Power conversion device

Abstract

The present application provides a power conversion device capable of determining an abnormal state of a cooler or a heat abnormal state at an earlier stage, and reliably performing a protection operation even in the heat abnormal state. A control unit (90) estimates a rate of change of a temperature detection value based on a loss calculation value of a semiconductor switching element calculated based on a current detection value, compares a temperature detection rate calculation value calculated based on the temperature detection value with a temperature detection rate estimation value, and estimates a heat abnormal state of the semiconductor switching element.

Description

Technical Field

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

[0002] Power conversion devices for electric vehicles are required to operate without failure under various conditions and to continue vehicle operation in the event of an anomaly.

[0003] Semiconductor switching elements in power conversion devices generate power losses during switching operations, which can lead to malfunctions if the junction temperature of the semiconductor switching element exceeds a specified value. Therefore, it is necessary to protect the junction temperature from exceeding the specified value, but the junction is the bonding part of the semiconductor chip and is difficult to measure directly. Therefore, a method for detecting the temperature of the semiconductor switching element and estimating the junction temperature using the temperature detection value and the losses calculated from the operation of the semiconductor switching element has been disclosed (for example, Patent Document 1).

[0004] However, the method disclosed in Patent Document 1 estimates the junction temperature based on the calculated correlation between losses and temperature rise, but does not consider changes in the cooler's condition. Therefore, when the cooler's condition changes, there is a problem that the junction temperature cannot be accurately estimated, and reliable protection cannot be implemented.

[0005] To address this issue, a method is disclosed that uses losses calculated from the operation of semiconductor switching elements and past temperature detection values ​​to estimate the current temperature detection value. This estimated temperature detection value is then compared with the actual temperature detection value to estimate the cooler state, and the current flowing through the semiconductor switching element is limited based on the estimated cooler state (Patent Document 2). More specifically, if the difference between the estimated temperature detection value and the actual temperature detection value exceeds a threshold, an abnormal cooler state is presumed. Existing technical documents Patent documents

[0006] Patent Document 1: Japanese Patent No. 5880734 Patent Document 2: Japanese Patent No. 6847158 Summary of the Invention The technical problem that the invention aims to solve

[0007] In the method disclosed in Patent Document 2, the abnormal state of the cooler is determined based on the difference between the estimated temperature value and the actual temperature value, which is calculated using the losses from the operation of the semiconductor switching element and past temperature detection values. However, when the cooler is in a normal state, it is mistakenly determined to be in an abnormal state. Even though there is no problem with current flowing through the semiconductor switching element, it becomes an operation that excessively restricts the current, rather than the expected operation under normal conditions. Therefore, it is necessary to avoid incorrectly determining an abnormal state. Thus, the threshold used to compare the difference between the estimated temperature value and the actual temperature value needs to be set considering the detection error of the temperature detection value and the estimation calculation error of the estimated temperature value. Therefore, the threshold must be set relatively large.

[0008] However, if the threshold is set too high, the timing when the difference between the estimated temperature value and the detected temperature value exceeds the threshold becomes delayed when the cooler is in an abnormal state, making it impossible to determine the abnormal state of the cooler early. In an abnormal state of the cooler, the temperature of the semiconductor switching element may rise sharply, requiring early overheat protection. Therefore, even the method disclosed in Patent Document 2 may not provide reliable protection.

[0009] This invention discloses a technology for solving the above-mentioned problems. Its purpose is to provide a power conversion device that calculates the rate of change of the loss-estimated temperature detection value based on the operation of the semiconductor switching element, and compares the rate of change of the temperature detection value calculated from the temperature detection value with the estimated value of the rate of change of the temperature detection value to determine the abnormal state of the cooler and other abnormal heating states. This enables the abnormal heating state to be determined earlier, and the protection action can be reliably implemented even in the case of abnormal heating. Technical means for solving technical problems

[0010] The power conversion device disclosed in this application includes: a semiconductor switching element that converts power through switching operation; a cooler for cooling the semiconductor switching element; a control unit for controlling the semiconductor switching element; a temperature detector for detecting the temperature of the semiconductor switching element; and a current detector for detecting the current flowing through the semiconductor switching element. The control unit includes: a semiconductor switching element loss calculation unit that calculates the loss of the semiconductor switching element based at least on the current detection value; a temperature detection change rate estimation calculation unit that estimates the rate of change of the temperature detection value based on the loss calculation value of the semiconductor switching element loss calculation unit; a temperature detection change rate calculation unit that calculates the rate of change of the temperature detection value based on the temperature detection value; and a heating abnormality determination unit that compares the estimated temperature change rate and the calculated temperature change rate and estimates the heating abnormality state of the semiconductor switching element. Invention Effects

[0011] According to the power conversion device disclosed in this application, by comparing the estimated value and the detected value of the temperature change rate that produces a significant difference compared with the normal heating state under abnormal heating conditions such as abnormal heating of the cooler, a power conversion device is obtained that can determine the abnormal heating state earlier and can reliably implement protection actions even under abnormal heating conditions. Attached Figure Description

[0012] Figure 1 This is a block diagram showing the structure of the power conversion device involved in Embodiment 1. Figure 2 This is a hardware structure diagram of the control unit in the power conversion device according to Embodiment 1. Figure 3 This is a functional block diagram of the control unit in the power conversion device according to Embodiment 1. Figure 4 This is a functional block diagram of the heating abnormality determination function of the control unit in the power conversion device according to Embodiment 1. Figure 5 This is a functional block diagram of a modified example of the heating abnormality determination function of the control unit in the power conversion device according to Embodiment 1. Figure 6 This is a diagram showing the thermal loop of the power conversion device according to Embodiment 1, from the semiconductor switching element to the temperature detector. Figure 7A This is a diagram illustrating the effect of the power conversion device according to Embodiment 1. Figure 7B This is a diagram illustrating the effect of the power conversion device according to Embodiment 1. Figure 8 This is a functional block diagram of the control unit in the power conversion device according to Embodiment 2. Figure 9 This is a functional block diagram of the heating abnormality determination function of the control unit in the power conversion device according to Embodiment 2. Figure 10 This is a block diagram showing the structure of a modified example of the power conversion device according to embodiments 1 and 2. Figure 11 This is a block diagram illustrating the structure of other variations of the power conversion device involved in embodiments 1 and 2. Figure 12 This is a block diagram illustrating the structure of other variations of the power conversion device involved in embodiments 1 and 2. Detailed Implementation

[0013] Implementation method 1. Embodiment 1 relates to a power conversion device, which includes: a semiconductor switching element for converting power, a cooler for cooling the semiconductor switching element, a control unit for controlling the semiconductor switching element, a temperature detector for detecting the temperature of the semiconductor switching element, and a current detector for detecting the current flowing through the semiconductor switching element. The control unit calculates at least the losses of the semiconductor switching element based on the current detection value, estimates the rate of change of the calculated temperature detection value based on the calculated loss value, and calculates the rate of change of the temperature detection value. By comparing the estimated rate of change of the temperature detection value with the calculated rate of change of the temperature detection value, an abnormal heating state of the semiconductor switching element is estimated. In particular, it relates to overheat protection for semiconductor switching elements such as IGBTs or MOSFETs used in power conversion devices.

[0014] Hereinafter, the structure and operation of the power conversion device according to Embodiment 1 will be described based on the accompanying drawings.

[0015] <Structure of the power conversion device> First, based on Figure 1 The structure of the power conversion device 100 in Embodiment 1 is explained. The power conversion device 100 in Embodiment 1 is assumed to be a power conversion device used in electric vehicles such as electric vehicles and plug-in hybrid electric vehicles, for driving an electric motor powered by electricity from a high-voltage battery.

[0016] exist Figure 1 The diagram shows a DC power supply 12, including a battery or similar device that supplies DC power to a power conversion device and is charged using regenerative power, and a motor 10 that is controlled. However, the controlled object is not limited to the motor 10; it can be any object other than the motor 10.

[0017] exist Figure 1 In this configuration, the power conversion device 100 is connected to the DC power supply 12 via the DC bus 1a on the positive side and the DC bus 1b on the negative side, exchanging drive power or regenerated power with the DC power supply 12. Furthermore, the power conversion device 100 is connected to the motor 10 via the AC bus 2, exchanging drive power or regenerated power with the motor 10.

[0018] Furthermore, the motor 10 is equipped with a rotation angle sensor 11 for detecting the rotation angle θm of the motor. In addition, the motor 10 is a motor that drives the load to rotate and regenerates the rotational energy of the load as electrical energy, such as a three-phase AC synchronous motor or a three-phase brushless motor using permanent magnets.

[0019] The power conversion device 100 consists of a power conversion unit 20, a control unit 90, and a cooler 35.

[0020] The power conversion unit 20 includes: a capacitor 21 connected between the DC bus 1a on the positive side of the power input side and the DC bus 1b on the negative side; a voltage detection unit 24 for detecting the DC bus voltage of the power conversion unit 20; an inverter circuit 25 composed of multiple switching elements and performing DC / AC power conversion; a current detection unit 26 for detecting the current flowing through the motor 10 on the AC bus 2; and a drive circuit 27 for performing drive control to switch the switching elements on and off.

[0021] The capacitor 21 has the functions of suppressing DC bus voltage ripple, reducing the power supply impedance of the power conversion unit 20 to improve the AC current driving capability of the power conversion unit 20, and absorbing surge voltage. In addition, the voltage detection unit 24 divides the DC bus voltage into a voltage read by the control unit 90 through voltage dividing resistors, etc., and outputs DC bus voltage information to the control unit 90.

[0022] Inverter circuit 25 is a commonly known inverter obtained by connecting six switching elements in a full-bridge configuration. That is, as shown... Figure 1 As shown, among the switching elements 51, 52, 53, 54, 55, and 56, the upper-level switching elements and the lower-level switching elements are connected in series and connected in parallel with the DC power supply 12.

[0023] In addition, the midpoints of switching elements 51 and 52 are connected to the input of the U phase of the motor 10, the midpoints of switching elements 53 and 54 are connected to the input of the V phase of the motor 10, and the midpoints of switching elements 55 and 56 are connected to the input of the W phase of the motor 10.

[0024] exist Figure 1 In this process, semiconductor switching elements 51, 52, 53, 54, 55, and 56 are respectively embedded in semiconductor modules 61, 62, 63, 64, 65, and 66.

[0025] Switching elements, for example, are in Figure 1 The diagram shows a MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) with a diode built into the source and drain. However, the type and number of semiconductor switching elements are not limited to this; for example, they can also be IGBTs (Insulated Gate Bipolar Transistors) and SiC-MOSFETs.

[0026] Furthermore, in the inverter circuit 25, temperature detectors 71, 72, 73, 74, 75, and 76 are respectively installed inside or near the semiconductor modules 61 to 66 in order to detect the temperature of the semiconductor switching elements 51 to 56. The temperature values ​​detected by the temperature detectors 71 to 76 are input to the control unit 90. Furthermore, temperature detectors 71-76, which detect the temperature of semiconductor switching elements 51-56, can be disposed inside semiconductor modules 61-66, or on the substrate on which semiconductor modules 61-66 are disposed, near semiconductor modules 61-66. It is assumed that the temperature detector is a thermistor. However, the temperature detector is not limited to a thermistor; it can also be configured to detect temperature using, for example, a temperature-sensing diode disposed on the semiconductor substrate of switching elements 51-56.

[0027] The current detection unit 26 comprises a U-phase current detection unit 261, a V-phase current detection unit 262, and a W-phase current detection unit 263. These units are configured, for example, using shunt resistors. The U-phase current detection unit 261 outputs the U-phase current detection value corresponding to the U-phase current Iu to the control unit 90. The V-phase current detection unit 262 outputs the V-phase current detection value corresponding to the V-phase current Iv to the control unit 90. The W-phase current detection unit 263 outputs the W-phase current detection value corresponding to the W-phase current Iw to the control unit 90. Furthermore, in the following description, the U-phase current detection value, V-phase current detection value, and W-phase current detection value are sometimes collectively referred to as the current detection value. Additionally, the current detection unit 26 may be configured using a current sensor such as a Hall element.

[0028] The drive circuit 27 is controlled based on the PWM signal input from the control unit 90. The drive circuit 27 has the function of switching the switching elements 51 to 56 on and off.

[0029] The rotation angle sensor 11 detects the rotor rotation angle θm of the motor 10 via a rotary transformer or encoder. The rotor rotation angle θm detected by the rotation angle sensor 11 is output to the switch control unit 90. In addition, the rotor rotation angle θm is converted into an electrical angle θe based on the number of pole pairs of the motor 10.

[0030] Cooler 35 cools semiconductor switching elements 51-56. Cooler 35 is, for example, a water-cooled cooler. Specifically, it is a structure that connects a water-cooled cooler, a radiator, and a motor-driven water pump via hoses, allowing a cooling medium such as water, oil, or LLC (Long Life Coolant) to flow from the motor-driven water pump into the water-cooled cooler. However, cooler 35 is not limited to water-cooled coolers; it can also be, for example, an air-cooled cooler. Cooler 35 can also be a radiator connected to and conducting heat to the switching elements 51-56.

[0031] <Hardware Structure of the Control Unit> Figure 2 This is a hardware structure diagram of the control unit 90 of the power conversion device 100 according to Embodiment 1. In this embodiment, the control unit 90 is a control device that controls the power conversion device 100. Each function of the control unit 90 is implemented by the processing circuitry provided by the control unit 90. Specifically, the control unit 90, as a processing circuitry, includes an arithmetic processing unit 80 (computer) such as a CPU (Central Processing Unit), a storage device 81 that exchanges data with the arithmetic processing unit 80, an input circuit 82 that inputs external signals to the arithmetic processing unit 80, and an output circuit 83 that outputs signals from the arithmetic processing unit 80 to the outside.

[0032] The arithmetic processing device 80 can include ASIC (Application Specific Integrated Circuit), IC (Integrated Circuit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits. Furthermore, the arithmetic processing device 80 can also include multiple similar or different arithmetic processing devices to share the execution of each process. The storage device 81 can include RAM (Random Access Memory) (volatile main storage device 81a) configured to read and write data from the arithmetic processing device 80, and ROM (Read Only Memory) (non-volatile auxiliary storage device 81b) configured to read data from the arithmetic processing device 80. The input circuit 82 includes a rotation angle sensor 11, a voltage detection unit 24, a current detection unit 26, and temperature detectors 71-76. It is connected to various sensors and switches and has interface circuits that input the output signals of these sensors and switches to the AD converter and input circuits of the arithmetic processing device 80. The output circuit 83 includes a drive circuit 27, which is connected to electrical loads such as switching elements and actuators, and has interface circuits such as drive circuits and communication circuits that convert the output signals from the arithmetic processing device 80 and output them to these electrical loads.

[0033] The various functions of the control unit 90 are implemented by the arithmetic processing unit 80 executing the software (program) stored in the auxiliary storage device 81b, and in cooperation with other hardware of the control unit 90 such as the storage device 81, the input circuit 82, and the output circuit 83. In addition, the setting data such as thresholds and judgment values ​​used by the control unit 90 are stored in the auxiliary storage device 81b as part of the software (program).

[0034] The functions inside the control unit 90 can be composed of software modules, or they can be composed of a combination of software and hardware.

[0035] <Functional blocks of the control section> Figure 3 This is a functional block diagram of the control unit 90 of the power conversion device 100 according to Embodiment 1. Figure 3 In the middle, the control unit 90 has a heating abnormality determination function unit 91, an overheat protection limit unit 92, a current command generation unit 93, a three-phase / two-phase conversion unit 94, a voltage command generation unit 95, a two-phase / three-phase conversion unit 96, a duty cycle conversion unit 97, and a PWM signal generation unit 98.

[0036] A torque command Trq* is input to the current command generation unit 93 from a higher-level system (not shown). Other control commands for controlling the motor 10 include torque commands, current commands, and voltage commands. In Embodiment 1, the case where the torque command Trq* is used as the control command is illustrated. The current command generation unit 93 generates a d-axis current command value Id* and a q-axis current command value Iq* based on the torque command value Trq*. Here, the d-axis represents the magnetic pole position of the motor 10, i.e., the direction of the magnetic flux, and the q-axis represents the direction electrically orthogonal to the d-axis, forming the dq-axis coordinate system. The dq-axis coordinate system is a rotating coordinate system; when the rotor of the motor 10 with magnets rotates, the dq-axis coordinate system also rotates.

[0037] The overheating abnormality determination function unit 91 has the following functions as a feature of this application: at least calculates the loss of the semiconductor switching element based on the current detection value, estimates the rate of change of the calculated temperature detection value based on the calculated loss value, calculates the temperature detection rate of change based on the temperature detection value, and estimates the overheating abnormality state of the semiconductor switching element by comparing the estimated temperature detection rate of change with the calculated temperature detection rate of change.

[0038] The overheating anomaly determination function unit 91 receives current detection values ​​Iu, Iv, and Iw from the current detection unit 26, temperature detection values ​​T1 to T6 from temperature detectors 71 to 76, and voltage detection value Vpn from the voltage detection unit 24. Based on this information, it estimates the overheating anomaly state of the semiconductor switching element and outputs the overheating anomaly determination result OT to the overheat protection limiting unit 92. Here, the current detection value of the current detection unit 26 consists of the U-phase current detection value corresponding to the U-phase current Iu detected by the U-phase current detection unit 261, the V-phase current detection value corresponding to the V-phase current Iv detected by the V-phase current detection unit 262, and the W-phase current detection value corresponding to the W-phase current Iw detected by the W-phase current detection unit 263. A more detailed structure of the overheating anomaly determination function unit 91 will be described later.

[0039] The overheat protection limiting unit 92, as a feature of this application, has the function of limiting the operation of a switching element to limit current based on the determination result of an abnormal heating state. When the overheat protection limiting unit 92 receives input d-axis current command values ​​Id* and Iq*, and an abnormal heating state determination result OT, and the OT indicates an abnormal heating state, it limits the d-axis current command values ​​Id* and Iq* to predetermined current command values ​​and generates d-axis current command values ​​Idc and Iqc. When the abnormal heating state determination result indicates a normal heating state, it generates d-axis current command values ​​Id* and Iq* to serve as d-axis current command values ​​Idc and Iqc.

[0040] The three-phase / two-phase conversion unit 94 calculates the d-axis current detection value Id and the q-axis current detection value Iq based on the current detection value from the current detection unit 26 and the angle detection value corresponding to the electrical angle θe detected by the rotation angle sensor 11. Here, the current detection value from the current detection unit 26 is composed of the U-phase current detection value corresponding to the U-phase current Iu detected by the U-phase current detection unit 261, the V-phase current detection value corresponding to the V-phase current Iv detected by the V-phase current detection unit 262, and the W-phase current detection value corresponding to the W-phase current Iw detected by the W-phase current detection unit 263.

[0041] The voltage command generation unit 95 performs current feedback calculations based on the d-axis current command Idc and the q-axis current command Iqc, as well as the d-axis current detection value Id and the q-axis current detection value Iq, thereby calculating the d-axis voltage command Vdc and the q-axis voltage command Vqc. Specifically, for example, the voltage command generation unit 95 is configured to calculate the d-axis voltage command Vdc and the q-axis voltage command Vqc, such that the deviation between the d-axis current command Idc and the d-axis current detection value Id (i.e., current deviation ΔId), and the deviation between the q-axis current command Iqc and the q-axis current detection value Iq (i.e., current deviation ΔIq) converge to "0". (ΔId and ΔIq are not shown)

[0042] The two-phase / three-phase conversion unit 96 calculates the three-phase voltage commands Vuc, Vvc, and Vwc based on the d-axis voltage command Vdc and q-axis voltage command Vqc obtained from the voltage command generation unit 95, and the electrical angle θe obtained from the rotation angle sensor 11. Furthermore, the three-phase voltage commands Vuc, Vvc, and Vwc are preferably set to be below or equal to the DC power supply voltage input to the power conversion unit 20, i.e., the input voltage Vpn detected by the voltage detection unit 24.

[0043] The duty cycle conversion unit 97 generates duty cycle commands Du, Dv, and Dw for each of the three phases based on the three-phase voltage commands Vuc, Vvc, and Vwc obtained from the two-phase / three-phase conversion unit 96 and the input voltage Vpn. The duty cycle conversion unit 97 generates and outputs the duty cycle commands Du, Dv, and Dw that correspond to the optimal correction control command.

[0044] The PWM signal generation unit 98 generates a PWM signal. Based on the duty cycle commands Du, Dv, and Dw of each phase obtained from the duty cycle conversion unit 97, the PWM signal generation unit 98 generates a PWM signal for switching the switching elements 51 to 56 to be turned on and off, respectively.

[0045] Specifically, the PWM signal generation unit 98 generates a PWM signal by comparing the duty cycle commands Du, Dv, and Dw of each phase with the carrier wave. The PWM signal generation unit 98 is configured, for example, to generate a PWM signal using a triangular wave comparison method or a sawtooth wave comparison method. In the triangular wave comparison method, a triangular wave with a bilateral triangle shape having equal rise and fall speeds is used as the carrier wave.

[0046] In addition, Figure 3 In the diagram, the PWM signals generated by the PWM signal generation unit 98 are shown as follows: PWM signal UH_SW provided to the switching element 51 of the upper arm of the U phase, PWM signal VH_SW provided to the switching element 53 of the upper arm of the V phase, PWM signal WH_SW provided to the switching element 55 of the upper arm of the W phase, PWM signal UL_SW provided to the switching element 52 of the lower arm of the U phase, PWM signal VL_SW provided to the switching element 54 of the lower arm of the V phase, and PWM signal WL_SW provided to the switching element 56 of the lower arm of the W phase.

[0047] The PWM signal generated by the PWM signal generation unit 98 is input from the control unit 90 to the drive circuit 27 of the power conversion unit 20. By using the drive circuit 27, the switching elements 51 to 56 are turned on and off according to the PWM signal, thereby converting DC power into AC power and supplying it to the motor 10, and charging the regenerative power generated by the motor 10 in the regenerative state to the DC power supply 12.

[0048] Here, the power conversion device according to Embodiment 1 is characterized in that a heating abnormality determination function unit 91 and an overheat protection limiting unit 92 are provided in the control unit 90. When the heating abnormality determination function unit 91 determines that the heating abnormality is abnormal, the overheat protection limiting unit 92 limits the d-axis current command value and the q-axis current command value to a predetermined current command value.

[0049] Furthermore, the power conversion device according to Embodiment 1 is characterized in that the heat abnormality determination function unit 91 at least calculates the loss of the semiconductor switching element based on the current detection value, estimates the rate of change of the calculated temperature detection value based on the loss calculation value, calculates the temperature detection rate of change based on the temperature detection value, and estimates the heat abnormality state of the semiconductor switching element by comparing the estimated temperature detection rate of change with the calculated temperature detection rate of change.

[0050] The following describes in detail the operation of the features of the power conversion device according to Embodiment 1, namely the heat generation abnormality determination function unit 91 and the overheat protection limiting unit 92.

[0051] <Functional blocks of the Fever Abnormality Determination Function> Figure 4 This is a functional block diagram of the overheating abnormality determination function unit 91 of the control unit 90 of the power conversion device 100 according to Embodiment 1. Figure 4 In the middle, the abnormal heating state determination function unit 91 is composed of a switching element loss calculation unit 911, a temperature detection change rate estimation calculation unit 912, a temperature detection change rate calculation unit 913, and an abnormal heating state determination unit 914.

[0052] In addition, Figure 4 The illustration focuses on the overheating abnormality determination function related to the switching element 51 on phase U, omitting descriptions of overheating abnormality determination functions related to other switching elements 52-56. In the following description, the overheating abnormality determination function related to the switching element 51 on phase U will also be used as an example. Other switching elements 52-56 can also similarly constitute an overheating abnormality determination function.

[0053] The switching element loss calculation unit 911 takes the current detection value Iu from the current detection unit 26 and the input voltage Vpn from the voltage detection unit 24 as inputs, calculates the loss of the semiconductor switching element 51, and outputs the semiconductor switching element loss calculation value LO1.

[0054] Specifically, the switching element loss calculation unit 911 pre-stores the loss characteristics of the switching element and the return diode, and calculates the sum of the conduction loss and switching loss calculated using them for the switching element and the return diode respectively as the semiconductor switching element loss calculation value LO1.

[0055] More specifically, the conduction losses of the switching elements and return diodes can be calculated based on the current flowing through the elements and the current conduction time. The current flowing through each element is calculated based on the current detection value Iu. The current conduction time of each element is calculated using a preset dead time and the switching frequency to avoid simultaneous conduction of the switching elements on the high-potential side and the low-potential side. The switching frequency is the same as the frequency of the PWM signal generated by the PWM signal generation unit 98 that generates the turn-on and turn-off signals to the switching elements, and the frequency of the PWM signal set by the PWM signal generation unit 98 is stored and used as the switching frequency. The switching losses of switching elements and return diodes can be calculated using the current flowing through each element, the voltage applied to each element, and the number of switching operations. The current flowing through each element is calculated based on the current sensing value Iu. The voltage applied to each element is calculated based on the input voltage Vpn. The number of switching operations is calculated using the switching frequency.

[0056] In calculating the semiconductor switching element loss value LO1 performed by the switching element loss calculation unit 911, all the information described above related to semiconductor switching element loss can be used, or only the minimum required information can be used. For example, if the switching frequency or dead time is fixed or varies very little, the semiconductor switching element loss can be calculated based solely on the current detection value and the input voltage. Furthermore, if the input voltage is also considered fixed or varies very little, the semiconductor switching element loss can be calculated based solely on the current detection value.

[0057] Furthermore, the conduction and switching losses of switching elements and return diodes exhibit temperature dependence based on the temperature-dependent characteristics of the elements. Therefore, as... Figure 5 As shown in the modified example, a structure can also be adopted in which the temperature detection value is further input as the input to the switching element loss calculation unit 911. For example, a structure can also be adopted to calculate the semiconductor switching element loss based on the characteristic change of the element's temperature reflected by the temperature detection value Ta. This allows for more accurate calculation of the semiconductor switching element loss. Furthermore, in the above-described... Figure 4 In a structure where temperature detection information is not input into the switching element loss calculation unit 911, it is preferable to use the characteristics of the element under the temperature condition where the semiconductor switching element loss is greatest to calculate the semiconductor switching element loss.

[0058] The temperature detection change rate estimation calculation unit 912 takes the semiconductor switching element loss LO1 from the switching element loss calculation unit 911 as input, estimates the change in temperature detection value T1 of temperature detector 71 per unit time, i.e., the temperature detection change rate, and outputs the temperature detection change rate estimation value dT1a. (Hereinafter, the change in temperature detection value per unit time will be referred to as the temperature detection change rate.)

[0059] Here, to facilitate understanding of the method for calculating the temperature change rate of a temperature detector based on the losses of semiconductor switching elements, based on... Figure 6 The relationship between semiconductor switching element losses and temperature rise of the temperature detector is explained in relation to the cooling effect of the cooler. Figure 6 This illustration shows a semiconductor switching element, a temperature detector, and the thermal loop of the cooler 35 in an example of a power conversion device using the cooler 35. The cooler 35 is assumed to be a water-cooled cooler.

[0060] based on Figure 6 The elements constituting the thermal circuit network of the cooler are explained. The semiconductor module 61 consists of a semiconductor switching element 51, a busbar 31, solder 32, a substrate 33, and a temperature detector 71. A semiconductor switching element 51 and a temperature detector 71 are disposed on a substrate 33, and a busbar 31 is connected to the semiconductor switching element 51 by solder 32. In addition, the semiconductor module 61 is connected to the cooler 35 via the insulating member 34, and the cooler 35 is cooled by cooling water 36.

[0061] Temperature detector 71 is provided for detecting the junction temperature of semiconductor switching element 51, but since it cannot be directly installed at the junction due to structural limitations, therefore... Figure 6 As shown, it is positioned near the semiconductor switching element 51.

[0062] Next, the thermal resistance that constitutes the thermal loop network will be explained. The thermal resistances that form the direct heat transfer path from the junction of the semiconductor switching element 51 to the temperature detector 71 are thermal resistances 37, 38a, 38b, and 40. The thermal resistance of the heat transfer path through the cooler 35 is set as thermal resistance 39a, 39b, 39c, 41a, 41b. In addition, the thermal resistance of the heat dissipation path to the cooling water 36 is set as thermal resistance 42a, 42b, 42c.

[0063] Here, assuming the cooler 35 is functioning normally, the temperature of the cooling water 36 is used as a reference. Figure 6 The thermal loop network determines the temperature rise corresponding to the losses generated by the semiconductor switching element 51. Therefore, the junction temperature of the semiconductor switching element 51, the temperature detection value of the temperature detector 71, and the temperature of the cooling water 36 are uniquely determined. That is, if it is known Figure 6In the thermal loop network, the temperature rise of the temperature detector 71, which is based on the temperature of the cooling water 36, can be calculated based on the loss of the semiconductor switching element 51.

[0064] Next, the changes in the relationship between thermal resistance or electrical loss and temperature rise accompanying changes in the cooler's condition will be explained.

[0065] As an example of an abnormal state of cooler 35, consider a case where a cooling water leak occurs. In the event of a cooling water leak, the cooling water 36 flows out, thus eliminating the heat dissipation path to the cooling water 36. In this case, Figure 6 The thermal resistances 42a to 42c in the thermal loop network disappear. Figure 6 For simplicity, the thermal loop is described using only thermal resistance, but in reality, thermal resistances in parallel have thermal capacity. The junction temperature of the semiconductor switching element 51 and the detection temperature of the temperature detector 71 are transient temperature shifts dominated by thermal capacity, with the initial temperature distribution after the cooling water 36 is lost.

[0066] That is, in the event of an abnormal cooling condition such as a cooling water leak in cooler 35, the thermal circuit changes, therefore, based on Figure 6 The temperature rise of the temperature detector 71, which is estimated based on the loss of the semiconductor switching element 51, deviates from the actual temperature rise of the detected temperature.

[0067] As mentioned above, if it is known Figure 6 In the thermal loop network, the temperature rise of the temperature detector 71, which is based on the temperature of the cooling water 36, can be estimated based on the loss of the semiconductor switching element 51.

[0068] Based on the principles explained above, the temperature detection change rate estimation calculation unit 912 estimates the estimated value dT1a of the temperature detection change rate of the temperature detector 71 based on the semiconductor switching element loss LO1 input from the switching element loss calculation unit 911.

[0069] More specifically, the temperature detection rate of change estimation calculation unit 912 pre-stores, for example, Figure 6 The thermal loop of the heat transfer path from the semiconductor switching element 51 to the temperature detector 71 is shown. Based on this thermal loop and the loss LO1 of the semiconductor switching element 51, the temperature rise ΔT1 of the temperature detector 71, with the temperature of the cooling water 36 as a reference, is calculated. In addition, in the calculation of the temperature rise ΔT1 based on the loss LO1 of the semiconductor switching element 51, the previously calculated temperature rise ΔT1old of the detection temperature is also used.

[0070] Then, the temperature change rate estimation calculation unit 912 calculates the change in temperature rise ΔT1 per unit time based on the calculated temperature rise ΔT1 of the detected temperature, and outputs it as the estimated temperature change rate dT1a. Furthermore, as described above, since the estimated temperature change rate dT1a is calculated using the temperature rise ΔT1 of the detected temperature of the temperature detector 71 calculated based on the pre-stored thermal circuit and the loss LO1 of the semiconductor switching element 51, the temperature information of the cooling water 36 itself is not required in the calculation.

[0071] The temperature detection change rate calculation unit 913 takes the temperature detection value T1 from the temperature detector 71 as input, calculates the temperature detection change rate as the amount of change of the temperature detection value T1 per unit time, and outputs it as the temperature detection change rate calculation value dT1b.

[0072] The abnormal heating state determination unit 914 takes the estimated value of temperature change rate dT1a and the calculated value of temperature change rate dT1b as inputs, detects abnormal heating of the switching element 51 due to excessive heating or cooling abnormality of the cooler 35 due to reduced cooling performance, and outputs the determination result as the abnormal heating state determination result OT1.

[0073] Specifically, the abnormal heating state determination unit 914 compares the estimated temperature change rate dT1a with the calculated temperature change rate dT1b. If the comparison result shows that the calculated temperature change rate dT1b is greater than the estimated temperature change rate dT1a, the abnormal heating state determination result OT1 is determined to be an abnormal heating state. Therefore, it is possible to detect when the actual temperature rise rate is greater than the assumed temperature rise rate under normal conditions, and to detect abnormal heating due to excessive heat generation of the switching element or reduced cooling performance of the cooler 35, and determine this as an abnormal heating state.

[0074] Furthermore, in a state where semiconductor switching losses are not occurring or are minimal, both the estimated temperature change rate dT1a and the calculated temperature change rate dT1b are near 0, regardless of whether it is a normal or abnormal state. In this case, if the abnormal heating state is determined by comparing the estimated temperature change rate dT1a and the calculated temperature change rate dT1b, it is possible to mistakenly identify a normal state as an abnormal heating state. Therefore, in comparing the estimated temperature change rate dT1a and the calculated temperature change rate dT1b, a predetermined lower limit greater than 0 can be set for the estimated temperature change rate dT1a. Thus, since the estimated temperature change rate dT1a can be set to a predetermined lower limit greater than 0, the calculated temperature change rate dT1b, which is near 0, will not be larger than the estimated temperature change rate dT1a in a state where semiconductor switching losses are not occurring or are minimal, preventing misjudgment of an abnormal heating state even in a normal state.

[0075] Furthermore, in comparing the estimated temperature change rate dT1a with the calculated temperature change rate dT1b, if the calculated temperature change rate dT1b is greater than the estimated temperature change rate dT1a by a specified value, the abnormal heating state determination result OT1 can also be determined as an abnormal heating state. Therefore, by setting a specified value considering the calculation error of the calculated temperature change rate dT1b or the estimation error of the estimated temperature change rate dT1a, it is possible to more reliably prevent misjudgment of an abnormal heating state under normal conditions.

[0076] <Operation of Overheat Protection Limiting Unit 92> The overheat protection limiting unit 92 has the function of limiting the operation of the switching element to limit the current based on the determination result of the abnormal heating state. The overheat protection limiting unit 92 inputs the d-axis current command value Id* and the q-axis current command value Iq* from the current command generation unit 93, and inputs the abnormal heating state determination result OT from the abnormal heating state determination function unit 91. If the abnormal heating result OT indicates an abnormal heating state, the d-axis current command value Id* and the q-axis current command value Iq* are restricted to specified current command values, the d-axis current command value Idc and the q-axis current command value Iqc are generated, and output to the voltage command generation unit 95. If the abnormal heating result OT indicates that the heating is normal, the d-axis current command value Id* and the q-axis current command value Iq* are generated as the d-axis current command value Idc and the q-axis current command value Iqc, and output to the voltage command generation unit 95.

[0077] Therefore, in the event of abnormal heating conditions such as cooler malfunction, limiting the operation by reducing the current flowing through the semiconductor switching element can prevent the temperature of the semiconductor switching element from rising sharply under such abnormal heating conditions.

[0078] Furthermore, when the overheating anomaly determination result OT indicates an overheating anomaly state, the structure that limits the d-axis current command value Id* and the q-axis current command value Iq* to the specified current command values ​​will not have any effect if the d-axis current command value Id* and the q-axis current command value Iq* are less than the specified current command values. Therefore, even in the event of an overheating anomaly, operation can be performed without excessive current limiting under current conditions where the semiconductor switching element is not overheated, thus preventing unnecessary restriction of the power conversion device's operation.

[0079] Furthermore, when the overheating anomaly determination result OT indicates an overheating anomaly state, the overheat protection limiting unit 92 limits the d-axis current command value Id* and the q-axis current command value Iq* to a predetermined current command value, generating the d-axis current command value Idc and the q-axis current command value Iqc. However, the method for limiting the current command value is not limited to this. For example, the command value obtained by multiplying the d-axis current command value Id* and the q-axis current command value Iq* by a predetermined ratio smaller than 1 can also be generated as the d-axis current command value Idc and the q-axis current command value Iqc.

[0080] <Effects of applying this implementation method> Here, using Figure 7A , Figure 7B This demonstrates that, by applying the above-described implementation method 1, abnormal fever conditions can be detected at an earlier stage compared to existing methods.

[0081] Figure 7A This is a graph illustrating an example of the temperature (junction temperature) of the semiconductor switching element in the power conversion device 100 according to Embodiment 1 and the temperature detection value of the temperature detector. The vertical axis represents temperature, and the horizontal axis represents time. Figure 7B This is a graph illustrating an example of the shift in the rate of temperature change detected by the temperature detector of the power conversion device 100 according to Embodiment 1. The vertical axis represents the rate of temperature change, and the horizontal axis represents time. Specifically, Figure 7A , Figure 7B This is a graph comparing the transition between normal heating state and abnormal heating state when the inverter circuit operates with a fixed output. More specifically, it is a graph assuming the normal heating state represents the case where the cooler is in a normal state, and the abnormal heating state represents the case where the cooler is in an abnormal state due to the disappearance of the cooling medium. exist Figure 7AIn this context, L1 represents the temperature detection value (normal heating state), L2 represents the temperature detection value (abnormal heating state), and L3 represents the junction temperature (abnormal heating state). Furthermore, in... Figure 7B In the diagram, M1 represents the temperature change rate (normal heating state), and M2 represents the temperature change rate (abnormal heating state).

[0082] like Figure 7A As shown, the temperature detection values ​​initially showed no significant difference between normal and abnormal heating states. A significant difference was observed between the normal and abnormal heating states after timing A1. After A1, the temperature detection values ​​in the abnormal heating state significantly increased relative to those in the normal heating state. On the other hand, as... Figure 7B As shown, regarding the shift in the rate of change of temperature detection, no significant difference was found between the normal and abnormal heating states in the very initial period. However, compared to time point A1, which showed a significant difference in temperature detection values ​​between the normal and abnormal heating states, a significant difference in the rate of change of temperature detection appeared at an earlier time point, B1. After B1, the rate of change of temperature detection in the abnormal heating state significantly increased relative to the rate of change of temperature detection in the normal heating state. Therefore, the change in the temperature detection value is the time integral of the rate of change of temperature detection, and the change in the temperature detection value represents a shift in delayed confirmation relative to the change in the rate of change of temperature detection.

[0083] Figure 7A It also shows the temperature (junction temperature) shift of the switching element under abnormal heating conditions. Figure 7A In the above, the junction temperature TA1 of timer A1, which can determine the abnormal heating state based on the temperature detection value, is higher than the junction temperature TB1 of timer B1, which can determine the abnormal heating state based on the temperature change rate.

[0084] As described above, as a feature of this application, the abnormal heating state is determined by comparing the calculated value of the temperature detection change rate with the estimated value of the temperature detection change rate. Compared with the conventional method of comparing the temperature detection value with the estimated value of the temperature detection value, the abnormal heating state can be detected earlier. Even in the case of an abnormal heating state, the operation can be limited and protection can be implemented before the semiconductor switching element reaches a high temperature.

[0085] As described above, the power conversion device 100 of Embodiment 1 calculates at least the losses of the semiconductor switching element based on the current detection value, estimates the rate of change of the temperature detection value based on the calculated losses of the semiconductor switching element, and compares the calculated value of the temperature detection rate of change with the estimated value of the temperature detection rate of change to determine an abnormal heating state. Therefore, by configuring the device to compare the estimated value and the detected value of the temperature rate of change that shows a significant difference compared to the normal heating state under abnormal heating states such as abnormal cooling, abnormal heating states can be detected earlier than conventional methods.

[0086] Furthermore, in the event of an abnormal heating condition, the operation can be reliably protected by limiting the current flowing through the semiconductor switching element, thus preventing overheating even in an abnormal heating condition where the temperature of the semiconductor switching element may rise sharply.

[0087] As described above, the switching elements 51 to 56 of the inverter circuit 25 can be constructed using any semiconductor element. For example, a wide-bandgap semiconductor can be used. Examples of materials used as wide-bandgap semiconductors include SiC and GaN.

[0088] By using these semiconductors, the heat resistance of the switching elements can be improved, thus contributing to improved performance. On the other hand, the switching elements 51-56, constructed using wide-bandgap semiconductors, are more expensive than conventional switching elements constructed using Si. Therefore, the cost of the inverter circuit 25 incorporating wide-bandgap semiconductors is higher.

[0089] In the power conversion device 100 of Embodiment 1, the maximum temperature reached by the semiconductor switching element can be reduced, allowing the use of semiconductor switching elements with lower heat resistance or higher losses, and enabling the device to be constructed from low-cost semiconductor switching elements. Furthermore, in the power conversion device 100 of Embodiment 1, since the temperature rise of the semiconductor switching element can be appropriately controlled, the maximum temperature reached by the semiconductor switching element can be brought close to its operating limit temperature. Therefore, it is possible to reduce the chip size of the semiconductor switching element, which would be impossible due to reduced heat dissipation performance, thereby reducing costs.

[0090] Implementation method 2. Compared to the power conversion device of Embodiment 1, the power conversion device of Embodiment 2 differs in the heating abnormality determination function unit and the overheat protection limiting unit of the control unit. More specifically, the power conversion device of Embodiment 2 uses temperature detection values ​​in the temperature detection change rate estimation calculation of the heating abnormality determination function unit, and also uses temperature detection values ​​in the overheat protection limiting unit.

[0091] Hereinafter, the operation of the power conversion device according to Embodiment 2 will be based on the functional block diagram of the control unit 90 of the power conversion device 100. Figure 8 And the functional block diagram of the abnormal fever state determination function unit 91 Figure 9 The explanation will focus on the differences from Implementation Method 1. The block diagram showing the structure of the control unit in Embodiment 2 is as follows: Figure 8 and Figure 9 In the text, the parts that are the same as or equivalent to those in Embodiment 1 are marked with the same reference numerals. In addition, to distinguish it from Embodiment 1, it is provided as a function unit 91B for determining abnormal heating status and an overheat protection limiting unit 92B.

[0092] The power conversion device of Embodiment 2 consists of a power conversion unit 20, a control unit 90, and a cooler 35. Since the power conversion unit 20 and the cooler 35 are the same as those of the power conversion device 100 of Embodiment 1, the structure and function of the control unit 90 will be described.

[0093] <Functional blocks of the control section> Figure 8 This is a functional block diagram of the control unit 90 of the power conversion device according to Embodiment 2. Figure 8 In the middle, the control unit 90 has a heating abnormality determination function unit 91B, an overheat protection limit unit 92B, a current command generation unit 93, a three-phase / two-phase conversion unit 94, a voltage command generation unit 95, a two-phase / three-phase conversion unit 96, a duty cycle conversion unit 97, and a PWM signal generation unit 98.

[0094] The current command generation unit 93, the three-phase / two-phase conversion unit 94, the voltage command generation unit 95, the two-phase / three-phase conversion unit 96, the duty cycle conversion unit 97, and the PWM signal generation unit 98 are the same as in Embodiment 1, so their descriptions are omitted.

[0095] The overheating anomaly determination function unit 91B has the following functions as a feature of this application: at least calculating the loss of the semiconductor switching element based on the current detection value, estimating the rate of change of the temperature detection value based on the calculated loss value and the temperature detection value, calculating the temperature detection rate of change based on the temperature detection value, and estimating the overheating anomaly state of the semiconductor switching element by comparing the estimated temperature detection rate of change with the calculated temperature detection rate of change. Specifically, unlike Embodiment 1, in the calculation of the estimated temperature detection rate of change, the calculation is based not only on the loss calculation value but also on the temperature detection value.

[0096] The overheating anomaly determination function unit 91B receives current detection values ​​Iu, Iv, and Iw from the current detection unit 26, temperature detection values ​​T1 to T6 from temperature detectors 71 to 76, and voltage detection value Vpn from the voltage detection unit 24. Based on this information, it estimates the overheating anomaly state of the semiconductor switching element and outputs the overheating anomaly determination result OT to the overheat protection limiting unit 92B. Here, the current detection value of the current detection unit 26 consists of the U-phase current detection value corresponding to the U-phase current Iu detected by the U-phase current detection unit 261, the V-phase current detection value corresponding to the V-phase current Iv detected by the V-phase current detection unit 262, and the W-phase current detection value corresponding to the W-phase current Iw detected by the W-phase current detection unit 263. A more detailed structure of the overheating anomaly determination function unit 91B will be described later.

[0097] The overheat protection limiting unit 92B, as a feature of this application, has the function of limiting the operation of the switching element to limit the current based on the determination result of the abnormal heating state and the temperature detection value. In particular, it differs from Embodiment 1 in that it limits the operation of the switching element based not only on the determination result of the abnormal heating state but also on the temperature detection value.

[0098] The overheat protection limiting unit 92B inputs the d-axis current command value Id*, the q-axis current command value Iq*, the overheating anomaly judgment result OT, and the temperature detection values ​​T1 to T6 from the temperature detectors 71 to 76. Based on the overheating anomaly judgment result OT and the temperature detection values ​​T1 to T6, it limits the d-axis current command value Id* and the q-axis current command value Iq* to the specified current command values ​​and generates the d-axis current command value Idc and the q-axis current command value Iqc.

[0099] Here, the power conversion device according to Embodiment 2 is characterized in that a heating abnormality determination function unit 91B and an overheat protection limiting unit 92B are provided in the control unit 90. When the heating abnormality determination function unit 91B determines that the heating abnormality is in a state, the overheat protection limiting unit 92B limits the d-axis current command value and the q-axis current command value to a predetermined current command value.

[0100] Furthermore, the power conversion device according to Embodiment 2 is characterized in that the heat abnormality determination function unit 91B at least calculates the loss of the semiconductor switching element based on the current detection value, estimates the rate of change of the temperature detection value based on the calculated loss value and the temperature detection value, calculates the temperature detection rate of change based on the temperature detection value, and estimates the heat abnormality state of the semiconductor switching element by comparing the estimated temperature detection rate of change with the calculated temperature detection rate of change.

[0101] The following describes in detail the operation of the features of the power conversion device according to Embodiment 2, namely the heat generation abnormality determination function unit 91B and the overheat protection limiting unit 92B.

[0102] <Functional blocks of the Fever Abnormality Determination Function> Figure 9 This is a functional block diagram of the overheating abnormality determination function unit 91B of the control unit 90 of the power conversion device according to Embodiment 2. Figure 9 In the middle, the heating abnormality determination function unit 91B is composed of a switching element loss calculation unit 911, a temperature detection change rate estimation calculation unit 912B, a temperature detection change rate calculation unit 913, and a heating abnormality determination unit 914.

[0103] The switching element loss calculation unit 911, the temperature detection change rate calculation unit 913, and the heating abnormality determination unit 914 are the same as in Embodiment 1, so the description is omitted.

[0104] In addition, Figure 9 The illustration focuses on the overheating abnormality determination function related to the switching element 51 on phase U, omitting descriptions of overheating abnormality determination functions related to other switching elements 52-56. In the following description, the overheating abnormality determination function related to the switching element 51 on phase U will also be used as an example. Other switching elements 52-56 can also similarly constitute an overheating abnormality determination function.

[0105] The temperature detection change rate estimation calculation unit 912B takes the semiconductor switching element loss LO1 from the switching element loss calculation unit 911 and the temperature detection value T1 from the temperature detector 71 as inputs, estimates the change in the temperature detection value T1 per unit time, i.e., the temperature detection change rate, and outputs the temperature detection change rate estimation value dT1a. (Hereinafter, the change in the temperature detection value per unit time will be referred to as the temperature detection change rate.)

[0106] More specifically, the temperature detection rate of change estimation calculation unit 912B pre-stores, for example, Figure 6 The thermal loop of the heat transfer path from the semiconductor switching element 51 to the temperature detector 71 is shown. Based on this thermal loop and the loss LO1 of the semiconductor switching element 51, the temperature rise ΔT1 of the temperature detector 71, with the temperature of the cooling water 36 as a reference, is calculated. In addition, in the calculation of the temperature rise ΔT1 based on the loss LO1 of the semiconductor switching element 51, the previously calculated temperature rise ΔT1old of the detection temperature is also used.

[0107] Furthermore, the temperature change rate estimation calculation unit 912B pre-stores the temperature characteristics of the detection error of the temperature detector 71. Using the temperature characteristics of the detection error of the temperature detector 71, the detection error Ter of the temperature detector 71 is calculated based on the input temperature detection value T1 of the temperature detector 71. Additionally, the temperature characteristics of the detection error of the temperature detector 71 can be stored, for example, as a table of detection error relative to temperature, or as a function with the detected temperature as the independent variable.

[0108] Then, the temperature detection change rate estimation calculation unit 912B calculates the temperature rise ΔT1a after error correction, taking into account the detection error Ter of the temperature detector 71, for the calculated temperature rise ΔT1. Based on this error-corrected temperature rise ΔT1a, the change in the error-corrected temperature rise ΔT1a per unit time is calculated and output as the temperature detection change rate estimation value dT1a. In addition, as mentioned above, since the temperature detection change rate estimation value dT1a is calculated using the temperature rise ΔT1 of the temperature detector 71 based on the pre-stored thermal circuit and the loss LO1 of the semiconductor switching element 51, the temperature information of the cooling water 36 itself is not required in the calculation.

[0109] By adopting the above structure, the estimated value dT1a of the temperature change rate can be calculated based on the temperature characteristics that include the detection error of the temperature detector 71. Therefore, in the heating abnormality determination unit 914, the comparison between the estimated value dT1a of the temperature change rate and the calculated value dT1b of the temperature change rate can be made based on the temperature characteristics that include the detection error of the temperature detector 71, thereby enabling a more accurate determination of the heating abnormality.

[0110] <Operation of Overheat Protection Limiting Unit 92B> The overheat protection limiting unit 92B has the function of limiting the operation of the switching element to limit the current based on the determination result of the abnormal heating state and the temperature detection value of the temperature detector. The overheat protection limiting unit 92B inputs the d-axis current command value Id* and the q-axis current command value Iq* from the current command generation unit 93, the abnormal heating state determination result OT from the abnormal heating state determination function unit 91, and the temperature detection values ​​T1 to T6 from the temperature detectors 71 to 76. Here, the highest temperature among the input temperature detection values ​​T1 to T6 is set as the maximum temperature detection value Tmax.

[0111] When the overheat protection limiting unit 92B determines that the overheating anomaly is in an abnormal state (OT), it compares the maximum temperature detected (Tmax) with a preset specified temperature (Tth1). If the maximum temperature detected (Tmax) is greater than the specified temperature (Tth1), it limits the d-axis current command value (Id*) and the q-axis current command value (Iq*) to specified current command values, generates the d-axis current command value (Idc) and the q-axis current command value (Iqc), and outputs them to the voltage command generation unit 95. On the other hand, when the overheating anomaly determination result (OT) is in an abnormal state, and the maximum temperature detected (Tmax) is less than the specified temperature (Tth1), it generates the d-axis current command value (Id*) and the q-axis current command value (Iq*) as the d-axis current command value (Idc) and the q-axis current command value (Iqc), and outputs them to the voltage command generation unit 95.

[0112] Furthermore, when the overheating anomaly determination result OT indicates a normal heating state, the overheat protection limiting unit 92B compares the maximum temperature detection value Tmax with a preset specified temperature Tth2. If the maximum temperature detection value Tmax is greater than the specified temperature Tth2, the d-axis current command value Id* and the q-axis current command value Iq* are limited to specified current command values, generating d-axis current command values ​​Idc and q-axis current command values ​​Iqc, and outputting them to the voltage command generation unit 95. On the other hand, when the overheating anomaly determination result OT indicates a normal heating state, and the maximum temperature detection value Tmax is less than the specified temperature Tth2, d-axis current command values ​​Id* and q-axis current command values ​​Iq* are generated as d-axis current command values ​​Idc and q-axis current command values ​​Iqc, and output to the voltage command generation unit 95. Additionally, it is preferable to set the specified temperature Tth2 to a temperature higher than the specified temperature Tth1.

[0113] Therefore, in the event of abnormal heating conditions such as cooler malfunction, limiting the operation by reducing the current flowing through the semiconductor switching element can prevent the temperature of the semiconductor switching element from rising sharply under such abnormal heating conditions.

[0114] Furthermore, by configuring the device such that even when the overheating anomaly determination result OT indicates an overheating anomaly, the current command value is limited only when the temperature detection value is greater than a specified temperature, the device can operate without excessively limiting the current even when an overheating anomaly occurs, provided that the semiconductor switching element becomes overheated without causing damage. This prevents unnecessarily limiting the operation of the power conversion device.

[0115] Furthermore, by configuring the current command value limit condition (i.e., the specified temperature 1) when the heating anomaly determination result OT1 is in a heating anomaly state, and setting the current command value limit condition (i.e., the specified temperature 2) when the heating anomaly determination result OT1 is in a heating normal state, the conditions for limiting the current command value are set higher. This allows for the appropriate setting of conditions for the semiconductor switching element to be in an overheated state without damage, for both heating anomaly states where the temperature rises rapidly and heating anomaly states where the temperature rises slowly. This enables operation without excessive current restriction, thus preventing unnecessary restriction of the power conversion device's operation.

[0116] As described above, the power conversion device 200 of Embodiment 2 calculates at least the losses of the semiconductor switching element based on the current detection value, estimates the rate of change of the temperature detection value based on the calculated losses of the semiconductor switching element, and compares the calculated value of the temperature detection rate of change with the estimated value of the temperature detection rate of change to determine an abnormal heating state. Therefore, by comparing the estimated value and the detected value of the temperature rate of change that shows a significant difference compared to the normal heating state under abnormal heating states such as cooler malfunctions, abnormal heating states can be detected earlier than conventional methods.

[0117] <Supplementary Matters> The semiconductor modules 61-66 in the power conversion device of the above embodiment are composed of a semiconductor switching element and a temperature detector, but are not limited thereto; for example, they can also be composed of... Figure 10 The variant shown consists of multiple semiconductor switching elements and a temperature detector. In this case, temperature detectors are installed at specified locations related to the temperature of each semiconductor switching element. In this case, the temperature detection change rate estimation calculation unit 912 pre-stores the heat transfer path from each semiconductor switching element to the temperature detector. Based on the losses of each heat circuit and each semiconductor switching element, it calculates the temperature rise of the temperature detector 71, which is based on the temperature of the cooling water 36, caused by the losses of each semiconductor switching element. It can calculate the temperature rise ΔT1 based on the sum of the temperature rises. Therefore, multiple semiconductor switching elements can be protected with a single temperature detector, overheat protection can be provided without increasing the number of components, and the power converter can be made cheaper and smaller.

[0118] Furthermore, although semiconductor modules 61, 63, and 65 are composed of an upper-level switching element and a temperature detector, and semiconductor modules 62, 64, and 66 are composed of a lower-level switching element and a temperature detector, the design is not limited to this. For example, other designs could also be used. Figure 11 The illustrated variation shows a semiconductor module structure consisting of an upper-side switching element, a lower-side switching element, and a temperature detector. Alternatively, for example, a different configuration could be used. Figure 12 The modified example shown has a structure in which all the switching elements of the inverter circuit 25 and a temperature detector constitute a semiconductor module. In these cases, temperature detectors are installed at specified locations related to the temperature of each semiconductor switching element. The temperature detection change rate estimation calculation unit 912 is the same as described above, pre-stores the heat transfer path from each semiconductor switching element to the temperature detector, calculates the temperature rise of the temperature detector 71 based on the temperature of the cooling water 36 caused by the loss of each semiconductor switching element, and can calculate the temperature rise ΔT1 based on the sum of the temperature rises. Therefore, multiple semiconductor switching elements can be protected with a single temperature detector, overheat protection can be provided without increasing the number of components, and the power converter can be made cheaper and smaller.

[0119] In the power conversion device described in the above embodiments, the cooler is a water-cooled cooler. While a cooling water leak is assumed to be an abnormal condition, this is not limited to this; for example, a decrease in cooling water volume due to a cooler pump malfunction is also included. In this case, since the thermal circuit network also changes, the assumed cooling performance cannot be obtained, and therefore, the above method can also detect an abnormal heating state without problems. Furthermore, although the cooler is a water-cooled cooler, it is not limited to this; for example, a cooling fan could also be used. In this case, a malfunction of the cooling fan or fan blockage is assumed to be an abnormal condition. In this case, since the thermal circuit network also changes, the assumed cooling performance cannot be obtained, and therefore, the above method can also detect an abnormal heating state without problems.

[0120] Furthermore, abnormal heating conditions are not limited to cooler malfunctions; they also include abnormal increases in the losses of semiconductor switching elements due to performance degradation caused by factors such as deterioration of the semiconductor switching elements. In such cases, since the losses of the semiconductor switching elements are greater than the losses calculated based on the known characteristics of the semiconductor switching elements, the calculated temperature change rate is greater than the estimated temperature change rate. Therefore, the above method can be used to detect abnormal heating conditions without any problems.

[0121] Furthermore, in the power conversion device of the above embodiment, the current limiting method is configured to limit the current command values ​​of the d-axis current command value Id* and the q-axis current command value Iq*. However, if the current command is to be limited to an equivalent method, the current limiting method is not limited to this. For example, it could also be a method of limiting the command input from a host system (not shown). More specifically, the current command value can be equivalently reduced by limiting the torque command Trq* to a predetermined torque command value, or by limiting it to a command value that is a predetermined ratio smaller than 1 to the torque command Trq*.

[0122] Furthermore, although the power conversion device described in the above embodiments envisions and describes an inverter that converts direct current to alternating current, the type of power conversion device is not limited to this. Any power conversion device that has semiconductor switching elements and converts power output can be used. For example, it could be an AC / DC converter that converts alternating current to direct current, or a DC / DC converter that changes the voltage and current levels of direct current and outputs it.

[0123] 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 the application of a particular embodiment and can be applied to the embodiment individually or in various combinations. Therefore, it can be assumed that numerous variations not illustrated are also included within the scope of the technology disclosed in this application. For example, this includes cases where at least one constituent element is modified, added to, or omitted, and cases where at least one constituent element is extracted and combined with constituent elements of other embodiments. Label Explanation

[0124] 90 Control Unit, 91 Heating Abnormal State Judgment Function Unit, 911 Switching Element Loss Calculation Unit, 912 Temperature Detection Change Rate Estimation Calculation Unit, 913 Temperature Detection Change Rate Calculation Unit, 914 Heating Abnormal State Judgment Unit.

Claims

1. A power conversion device, comprising: The power conversion device comprises a semiconductor switching element that converts power via a switching action, a cooler for cooling the semiconductor switching element, a control unit for controlling the semiconductor switching element, a temperature detector for detecting the temperature of the semiconductor switching element, and a current detector for detecting the current flowing through the semiconductor switching element. The control unit includes: A semiconductor switching element loss calculation unit calculates the loss of the semiconductor switching element based on the current detection value obtained by the current detector. The temperature detection change rate estimation calculation unit estimates the change rate of the temperature detection value obtained by the temperature detector based on the loss calculation value of the semiconductor switching element loss calculation unit. A temperature detection change rate calculation unit, which calculates the temperature detection change rate based on the detected temperature value; and The abnormal heating state determination unit compares the estimated value of the temperature change rate obtained by the temperature change rate estimation calculation unit with the calculated value of the temperature change rate obtained by the temperature change rate calculation unit to determine the abnormal heating state of the semiconductor switching element. The temperature detection change rate estimation calculation unit estimates the rate of change of the temperature detection value when the heating state is normal, which is the temperature detection change rate. The abnormal heating state determination unit determines an abnormal heating state when the calculated value of the temperature change rate is greater than the estimated value of the temperature change rate. The abnormal heating state determination unit sets a lower limit value of 0 or above for the estimated value of the temperature change rate. The semiconductor switching element loss calculation unit calculates the loss of the semiconductor switching element based at least on the current detection value and the temperature detection value.

2. The power conversion device as described in claim 1, characterized in that, Includes a voltage detector that detects the voltage applied to the semiconductor switching element. The semiconductor switching element loss calculation unit calculates the loss of the semiconductor switching element based on the current detection value and the voltage detection value obtained by the voltage detector.

3. The power conversion device as described in claim 1 or 2, characterized in that, The semiconductor switching element loss calculation unit calculates the loss of the semiconductor switching element based on the current detection value and the switching frequency of the semiconductor switching element.

4. The power conversion device as described in claim 1 or 2, characterized in that, The power conversion device is a power conversion device comprising multiple sets of series-connected switching elements on the high-potential side and low-potential side. The control unit is a control unit that, for each group of series circuits, alternately turns on the switching elements on the high-potential side and the switching elements on the low-potential side with a dead time. The semiconductor switching element loss calculation unit calculates the loss of the semiconductor switching element based at least on the current detection value and the dead time of the switch.

5. The power conversion device as described in claim 1 or 2, characterized in that, In the temperature detection rate of change estimation calculation unit A thermal loop is pre-stored for the heat transfer path from the semiconductor switching element to the temperature detector. Using the switching element loss calculation value obtained by the semiconductor switching element loss calculation unit and the thermal loop, an estimated value of the temperature change of the temperature detector is calculated. Based on the calculated estimated value of the temperature change, an estimated value of the temperature change rate is calculated.

6. The power conversion device as described in claim 1 or 2, characterized in that, In the temperature detection rate of change estimation calculation unit A thermal loop is pre-stored for the heat transfer path from the semiconductor switching element to the temperature detector. Using the switching element loss calculation value obtained by the semiconductor switching element loss calculation unit and the thermal loop, an estimated value of the temperature change of the temperature detector is calculated. Based on the calculated estimated value of the temperature change and the temperature detection value, an estimated value of the temperature change rate is calculated.

7. The power conversion device as described in claim 1 or 2, characterized in that, The control unit includes an overheat protection limiting unit, which limits the operation of the switching element at least based on the result of the abnormal heating determination.

8. The power conversion device as described in claim 7, characterized in that, When the overheat protection limiting unit determines that an abnormal overheating state has been detected, it restricts the operation of the switching element to limit the current flowing through the semiconductor switching element.

9. The power conversion device as described in claim 7, characterized in that, When the overheat protection limiting unit determines that the overheating is abnormal and the temperature detection value is higher than the specified temperature TA, it restricts the operation of the switching element to limit the current flowing through the semiconductor switching element.

10. The power conversion device as claimed in claim 7, characterized in that, When the overheat protection limiting unit determines that the semiconductor switching element is in an abnormal heating state and the current flowing through the semiconductor switching element is greater than the specified current TA, it limits the operation of the switching element to limit the current flowing through the semiconductor switching element.

11. The power conversion device as claimed in claim 9, characterized in that, The overheat protection limiting unit restricts the operation of the switching element when the detected temperature value is higher than the specified temperature TB, thereby limiting the current flowing through the semiconductor switching element.

12. The power conversion device as claimed in claim 11, characterized in that, The specified temperature TB set in the overheat protection limiting section is higher than the specified temperature TA.

13. The power conversion device as described in claim 1 or 2, characterized in that, The abnormal heating state is an abnormal state of the cooler where the cooling performance is reduced.

14. The power conversion device as described in claim 1 or 2, characterized in that, The cooler is a water-cooled cooler.

15. The power conversion device as described in claim 1 or 2, characterized in that, The cooler is an air-cooled cooler.

16. The power conversion device as described in claim 1 or 2, characterized in that, The aforementioned abnormal heating state refers to an abnormal heating state in which the semiconductor switching element generates excessive heat.

17. The power conversion device as described in claim 1 or 2, characterized in that, The semiconductor switching element is configured as a plurality of semiconductor switching elements connected in parallel, and the temperature detector detects the temperature of the plurality of semiconductor switching elements.

18. The power conversion device as described in claim 1 or 2, characterized in that, The semiconductor switching element is made of a wide-bandgap semiconductor.

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