Fault Detection Circuit

Abstract

To deal with a problem in that in a conventional fault detection circuit, a fault in an inverter cannot be detected with a small amount of arithmetic processing.SOLUTION: A fault detection circuit of the present invention includes: a rectangular pulse comparison circuit 15 configured to generate, for each combination of pulse width modulated signals, detection signals UV, VW, WV each indicating a difference component between pulse widths of two of the pulse width modulated signals having phases adjacent to each other; and a fault diagnosis unit 23 configured to detect a fault in an inverter 11 based on a shift in a combination of logic levels of the plurality of detection signals UV, VW, WV output by the rectangular pulse comparison circuit 15 from a preset determination value DV. The fault diagnosis unit 23 uses the determination value DV that is different for each motor rotation angle obtained by assuming in advance that two alternating-current signals having phases adjacent to each other among three-phase alternating-current signals have the same voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a fault detection circuit that detects a fault in an inverter that outputs a three-phase AC signal to drive a motor. [Background technology]

[0002] One of the motor drive methods is a three-phase drive method in which a motor is controlled by a three-phase AC signal. In this three-phase drive method, a PWM signal is output by an inverter, and the average voltage of this PWM signal is used as the AC signal. In addition, in the three-phase drive method, it is important that the phase difference between the drive signals and the amplitude of the drive signals are maintained at preset values. Therefore, Patent Document 1 discloses a method for inspecting a signal output by an inverter in the three-phase drive method.

[0003] The motor drive device disclosed in Patent Document 1 includes an inverter that supplies AC power to a three-phase brushless motor, a shunt resistor connected in series between the lower arm of each phase of the inverter and ground, a first detection circuit that detects a potential difference across the shunt resistor, a second detection circuit that detects a potential difference across the shunt resistor, a third detection circuit that detects the potential difference across the shunt resistor, and a control unit that receives as input the output of the first detection circuit, the output of the second detection circuit, and the output of the third detection circuit and controls the inverter, wherein the control unit compares the output of the first detection circuit, the output of the second detection circuit, and the output of the third detection circuit to determine which of the first detection circuit, the second detection circuit, and the third detection circuit is faulty, and controls the inverter based on the output of the detection circuit other than the detection circuit determined to be faulty among the first detection circuit, the second detection circuit, and the third detection circuit. In addition, the control unit described in Patent Document 1 includes a first analog-to-digital conversion circuit that performs analog-to-digital conversion of the output of the first detection circuit and the output of the second detection circuit, and a second analog-to-digital conversion circuit that performs analog-to-digital conversion of the output of the second detection circuit and the output of the third detection circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-184668 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in an inverter used in a three-phase drive system, the frequency of a carrier signal (e.g., a PWM signal) is generally set higher than the frequency of a three-phase AC signal (e.g., about 20 kHz) in order to suppress current ripple. When sampling this carrier signal, it is necessary to sample and process the signal at a frequency (e.g., 2 MHz) sufficiently higher than the frequency of the carrier signal. In Patent Document 1, analog-to-digital conversion is performed on the three-phase AC signal, and inverter fault detection is performed based on the value obtained by the analog-to-digital conversion. Therefore, the motor drive device described in Patent Document 1 needs to use an MCU (Micro Controller Unit) capable of operating at a high frequency in order to detect faults, which causes a problem of increased current consumption.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and proposes a fault detection circuit capable of detecting a fault in an inverter with a reduced amount of calculation processing. [Means for solving the problem]

[0007] The fault detection circuit according to the present disclosure detects a fault in an inverter that outputs three-phase pulse-width modulated signals that become three-phase AC signals that drive a motor, and includes a rectangular pulse comparison circuit that generates a detection signal indicating a difference component in pulse widths between two pulse-width modulated signals of adjacent phases for each combination of the pulse-width modulated signals, and a fault diagnosis unit that detects a fault in the inverter based on a deviation of a combination of logical levels of the detection signals output by the rectangular pulse comparison circuit from a preset judgment value, and the fault diagnosis unit uses a different judgment value for each motor rotation angle that is previously assumed to result in the same voltage for two AC signals of adjacent phases among the three-phase AC signals.

[0008] The fault detection circuit according to the present disclosure compares the combination of the presence or absence of a difference in the pulse width of the pulse-width modulated signal with a judgment value set for each rotation angle of the motor. Effect of the Invention

[0009] According to the present disclosure, an abnormality in an inverter can be detected by a calculation device with low processing power. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram of a motor drive device according to a first embodiment. [Diagram 2] 1 is a circuit diagram of a rectangular pulse comparison circuit according to a first embodiment. [Diagram 3] 1 is a circuit diagram of a filter circuit according to a first embodiment. [Figure 4] 4 is a timing chart of a modulated wave output by an inverter when a three-phase AC signal is normal. [Diagram 5] 4 is a timing chart illustrating the operation of the rectangular pulse comparison circuit when the three-phase AC signal is normal. [Figure 6] 4 is a table illustrating determination values ​​applied to the fault diagnosis unit according to the first embodiment. [Figure 7] 4 is a timing chart illustrating an operation of the fault diagnosis unit according to the first embodiment. [Figure 8] 11 is a timing chart of a modulated wave output by an inverter when a phase shift fault occurs in the V phase of a three-phase AC signal. [Figure 9] 4 is a timing chart illustrating an operation of the rectangular pulse comparator circuit when a phase shift fault occurs in the V phase of a three-phase AC signal. [Figure 10] 11 is a timing chart of a modulated wave output by an inverter when a fault occurs that causes an increase in the frequency of the V-phase of a three-phase AC signal. [Figure 11] 4 is a timing chart illustrating the operation of the rectangular pulse comparator circuit when a fault occurs that increases the frequency of the V-phase of the three-phase AC signal. [Figure 12] 10 is a timing chart of a modulated wave output by an inverter when a fault occurs that reduces the frequency of the V-phase of a three-phase AC signal. [Figure 13] 10 is a timing chart illustrating the operation of the rectangular pulse comparator circuit when a fault occurs that reduces the frequency of the V-phase of the three-phase AC signal. [Figure 14] 11 is a timing chart of a modulated wave output by an inverter when a fault occurs in which the V phase of a three-phase AC signal is stuck to the low side. [Figure 15] 10 is a timing chart illustrating the operation of the rectangular pulse comparison circuit when a fault occurs in which the V phase of the three-phase AC signal is stuck to the low side. [Figure 16] FIG. 11 is a circuit diagram of a rectangular pulse comparison circuit according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described below through embodiments of the invention, but the invention according to the claims is not limited to the following embodiments. Also, not all of the configurations described in the embodiments are necessarily essential as means for solving the problems. The embodiments will be described below with reference to the drawings.

[0012] First embodiment First, a block diagram of a motor drive device according to the first embodiment is shown in Fig. 1. The motor drive device according to the first embodiment changes the frequency and pulse width of a drive signal according to a rotation angle and a speed command value (not shown) of a motor 12 using an MCU (Micro Controller Unit) 10, and generates a three-phase AC signal for driving the motor by providing the drive signal to an inverter 11. Here, the MCU 10 is a semiconductor device incorporating various processing units such as a calculation unit capable of executing a program, a PWM processing unit that generates a PWM (Pulse Width Modulation) signal that serves as the drive signal, a digital input interface, an analog input interface, a timer, etc.

[0013] The fault detection circuit 1 according to the first embodiment is incorporated into a part of the motor drive device shown in Fig. 1. Specifically, a part of the fault detection circuit 1 is realized using the functions of the MCU 10. Therefore, in the following description, the motor drive device according to the first embodiment will be described as a whole, and then the fault detection circuit 1 will be described in detail.

[0014] 1, the motor drive device according to the first embodiment includes an MCU 10, an inverter 11, a motor 12, an angle sensor 13, a level conversion circuit 14, a rectangular pulse comparison circuit 15, and a filter circuit 16. The MCU 10 also includes a motor control unit 20, a rotation angle acquisition unit 21, an analog input unit 22, and a fault diagnosis unit 23.

[0015] The motor control unit 20 changes the frequency and pulse width of the drive signal provided to the inverter 11 in accordance with the rotation angle of the motor 12 acquired by a rotation angle acquisition unit 21 and a speed command value provided from a higher-level system (not shown). The motor control unit 20 is realized using a calculation function, a PWM processing unit, a timer, etc.

[0016] The inverter 11 generates a three-phase AC signal from a power source given as a direct current. Specifically, the inverter 11 has a first inverter that generates a U-phase AC signal, a second inverter that generates a V-phase AC signal, and a third inverter that generates a W-phase AC signal. The first to third inverters generate three-phase AC signals with phases differing by 120° according to a drive signal output by the motor control unit 20.

[0017] The first inverter has transistors T1 and T2 connected in series between a power supply line and a ground line. The first inverter outputs a U-phase AC signal from a node where the transistors T1 and T2 are connected. The second inverter has transistors T3 and T4 connected in series between a power supply line and a ground line. The second inverter outputs a V-phase AC signal from a node where the transistors T3 and T4 are connected. The third inverter has transistors T5 and T6 connected in series between a power supply line and a ground line. The third inverter outputs a W-phase AC signal from a node where the transistors T5 and T6 are connected.

[0018] In the inverter 11, the first to third inverters output PWM (pulse width modulation) signals whose duty ratio changes according to the pulse width of the drive signal output by the motor control unit 20. The average voltage of the PWM signal output by each inverter within a predetermined period changes over time. In other words, the average voltage of the PWM signal output by each inverter within a predetermined period becomes an AC signal.

[0019] The motor 12 is a three-phase AC motor. The motor 12 is also equipped with an angle sensor 13. The angle sensor 13 detects the rotation angle of the motor 12 and outputs information on the detected rotation angle of the motor 12. This rotation angle information is transmitted to a rotation angle acquisition unit 21 and used in processing within the MCU 10.

[0020] The level conversion circuit 14 converts the amplitude of the PWM signal corresponding to each phase of the three-phase AC signal into a logic level (for example, an amplitude of about 3.3 V or 5.0 V). The rectangular pulse comparison circuit 15 generates a detection signal indicating a difference component in the pulse width of two PWM signals of adjacent phases for each combination of PWM signals. More specifically, the rectangular pulse comparison circuit 15 outputs the difference component in the pulse width between the U-phase PWM signal and the V-phase PWM signal as a detection signal UV, outputs the difference component in the pulse width between the V-phase PWM signal and the W-phase PWM signal as a detection signal VW, and outputs the difference component in the pulse width between the W-phase PWM signal and the U-phase PWM signal as a detection signal WU.

[0021] Here, an example of a specific circuit of the rectangular pulse comparison circuit 15 will be described. FIG. 2 shows a circuit diagram of the rectangular pulse comparison circuit 15 according to the first embodiment. As shown in FIG. 2, the rectangular pulse comparison circuit 15 has exclusive OR circuits 31 to 33. The exclusive OR circuit 31 outputs the exclusive OR operation result of the U-phase PWM signal and the V-phase PWM signal as a detection signal UV. The exclusive OR circuit 32 outputs the exclusive OR operation result of the V-phase PWM signal and the W-phase PWM signal as a detection signal VW. The exclusive OR circuit 33 outputs the exclusive OR operation result of the W-phase PWM signal and the U-phase PWM signal as a detection signal WU.

[0022] The filter circuit 16 smoothes each of the multiple detection signals (for example, detection signals UV, VW, WU) and transmits the smoothed detection signals to an analog input unit 22 in the motor control unit 20. More specifically, each of the multiple detection signals is a pulse wave, and the filter circuit 16 outputs a DC voltage having an average voltage of the multiple detection signals within a predetermined time. This DC voltage can be regarded as a DC voltage when viewed over a predetermined time period, and the voltage fluctuates when viewed over a time period longer than the predetermined time period.

[0023] Here, an example of a specific circuit of the filter circuit 16 will be described. FIG. 3 shows a circuit diagram of the filter circuit 16 according to the first embodiment. As shown in FIG. 3, the filter circuit 16 has unit filter circuits 41 to 43. The unit filter circuits 41 to 43 are first-order low-pass filters each composed of a resistor inserted in a signal transmission line and a capacitor provided between the output side wiring of the resistor and the ground wiring. The unit filter circuit 41 smoothes the detection signal UV and outputs the monitor signal UVm. The unit filter circuit 42 smoothes the detection signal VW and outputs the monitor signal VWm. The unit filter circuit 43 smoothes the detection signal WU and outputs the monitor signal WUm.

[0024] The analog input unit 22 determines the voltage levels of each of a plurality of monitor signals (e.g., monitor signals UVm, VWm, WUm), and transmits a high-level monitor signal to the fault diagnosis unit 23 if the monitor signal is above a threshold (a voltage level that can be recognized as a high level as a logical level), and transmits a low-level monitor signal to the fault diagnosis unit 23 if the monitor signal is below the threshold (a voltage level that can be recognized as a low level as a logical level).

[0025] The fault diagnosis unit 23 detects that the inverter 11 has a fault based on the fact that the combination of the logical levels of the multiple detection signals output by the rectangular pulse comparison circuit 15 deviates from a preset judgment value DV. At this time, the fault diagnosis unit 23 uses a judgment value DV that differs for each motor rotation angle that is assumed in advance to cause two AC signals of adjacent phases among the three-phase AC signals to have the same voltage. The judgment value DV will be described in detail later.

[0026] The rotation angle acquisition unit 21 transmits the motor rotation angle information acquired from the angle sensor 13 to the motor control unit 20 and the fault diagnosis unit 23. The fault diagnosis unit 23 switches the judgment value DV used as a judgment criterion based on the motor rotation angle information transmitted from the rotation angle acquisition unit 21.

[0027] In the above description, the fault detection circuit 1 according to the first embodiment is configured with the level conversion circuit 14, the rectangular pulse comparison circuit 15, the filter circuit 16, the rotation angle acquisition unit 21, the analog input unit 22, and the fault diagnosis unit 23. It is also possible to delete the filter circuit 16 and change the analog input unit 22 to an analog input unit that samples a digital signal, or to change the analog input unit 22 to a counter that counts the rising edges of a pulse. In this case, the counter counts the number of pulses of the multiple output signals output by the rectangular pulse comparison circuit 15, and the fault diagnosis unit 23 compares a combination of count values ​​for each detection signal with a judgment value to detect a fault in the inverter 11.

[0028] Next, the operation of the fault detection circuit 1 will be described. First, the PWM signal used for the judgment of the fault detection circuit 1 will be described. Fig. 4 shows a timing chart of the modulated wave (e.g., PWM signal) output by the inverter 11 when the three-phase AC signal is normal. Fig. 4 shows a timing chart of the three-phase AC signal output by the inverter 11 and the PWM signals of the U-phase, V-phase, and W-phase when the motor rotation angle is approximately 30°.

[0029] As shown in Fig. 4, the three-phase AC signal includes U-phase, V-phase, and W-phase AC signals, each of which has a phase difference of 120°. Also, each AC signal has one period of fluctuation during one rotation (0 to 360°) of the motor. Therefore, in the three-phase AC signal, the voltages of the U-phase and V-phase AC signals are the same when the motor rotation angle is 30° and 210°, the voltages of the V-phase and W-phase AC signals are the same when the motor rotation angle is 90° and 270°, and the voltages of the W-phase and U-phase AC signals are the same when the motor rotation angle is 150° and 330°.

[0030] Moreover, the PWM signal outputted to generate the three-phase AC signal changes its pulse width so that the higher the voltage of the AC signal, the larger the duty ratio becomes, and the lower the voltage of the AC signal, the smaller the duty ratio becomes. Here, FIG. 4 shows an enlarged view of the PWM signal when the motor rotation angle is about 30°. Looking at this enlarged view (lower view of FIG. 4), the PWM signals have the same frequency and phase, and have a pulse width change pattern that matches the phase of the corresponding AC signal. Furthermore, when the voltage of the AC signal is the same, the PWM signals have approximately the same duty ratio. The fault detection circuit 1 according to the first embodiment detects an abnormality in the inverter 11 by utilizing the characteristics of this PWM signal.

[0031] Next, FIG. 5 shows a timing chart for explaining the operation of the rectangular pulse comparator circuit 15 when the three-phase AC signal is normal. FIG. 5 shows a timing chart of the detection signal output by the rectangular pulse comparator circuit 15 when the motor rotation angle is around 30°. As shown in FIG. 5, when the inverter 11 is normal and the motor rotation angle is around 30°, the pulse widths of the U-phase and V-phase PWM signals are almost the same, so the detection signal UV, which is the result of the exclusive OR operation of the U-phase PWM signal and the V-phase PWM signal, becomes low level. In the example shown in FIG. 5, the detection signal UV is low level when the motor rotation angle is in the range of 25° to 35°. On the other hand, the detection signals VW and WU output by the rectangular pulse comparator circuit 15 include pulses whose high-level period is significantly longer than that of the detection signal UV.

[0032] In the fault detection circuit 1 according to the first embodiment, the detection signal shown in Fig. 5 is smoothed by the filter circuit 16, and a detection signal that is at a low level during a period when there is no pulse and at a high level during a period when the duty ratio is equal to or greater than a predetermined value (e.g., 20%) is provided to the fault diagnosis unit 23. Then, the fault diagnosis unit 23 diagnoses a fault in the inverter 11 based on whether or not a combination of high and low levels of the multiple detection signals matches a preset judgment value. Here, the judgment value DV used by the fault diagnosis unit 23 will be described.

[0033] FIG. 6 shows a table for explaining the judgment value DV applied to the fault diagnosis unit 23 according to the first embodiment. As shown in FIG. 6, the judgment value DV differs for each motor rotation angle that is assumed in advance to have the same voltage as the AC signal. More specifically, the judgment value DV when the motor rotation angle at which the U-phase AC signal and the V-phase AC signal have the same voltage is 30° or 210° is specified as normal if the monitor signal UVm, which is a comparison result of the U-phase and V-phase PWM signals, is at a low level, and as abnormal if it is at a high level. The judgment value DV when the motor rotation angle at which the V-phase AC signal and the W-phase AC signal have the same voltage is 90° or 270° is specified as normal if the monitor signal VWm, which is a comparison result of the V-phase and W-phase PWM signals, is at a low level, and as abnormal if it is at a high level. The judgment value DV when the motor rotation angle at which the W-phase AC signal and the U-phase AC signal have the same voltage is 150° or 330° is specified as normal if the monitor signal WUm, which is a comparison result of the W-phase and U-phase PWM signals, is at a low level, and as abnormal if it is at a high level. In FIG. 6, blank judgment values ​​DV indicate monitor signals that are not subject to judgment.

[0034] Next, the operation of the fault diagnosis unit 23 will be described in detail. Fig. 7 shows a timing chart for explaining the operation of the fault diagnosis unit 23 according to the first embodiment. As shown in Fig. 7, the fault diagnosis unit 23 checks the motor rotation angle θ when it starts operating (steps S1, S3, S5). Then, the fault diagnosis unit 23 executes step S2 when the motor rotation angle θ is 30° or 210° (YES branch of step S1), executes step S4 when the motor rotation angle θ is 90° or 270° (YES branch of step S3), and executes step S6 when the motor rotation angle θ is 150° or 330° (YES branch of step S5).

[0035] In step S2, it is determined whether or not the exclusive OR value of the U-phase PWM signal and the V-phase PWM signal (for example, detection signal UV) is at a low level. If the detection signal UV is at a high level in step S2, the fault diagnosis unit 23 determines that a fault has occurred in the inverter 11, and ends the operation. On the other hand, if the detection signal UV is at a low level in step S2, the fault diagnosis unit 23 continues to monitor the motor rotation angle (steps S1, S3, S5).

[0036] In step S4, it is determined whether or not the exclusive OR value (e.g., detection signal VW) of the V-phase PWM signal and the W-phase PWM signal is at a low level. If the detection signal VW is at a high level in step S4, the fault diagnosis unit 23 determines that a fault has occurred in the inverter 11, and ends the operation. On the other hand, if the detection signal VW is at a low level in step S4, the fault diagnosis unit 23 continues to monitor the motor rotation angle (steps S1, S3, S5).

[0037] In step S6, it is determined whether or not the exclusive OR value of the W-phase PWM signal and the U-phase PWM signal (for example, detection signal WU) is at a low level. If the detection signal WU is at a high level in step S6, the fault diagnosis unit 23 determines that a fault has occurred in the inverter 11, and ends the operation. On the other hand, if the detection signal UV is at a low level in step S6, the fault diagnosis unit 23 continues to monitor the motor rotation angle (steps S1, S3, S5).

[0038] The fault diagnosis unit 23 repeats the processing of steps S1 to S6 at a predetermined cycle until it detects an abnormality in the inverter 11. In the fault detection circuit 1, the detection signals (more specifically, monitor signals UVm, VWm, WUm) used by the fault diagnosis unit 23 to determine whether or not there is a fault in the inverter 11 are generated by an asynchronous circuit, so that operation can be achieved regardless of the level of the computing power of the MCU 10.

[0039] Here, a description will be given of failure modes of the inverter 11 that can be detected by the failure detection circuit 1. Four failure modes that can be detected by the failure detection circuit 1 will be described below.

[0040] First, as a first failure mode, an abnormal state in which a phase shift occurs in the V-phase AC signal of the three-phase AC signals will be described. FIG. 8 shows a timing chart of a modulated wave output by the inverter 11 when a phase shift failure occurs in the V-phase of the three-phase AC signals. In the example shown in FIG. 8, the phase of the V-phase AC signal is delayed by 180° compared to the normal state shown in FIG. 4. When the V-phase AC signal is delayed, a voltage shift occurs between the V-phase AC signal and the U-phase AC signal when the motor rotation angle is around 30°. In addition, the V-phase AC signal when the motor rotation angle is around 30° has a voltage value close to the highest voltage on the high voltage side. Therefore, in the example shown in FIG. 8, the duty ratio of the V-phase PWM signal is higher than the duty ratio of the U-phase PWM signal.

[0041] Next, a timing chart is shown in Fig. 9 to explain the operation of the rectangular pulse comparator circuit 15 when a phase shift fault occurs in the V phase of the three-phase AC signal. Fig. 9 shows a timing chart of the detection signal output by the rectangular pulse comparator circuit 15 to which the PWM signal shown in Fig. 8 is input when the motor rotation angle is around 30°. As shown in Fig. 9, when a phase shift such as that shown in Fig. 8 occurs, the detection signal UV when the motor rotation angle is around 30° contains a pulse and does not become low level. Therefore, when a phase shift as shown in Figs. 8 and 9 occurs, the fault detection circuit 1 refers to the determination value DV to determine that an abnormality has occurred in the inverter 11.

[0042] Next, as a second failure mode, an abnormal state in which the frequency of the V-phase AC signal among the three-phase AC signals becomes high will be described. FIG. 10 shows a timing chart of a modulated wave output by the inverter 11 when a failure occurs in which the frequency of the V-phase of the three-phase AC signals becomes high. In the example shown in FIG. 10, the frequency of the V-phase AC signal is about twice as high as that of the normal state shown in FIG. 4. When the frequency of the V-phase becomes high in this way, a difference occurs in the voltage between the V-phase AC signal and the U-phase AC signal when the motor rotation angle is around 30°. Specifically, in FIG. 10, the voltage of the V-phase AC signal is lower than the voltage of the U-phase AC signal when the motor rotation angle is around 30°. Therefore, in the example shown in FIG. 10, the duty ratio of the V-phase PWM signal is lower than the duty ratio of the U-phase PWM signal.

[0043] Next, Fig. 11 shows a timing chart for explaining the operation of the rectangular pulse comparator circuit 15 when a fault occurs that increases the frequency of the V phase of the three-phase AC signal. Fig. 11 shows a timing chart of the detection signal output by the rectangular pulse comparator circuit 15 to which the PWM signal shown in Fig. 10 is input when the motor rotation angle is around 30°. As shown in Fig. 11, when a shift to the high frequency side occurs as shown in Fig. 10, the detection signal UV when the motor rotation angle is around 30° contains a pulse and does not become low level. Therefore, when the frequency shift shown in Figs. 10 and 11 occurs, the fault detection circuit 1 refers to the determination value DV and determines that an abnormality has occurred in the inverter 11.

[0044] Next, as a third failure mode, an abnormal state in which the frequency of the V-phase AC signal among the three-phase AC signals is low will be described. FIG. 12 shows a timing chart of a modulated wave output by the inverter 11 when a failure occurs in which the frequency of the V-phase of the three-phase AC signals is low. In the example shown in FIG. 12, the frequency of the V-phase AC signal is about 1 / 2 times lower than that of the normal state shown in FIG. 4. When the frequency of the V-phase is thus low, a difference occurs in the voltage between the V-phase AC signal and the U-phase AC signal when the motor rotation angle is around 30°. Specifically, in FIG. 12, the voltage of the V-phase AC signal is higher than the voltage of the U-phase AC signal when the motor rotation angle is around 30°. Therefore, in the example shown in FIG. 12, the duty ratio of the V-phase PWM signal is higher than the duty ratio of the U-phase PWM signal.

[0045] Next, Fig. 13 shows a timing chart for explaining the operation of the rectangular pulse comparator circuit 15 when a fault occurs that reduces the frequency of the V phase of the three-phase AC signal. Fig. 13 shows a timing chart of the detection signal output by the rectangular pulse comparator circuit 15 to which the PWM signal shown in Fig. 12 is input when the motor rotation angle is around 30°. As shown in Fig. 13, when a shift to the high frequency side occurs as shown in Fig. 12, the detection signal UV when the motor rotation angle is around 30° contains a pulse and does not become low level. Therefore, when the frequency shift shown in Figs. 12 and 13 occurs, the fault detection circuit 1 refers to the determination value DV and determines that an abnormality has occurred in the inverter 11.

[0046] Next, as a fourth failure mode, an abnormal state in which the V-phase AC signal of the three-phase AC signal sticks to the low side will be described. FIG. 14 shows a timing chart of a modulated wave output by the inverter 11 when a failure occurs in which the V-phase of the three-phase AC signal sticks to the low side. In the example shown in FIG. 14, the V-phase AC signal, which is originally a sine wave as shown in FIG. 4, remains stuck to the low side. When the V-phase voltage sticks to a low level in this way, a voltage difference occurs between the V-phase AC signal and the U-phase AC signal when the motor rotation angle is around 30°. Specifically, in FIG. 14, the voltage of the V-phase AC signal is lower than the voltage of the U-phase AC signal when the motor rotation angle is around 30°. Therefore, in the example shown in FIG. 14, the duty ratio of the V-phase PWM signal is lower than the duty ratio of the U-phase PWM signal.

[0047] Next, FIG. 15 shows a timing chart for explaining the operation of the rectangular pulse comparator circuit 15 when a fault occurs in which the V-phase of the three-phase AC signal sticks to the low side. FIG. 15 shows a timing chart of the detection signal output by the rectangular pulse comparator circuit 15 to which the PWM signal shown in FIG. 14 is input when the motor rotation angle is around 30°. As shown in FIG. 15, when the V-phase AC signal shown in FIG. 14 sticks to the low side, the detection signal UV when the motor rotation angle is around 30° contains a pulse and does not become low level. Therefore, when a fault occurs in which the AC signal sticks to the low side as shown in FIG. 14 and FIG. 15, the fault detection circuit 1 refers to the determination value DV and determines that an abnormality has occurred in the inverter 11.

[0048] As described above, in the fault detection circuit 1 according to the first embodiment, the rectangular pulse comparator circuit 15 compares the pulse widths of the PWM signals, which are three-phase AC signals, between adjacent phases, and generates a detection signal indicating the difference component of the pulse widths. Then, in the fault detection circuit 1 according to the first embodiment, the fault of the inverter 11 is determined by verifying the magnitude of the difference component of the input detection signal with reference to the determination value DV set for each motor rotation angle at which the difference component of the pulse width disappears in normal operation. At this time, in the fault detection circuit 1 according to the first embodiment, since the detection signal including the difference component of the pulse width of the PWM signal is generated by an asynchronous circuit, the MCU 10 does not need to have high computing power to generate the detection signal. As a result, in the fault detection circuit 1 according to the first embodiment, an arithmetic device with low processing power (for example, the MCU 10) can detect an abnormality of the inverter, and the power consumption of the MCU 10 can be reduced.

[0049] Furthermore, in the fault detection circuit 1 according to the first embodiment, the detection signal output by the rectangular pulse comparison circuit 15 is smoothed by the filter circuit 16, and the detection signal is provided to the MCU 10 as a monitor signal that is essentially a DC signal, thereby further reducing consumption of the processing power of the MCU 10.

[0050] In addition, in the fault detection circuit 1 according to the first embodiment, the fault diagnosis unit 23 changes the judgment value DV to be applied based on the motor rotation angle. However, the motor rotation angle is information used for the control of the motor 12 by the motor control unit 20, and there is no need to add a new separate circuit to acquire the motor rotation angle.

[0051] Embodiment 2 In the second embodiment, a rectangular pulse comparison circuit 15a will be described, which is another embodiment of the rectangular pulse comparison circuit 15. In the description of the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the description thereof will be omitted.

[0052] FIG. 16 shows a circuit diagram of the rectangular pulse comparison circuit 15a according to the second embodiment. As shown in FIG. 16, the rectangular pulse comparison circuit 15a has pulse width difference extraction circuits 51 to 53. The pulse width difference extraction circuits 51 to 53 operate in the same manner as the exclusive OR circuits 31 to 33, but have different circuits. The pulse width difference extraction circuit 51 outputs a difference component between the pulse widths of the U-phase PWM signal and the V-phase PWM signal as a detection signal UV. The pulse width difference extraction circuit 52 outputs a difference component between the pulse widths of the V-phase PWM signal and the W-phase PWM signal as a detection signal VW. The pulse width difference extraction circuit 53 outputs a difference component between the pulse widths of the W-phase PWM signal and the U-phase PWM signal as a detection signal WU.

[0053] Since the pulse width difference extraction circuits 51 to 53 have the same circuit configuration but different inputs and outputs, the circuit configuration of the pulse width difference extraction circuit will be described using the pulse width difference extraction circuit 51 as an example. The pulse width difference extraction circuit 51 has AND circuits 511 and 512, and an OR circuit 513. The AND circuit 511 outputs the logical product of the inverted logic of the U-phase PWM signal and the V-phase PWM signal. The AND circuit 512 outputs the logical product of the U-phase PWM signal and the inverted logic of the V-phase PWM signal. The OR circuit 513 outputs the logical sum of the outputs of the AND circuits 511 and 512 as a detection signal UV.

[0054] In this way, if it is possible to output the same logical operation result as that of an exclusive OR circuit, it is also possible to configure a rectangular pulse comparison circuit using a circuit configuration other than that of an exclusive OR circuit.

[0055] The present disclosure is not limited to the above-described embodiment, and can be appropriately modified without departing from the spirit and scope of the present disclosure. In addition, the present disclosure includes implementation in which the examples in the above-described embodiment are appropriately combined. [Explanation of symbols]

[0056] 1 Fault detection circuit 10 MCU 11 Inverter 12 Motor 13 Angle Sensor 14 Level conversion circuit 15 Square Pulse Comparison Circuit 16 Filter Circuit 20 Motor control unit 21 Rotation angle acquisition unit 22 Analog input section 23 Fault diagnosis section 31~33 Exclusive OR circuit 41~43 Unit filter circuit 51-53 Pulse width difference extraction circuit 511, 512, 521, 522, 531, 532 AND circuit 513, 523, 533 OR circuit DV Judgment Value

Claims

1. A fault detection circuit for detecting a fault in an inverter that outputs a three-phase pulse width modulation signal that becomes a three-phase AC signal for driving a motor, comprising: a rectangular pulse comparator circuit that generates a detection signal indicating a difference component between the pulse widths of two of the pulse width modulation signals having adjacent phases for each combination of the pulse width modulation signals; a fault diagnosis unit that detects a fault in the inverter based on a deviation of a combination of logic levels of the plurality of detection signals output by the rectangular pulse comparison circuit from a preset judgment value; a rotation angle acquisition unit that acquires a motor rotation angle from an angle sensor that detects a rotation angle of the motor and transmits the acquired motor rotation angle to the fault diagnosis unit, The fault diagnosis unit is a fault detection circuit that uses the determination value that differs for each motor rotation angle that is assumed in advance to cause two AC signals of adjacent phases among the three-phase AC signals to have the same voltage.

2. a filter circuit between the rectangular pulse comparator circuit and the fault diagnosis unit for smoothing each of the detection signals; 2. The fault detection circuit according to claim 1, wherein the fault diagnosis unit detects a fault in the inverter based on a logic level of the detection signal after smoothing.

3. 2. The fault detection circuit according to claim 1, wherein the rectangular pulse comparison circuit has an exclusive-OR circuit for each combination of the pulse-width modulated signals to be compared, and each of the multiple exclusive-OR circuits outputs an exclusive-OR result of two of the pulse-width modulated signals as the detection signal.

4. 2. The fault detection circuit according to claim 1, wherein the plurality of pulse width modulated signals have the same frequency and phase as one another and have a pulse width change pattern that matches the phase of the corresponding AC signal.

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