Power converter diagnostic device, diagnostic system, diagnostic method, and diagnostic program

Abstract

To provide a diagnostic device for a power converter for appropriately determining a deterioration state of a semiconductor element without generating a short-circuit current in the power converter.SOLUTION: According to an embodiment, a diagnostic device for a power converter is provided. The power converter drives an electric motor by outputting converted AC power to the electric motor. The diagnostic device includes an output control unit and a deterioration determination unit. The output control unit controls operations of a plurality of semiconductor elements of the power converter to cause the power converter to output electric power to the electric motor at a constant voltage output that makes an output voltage to the electric motor constant in a target voltage pattern. The deterioration determination unit determines a deterioration state about one or more the semiconductor elements based on a current flowing through the electric motor in the constant voltage output from the power converter to the electric motor.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a diagnostic device, a diagnostic system, a diagnostic method, and a diagnostic program for a power converter. [Background technology]

[0002] In the drive control of an electric motor, a power converter including an inverter circuit converts DC power into multi-phase AC power, such as three-phase AC power, and the converted multi-phase AC power is output from the power converter to the electric motor. In this process, a drive control device or the like controls the operation of each of a plurality of semiconductor elements provided in the power converter, thereby controlling the output from the power converter to the electric motor and controlling the drive of the electric motor. In a system in which the drive control of an electric motor is performed in this manner, the power converter is diagnosed by determining the deterioration state and lifespan of the semiconductor elements. In one example, a short-circuit current that does not flow through the electric motor is generated in the power converter, and the deterioration state of the semiconductor elements is determined based on the generated short-circuit current.

[0003] In a power converter, the allowable time for which the short-circuit current can flow is strictly limited. Therefore, it is required to diagnose the power converter without causing a short-circuit current to flow in the power converter. Furthermore, it is required to diagnose the power converter in a way that the deterioration state of the semiconductor elements provided in the power converter can be appropriately determined without causing a short-circuit current to flow in the power converter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-17822 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-19953 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a power converter diagnostic device, diagnostic system, diagnostic method, and diagnostic program that appropriately determine the degradation state of semiconductor elements without generating a short-circuit current in the power converter. [Means for solving the problem]

[0006] According to an embodiment, a diagnostic device for a power converter is provided, in which the power converter outputs converted AC power to an electric motor to drive the electric motor. The diagnostic device includes an output control unit and a deterioration determination unit, and the output control unit controls the operation of a plurality of semiconductor elements of the power converter to determine whether or not the electric motor is deteriorated. Multi-phase Output Voltage Each of of DC voltage with the target voltage set for diagnosis over time The power converter outputs power to the motor at a constant voltage output, and the degradation determination unit determines the degradation state of one or more semiconductor elements based on the current flowing through the motor when the power converter outputs a constant voltage to the motor. The output control unit executes constant voltage output to keep each of the multiple phase output voltages to the motor constant over time at a DC voltage of a target voltage value during each of a first period and a second period following the first period. The degradation determination unit determines the degradation state of one or more of the semiconductor elements by comparing the current flowing through the motor during the constant voltage output during the first period with the current flowing through the motor during the constant voltage output during the second period. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an example of a configuration for controlling the driving of an electric motor. [Figure 2] FIG. 2 is a schematic diagram illustrating the characteristics of a semiconductor element provided in a power converter that outputs electric power to an electric motor. [Figure 3] FIG. 3 is a schematic diagram showing an example of the relationship between the ambient temperature and the saturation voltage of a semiconductor element when the semiconductor element is not energized for a long period of time. [Figure 4] FIG. 4 is a schematic diagram showing an example of a change over time in the saturation voltage of a semiconductor element as a result of correction (conversion) to the saturation voltage when the environmental temperature is the reference temperature. [Figure 5] FIG. 5 is a schematic diagram showing an example of the temperature characteristics of the winding resistance of the electric motor. [Figure 6]FIG. 6 is a schematic diagram illustrating changes due to deterioration of semiconductor elements in the current flowing through the power converter and the electric motor in an output in which each of the output voltages of a plurality of phases is kept constant at a fixed voltage value. [Figure 7] FIG. 7 is a schematic diagram illustrating an example of a diagnostic system for a power converter according to an embodiment. [Figure 8] FIG. 8 is a schematic diagram illustrating six target voltage patterns for outputting a constant voltage to the motor in diagnosing the power converter in this embodiment. [Figure 9] FIG. 9 is a schematic diagram showing target voltage values ​​of three-phase output voltages for six target voltage patterns in which constant voltages are output to the motor in diagnosing the power converter in this embodiment. [Figure 10] FIG. 10 is a schematic diagram showing the currents flowing through the power converter and the motor when a constant voltage is output to the motor for each of the six target voltage patterns shown in FIG. [Figure 11] FIG. 11 is a schematic diagram showing an example of changes over time in three-phase output voltages output from a power converter to an electric motor in the diagnosis of the power converter in the embodiment. [Figure 12] FIG. 12 is a flowchart schematically illustrating an example of processing performed by the processor and the like of the diagnostic device according to the embodiment. [Figure 13] FIG. 13 is a flowchart schematically illustrating an example of a diagnostic process for the power converter shown in FIG. [Figure 14] FIG. 14 is a schematic diagram showing the change over time in the U-phase current flowing through the motor when constant voltage output is performed sequentially with six target voltage patterns for two mutually different diagnostic times in the first verification. [Figure 15] FIG. 15 is a schematic diagram showing the relationship between the number of power cycles and the U-phase current flowing through the motor in a constant voltage output with the corresponding target voltage pattern, as a verification result of the first verification. [Figure 16] FIG. 16 is a schematic diagram showing the results of correcting the detected U-phase current to a corrected value when the temperature of the motor is 20° C. based on the relationship shown in FIG. [Figure 17] 15 is a schematic diagram showing voltage signals generated by amplifying and A / D converting each of the time-varying changes in the U-phase current shown in FIGS. 14 and 15, and then further D / A converting the same. [Figure 18] FIG. 18 is a schematic diagram showing the relationship between the number of power cycles and the correction value of the current detected in the constant voltage output in each of the six target voltage patterns, as a verification result of the second verification. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings.

[0009] (Control configuration for driving electric motors) First, as a matter related to the embodiments, a configuration for controlling the drive of an electric motor will be described. FIG. 1 shows an example of a configuration for controlling the drive of an electric motor. In the example shown in FIG. 1, the drive of an electric motor 1, which is a three-phase synchronous motor, is controlled. A system for controlling the drive of the electric motor 1 includes a power converter 2, which is an inverter. DC power is supplied to the power converter 2 from a DC power supply 3, which is a drive power supply. The power converter 2 includes a plurality of semiconductor elements 5, such as IGBTs (Insulated Gate Bipolar Transistors). In the power converter 2, the semiconductor elements 5 form a multi-phase half-bridge circuit, and each half-bridge circuit includes two semiconductor elements 5, a positive-side semiconductor element 5p and a negative-side semiconductor element 5m. The multi-phase half-bridge circuits are electrically connected in parallel with each other between a positive-side power supply line and a negative-side power supply line. In the example shown in FIG. 1, six semiconductor elements 5 are provided, and three-phase half-bridge circuits are formed electrically in parallel with each other.

[0010] In each of the semiconductor elements 5 provided in the power converter 2, a freewheeling diode 6 is connected between the collector and emitter. Each of the freewheeling diodes 6 is electrically connected in parallel to a corresponding one of the semiconductor elements 5. In each of the half-bridge circuits, an output terminal is formed between the positive-side semiconductor element 5p and the negative-side semiconductor element 5m, and the electric motor 1 is provided with windings (stator windings) 7 in the same number as the number of phases of the half-bridge circuit. Each output terminal of the half-bridge circuit is connected to a corresponding one of the windings 7 of the electric motor 1. In the example of FIG. 1 , each output terminal of the three-phase half-bridge circuits of U-phase, V-phase, and W-phase is connected to a corresponding one of the three windings 7.

[0011] A system for controlling the drive of the electric motor 1 includes a drive control device 8. The drive control device 8 controls the operation of the power converter 2 to thereby control the drive of the electric motor 1. The drive control device 8 is equipped with an integrated circuit including a processor and a storage medium, etc. The processor of the integrated circuit may include a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc. In the drive control device 8, the processor controls the operation of the power converter 2 by executing a program, etc. stored in a storage medium, etc. The drive control device 8 controls the operation of each of the semiconductor elements 5 by controlling the on / off timing of each of the semiconductor elements 5, thereby controlling the operation of the power converter 2. The drive control device 8 also controls the on / off timing of each of the semiconductor elements 5 using pulse signals such as pulse width modulation (PWM) signals. In each of the semiconductor elements 5, the pulse signal from the drive control device 8 is input to, for example, a gate.

[0012] The operation of the power converter 2 is controlled by the drive control device 8, and the power converter 2 converts DC power from the DC power supply 3 into multi-phase AC power. In the example shown in FIG. 1 , the DC power is converted into three-phase AC power. The power converter 2 outputs the converted multi-phase AC power to the electric motor 1, thereby driving the electric motor 1 and causing the rotor of the electric motor 1 to rotate. When the electric motor 1 is in a driving state, multi-phase AC voltages out of phase with each other are output from the power converter 2 to the electric motor 1 as output voltages. In the example shown in FIG. 1 , three-phase AC voltages, namely, U-phase, V-phase, and W-phase, are output from the power converter 2 to the electric motor 1, out of phase with each other. The phase of the U-phase AC voltage is shifted by 120° from the phases of the V-phase AC voltage and the W-phase AC voltage, respectively, and the phase of the V-phase AC voltage is shifted by 120° from the phase of the W-phase AC voltage. When the electric motor 1 is driven by the supply of multi-phase AC power, the output voltage from the power converter 2 to the electric motor 1, i.e., the state of voltage application at the electric motor 1, changes over time, with one cycle of the AC power being one cycle.

[0013] In addition, in the example shown in FIG. 1, a current detection circuit 11 is provided. The current detection circuit 11 detects the current flowing through the electric motor 1 when the electric motor 1 is driven by a supply of multi-phase (three-phase) AC power. In the example shown in FIG. 1, the current detection circuit 11 includes a shunt resistor disposed at one location on the negative-side power supply line of the power converter 2, and detects the current flowing through the electric motor 1 based on the voltage of the shunt resistor. In one example, a shunt resistor is disposed between the negative-side semiconductor element 5m and the negative-side power supply line in each of the multi-phase (three-phase) half-bridge circuits, and the shunt resistors are disposed at multiple locations (three locations) in the power converter 2. The current detection circuit then detects the current flowing through the electric motor 1 based on the voltages of the respective shafts.

[0014] In the example shown in FIG. 1 , an analog signal indicating the current detection result from the current detection circuit 11 is amplified by an amplifier 12, and the amplified analog signal is transmitted to the drive control device 8. The analog signal indicating the current detection result is converted into a digital signal by an A / D (Analog to Digital) converter in the drive control device 8. As a result, the drive control device 8 acquires a digital signal indicating the detection result of the current flowing through the electric motor 1. The drive control device 8 generates pulse signals such as PWM signals that control the operation of each of the semiconductor elements 5 based on the detection result of the current flowing through the electric motor 1, and controls the operation of each of the semiconductor elements 5 using the generated pulse signals. As a result, each of the multi-phase (three-phase) output voltages is controlled based on the detection result of the current flowing through the electric motor 1. In one example, the drive control device 8 adjusts the magnitude of each of the multi-phase output voltages to the electric motor 1 by performing PI control on the current flowing through the electric motor 1.

[0015] In the system that controls the drive of the electric motor 1 as described above, each of the semiconductor elements 5 of the power converter 2 repeatedly turns on and off in a short cycle. Therefore, in each of the semiconductor elements 5, self-heating when on and cooling when off occur repeatedly in a short cycle. Because each of the semiconductor elements 5 repeatedly generates self-heat and cools in a short cycle as described above, it is necessary to properly determine the degradation state of each of the semiconductor elements 5, for example, by properly determining the occurrence of cracks at the connection portions of members with different thermal expansion coefficients. It is then necessary to properly diagnose the power converter 2 by properly determining the degradation state of each of the semiconductor elements 5.

[0016] (Matters related to determining the deterioration state of semiconductor elements) The following describes matters related to determining the degradation state of semiconductor elements, such as the semiconductor element 5 used in the power converter 2. FIG. 2 shows parameters indicating the characteristics of a semiconductor element. In FIG. 2, the saturation voltage Vce(sat) between the collector and emitter is shown as a parameter indicating the characteristics of the semiconductor element. In the following description, the saturation voltage Vce(sat) between the collector and emitter is simply referred to as the "saturation voltage." In semiconductor elements such as IGBTs, the saturation voltage increases as the degree of degradation increases. However, for semiconductor elements, the difference between the saturation voltage in a highly degraded state and that in an undegraded state is small. In one example semiconductor element, the difference between the saturation voltage after 16,000 power cycles (16,000 cycles) under specified conditions and the saturation voltage before the power cycles was approximately 100 mV (0.1 V). Therefore, when determining the degradation state of a semiconductor element, it is necessary to appropriately detect small changes in the saturation voltage between a highly degraded state and an undegraded state.

[0017] Furthermore, in semiconductor devices such as IGBTs, the saturation voltage described above changes in response to the temperature of the junction surface of the semiconductor device to the chip, i.e., the junction temperature Tj. In one example, a 50°C change in junction temperature results in a 0.14V change in the saturation voltage of the semiconductor device. In this case, the change in saturation voltage due to a change in junction temperature is approximately the same as the difference in saturation voltage between a highly degraded state and a non-degraded state. Therefore, when determining the degradation state of a semiconductor device based on the saturation voltage, the influence of the junction temperature Tj must be taken into consideration. The junction temperature Tj is calculated using the ambient temperature Ta of the environment in which the semiconductor device is placed, the thermal resistance Rth(ja) between the junction surface (the chip junction) and the environment in which the semiconductor device is placed, and the power P supplied to the semiconductor device, as shown in Equation (1).

[0018]

number

[0019] However, the thermal resistance Rth(ja) changes depending on the time that voltage is applied to the semiconductor element. Furthermore, when an electric motor is driven by power supplied from a power converter, each semiconductor element repeatedly turns on and off in a short period of time, as described above. Therefore, each semiconductor element repeatedly switches between a powered and non-powered state in a short period of time. Therefore, when an electric motor is driven by power supplied from a power converter, it is difficult to properly grasp the effect of the power supplied to the semiconductor element on the thermal resistance Rth(ja), making it difficult to properly derive the thermal resistance Rth(ja). Therefore, it is difficult to calculate the junction temperature Tj taking the thermal resistance Rth(ja) into account.

[0020] Here, when the semiconductor element is not energized for a long time, such as when the electric motor is not driven for a long time, the junction temperature of the semiconductor element can be considered to be equal to the ambient temperature of the environment in which the semiconductor element is placed, i.e., the ambient temperature of the power converter. Therefore, when the semiconductor element is not energized for a long time, the ambient temperature of the semiconductor element can be used instead of the junction temperature to correct the detected saturation voltage of the semiconductor element. For example, when determining the deterioration state of the semiconductor element immediately before the electric motor starts to operate, the ambient temperature of the semiconductor element can be used to correct the detection result of the saturation voltage of the semiconductor element.

[0021] 3 shows an example of the relationship between the ambient temperature Ta and the saturation voltage Vce(sat) of a semiconductor element when the semiconductor element is not energized for a long period of time. In FIG. 3, the horizontal axis represents the ambient temperature Ta of the semiconductor element (power converter), and the vertical axis represents the saturation voltage Vce(sat). When the semiconductor element is not energized for a long period of time, the detected saturation voltage can be corrected to the saturation voltage in an environment where the ambient temperature Ta is equal to a reference temperature Taref, based on the example relationship shown in FIG. 3 and the detection result of the ambient temperature Ta. Here, the reference temperature Taref is, for example, 20°C.

[0022] Furthermore, when determining the degradation state of a semiconductor element while the semiconductor element has not been energized for a long period of time, the degradation state of the semiconductor element, such as whether or not a failure has occurred in the semiconductor element, can be appropriately determined based on the result of correcting the ambient temperature Ta to the saturation voltage at the reference temperature Taref. FIG. 4 shows an example of the change over time in the correction result (conversion result) of the ambient temperature Ta to the saturation voltage at the reference temperature Taref for the saturation voltage of a semiconductor element. In FIG. 4, the horizontal axis represents time relative to the start of use of the semiconductor element (power converter), and the vertical axis represents the correction result to the saturation voltage at the reference temperature Taref. In the example of FIG. 4, at time ta, the correction result to the saturation voltage at the reference temperature Taref exceeds the threshold value Vce(sat)th. Therefore, after time ta, it is determined that a failure or the like has occurred in the semiconductor element.

[0023] Furthermore, in a power converter that drives an electric motor, as described above, each of the multi-phase half-bridge circuits is connected to a corresponding one of the windings of the electric motor, and each of the semiconductor elements is connected to a corresponding one of the windings of the electric motor. Therefore, the saturation voltage of each of the semiconductor elements is affected by the one of the windings to which it is connected. Each of the windings of the electric motor has a winding resistance, and the winding resistance of each of the windings changes in response to the temperature of the electric motor. Figure 5 shows an example of the temperature characteristics of the winding resistance of an electric motor. In Figure 5, the horizontal axis represents the temperature T of the electric motor, and the vertical axis represents the winding resistance of the electric motor winding. As shown in the example of Figure 5, the winding resistance of the electric motor increases as the temperature rises. Furthermore, in one example, the winding resistance R of the winding at the temperature T of the electric motor is T can be calculated as shown in equation (2). In equation (2), the winding resistance R when the motor reaches the reference temperature Tref is Tref is specified, and the winding resistance R T The slope α T is prescribed.

[0024]

number

[0025] In one example, when the motor temperature is 20°C, which is the reference temperature Tref, the winding resistance is 1.70Ω. Then, based on the calculation results using equation (2) and other formulas, the winding resistance at a motor temperature of 100°C is 2.24Ω. In this case, if the current flowing through the motor is 5A, a change in the motor temperature from 20°C to 100°C causes the voltage applied to the motor's winding resistance to change from 8.5V to 11.2V, a change of approximately 3V. Therefore, the change in voltage applied to the winding resistance due to a change in motor temperature is greater than the difference in saturation voltage between a highly deteriorated state and a non-deteriorated state. For these reasons, when determining the state of deterioration of semiconductor elements in a power converter based on their saturation voltage, it is important to consider the influence of the motor's winding resistance on the saturation voltage of the semiconductor elements.

[0026] Furthermore, as described above, each semiconductor element of the power converter is connected to a corresponding one of the windings of the motor. Therefore, the saturation voltage of each semiconductor element can be detected by detecting when the current flowing through the connected winding reaches saturation. In one example, the winding of the motor connected to the semiconductor element has a winding resistance of 1.7 Ω and an inductance of 0.027 H. In this case, the time constant of the winding is 0.016 s. In a motor with a controlled drive, the time constant of the winding is not significantly different from the example described above. Therefore, in a motor, the current flowing through the winding reaches saturation after approximately 0.1 s of current flow. Therefore, the saturation voltage of the semiconductor element can be detected by continuously passing a current through the semiconductor element and the connected winding for approximately 0.1 s.

[0027] Because the saturation voltage of a semiconductor element can be detected by energizing it for about 0.1 seconds, the time for energizing the semiconductor element can be shortened when detecting the saturation voltage of the semiconductor element. By shortening the time for energizing the semiconductor element, the rise in the junction temperature of the semiconductor element due to energization can be suppressed when detecting the saturation voltage. As a result, the environmental temperature of the semiconductor element (power converter) can be considered to be the same as the junction temperature, and the deterioration state of the semiconductor element can be determined based on the saturation voltage mentioned above.

[0028] In systems that control the drive of electric motors, the aforementioned changes in the saturation voltage of semiconductor elements can be detected using the output voltage from a power converter to the motor in control of maintaining the current flowing through the motor at a target state. For example, the saturation voltage of each semiconductor element of a power converter can be detected using the output voltage from the power converter to the motor in PI control of the current flowing through the motor. However, in control of maintaining the current flowing through the motor at a target state, it is necessary to detect the current flowing through the motor in real time. Therefore, when detecting the saturation voltage of each semiconductor element in control of maintaining the current flowing through the motor at a target state, the accuracy of current detection is significantly affected, which significantly affects current control.

[0029] The aforementioned change in the saturation voltage of the semiconductor elements can be detected by measuring the current flowing through the motor when the multiple phase output voltages from the power converter to the motor are each constant at a fixed voltage over time. If the multiple phase output voltages from the power converter to the motor are each constant at a fixed voltage, then if the saturation voltage of a semiconductor element increases due to degradation, the current flowing through the degraded semiconductor element and the winding (winding resistance) connected to the degraded semiconductor element decreases. Figure 6 shows the change in the current flowing through the power converter and motor due to degradation of the semiconductor elements when the multiple phase output voltages are each constant at a fixed voltage. Figure 6 shows the semiconductor element 5α, one of the two semiconductor elements 5, and the winding resistance Rα of the motor winding for one of the multiple phases.

[0030] In an output where each output voltage from the power converter to the motor is constant at a fixed voltage value, the voltage applied across one of the two semiconductor elements and the winding resistance of the motor in each of the multiple phases is constant at a fixed voltage value. In this case, in one phase shown in FIG. 6, a voltage of fixed voltage value V0 is applied across semiconductor element 5α and winding resistance Rα. When semiconductor element 5α is not degraded, in the above-mentioned output where each output voltage to the motor is constant at a fixed voltage value, the saturation voltage of semiconductor element 5α is Vα, and the voltage applied to winding resistance Rα is V0-Vα. The current flowing through semiconductor element 5α and winding resistance Rα is Iα.

[0031] On the other hand, when the semiconductor element 5α is highly deteriorated, the saturation voltage of the semiconductor element 5α increases compared to when the semiconductor element 5α is not deteriorated. Even when the semiconductor element 5α is highly deteriorated, a fixed voltage V0 is applied across the semiconductor element 5α and the winding resistance Rα in the output where the output voltages from the power converter to the motor are kept constant at fixed voltages. Therefore, when the semiconductor element 5α is highly deteriorated, the saturation voltage of the semiconductor element 5α becomes Vα+ΔV, and the voltage applied to the winding resistance Rα becomes V0-Vα-ΔV in the output where the output voltages to the motor are kept constant at fixed voltages. When the semiconductor element 5α deteriorates, the voltage applied to the winding resistance Rα decreases to V0-Vα-ΔV, as described above, and the current flowing through the semiconductor element 5α and the winding resistance Rα decreases to Iα-ΔI.

[0032] As described above, a power converter that maintains each of the multiple-phase output voltages to a motor at a constant fixed voltage can detect changes in current flowing through the motor, corresponding to changes in the saturation voltage of each semiconductor element of the power converter, thereby enabling the deterioration state of the semiconductor elements to be determined. Here, the resistance of the winding resistor Rα is 1.7 Ω, and the fixed voltage V0 applied across the semiconductor element 5α and the winding resistor Rα is 10 V. Assume that the saturation voltage of the semiconductor element 5α increases from 1.5 V to 1.6 V due to deterioration of the semiconductor element 5α. In this case, the current flowing through the semiconductor element 5α and the winding resistor Rα in the output that maintains each of the multiple output voltages to the motor at a constant fixed voltage drops from 5.00 A in an undegraded state to 4.94 A in a highly degraded state, a change of approximately 0.06 A. To determine the deterioration state of each semiconductor element of the power converter that outputs power to the motor, such as the semiconductor element 5α, it is necessary to appropriately detect the aforementioned change in current of approximately 0.06 A.

[0033] In one example, in a system for controlling the drive of an electric motor, the resolution of the detected current is determined by the maximum current detectable by the system and the number of bits of the A / D converter that converts the analog signal of the detected current into a digital signal. For example, suppose the maximum current detectable by the system is 37.5 A and the number of bits of the A / D converter is 12. In this case, the resolution of the detected current is 0.018 A. Therefore, if the change in current due to semiconductor element degradation is about 0.06 A as described above, it is theoretically possible to detect the change in current due to semiconductor element degradation.

[0034] However, the lower few bits of an A / D converter are subject to errors in conversion to a digital signal. For this reason, when detecting current changes of around 0.06 A, the analog signal of the detected current must be amplified with a high gain before being input to the A / D converter to increase the resolution of the detected current. Therefore, when detecting current changes caused by the degradation of semiconductor elements, the analog signal of the detected current must be amplified with a high gain and input to the A / D converter, compared to detecting current when an electric motor is being driven by AC power.

[0035] (Diagnostic device, diagnostic system, diagnostic method, and diagnostic program) Taking the above into consideration, a diagnostic device, a diagnostic system, a diagnostic method, a diagnostic program, and the like according to embodiments will be described below. In the embodiments, the deterioration state of multiple semiconductor elements of a power converter is determined as follows. FIG. 7 shows a diagnostic system 10 as an example of a diagnostic system for a power converter according to the embodiment. Similar to the example of FIG. 1, the diagnostic system 10 of FIG. 7 includes an electric motor 1, a power converter 2, a DC power supply 3, a drive control device 8, a current detection circuit 11, and an amplifier 12. In the power converter 2 serving as an inverter, six semiconductor elements 5 form a three-phase (multi-phase) half-bridge circuit. Similarly to the example of FIG. 1, in the power converter 2, each of the freewheeling diodes 6 is electrically connected in parallel to a corresponding one of the semiconductor elements 5, and each output terminal of the three-phase half-bridge circuit is connected to a corresponding one of the three windings (stator windings) 7 of the electric motor 1. In the present embodiment, similar to the example of FIG. 1, the drive control device 8 controls the operation of the power converter 2, thereby controlling the output voltage from the power converter 2 to the electric motor 1 and controlling the drive of the electric motor 1.

[0036] 7 , the diagnostic system 10 includes a diagnostic device 15, an amplifier 16, and temperature sensors 17 and 18. The diagnostic device 15 includes an A / D converter 21, an output control unit 22, a degradation determination unit 23, a correction unit 25, and a storage unit 26. The diagnostic device 15 diagnoses the power converter 2 and determines, for example, the degradation state of each of the multiple semiconductor elements 5 of the power converter 2. In the diagnostic device 15, an analog signal is input to the A / D converter 21, which converts the analog signal into a digital signal. Here, the number of bits of the A / D converter 21 is the same as the number of bits of the A / D converter mounted in the drive control device 8, for example.

[0037] The diagnostic device 15 is equipped with an integrated circuit including a processor, a storage medium, etc. In the diagnostic device 15, the processor of the integrated circuit also includes a CPU, an ASIC, an FPGA, etc. In the diagnostic device 15, the processor executes a program, etc. stored in the storage medium, etc., thereby performing processing related to the diagnosis of the power converter 2. In the diagnostic device 15, the output control unit 22, the deterioration determination unit 23, and the correction unit 25 each perform part of the processing of the processor, etc., and the storage unit 26 functions as the storage medium.

[0038] In the diagnostic device 15, the output control unit 22 controls the operation of each of the semiconductor elements 5 of the power converter 2, thereby controlling the output of power from the power converter 2 to the electric motor 1. In a diagnosis using the diagnostic device 15, the output control unit 22 controls the operation of the power converter 2 to output power from the power converter 2 to the electric motor 1 at a constant voltage that keeps the output voltage to the electric motor 1 constant at a target voltage pattern. With the constant voltage output from the power converter 2 to the electric motor 1, the three-phase (multiple phase) output voltage from the power converter 2 to the electric motor 1, i.e., the voltage application state at the electric motor 1, becomes constant or approximately consistent over time. Therefore, with the constant voltage output of the electric motor 1, each of the three-phase output voltages of the U phase, V phase, and W phase becomes constant or approximately constant over time at a target voltage value (fixed voltage value). Note that the output control unit 22, like the drive control device 8, controls the operation of each of the semiconductor elements 5 by, for example, inputting a pulse signal to the gate of each of the semiconductor elements 5.

[0039] In this embodiment, in diagnosing the power converter 2, the output control unit 22 sequentially executes a constant voltage output for keeping the output voltage to the electric motor 1 constant using a plurality of target voltage patterns. The plurality of target voltage patterns differ from one another in the application state of the output voltage from the power converter 2 to the electric motor 1. Therefore, the target voltage value (fixed voltage value) of the output voltage from the power converter 2 to the electric motor 1 differs between the plurality of target voltage patterns in at least one phase of the three phases (multiple phases). The number of target voltage patterns for performing a constant voltage output for keeping the output voltage to the electric motor 1 constant is preferably equal to or greater than the number of semiconductor elements 5 provided in the power converter 2. In one example such as FIG. 7 , in diagnosing the power converter 2, a constant voltage is output from the power converter 2 to the electric motor 1 using each of six target voltage patterns γ1 to γ6, the same number as the number of semiconductor elements 5.

[0040] Here, six target voltage patterns γ1 to γ6 for performing constant voltage output to the electric motor 1 in diagnosis will be described with reference to Fig. 8. Fig. 8 shows the voltage waveforms of three-phase AC voltages, namely, U-phase, V-phase, and W-phase. As mentioned above, the phases of the three-phase AC voltages are shifted by 120° relative to each other. In Fig. 8, the horizontal axis represents the phase of the U-phase AC voltage, and the vertical axis represents the voltage. In the three-phase AC voltages of Fig. 8, the AC voltages of the U-phase, V-phase, and W-phase each vary periodically with a peak-to-peak value of 2Vq.

[0041] Comparing the six target voltage patterns γ1 to γ6 for which constant voltage output is performed in the diagnosis with the three-phase AC voltage of Fig. 8, the target voltage pattern γ1 corresponds to the voltage application state of the electric motor 1 when the U-phase AC voltage is at phase θ1 in the three-phase AC voltage of Fig. 8. The target voltage pattern γ2 corresponds to the voltage application state of the electric motor 1 when the U-phase AC voltage is at phase θ2 in the three-phase AC voltage of Fig. 8, the target voltage pattern γ3 corresponds to the voltage application state of the U-phase AC voltage of Fig. 8 when the U-phase AC voltage is at phase θ3 in the three-phase AC voltage of Fig. 8, the target voltage pattern γ4 corresponds to the voltage application state of the U-phase AC voltage of Fig. 8 when the U-phase AC voltage is at phase θ4 in the three-phase AC voltage of Fig. 8, the target voltage pattern γ5 corresponds to the voltage application state of the U-phase AC voltage of Fig. 8 when the U-phase AC voltage is at phase θ5 in the three-phase AC voltage of Fig. 8, and the target voltage pattern γ6 corresponds to the voltage application state of the U-phase AC voltage of Fig. 8 when the U-phase AC voltage is at phase θ6 in the three-phase AC voltage of Fig. 8. In the U-phase AC voltage in FIG. 8, the phases θ1 to θ6 are shifted from one another at intervals of 60°.

[0042] Fig. 9 shows target voltage values ​​of three-phase output voltages for each of six target voltage patterns γ1 to γ6 for which constant voltage output is performed to the electric motor 1. In one example such as Fig. 7, in the constant voltage output for each of the target voltage patterns γ1 to γ6, control is performed to keep each of the three-phase output voltages constant at the target voltage values ​​shown in Fig. 9. As shown in Fig. 9, the target voltage value of the U-phase output voltage is set to Vq for target voltage pattern γ1, Vq / 2 for target voltage pattern γ2, -Vq / 2 for target voltage pattern γ3, -Vq for target voltage pattern γ4, -Vq / 2 for target voltage pattern γ5, and Vq / 2 for target voltage pattern γ6. The target voltage value of the V-phase output voltage is set to −Vq / 2 for target voltage pattern γ1, Vq / 2 for target voltage pattern γ2, Vq for target voltage pattern γ3, Vq / 2 for target voltage pattern γ4, −Vq / 2 for target voltage pattern γ5, and −Vq for target voltage pattern γ6. The target voltage value of the W-phase output voltage is set to −Vq / 2 for target voltage pattern γ1, −Vq for target voltage pattern γ2, −Vq / 2 for target voltage pattern γ3, Vq / 2 for target voltage pattern γ4, Vq for target voltage pattern γ5, and Vq / 2 for target voltage pattern γ6.

[0043] FIG. 10 shows the currents flowing through the power converter 2 and the motor 1 when a constant voltage is output to the motor 1 for each of the target voltage patterns γ1 to γ6. In FIG. 10, the flow of current is indicated by arrows. Furthermore, for the three windings 7, the U-phase is indicated as winding 7U, the V-phase is indicated as winding 7V, and the W-phase is indicated as winding 7W. For the three positive-side semiconductor elements 5p, the U-phase is indicated as semiconductor element 5Up, the V-phase is indicated as semiconductor element 5Vp, and the W-phase is indicated as semiconductor element 5Wp. For the three negative-side semiconductor elements 5m, the U-phase is indicated as semiconductor element 5Um, the V-phase is indicated as semiconductor element 5Vm, and the W-phase is indicated as semiconductor element 5Wm.

[0044] As shown in FIG. 10 and other figures, in the constant voltage output with target voltage pattern γ1, current flows from the positive power line through semiconductor element 5Up to motor 1. Then, current flows from motor 1 to the negative power line through either semiconductor element 5Vm or 5Wm. Also, in the constant voltage output with target voltage pattern γ1, the voltage applied across semiconductor element 5Up and the winding resistance of winding 7U is constant or approximately constant at a fixed voltage value corresponding to the target voltage value Vq of the U-phase output voltage. Also, in the constant voltage output with target voltage pattern γ2, current flows from the positive power line through either semiconductor element 5Up or 5Vp to motor 1. Then, current flows from motor 1 to the negative power line through semiconductor element 5Wm. Also, in the constant voltage output with target voltage pattern γ2, the voltage applied across the winding resistance of winding 7W and semiconductor element 5Wm is constant or approximately constant at a fixed voltage value corresponding to the target voltage value −Vq of the W-phase output voltage.

[0045] In the constant voltage output with target voltage pattern γ3, current flows from the positive power line through semiconductor element 5Vp to motor 1. Then, current flows from motor 1 to the negative power line through either semiconductor element 5Um or 5Wm. In addition, in the constant voltage output with target voltage pattern γ3, the voltage applied across semiconductor element 5Vp and the winding resistance of winding 7V is constant or approximately constant at a fixed voltage value corresponding to the target voltage value Vq of the V-phase output voltage. In addition, in the constant voltage output with target voltage pattern γ4, current flows from the positive power line through either semiconductor element 5Vp or 5Wp to motor 1. Then, current flows from motor 1 to the negative power line through semiconductor element 5Um. In addition, in the constant voltage output with target voltage pattern γ4, the voltage applied across the winding resistance of winding 7U and semiconductor element 5Um is constant or approximately constant at a fixed voltage value corresponding to the target voltage value -Vq of the U-phase output voltage.

[0046] In the constant voltage output with target voltage pattern γ5, current flows from the positive power line through semiconductor element 5Wp to motor 1. Then, current flows from motor 1 to the negative power line through either semiconductor element 5Um or 5Vm. In the constant voltage output with target voltage pattern γ5, the voltage applied across semiconductor element 5Wp and the winding resistance of winding 7W is constant or approximately constant at a fixed voltage value corresponding to the target voltage value Vq of the W-phase output voltage. In the constant voltage output with target voltage pattern γ6, current flows from the positive power line through either semiconductor element 5Up or 5Wp to motor 1. Then, current flows from motor 1 to the negative power line through semiconductor element 5Vm. In the constant voltage output with target voltage pattern γ6, the voltage applied across the winding resistance of winding 7V and semiconductor element 5Vm is constant or approximately constant at a fixed voltage value corresponding to the target voltage value -Vq of the V-phase output voltage.

[0047] In diagnosing the power converter 2, the current detection circuit 11 detects the current flowing through the motor 1, etc., in the constant voltage output in each of the above-mentioned target voltage patterns γ1 to γ6. In the constant voltage output in the target voltage pattern γ1, the current detection circuit 11 detects the current flowing through the shunt resistor, thereby detecting a current equivalent to the current IUp flowing through the semiconductor element 5Up and the winding 7U. Similarly, by detecting the current flowing through the shunt resistor of current detection circuit 11, a current equivalent to the current IWm flowing through semiconductor element 5Wm and winding 7W is detected in the constant voltage output with target voltage pattern γ2; a current equivalent to the current IVp flowing through semiconductor element 5Vp and winding 7V is detected in the constant voltage output with target voltage pattern γ3; a current equivalent to the current IUm flowing through semiconductor element 5Um and winding 7U is detected in the constant voltage output with target voltage pattern γ4; a current equivalent to the current IWp flowing through semiconductor element 5Wp and winding 7W is detected in the constant voltage output with target voltage pattern γ5; and a current equivalent to the current IVm flowing through semiconductor element 5Vm and winding 7V is detected in the constant voltage output with target voltage pattern γ6.

[0048] Furthermore, in this embodiment, the analog signal indicating the current detection result in the current detection circuit 11 in the above-mentioned constant voltage output is amplified by the amplifier 12 and then further amplified by the amplifier 16. The analog signal amplified by the amplifier 16 is then input to the A / D converter 21 of the diagnostic device 15. In contrast, when the electric motor 1 is driven by three-phase AC power from the power converter 2, the analog signal indicating the current detection result in the current detection circuit 11 is amplified by the amplifier 12, but is not amplified by the amplifier 16 and is then input to the A / D converter (not shown) of the drive control device 8. Therefore, the analog signal indicating the current detection result in the constant voltage output is amplified with a higher amplification factor than the analog signal indicating the current detection result in the state when the electric motor 1 is driven. The analog signal amplified with a higher amplification factor is then transmitted to the diagnostic device 15.

[0049] In the diagnostic device 15, the A / D converter 21 converts an analog signal indicating the current detection result into a digital signal and inputs it to the degradation determination unit 23 and the correction unit 25. The degradation determination unit 23 and the correction unit 25 then perform processing based on the current detection result indicated by the digital signal. Here, in an example such as FIG. 7 , the number of bits of the A / D converter 21 is the same as the number of bits of the A / D converter of the drive control device 8, and the analog signal transmitted to the diagnostic device 15 as the current detection result of the current detection circuit 11 is amplified with a higher amplification factor than the analog signal transmitted to the drive control device 8 as the current detection result of the current detection circuit 11. Therefore, when the electric motor 1 is driven by constant voltage output, the resolution of the current detected by the current detection circuit 11 is higher than when the electric motor 1 is driven by AC power. In other words, the degradation determination unit 23 and the correction unit 25 obtain the detection result of the current flowing through the electric motor 1 at constant voltage output with higher resolution than the detection result of the current flowing through the electric motor 1 when the electric motor 1 is driven.

[0050] FIG. 11 shows an example of temporal changes in the three-phase output voltages output from the power converter 2 to the motor 1 during a diagnosis of the power converter 2. In FIG. 11, the horizontal axis represents time relative to the start of the diagnosis, and the vertical axis represents voltage. In the example shown in FIG. 11, in one diagnosis of the power converter 2, the constant voltages are sequentially output in the order of target voltage patterns γ1, γ2, γ3, γ4, γ5, and γ6. In the diagnosis of the power converter 2, a specified time Yareg is set as the duration for which the constant voltage output continues for each of the target voltage patterns γ1 to γ6. The specified time Yareg is set longer than the time from the start of output until the current flowing through the motor 1 reaches saturation. However, the specified time Yareg is set to a short time sufficient to suppress an increase in the junction temperature of the semiconductor element 5 due to current flow. As described above, the current flowing through the motor 1 reaches saturation after a short current flow of approximately 0.1 seconds. Therefore, the specified time Yareg during which the constant voltage output continues in each of the target voltage patterns γ1 to γ6 can be set to a short time.

[0051] Furthermore, in the diagnosis of the power converter 2, a specified time Ybreg is set as the interval time between constant voltage outputs of the target voltage patterns γ1 to γ6. Therefore, in the diagnosis of the power converter 2, a constant voltage output of the next target voltage pattern is started after the specified time Ybreg has elapsed since the end of constant voltage output of a certain target voltage pattern. Note that the specified time Ybreg is preferably longer than the specified time Yareg during which the constant voltage output continues. The deterioration determination unit 23, the correction unit 25, etc. calculate the average value of the current detected by the current detection circuit 11 during the constant voltage output of each of the target voltage patterns γ1 to γ6. Therefore, the deterioration determination unit 23, the correction unit 25, etc. obtain the average value (time average value) of the current during the specified time Yareg as the detection result of the current flowing through the electric motor 1 for the constant voltage output of each of the target voltage patterns γ1 to γ6.

[0052] Temperature sensor 17 detects the ambient temperature Ta of power converter 2 (semiconductor element 5), and temperature sensor 18 detects the temperature T of electric motor 1. A / D converter 21 of diagnostic device 15 converts analog signals indicating the detected ambient temperature Ta and temperature T into digital signals and inputs them to correction unit 25. Storage unit 26 stores information related to the temperature characteristics of semiconductor element 5, including information indicating the relationship between the saturation voltage of semiconductor element 5 and the ambient temperature Ta of power converter 2. Correction unit 25 corrects the detected results of the current flowing through electric motor 1 when the ambient temperature Ta of power converter 2 is constant-voltage output for each of target voltage patterns γ1 to γ6, based on the detected results of the current flowing through electric motor 1 when the ambient temperature Ta of power converter 2 is constant-voltage output for each of target voltage patterns γ1 to γ6. In this case, the detected results are corrected (converted) to information when the ambient temperature Ta of power converter 2 is equal to reference temperature Taref.

[0053] Furthermore, memory unit 26 stores information relating to the temperature characteristics of the winding resistance of the motor. Correction unit 25 corrects the detection results for the current flowing through motor 1 when constant voltage output is performed for each of target voltage patterns γ1 to γ6, based on the detection results for motor temperature T and the information relating to the temperature characteristics of the winding resistance. At this time, with respect to the current flowing through motor 1 when constant voltage output is performed for each of target voltage patterns γ1 to γ6, the detection results are corrected (converted) to information when temperature T of motor 1 is equal to reference temperature Tref. In this way, correction unit 25 corrects the detection results of current detection circuit 11 for the current flowing through motor 1 when constant voltage output is performed to any one of information when ambient temperature Ta of power converter 2 is reference temperature Taref, information when temperature T of motor 1 is reference temperature Tref, and information when ambient temperature Ta of power converter 2 is reference temperature Taref and temperature T of motor 1 is reference temperature Tref. The deterioration determination unit 23 and the correction unit 25, etc. store in the memory unit 26 either the detection results including the average value over the specified time Yareg for the current flowing through the motor 1 at the constant voltage output for each of the target voltage patterns γ1 to γ6, or information obtained by correcting the detection results as described above by the correction unit 25.

[0054] Furthermore, the diagnosis of the power converter 2 is performed periodically after the start of use of the power converter 2. The deterioration determination unit 23 compares information from a real-time diagnosis with information from any of the previous or previous diagnoses regarding the current flowing through the motor 1 during constant voltage output for each of the target voltage patterns γ1 to γ6. Then, the deterioration determination unit 23 determines the deterioration state of the corresponding semiconductor element 5 based on the comparison result regarding the current between the information from any of the previous or previous diagnoses and the information from the real-time diagnosis.

[0055] In addition, when comparing the currents flowing through the motor 1 during constant voltage output for each of the target voltage patterns γ1 to γ6, the detection results of the current detection circuit 11 may be compared, or information corrected by the correction unit 25 as described above may be compared. However, in the above-described current comparison, it is preferable to compare information when the environmental temperature Ta of the power converter 2 is the reference temperature Taref and the temperature T of the motor 1 is the reference temperature Tref. Here, a first period and a second period following the first period are defined. Furthermore, it is assumed that one of the previous or previous diagnoses is performed during the first period, and real-time diagnosis is performed during the second period. In this embodiment, constant voltage output is performed to keep the output voltage to the motor 1 constant for each of the target voltage patterns γ1 to γ6 during each of the first and second periods.

[0056] In the examples shown in FIGS. 7, 9 to 11, etc., information on the current IUp flowing through the semiconductor element 5Up during constant voltage output with the target voltage pattern γ1 is compared between information on the first period (previous or previous diagnosis) and information on the second period (real-time diagnosis). In this case, the deterioration state of the positive-side semiconductor element 5Up of the U phase is determined based on the comparison result of the current IUp. The deterioration determination unit 23 reads information on the current IUp during the first period from the storage unit 26. Then, with regard to the current flowing through the semiconductor element 5Up during constant voltage output with the target voltage pattern γ1, the deterioration determination unit 23 determines whether the current indicated as the information on the second period has decreased by more than a reference level compared to the current indicated as the information on the first period. If the current during the second period has decreased by more than the reference level compared to the current during the first period, the deterioration determination unit 23 determines that the degree of deterioration of the semiconductor element 5Up has exceeded the reference level and that the semiconductor element 5Up is nearing the end of its life.

[0057] Similarly, information from the first period (previous or previous diagnosis) is compared with information from the second period (real-time diagnosis) for the currents flowing through the corresponding semiconductor elements 5 during constant voltage output for each of the target voltage patterns γ2 to γ6. This allows a determination to be made as to whether the degree of degradation of each of the semiconductor elements 5 corresponding to each of the target voltage patterns γ2 to γ6 exceeds a reference level. That is, information from the first period is compared with information from the second period for each of the current IWm flowing through the semiconductor element 5Wm during constant voltage output for the target voltage pattern γ2, the current IVp flowing through the semiconductor element 5Vp during constant voltage output for the target voltage pattern γ3, the current IUm flowing through the semiconductor element 5Um during constant voltage output for the target voltage pattern γ4, the current IWp flowing through the semiconductor element 5Wp during constant voltage output for the target voltage pattern γ5, and the current IVm flowing through the semiconductor element 5Vm during constant voltage output for the target voltage pattern γ6. Then, the degree of deterioration, lifespan, etc. of each of the semiconductor elements 5Um, 5Vp, 5Vm, 5Wp, and 5Wm are determined in the same manner as for the semiconductor element 5Up.

[0058] The deterioration determination unit 23 issues a warning when the degree of deterioration of any of the semiconductor elements 5 of the power converter 2 exceeds a reference level. The warning is issued using the diagnostic device 15 or a user interface (not shown) provided separately from the diagnostic device 15, for example, by displaying a screen or emitting a sound. When issuing a warning, the deterioration determination unit 23 may notify which of the multiple semiconductor elements 5 has a higher degree of deterioration. In one example, when the degree of deterioration of any of the semiconductor elements 5 exceeds a reference level, the deterioration determination unit 23 sends a command to the drive control device 8 to reduce the output of AC power from the power converter 2 to the electric motor 1 when the electric motor 1 is driven, instead of or in addition to issuing a warning. In this case, while the electric motor 1 is driving, the drive control device 8 controls the operation of the power converter 2 based on the command from the diagnostic device 15, thereby reducing the output of AC power to the electric motor 1 compared to before the diagnosis.

[0059] In this embodiment, the diagnosis of the power converter 2 is performed when the electric motor 1 has not been driven for a long time, i.e., when the semiconductor elements 5 have not been energized for a long time. The diagnosis of the power converter 2 is performed immediately before the electric motor 1 starts to be driven. In one example shown in FIG. 7 , the diagnosis device 15 is capable of communicating with the drive control device 8 and acquires from the drive control device 8 whether a drive command to drive the electric motor 1 has been input. If a drive command has been input, the output control unit 22 causes the power converter 2 to output constant voltage power to the electric motor 1 using each of the target voltage patterns, as described above, before the electric motor 1 is driven by the control of the drive control device 8. As a result, the deterioration state of each of the semiconductor elements 5 is determined and the power converter 2 is diagnosed before the electric motor 1 is driven by the control of the drive control device 8.

[0060] Furthermore, the determination as to whether or not to diagnose the power converter 2 may be made based on either the time Xa elapsed since the previous diagnosis or the time Xb elapsed since the previous drive of the motor 1 was completed, in addition to whether or not a drive command for the motor 1 has been input. In one example, even if a drive command for driving the motor 1 is input, if the time Xa elapsed since the previous diagnosis is shorter than the reference time Xaref, the constant voltage output to the motor 1 is not performed, and the diagnosis of the power converter 2 is not made. In another example, even if a drive command for driving the motor 1 is input, if the time Xb elapsed since the previous drive of the motor 1 was completed is shorter than the reference time Xbref, the constant voltage output to the motor 1 is not performed, and the diagnosis of the power converter 2 is not made.

[0061] FIG. 12 shows an example of processing performed by the processor and the like of the diagnostic device 15. The processing of FIG. 12 is started in a state in which AC power is not supplied to the electric motor 1 and the electric motor 1 is not being driven. When the processing of FIG. 12 is started, the diagnostic device 15 determines whether a drive command to drive the electric motor 1 has been input based on information from the drive control device 8 and the like (S51). If a drive command has not been input (S51-No), the diagnostic device 15 waits in S51. Then, when a drive command is input (S51-Yes), the diagnostic device 15 determines whether the elapsed time Xa since the previous diagnosis is equal to or greater than the reference time Xaref based on information and the like stored in the memory unit 26 (S52).

[0062] If the elapsed time Xa is equal to or greater than the reference time Xaref (S52-Yes), the diagnostic device 15 determines whether the elapsed time Xb since the end of the previous drive of the electric motor 1 is equal to or greater than the reference time Xbref, based on information from the drive control device 8, etc. (S53). If the elapsed time Xb is equal to or greater than the reference time Xbref (S53-Yes), the diagnostic device 15 performs diagnostic processing on the power converter 2 (S54). Then, when the diagnostic processing ends, the diagnostic device 15 transmits information indicating that the diagnosis has ended to the drive control device 8, and causes the drive control device 8 to drive the electric motor 1. Then, the drive control device 8 controls the drive of the electric motor 1 as described above (S55). On the other hand, if the elapsed time Xa is shorter than the reference time Xaref (S52-No) and if the elapsed time Xb is shorter than the reference time Xbref (S53-No), the diagnostic processing is not performed and the electric motor 1 is driven, and the drive control device 8 controls the drive of the electric motor 1 (S55).

[0063] FIG. 13 shows an example of the diagnostic process (S54) for the power converter 2. In the process of FIG. 13, a count value N is defined, and the count value N can be set to a natural number greater than or equal to 1 and less than or equal to a reference value Nref. In one example, in the diagnostic process, a constant voltage is output for each of the six target voltage patterns γ1 to γ6, and the reference value Nref is 6. The count value N can be set to a natural number greater than or equal to 1 and less than or equal to 6. When the diagnostic process of FIG. 13 is started, the output control unit 22 sets the count value N to 1 (S61). Then, the output control unit 22 causes the power converter 2 to output a constant voltage to the electric motor 1 in a target voltage pattern corresponding to the count value N that is set among the multiple target voltage patterns (S62). In one example, when the count value N is set to 1, a constant voltage is output in accordance with the target voltage pattern γ1. Then, the degradation determination unit 23 and the like acquire a detection result of the current flowing through the electric motor 1 in the constant voltage output in the target voltage pattern corresponding to the count value N (S63). At this time, the deterioration determination unit 23 and the like calculate the average value (time average value) of the current flowing through the electric motor 1.

[0064] Then, the output control unit 22 determines whether the duration Ya of the constant voltage output is equal to or greater than the specified time Yareg (S64). If the duration Ya is shorter than the specified time Yareg (S64-No), the process returns to S63, and the processes from S63 onwards are performed sequentially. Therefore, the constant voltage output in the target voltage pattern corresponding to the count value N is continued. On the other hand, if the duration Ya is equal to or greater than the specified time Yareg (S64-Yes), the output from the power converter 2 to the motor 1 is stopped (S65), and the constant voltage output is terminated. Note that while the constant voltage output is being performed, the deterioration determination unit 23 and the like calculate the average value of the current flowing through the motor 1, and obtain the average value of the current during the specified time Yareg as the detection result of the current flowing through the motor 1 for the constant voltage output in the target voltage pattern corresponding to the count value N.

[0065] The correction unit 25 then corrects the detection result of the current flowing through the motor 1 during constant voltage output with the target voltage pattern corresponding to the count value N, based on the detection result of the environmental temperature Ta of the power converter 2 and the detection result of the temperature T of the motor 1 (S66). The correction of the current detection result based on the environmental temperature Ta and the temperature T is performed as described above. The correction unit 25 and the like then store information obtained by correcting the detection result of the current flowing through the motor 1 during constant voltage output with the target voltage pattern corresponding to the count value N in the storage unit 26 (S67). The output control unit 22 then determines whether the elapsed time Yb from the end of the previous constant voltage output is equal to or greater than the specified time Ybreg (S68-No). If the elapsed time Yb is shorter than the specified time Ybreg (S68-Yes), the process waits in S68. On the other hand, if the elapsed time Yb is equal to or greater than the specified time Ybreg (S68-Yes), the output control unit 22 and the like determine whether the count value N is equal to or greater than the reference value Nref (S69).

[0066] If the count value N is smaller than the reference value Nref (S69-No), the output control unit 22 and the like increment the count value N by one (S70) to update the count value N. Then, the process returns to S62, and the processes from S62 onward are sequentially performed. Therefore, a constant voltage is output from the power converter 2 to the motor 1 in the target voltage pattern corresponding to the updated count value N. If the count value N is equal to or greater than the reference value Nref in S69 (S69-Yes), the deterioration determination unit 23 compares information from the second period (the diagnosis performed in real time) with information from the first period (any diagnosis performed before the last time) regarding the current flowing through the motor 1 in the constant voltage output in each of a plurality of target voltage patterns (the same number as the reference value Nref) (S71). In the example of FIG. 13, information regarding the current flowing through the motor 1 in the constant voltage output in each of the target voltage patterns is compared when the environmental temperature Ta of the power converter 2 is the reference temperature Taref and the temperature T of the motor 1 is the reference temperature Tref. The comparison of the current between the first and second time periods is performed as described above.

[0067] Then, based on the comparison result in S71, the deterioration determination unit 23 determines whether any of the semiconductor elements 5 of the power converter 2 has deteriorated beyond a reference level (S72). The determination of the deterioration state of each semiconductor element 5 based on the comparison result of the current between the first period and the second period is performed as described above. If the degree of deterioration of any of the semiconductor elements 5 exceeds the reference level (S72-Yes), the deterioration determination unit 23 etc. issues a warning or the like (S73). On the other hand, if the degree of deterioration of none of the semiconductor elements 5 exceeds the reference level (S72-No), the diagnosis process ends without issuing a warning or the like.

[0068] As described above, in this embodiment, in diagnosing the power converter 2, the output control unit 22 of the diagnostic device 15 controls the operation of the semiconductor elements 5 to cause the power converter 2 to output power to the motor 1 at a constant voltage, which keeps the output voltage to the motor 1 constant at a target voltage pattern. The degradation determination unit 23 then determines the degradation state of one or more of the semiconductor elements 5 based on the current flowing through the motor 1 at the constant voltage output. This allows the degradation state of the semiconductor elements 5 provided in the power converter 2 to be determined without generating a short-circuit current in the power converter 2. Furthermore, as described above, the current flowing through the motor 1 at the constant voltage output changes in response to changes in the saturation voltage of the corresponding semiconductor element 5. Therefore, by detecting a change in the current flowing through the motor 1 at the constant voltage output, a change (increase) in the saturation voltage of the corresponding semiconductor element 5 can be properly detected, and the degradation state of the corresponding semiconductor element 5 can be properly determined.

[0069] Furthermore, in this embodiment, the constant voltage output that keeps the output voltage to the electric motor 1 constant at the target voltage pattern is performed sequentially at a plurality of target voltage patterns (e.g., γ1 to γ6) in which the application state of the output voltage from the power converter 2 to the electric motor 1 differs from one another. Then, the deterioration state of the corresponding semiconductor element 5 is determined based on the current flowing through the electric motor 1 during the constant voltage output at each of the plurality of target voltage patterns. By performing constant voltage output from the power converter 2 at a plurality of target voltage patterns in which the application state of voltage at the electric motor 1 differs from one another, it becomes possible to appropriately determine the deterioration state, etc., of the plurality of semiconductor elements 5 mounted on the power converter 2. For example, the deterioration state of the semiconductor element 5Up is appropriately determined as described above based on the current flowing through the electric motor 1 during the constant voltage output at the target voltage pattern γ1, and the deterioration state of the semiconductor element 5Wm is appropriately determined as described above based on the current flowing through the electric motor 1 during the constant voltage output at the target voltage pattern γ2.

[0070] 7 and 9 to 11, the number of target voltage patterns for which constant voltage output is performed in diagnosing the power converter 2 is equal to or greater than the number of semiconductor elements 5 of the power converter 2. This makes it possible to appropriately determine the state of deterioration, etc., of all the semiconductor elements 5 mounted on the power converter 2. This makes it possible to appropriately determine which of the semiconductor elements 5 mounted on the power converter 2 has a higher degree of deterioration, etc. This improves the accuracy of diagnosing the power converter 2.

[0071] Furthermore, in this embodiment, correction unit 25 corrects the detection result of the current flowing through motor 1 at constant voltage output, based on the detection result of temperature T of motor 1 and the temperature characteristics of the winding resistance of motor 1. Then, deterioration determination unit 23 determines the deterioration state of semiconductor element 5 based on information obtained by correcting the detection result of the current in accordance with temperature T of motor 1, etc. Therefore, the deterioration state of semiconductor element 5 is determined by appropriately considering the influence of winding resistance of motor 1 on the current flowing through motor 1 at constant voltage output, i.e., the influence of winding resistance of motor 1 on the saturation voltage of the corresponding semiconductor element 5.

[0072] Furthermore, in this embodiment, the correction unit 25 corrects the detection result of the current flowing through the electric motor 1 at constant voltage output, based on the detection result of the environmental temperature Ta of the power converter 2 (semiconductor element 5) and the temperature characteristics of the semiconductor element 5. Then, the deterioration determination unit 23 determines the deterioration state of the semiconductor element 5 based on information obtained by correcting the detection result of the current in accordance with the environmental temperature Ta of the power converter 2, etc. Therefore, the deterioration state of the semiconductor element 5 is determined by appropriately considering the influence of the temperature of the semiconductor element 5 on the current flowing through the electric motor 1 at constant voltage output, i.e., the temperature characteristics of the saturation voltage of the semiconductor element 5.

[0073] In this embodiment, a diagnostic process for the power converter 2 is performed immediately before the motor 1 starts to be driven by AC power. The diagnostic process for the power converter 2 is performed only when the elapsed time Xb since the previous drive of the motor 1 ended is equal to or greater than the reference time Xbref. This allows the power converter 2 to be properly diagnosed when no current is applied to each of the semiconductor elements 5 for a long period of time. In the above-described embodiment, the constant voltage output is continued for a short period of time during the diagnostic process, and the time during which each of the semiconductor elements 5 is energized with the constant voltage output is short. Therefore, the rise in the junction temperature of the semiconductor elements 5 due to the application of current with the constant voltage output is properly suppressed. This makes it possible to properly determine the deterioration state of the semiconductor elements 5, as described above, even if the ambient temperature of the semiconductor elements 5 (power converter 2) is considered to be the same as the junction temperature of each of the semiconductor elements 5.

[0074] Furthermore, since the deterioration state of each semiconductor element 5 is determined assuming that the environmental temperature is equal to the junction temperature, there is no need to provide the power converter 2 with a sensor or the like for detecting the junction temperature of each semiconductor element 5. This appropriately prevents the configuration of the power converter 2 from becoming complicated. Furthermore, in this embodiment, each time a diagnosis is performed on the power converter 2, information about the current flowing through the motor 1 at constant voltage output for each target voltage pattern is stored in the storage unit 26 as the diagnosis result. This makes it possible to compare information from the previous diagnosis (first period) with information from the real-time diagnosis (second period) regarding the current flowing through the motor 1 at constant voltage output. This makes it possible to more appropriately determine the deterioration state, etc., of the semiconductor elements 5.

[0075] Furthermore, in this embodiment, the diagnostic device 15 obtains detection results for the current flowing through the electric motor 1 at the constant voltage output with higher resolution than detection results for the current flowing through the electric motor 1 when the electric motor 1 is in a driving state. Here, with regard to the current flowing through the electric motor 1 at the constant voltage output, the amount of change between a state in which the corresponding semiconductor element 5 is not degraded and a state in which the corresponding semiconductor element 5 is highly degraded is small, as described above. In this embodiment, since the detection results for the current flowing at the constant voltage output are obtained with high resolution, it is possible to appropriately detect small changes in the current caused by degradation of the corresponding semiconductor element 5. This allows for a more appropriate determination of the degradation state of the semiconductor element 5.

[0076] 7, the diagnostic device 15 and the drive control device 8 are provided separately from each other, but the present invention is not limited to this. In one example, the diagnostic device 15 may diagnose the power converter 2 in the same manner as in the above-mentioned embodiment and may also perform the processing performed by the drive control device 8 in the above-mentioned embodiment. In this case, when the electric motor 1 is driven by the supply of AC power, the diagnostic device 15 controls the operation of the semiconductor elements 5 of the power converter 2, thereby controlling the output of multi-phase AC power from the power converter 2 to the electric motor 1.

[0077] In one example, a voltage detection circuit is provided that detects the output voltage output from the DC power supply 3 to the power converter 2. In this case, the output control unit 22 of the diagnostic device 15 acquires the detection result of the output voltage from the DC power supply 3. Then, the output control unit 22 controls the operation of the multiple semiconductor elements 5 of the power converter 2 based on the output voltage from the DC power supply 3, thereby causing the power converter 2 to output power to the motor 1 at a constant voltage output that keeps the output voltage to the motor 1 constant according to the target voltage pattern, as described above. Therefore, even if the output voltage from the DC power supply 3 changes, the output from the power converter 2 is controlled in response to the change in the output voltage from the DC power supply 3, so that the power converter 2 outputs power to the motor 1 at a constant voltage output that keeps the output voltage to the motor 1 constant according to the target voltage pattern.

[0078] (Verification related to the embodiment) Furthermore, the following first verification was performed as a verification related to the above-described embodiment. In the first verification, a power cycle test was performed in which a power converter similar to power converter 2 was operated in a power cycle under predetermined conditions. During the power cycle test, the power converter was periodically diagnosed. In this verification, the power converter was diagnosed in multiple states, including a state in which 30 power cycles were performed and a state in which 15,360 power cycles were performed. In each of the multiple diagnoses, constant voltage outputs that maintain constant output voltages to the motor using target voltage patterns were performed sequentially in the order of target voltage patterns γ1, γ2, γ3, γ4, γ5, and γ6, similar to the examples shown in FIGS. 7 and 9 to 11 of the above-described embodiment. The constant voltage outputs for each of the target voltage patterns γ1 to γ6 were continued for a duration sufficient to suppress an increase in the junction temperature of the semiconductor elements, and an interval was provided between the constant voltage outputs for one target voltage pattern and the constant voltage outputs for the next target voltage pattern. In each of the diagnoses performed in the power cycle test, the U-phase current flowing through the motor during constant voltage output in each of the target voltage patterns γ1 to γ6 was detected.

[0079] FIG. 14 shows the change over time in the U-phase current flowing through the motor when constant voltage output is performed sequentially using six target voltage patterns γ1 to γ6 for two mutually different diagnostics. In FIG. 14, the horizontal axis represents time relative to the start of the diagnostics, and the vertical axis represents the U-phase current. Also in FIG. 14, the current IUp flowing from the positive-side semiconductor element (e.g., 5Up) to the motor is represented by a positive value, and the current IUm flowing from the motor to the negative-side semiconductor element (e.g., 5Um) is represented by a negative value. FIG. 14 also shows the change over time in the U-phase current during the diagnostics after 30 power cycles (solid line), which is immediately after the start of the power cycle test, and after 15,360 power cycles (dashed line). As shown in Fig. 14, in this verification, the U-phase current IUp flowing through the motor at a constant voltage output with the target voltage pattern γ1 decreased by 170 mA after 15,360 power cycles compared to 30 power cycles. In the power cycle test in this verification, a failure occurred in a semiconductor element (e.g., 5Up) on the positive side of the U-phase immediately after 15,360 power cycles.

[0080] Figure 15 shows the relationship between the number of power cycles and the U-phase current IUp flowing through the motor when the target voltage pattern γ1 corresponds to a constant voltage output, as a result of this verification. In Figure 15, the horizontal axis represents the number of power cycles (cycle count), and the vertical axis represents the U-phase current IUp flowing from the positive-side semiconductor element to the motor. As shown in Figure 15 and other figures, this verification demonstrated that the U-phase current IUp flowing through the motor when the target voltage pattern γ1 corresponds to a constant voltage output decreases as the number of power cycles increases.

[0081] In this verification, the temperature T of the electric motor was detected. Then, in each of the multiple power converter diagnoses, the detection result of the U-phase current IUp flowing through the electric motor at a constant voltage output with the target voltage pattern γ1 was corrected based on the detected electric motor temperature T and the temperature characteristics of the electric motor winding resistance, as in the above-described embodiment. In this verification, the reference temperature Tref for the electric motor temperature T was set to 20°C, and the detection result of the U-phase current IUp was corrected, and information for the temperature T of 20°C was calculated as a correction value (correction information) for the U-phase current IUp flowing through the electric motor at a constant voltage output with the target voltage pattern γ1.

[0082] Fig. 16 shows the results of correcting the detected U-phase current IUp to a corrected value when the motor temperature T is 20°C, based on the relationship shown in Fig. 15. In Fig. 16, the horizontal axis shows the number of power cycles (cycle count), and the vertical axis shows the corrected value for the U-phase current IUp when the motor temperature T is 20°C. As shown in Fig. 16, by correcting the detection result for the U-phase current IUp flowing through the motor at a constant voltage output with the target voltage pattern γ1 to a corrected value when the motor temperature T is 20°C, the decrease in the current IUp at the constant voltage output with the target voltage pattern γ1 that occurs with an increase in the number of power cycles is more clearly shown.

[0083] In this verification, the analog signal indicating the time-dependent change in the U-phase current while the target voltage patterns γ1 to γ6 were sequentially applied to each diagnosis performed in the power cycle test was amplified using an amplifier. The amplified analog signal was then converted into a digital signal by an A / D converter, and the digital signal indicating the time-dependent change in the U-phase current was then converted into a voltage signal, which is then converted into an analog signal, by a D / A converter.

[0084] FIG. 17 shows voltage signals generated by amplifying and A / D converting each of the time-varying changes in the U-phase current shown in FIG. 14, and then D / A converting the resulting signal. In FIG. 17, the horizontal axis represents time relative to the start of the diagnosis, and the vertical axis represents the voltage signal corresponding to the U-phase current. In this verification, the analog signal was inverted and amplified when amplifying the U-phase current. Therefore, the voltage signal shown in FIG. 17 has an inverted polarity compared to the U-phase current shown in FIG. 13. That is, in FIG. 17, the voltage corresponding to the current IUp flowing from the positive-side semiconductor element (e.g., 5Up) toward the motor is shown as a negative value, and the voltage corresponding to the current IUm flowing from the motor toward the negative-side semiconductor element (e.g., 5Um) is shown as a positive value.

[0085] As shown in Figure 17, in this test, the magnitude of the voltage corresponding to the U-phase current IUp flowing through the motor during constant voltage output with target voltage pattern γ1 decreased by 50 mV after 15,360 power cycles compared to 30 power cycles. A 50 mV change in the voltage signal corresponds to a 130 mA change in the U-phase current. In this test, the decrease in current IUp during constant voltage output with target voltage pattern γ1 as the number of power cycles increased was properly detected. This demonstrates that the deterioration state of the positive-side semiconductor element (e.g., 5Up) of the U-phase can be properly determined based on the decrease in current IUp during constant voltage output with target voltage pattern γ1.

[0086] In addition, the following second verification was conducted as a verification separate from the first verification. In the second verification, a cycle test was conducted in which a power converter similar to power converter 2 was operated in a power cycle under predetermined conditions different from those used in the first verification. During the power cycle test, the power converter was periodically diagnosed. In each of the multiple diagnoses, constant voltage output was sequentially performed for target voltage patterns γ1 to γ6, similar to the examples shown in FIGS. 7 and 9 to 11 of the above-described embodiment, to keep the output voltage to the motor constant. The duration of the constant voltage output for each of the target voltage patterns γ1 to γ6 and the interval time between the constant voltage output for one target voltage pattern and the constant voltage output for the next target voltage pattern were set in the same manner as in the first verification.

[0087] In each of the diagnoses performed in this verification, the current flowing through the motor during constant voltage output was detected, as in the above-described embodiment, etc. The following were detected: U-phase current IUp flowing from a positive-side semiconductor element (e.g., 5Up) to the motor during constant voltage output with target voltage pattern γ1; W-phase current IWm flowing from the motor to a negative-side semiconductor element (e.g., 5Wm) during constant voltage output with target voltage pattern γ2; V-phase current IVp flowing from a positive-side semiconductor element (e.g., 5Vp) to the motor during constant voltage output with target voltage pattern γ3; U-phase current IUm flowing from the motor to a negative-side semiconductor element (e.g., 5Um) during constant voltage output with target voltage pattern γ4; W-phase current IWp flowing from a positive-side semiconductor element (e.g., 5Wp) to the motor during constant voltage output with target voltage pattern γ5; and V-phase current IVm flowing from the motor to a negative-side semiconductor element (e.g., 5Vm) during constant voltage output with target voltage pattern γ6.

[0088] In this verification, the temperature T of the electric motor was also detected. Then, in each of the multiple power converter diagnoses, the detection results for each of the currents IUp, IUm, IVp, IVm, IWp, and IWm were corrected based on the detected temperature T of the electric motor and the temperature characteristics of the winding resistance of the electric motor, as in the above-mentioned embodiment. In this verification, the reference temperature Tref for the electric motor temperature T was set to 20°C, and the detection results for each of the currents IUp, IUm, IVp, IVm, IWp, and IWm were corrected, and information when the temperature T was 20°C was calculated as a correction value (correction information) for the current flowing through the electric motor during constant voltage output in each of the target voltage patterns γ1 to γ6.

[0089] FIG. 18 shows the relationship between the number of power cycles and the correction value of the detected current when the constant voltage output is performed for each of the six target voltage patterns γ1 to γ6. Specifically, FIG. 18 shows the relationship between the number of power cycles and the correction value for each of the detected currents IUp, IUm, IVp, IVm, IWp, and IWm when the temperature T is 20°C. In FIG. 18, the horizontal axis represents the number of power cycles (cycle count), and the vertical axis represents the correction value for the current when the temperature T is 20°C. As shown in FIG. 18 and other figures, this verification demonstrated that the current flowing through the motor when the constant voltage output is performed for each of the target voltage patterns γ1 to γ6 decreases as the number of power cycles increases. Specifically, it was demonstrated that the currents IUp, IUm, IVp, IVm, IWp, and IWm each decrease as the number of power cycles increases.

[0090] 18, immediately after the start of the power cycle test, the correction values ​​for the currents IUp, IUm, IVp, IVm, IWp, and IWm decrease only slightly as the number of power cycles increases. On the other hand, after a certain number of power cycles have been performed, the correction values ​​for the currents IUp, IUm, IVp, IVm, IWp, and IWm decrease significantly as the number of power cycles increases. Therefore, it has been demonstrated that by comparing the amount of change between the real-time diagnostic information and the previous diagnostic information for each of the currents IUp, IUm, IVp, IVm, IWp, and IWm, the degradation state of the corresponding semiconductor device can be appropriately determined.

[0091] Furthermore, in this verification, a failure occurred in a semiconductor element (e.g., 5Vp) on the positive side of the V phase immediately after the final diagnosis of the power converter. Here, the deterioration of the semiconductor element on the positive side of the V phase significantly affects the current IVp, i.e., the current flowing through the motor during constant voltage output with the target voltage pattern γ3. As shown in FIG. 18 and other figures, in this verification, the correction value for the current IVp in the final diagnosis was approximately 4% lower than the correction value in the initial diagnosis at the start of the power cycle test. Therefore, it was demonstrated that by comparing the information from the initial diagnosis with the information from the real-time diagnosis regarding the current flowing through the motor during constant voltage output, it is possible to appropriately determine the deterioration state of the corresponding semiconductor element.

[0092] According to at least one of these embodiments or examples, the operation of multiple semiconductor elements of the power converter is controlled to output power from the power converter to the motor at a constant voltage that keeps the output voltage to the motor constant at a target voltage pattern. Then, the degradation state of one or more of the semiconductor elements is determined based on the current flowing through the motor during the constant voltage output from the power converter to the motor. This makes it possible to provide a power converter diagnostic device, diagnostic system, diagnostic method, and diagnostic program that appropriately determine the degradation state of the semiconductor elements without generating a short-circuit current in the power converter.

[0093] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. The following are additional notes. [1] A diagnostic device for diagnosing a power converter that drives an electric motor by outputting converted AC power to the electric motor, an output control unit that controls the operation of a plurality of semiconductor elements of the power converter to output electric power from the power converter to the electric motor at a constant voltage output that keeps the output voltage to the electric motor constant according to a target voltage pattern; a degradation determination unit that determines a degradation state of one or more of the semiconductor elements based on a current flowing through the electric motor when the constant voltage is output from the power converter to the electric motor; A diagnostic device comprising: [2] The output control unit sequentially executes the constant voltage output that keeps the output voltage to the electric motor constant using the target voltage pattern using a plurality of target voltage patterns in which the application states of the output voltage from the power converter to the electric motor are different from each other, the deterioration determination unit determines the deterioration state of one or more of the semiconductor elements based on the current flowing through the electric motor when the constant voltage is output in each of the plurality of target voltage patterns. [1] Diagnostic device. [3] The output control unit sequentially executes the constant voltage output that keeps the output voltage to the electric motor constant with the target voltage pattern with target voltage patterns in which the application states of the output voltage from the power converter at the electric motor are different from each other and the number of patterns is equal to or greater than the number of semiconductor elements of the power converter. [4] The output control unit executes the constant voltage output to keep the output voltage to the electric motor constant according to the target voltage pattern during each of a first period and a second period after the first period; the degradation determination unit determines the degradation state of one or more of the semiconductor elements by comparing the current flowing through the electric motor when the constant voltage output is performed during the first period with the current flowing through the electric motor when the constant voltage output is performed during the second period. A diagnostic device according to any one of [1] to [3]. [5] Further comprising a correction unit that performs at least one of correcting a detection result of the current flowing through the motor at the constant voltage output based on a detection result of the temperature of the motor and information about the temperature characteristics of a winding resistance of the motor, and correcting a detection result of the current flowing through the motor at the constant voltage output based on a detection result of the environmental temperature of the power converter and information about the temperature characteristics of the semiconductor element, the deterioration determination unit determines the deterioration state of one or more of the semiconductor elements based on information corrected from the detection result regarding the current flowing through the electric motor when the constant voltage is output. A diagnostic device according to any one of [1] to [4]. [6] A diagnostic device according to any one of [1] to [5], wherein the deterioration determination unit obtains detection results for the current flowing through the motor at the constant voltage output with higher resolution than detection results for the current flowing through the motor when the motor is driven by the AC power from the power converter. [7] The output control unit executes the constant voltage output to keep the output voltage to the electric motor constant according to the target voltage pattern before the electric motor starts to be driven by the AC power from the power converter, the deterioration determination unit determines the deterioration state of one or more of the semiconductor elements based on the current flowing through the electric motor in the constant voltage output before the electric motor starts to be driven by the AC power from the power converter. [1] to [6]. [8] Any one of the diagnostic devices according to [1] to [7]; the power converter including a plurality of the semiconductor elements, the operation of each of the semiconductor elements being controlled by the output control unit of the diagnostic device; the electric motor that is driven by the AC power converted by the power converter and output from the power converter; Equipped with The power converter outputs the power to the electric motor with the constant voltage output that keeps the output voltage to the electric motor constant according to the target voltage pattern by controlling the operation of each of the semiconductor elements by the output control unit. A diagnostic system for the power converter. [9] A diagnostic method for diagnosing a power converter that drives an electric motor by outputting converted AC power to the electric motor, comprising: outputting electric power from the power converter to the electric motor at a constant voltage output that keeps the output voltage to the electric motor constant according to a target voltage pattern by controlling the operation of a plurality of semiconductor elements of the power converter; determining a state of deterioration of one or more of the semiconductor devices based on a current flowing through the electric motor at the constant voltage output from the power converter to the electric motor; A diagnostic method comprising:

[10] A diagnostic program for diagnosing a power converter that drives an electric motor by outputting converted AC power to the electric motor, the program comprising: By controlling the operation of a plurality of semiconductor elements of the power converter, power is output from the power converter to the motor at a constant voltage that keeps the output voltage to the motor constant according to a target voltage pattern; determining a state of deterioration of one or more of the semiconductor elements based on a current flowing through the electric motor when the constant voltage is output from the power converter to the electric motor; Diagnostic program. [Explanation of symbols]

[0094] 1...electric motor, 2...power converter, 5 (5Up, 5Vp, 5Wp, 5Um, 5Vm, 5Wm)...semiconductor elements, 7 (7U, 7V, 7W) windings, 8...drive control device, 11...current detection circuit, 12, 16...amplifier, 15...diagnostic device, 21...A / D converter, 22...output control unit, 23...deterioration determination unit, 25...correction unit, 26...memory unit

Claims

1. A diagnostic device that diagnoses a power converter that drives an electric motor by outputting converted AC power to the electric motor, an output control unit that controls the operation of a plurality of semiconductor elements of the power converter to output electric power from the power converter to the electric motor at a constant voltage output that keeps each of the output voltages of a plurality of phases to the electric motor constant over time at a DC voltage of a target voltage value set for diagnosis; a degradation determination unit that determines a degradation state of one or more of the semiconductor elements based on a current flowing through the electric motor when the constant voltage is output from the power converter to the electric motor; Equipped with the output control unit executes the constant voltage output to keep each of the output voltages of the multiple phases to the electric motor constant over time at the DC voltage of the target voltage value during each of a first period and a second period after the first period; the deterioration determination unit determines the deterioration state of one or more of the semiconductor elements by comparing the current flowing through the electric motor when the constant voltage output is performed during the first period with the current flowing through the electric motor when the constant voltage output is performed during the second period. Diagnostic equipment.

2. the output control unit sequentially executes the constant voltage output, which keeps each of the output voltages of the multiple phases to the electric motor constant over time at the DC voltage of the target voltage value, in each of the first period and the second period, in a plurality of patterns in which the target voltage value of the output voltage is different from each other for at least one phase among the multiple phases, with respect to combinations of the target voltage values ​​of the output voltages of the multiple phases; the deterioration determination unit determines the deterioration state of one or more of the semiconductor elements by comparing the current flowing through the electric motor during the first period with the current flowing through the electric motor during the constant voltage output for each of the plurality of patterns, between the first period and the second period. The diagnostic device of claim 1.

3. 3. The diagnostic device of claim 2, wherein the output control unit sequentially executes the constant voltage output that keeps each of the output voltages of the multiple phases to the electric motor constant over time at the DC voltage of the target voltage value during each of the first period and the second period, with respect to combinations of the target voltage values ​​of the output voltages of the multiple phases, in patterns in which the target voltage values ​​of the output voltages of at least one of the multiple phases are different from each other, and the number of patterns is equal to or greater than the number of semiconductor elements of the power converter.

4. The device further comprises a correction unit that, during each of the first period and the second period, corrects the detection result of the current flowing through the motor at the constant voltage output based on the detection result of the temperature of the motor and information related to the temperature characteristics of the winding resistance of the motor, and corrects the detection result of the current flowing through the motor at the constant voltage output based on the detection result of the ambient temperature of the power converter and information related to the temperature characteristics of the semiconductor element; the deterioration determination unit determines the deterioration state of one or more of the semiconductor elements by comparing information corrected from the detection result regarding the current flowing through the electric motor during the constant voltage output, between the first period and the second period; The diagnostic device according to any one of claims 1 to 3.

5. 5. The diagnostic device according to claim 1, wherein a resolution of the detection result regarding the current flowing through the electric motor obtained by the degradation determination unit is higher in the constant voltage output during each of the first period and the second period than in a state in which the electric motor is driven by the AC power from the power converter.

6. the output control unit executes the constant voltage output to keep each of the output voltages of the multiple phases to the electric motor constant over time at the DC voltage of the target voltage value before the electric motor starts to be driven by the AC power from the power converter during each of the first period and the second period; the deterioration determination unit, during the second period, before the electric motor is started to be driven by the AC power from the power converter, compares the current flowing through the electric motor in the constant voltage output between the first period and the second period, thereby determining the deterioration state of one or more of the semiconductor elements; The diagnostic device according to any one of claims 1 to 5.

7. The diagnostic device according to any one of claims 1 to 6, the power converter including a plurality of the semiconductor elements, the operation of each of the semiconductor elements being controlled by the output control unit of the diagnostic device; the electric motor that is driven by the AC power converted by the power converter and output from the power converter; Equipped with The power converter outputs the power to the electric motor at the constant voltage output that keeps each of the output voltages of the multiple phases to the electric motor constant over time at the DC voltage of the target voltage value by controlling the operation of each of the semiconductor elements by the output control unit during each of the first period and the second period. A diagnostic system for the power converter.

8. A diagnostic method for diagnosing a power converter that drives an electric motor by outputting converted AC power to the electric motor, comprising: an output control unit controls the operation of a plurality of semiconductor elements of the power converter to output electric power from the power converter to the electric motor at a constant voltage output that keeps each of the output voltages of a plurality of phases to the electric motor constant over time at a DC voltage of a target voltage value set for diagnosis; a degradation determination unit determining a degradation state of one or more of the semiconductor elements based on a current flowing through the electric motor when the electric power converter outputs the constant voltage to the electric motor; Equipped with the output control unit executes the constant voltage output, which keeps each of the output voltages of the plurality of phases to the electric motor constant over time at the DC voltage of the target voltage value, during a first period and a second period subsequent to the first period; the deterioration determination unit determines the deterioration state of one or more of the semiconductor elements by comparing the current flowing through the electric motor when the constant voltage output is performed during the first period with the current flowing through the electric motor when the constant voltage output is performed during the second period. Diagnostic methods.

9. A diagnostic program for diagnosing a power converter that drives an electric motor by outputting converted AC power to the electric motor, the program comprising: By controlling the operation of a plurality of semiconductor elements of the power converter, power is output from the power converter to the motor at a constant voltage output that keeps each of the output voltages of a plurality of phases to the motor constant over time at a DC voltage of a target voltage value set for diagnosis, determining a degradation state of one or more of the semiconductor elements based on a current flowing through the electric motor when the constant voltage is output from the power converter to the electric motor; executing the constant voltage output for making each of the output voltages of the plurality of phases to the electric motor constant over time at the DC voltage of the target voltage value during a first period and during a second period subsequent to the first period; determining the degradation state of one or more of the semiconductor elements by comparing the current flowing through the electric motor at the constant voltage output during the first period with the current flowing through the electric motor at the constant voltage output during the second period; Diagnostic program.

Images