power conversion device 1 in Embodiment 1, can be miniaturized and prevents a rapid temperature rise. The second power conversion device 1 in Embodiment 3 achieves the same effect as the first power conversion device 1 in Embodiment 3.

[0098] Furthermore, as a method to increase the voltage value of the gate drive signal sg4, an example using a boost converter 31 was described, but the method is not limited to this example. The unit for increasing the voltage value of the gate drive signal sg4 can be a unit that switches to a power supply with a different voltage, etc. Additionally, when simultaneously performing the method for increasing the switching speed of the gate drive signal sg4 as described in Embodiment 2 and the method for increasing the voltage value of the gate drive signal sg4, the loss reduction signal output from the loss reduction unit 26 can be one. In this case, the switching speed change signal sig4 can also be used as the gate voltage change signal sig5, and the gate voltage change signal sig5 can also be used as the switching speed change signal sig4.

[0099] Implementation method 4.

[0100] The power conversion device 1 of Embodiment 4 accurately estimates the temperature rise ΔTdi of the return diode 6 in the power conversion devices 1 of Embodiments 1 to 3. That is, the power conversion device 1 of Embodiment 4 is an example of an element temperature estimation unit 25 that outputs a high-precision temperature rise ΔTdi. Figure 14 This is a diagram showing the structure of the power conversion device according to Embodiment 4. Figure 14 The power conversion device 1 shown is illustrated in the following example: for Figure 1 The power conversion device 1 is supplemented with a voltage detector 28 that detects the input voltage value Vi of the power conversion circuit 4, and the component temperature estimation unit 25 has a loss mapping 42 for reading the diode loss Pld and a thermal resistance storage unit 43 for reading the thermal resistance value Rth of the return diode 6. The main differences from the power conversion device 1 of Embodiment 1 will be described.

[0101] The loss of the return diode 6 will be explained when the temperature rise of the return diode 6 is estimated to be ΔTdi. The loss of the return diode 6 is the loss of the return diode in each arm, i.e., the diode loss Pld, which is a part of equation (1) in embodiment 1. The diode loss Pld is expressed by equation (8).

[0102] Pld=Pf+Pr···(8)

[0103] The loss mapping 42 stores data on diode losses PLD associated with the rotational speed Nm of the motor 2, the output current values ​​iu, iv, and iw of the power conversion circuit 4, and the input voltage value Vi of the power conversion circuit 4. The component temperature estimation unit 25 reads the diode losses PLD using the rotational speed Nm of the motor 2 calculated based on the rotor position θ output from the rotation detector 9, the output current values ​​iu, iv, and iw output from the current detector 7, and the input voltage value Vi output from the voltage detector 28.

[0104] Next, the thermal resistance value will be explained. The thermal resistance value Rth of the return diode 6 varies depending on the construction of the cooling system, but it is a known value in the design. The thermal resistance storage unit 43 stores data on the thermal resistance value Rth of each return diode 6 mounted in the power conversion circuit 4. Figure 2 In the case of the power conversion circuit 4 shown, for each of the six return diodes 6a to 6f, six thermal resistance values ​​Rth are stored in the thermal resistance storage unit 43. The thermal resistance storage unit 43 stores thermal resistance values ​​Rth with constant thermal resistance values, which are independent of the rotational speed Nm of the motor 2, the output current values ​​iu, iv, and iw of the power conversion circuit 4, and the input voltage value Vi of the power conversion circuit 4.

[0105] When calculating the temperature rise ΔTdi of each return diode 6, the component temperature estimation unit 25 reads the diode loss Pld from the loss map 42 based on the motor speed Nm, output current values ​​iu, iv, iw, and input voltage value Vi calculated from the rotor position θ output from the rotation detector 9. Then, triggered by reading the diode loss Pld, the component temperature estimation unit 25 reads the thermal resistance value Rth from the thermal resistance storage unit 43. Afterward, the component temperature estimation unit 25 calculates the temperature rise ΔTdi of the return diode 6 using equation (9).

[0106] ΔTdi=Pld×Rth···(9)

[0107] The power conversion device 1 of Embodiment 4 can calculate the temperature rise ΔTdi of the return diode 6 with high accuracy. Therefore, it can prevent excessive loss distribution that would occur if the accuracy of the temperature rise ΔTdi of the return diode 6 is poor. In the event of excessive loss distribution, damage to the switching element 5 is also considered. The power conversion device 1 of Embodiment 4 can prevent excessive loss distribution, and therefore, compared to the case where the accuracy of the temperature rise ΔTdi of the return diode 6 is poor, the size of the return diode 6 can be miniaturized.

[0108] Similar to the power conversion device 1 of Embodiment 1, the power conversion device 1 of Embodiment 4, when determining that the motor 2 is in a stall state, uses the loss reduction unit 26 to reduce the loss of the switching element 5. Then, the duty cycle control unit 23 changes the energizing time of each phase's power conversion element, namely the switching element 5 and the return diode 6, and distributes the losses between the P-side and N-side power conversion elements. Therefore, it can be miniaturized and prevents a rapid temperature rise. Furthermore, the power conversion device 1 of Embodiment 4 can calculate the temperature rise ΔTdi of the return diode 6 with high accuracy. Therefore, compared to cases where the accuracy of the temperature rise ΔTdi of the return diode 6 is poor, a smaller power conversion device can be realized.

[0109] In addition, the element temperature estimation unit 25, which includes the voltage detector 28, loss mapping 42 and thermal resistance storage unit 43 described in Embodiment 4, can also be applied to the power conversion device 1 of Embodiments 2 and 3.

[0110] Implementation method 5.

[0111] The power conversion device 1 of Embodiment 5 is similar to the power conversion device 1 of Embodiment 4, and is an example of an element temperature estimation unit 25 that outputs a high-precision temperature rise ΔTdi. Figure 15 This is a diagram showing the structure of the power conversion device according to Embodiment 5. Figure 15 The power conversion device 1 shown is illustrated in the following example: Figure 1 The component temperature estimation unit 25 of the power conversion device 1 includes a proportional calculation unit 44 that calculates the temperature rise ΔTdi. The main differences from the power conversion device 1 of Embodiment 1 will be explained.

[0112] In Embodiment 4, an example is described where a thermal resistance value Rth, having a constant thermal resistance, is used to calculate the temperature rise ΔTdi of the return current diode 6. However, the constant thermal resistance value includes manufacturing variations, therefore, the calculated temperature rise ΔTdi of the return current diode 6 is sometimes higher than the actual temperature rise. Therefore, in cases where losses are excessively distributed from the return current diode 6 to the switching element 5, damage to the switching element 5 is also considered. The power conversion device 1 of Embodiment 5 is an example that can calculate the temperature rise ΔTdi of the return current diode 6 with higher accuracy than the power conversion device 1 of Embodiment 4.

[0113] In embodiment 5, the focus is on connecting the return diodes 6 in reverse parallel to the switching element 5 in each arm. The temperature rise of the return diodes 6 and the switching element 5 constituting the same arm is known in the design, and the relationship between the temperature rise ΔTdi of the return diodes 6 constituting the same arm and the temperature rise ΔTsw of the switching element 5 is known in the design. Therefore, the temperature rise ΔTdi of each return diode 6 can be calculated using the temperature rise ΔTsw of the switching element 5 constituting the same arm, the coefficient α, and as in equation (10).

[0114] ΔTdi=α×ΔTsw···(10)

[0115] The proportional calculation unit 44 performs the calculation of formula (10) based on the temperature rise ΔTswa of the switching element 5a output from the temperature monitor 24a, and outputs α×ΔTswa as ΔTdia. Similarly, the proportional calculation unit 44 performs the calculation of formula (10) based on the temperature rise ΔTswb of the switching element 5b output from the temperature monitor 24b, and outputs α×ΔTswb as ΔTdib. The proportional calculation unit 44 performs the calculation of formula (10) based on the temperature rise ΔTswc to ΔTswf of the switching elements 5c to 5f output from the temperature monitors 24c to 24f, respectively, and outputs ΔTdic to ΔTdif.

[0116] In the power conversion device 1 of embodiment 5, the proportional calculation unit 44 performs the calculation shown in equation (10), that is, multiplying ΔTsw, which is the first temperature information, by the coefficient α, so that the thermal resistance value containing manufacturing deviation is not used, thereby calculating the temperature rise ΔTdi of the return diode 6 with higher accuracy than that of the power conversion device 1 of embodiment 4.

[0117] Similar to the power conversion device 1 of Embodiment 1, the power conversion device 1 of Embodiment 5, when determining that the motor 2 is in a stall state, uses the loss reduction unit 26 to reduce the loss of the switching element 5. Then, the duty cycle control unit 23 changes the energizing time of the power conversion elements of each phase, namely the switching element 5 and the return diode 6, and distributes the losses between the P-side and N-side power conversion elements. Therefore, it can be miniaturized and prevents a rapid temperature rise. Furthermore, the power conversion device 1 of Embodiment 5 can calculate the temperature rise ΔTdi of the return diode 6 with higher accuracy than the power conversion device 1 of Embodiment 4, thus further realizing a miniaturized power conversion device.

[0118] In addition, the element temperature estimation unit 25, which includes the proportional calculation unit 44 described in Embodiment 5, can also be applied to the power conversion device 1 of Embodiments 2 and 3.

[0119] Implementation method 6.

[0120] The power conversion device 1 of Embodiment 6 is similar to the power conversion device 1 of Embodiment 4, and is an example of an element temperature estimation unit 25 that outputs a high-precision temperature rise ΔTdi. Figure 16 This is a diagram showing the structure of the power conversion device according to Embodiment 6. In the power conversion device 1 of Embodiment 5, the following example is shown: the proportional calculation unit 44 uses a fixed value coefficient α to perform calculations as in equation (10). There are many stall conditions, but during stall at extremely low speeds, the temperature rise of the power conversion element changes over time. Therefore, it is sometimes difficult to accurately calculate the temperature rise ΔTdi of the return diode 6 using only a fixed value coefficient α. In the power conversion device 1 of Embodiment 6, the coefficient α is associated with the speed Nm of the motor 2, the output current values ​​iu, iv, iw, and the input voltage value Vi. The power conversion device 1 of Embodiment 6 uses a coefficient α that varies according to the condition of the motor 2 to calculate the temperature rise ΔTdi of the return diode 6 as in equation (10). The difference between the power conversion device 1 of Embodiment 6 and the power device device 1 of Embodiment 5 is that a voltage detector 28 for the input voltage value Vi of the output power conversion circuit 4 is added, and the element temperature estimation unit 25, together with the proportional calculation unit 44, has a coefficient model 45 for the output coefficient α. The main focus is on the parts that differ from the power conversion device 1 in Embodiment 5.

[0121] The coefficient model 45 outputs the coefficient α using the motor 2's rotational speed Nm calculated based on the rotor position θ output from the rotation detector 9, the output current values ​​iu, iv, and iw output from the current detector 7, and the input voltage value Vi output from the voltage detector 28. The input information to the coefficient model 45—the rotational speed Nm, the output current values ​​iu, iv, and iw, and the input voltage value Vi—are time-varying parameters, thus allowing the coefficient α to change from a fixed value to a variable value. By using the coefficient model 45, a coefficient α that varies according to the condition of the motor 2 can be obtained.

[0122] The power conversion device 1 of embodiment 6 generates a coefficient α based on the rotational speed Nm of the motor 2, the output current values ​​iu, iv, iw output from the current detector 7, and the input voltage value Vi output from the voltage detector 28. The temperature rise ΔTdi of the return diode 6 is calculated using the coefficient α that changes according to the changes in these input information, as in equation (10). Therefore, the temperature rise ΔTdi of the return diode 6 can be calculated with high accuracy even when stalling at a very low speed.

[0123] Similar to the power conversion device 1 of Embodiment 1, the power conversion device 1 of Embodiment 6, when determining that the motor 2 is in a stall state, uses the loss reduction unit 26 to reduce the loss of the switching element 5, and then uses the duty cycle control unit 23 to change the energizing time of the power conversion elements of each phase, namely the switching element 5 and the return diode 6, and performs loss distribution between the P-side power conversion elements and the N-side power conversion elements. Therefore, it can be miniaturized and prevents a sharp rise in temperature. In addition, the power conversion device 1 of Embodiment 6 can also calculate the temperature rise ΔTdi of the return diode 6 with high accuracy when stalling at a very low speed ramp. Therefore, a power conversion device that is even smaller than the power conversion device 1 of Embodiment 5 can be realized.

[0124] In addition, the element temperature estimation unit 25, which includes the proportional calculation unit 44 and the coefficient model 45 described in Embodiment 6, can also be applied to the power conversion device 1 of Embodiments 2 and 3.

[0125] Furthermore, although this application describes various exemplary embodiments and examples, the various features, methods, and functions described in one or more embodiments are not limited to specific embodiments, but can also be applied individually to embodiments, or combined in various ways to be applicable to embodiments. Therefore, it can be considered that numerous modifications not illustrated are also included within the technical scope disclosed in this application. For example, this may include modifications, additions, or omissions of at least one constituent element, as well as extraction of at least one constituent element and combination with constituent elements of other embodiments.

[0126] Label Explanation

[0127] 1 Power conversion device

[0128] 2 Electric motor

[0129] 3. Control and arithmetic unit

[0130] 4 Power Conversion Circuit

[0131] 5, 5a, 5b, 5c, 5d, 5e, 5f Switching elements

[0132] 6, 6a, 6b, 6c, 6d, 6e, 6f Return current diodes

[0133] 7, 7a, 7b, 7c Current detectors

[0134] 8 Gate drive circuit

[0135] 9. Rotation Detector

[0136] 19. Triangular wave oscillator (oscillator)

[0137] 23 Duty Cycle Control Department

[0138] Temperature monitors 24a, 24b, 24c, 24d, 24e, 24f

[0139] 25. Component Temperature Estimation Section

[0140] 26 Loss Reduction Section

[0141] 27 Stall Detection Unit

[0142] 28 Voltage Detector

[0143] 43 Thermal resistance storage section

[0144] 44 Proportional Calculation Section

[0145] 45-coefficient model

[0146] α coefficient

[0147] θ rotor position

[0148] fc frequency

[0149] iu, iv, iw output current values

[0150] Nm rotational speed

[0151] Pld diode loss

[0152] Pldp P-side diode loss

[0153] Pldn N-side diode loss

[0154] Rth thermal resistance

[0155] sig2 frequency-changing signal (loss reduction signal)

[0156] SIG4 switching speed change signal (loss reduction signal)

[0157] sig5 gate voltage change signal (loss reduction signal)

[0158] vc carrier

[0159] ΔTdi, ΔTdia, ΔTdib, ΔTdic, ΔTdid, ΔTdie, ΔTdif: Temperature rise (secondary temperature information)

[0160] ΔTsw, ΔTswa, ΔTswb, ΔTswc, ΔTswd, ΔTswe, ΔTswf: Temperature rise (first temperature information)

[0161] sg2 gate drive signal (first drive signal)

[0162] SG3 gate drive signal (second drive signal)

[0163] SG4 gate drive signal (third drive signal)

[0164] Vi is the input voltage value.

Claims

1. A power conversion device for providing alternating current converted from direct current to drive an electric motor, the power conversion device being characterized by comprising: A power conversion circuit having multiple switching elements and a return diode, and multiple temperature monitors that output temperature information, i.e., first temperature information, for each of the switching elements, and providing the AC power to drive the motor; A control and calculation unit determines the switching timing of the plurality of switching elements in the power conversion circuit and generates a first drive signal; A rotary detector that detects the rotor position of the electric motor; The component temperature estimation unit estimates the temperature information of the return diode, i.e., the second temperature information, based on the first temperature information. A stall determination unit determines the stall state of the motor based on the rotor position of the motor. The loss reduction unit reduces the heat generation of the switching element when the stall determination unit determines that a stall state has occurred. The duty cycle control unit outputs the first drive signal as a second drive signal without changing the first drive signal, or outputs a second drive signal obtained by changing the on-time of the switching element in the first drive signal. as well as A gate driving circuit, which outputs a third driving signal to the power conversion circuit based on the second driving signal, causing the plurality of switching elements to switch. The duty cycle control unit outputs a second drive signal, obtained by changing the on-time of the switch element in the first drive signal, to the gate drive circuit only when the stall determination unit determines that the stall state is reached and the first temperature information of the switch element connected in series with the return diode with the maximum second temperature information is reduced by the operation of the loss reduction unit. This is done so that the current flowing through the return diode with the maximum second temperature information is distributed to the switch element connected in series with the return diode.

2. The power conversion device as described in claim 1, characterized in that, The control and arithmetic unit includes an oscillator that generates the carrier wave used in the generation of the first drive signal. When the stall determination unit determines that a stall state has occurred, the loss reduction unit outputs a loss reduction signal to the oscillator, which makes the carrier frequency lower than before the determination.

3. The power conversion device as described in claim 1, characterized in that, When the stall determination unit determines that a stall state has occurred, the loss reduction unit outputs a loss reduction signal to the gate drive circuit, which makes the switching speed of the third drive signal faster than before the determination.

4. The power conversion device as described in claim 1, characterized in that, When the stall determination unit determines that a stall state has occurred, the loss reduction unit outputs a loss reduction signal to the gate drive circuit, which makes the voltage value of the third drive signal larger than before the determination.

5. The power conversion device as described in claim 1, characterized in that, When the stall determination unit determines that a stall state has occurred, the loss reduction unit outputs a loss reduction signal to the gate drive circuit, which makes the switching speed of the third drive signal faster than before the determination and makes the voltage value of the third drive signal larger than before the determination.

6. The power conversion device as described in claim 1, characterized in that, The control and arithmetic unit includes an oscillator that generates the carrier wave used in the generation of the first drive signal. When the stall determination unit determines that a stall state has occurred, the loss reduction unit outputs a first loss reduction signal to the oscillator, which makes the frequency of the carrier wave lower than before the determination, and outputs a second loss reduction signal to the gate drive circuit, which makes the switching speed of the third drive signal faster than before the determination.

7. The power conversion device as claimed in claim 1, characterized in that, The control and arithmetic unit includes an oscillator that generates the carrier wave used in the generation of the first drive signal. When the stall determination unit determines that a stall state has occurred, the loss reduction unit outputs a first loss reduction signal to the oscillator, which makes the frequency of the carrier wave lower than before the determination, and outputs a second loss reduction signal to the gate drive circuit, which makes the voltage value of the third drive signal higher than before the determination.

8. The power conversion device as claimed in claim 1, characterized in that, The control and arithmetic unit includes an oscillator that generates the carrier wave used in the generation of the first drive signal. When the stall determination unit determines that a stall state has occurred, the loss reduction unit outputs a first loss reduction signal to the oscillator, which makes the frequency of the carrier wave lower than before the determination, and outputs a second loss reduction signal to the gate drive circuit, which makes the switching speed of the third drive signal faster than before the determination and makes the voltage value larger than before the determination.

9. The power conversion device as described in any one of claims 1 to 8, Its features are, It includes: a voltage detector that detects the value of the input voltage to the power conversion circuit; and a current detector that detects the value of the output current from the power conversion circuit to the motor. The element temperature estimation section includes: A thermal resistance storage unit stores the thermal resistance value of the return current diode; and A loss map, which stores the diode losses of the return diodes associated with the motor speed calculated based on the rotor position, the output current value of the power conversion circuit, and the input voltage value. The second temperature information is estimated based on the thermal resistance value and the diode loss.

10. The power conversion device according to any one of claims 1 to 8, characterized in that, The element temperature estimation unit includes a proportional calculation unit, which multiplies the first temperature information by a coefficient to calculate the second temperature information.

11. The power conversion device as claimed in claim 10, characterized in that, It includes: a voltage detector that detects the value of the input voltage to the power conversion circuit; and a current detector that detects the value of the output current from the power conversion circuit to the motor. The component temperature estimation unit has a coefficient model that outputs the coefficients based on the motor speed calculated according to the rotor position, the output current value of the power conversion circuit, and the input voltage value.

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