CN113965138A

CN113965138A - Electric motor control device

Info

Publication number: CN113965138A
Application number: CN202110723479.1A
Authority: CN
Inventors: 木下雄介
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2020-07-01
Filing date: 2021-06-29
Publication date: 2022-01-21
Also published as: DE102021116349A1; JP2022012534A

Abstract

An electric motor control device controls an electric motor (30) having a plurality of coils of a plurality of phases. The electric motor control device includes: an inverter including a plurality of switching elements driven by pulse width modulation to control a voltage applied to each of a plurality of coils of a plurality of phases; a smoothing capacitor (C2) that smoothes the voltage applied to the plurality of coils of the plurality of phases via the inverter; a controller (14, 15) that outputs a pulse width modulation drive signal having a duty ratio set for rotating the electric motor according to a target value to the plurality of switching elements; a detection unit (23, 25) that detects a voltage applied to at least one of the plurality of coils; and abnormality determination sections (24, 26) that determine abnormality of the smoothing capacitor for determining the life of the smoothing capacitor when the voltage detected by the detection section exceeds a threshold value when the plurality of switching elements are driven by pulse width modulation.

Description

Electric motor control device

Technical Field

The present disclosure relates to an electric motor control apparatus that controls an electric motor (also referred to as an electric motor) having a plurality of phase coils.

Background

For example, patent document 1 shows an electric motor control device capable of estimating the lifetime of a main circuit capacitor serving as a smoothing capacitor (smoothing capacitor). The electric motor control device in patent document 1 estimates a ripple current (ripple current) flowing into a main circuit capacitor based on output power to the electric motor, a system impedance, a carrier frequency, and ripple current calculation data. Further, the electric motor control device estimates the internal temperature of the capacitor and the life data of the capacitor based on the direct voltage (direct voltage) detected by the voltage detector and applied to the main circuit capacitor, the ambient temperature of the main circuit capacitor detected by the ambient temperature sensor, and the estimated ripple current. Further, the electronic motor control device estimates a lifetime time of the main circuit capacitor, and calculates a capacitor lifetime integration time (capacitor lifetime integration time) based on the estimated lifetime time of the main circuit capacitor. When the capacitor life integration time is substantially equal to the predetermined basic life, it is determined that the main circuit capacitor reaches the end of life.

Documents of the related art

Patent document

Patent document 1: JP 5197897B 1

Disclosure of Invention

However, in the case where the smoothing capacitor life is determined by a method such as the electric motor controller in patent document 1, it is necessary to provide many additional components and additional configurations such as a voltage detector, an ambient temperature sensor, a system impedance setting section, a ripple current calculation data storage device, a ripple current estimation section, a capacitor life data storage device, and a capacitor life estimation section.

Further, the method such as the electric motor control apparatus in patent document 1 does not directly measure the lifetime but estimates the lifetime. Further, there is a variation in the capacitance of the main circuit capacitor and the like. Therefore, it is necessary to increase the margin of the lifetime setting, and thus the accuracy of determining the lifetime may be low.

An object of the present disclosure is to provide an electric motor control device capable of determining the lifetime of a smoothing capacitor with high accuracy without many additional components and many additional configurations.

According to the present disclosure, an electric motor control device controls an electric motor having a plurality of coils of a plurality of phases. The electric motor control device includes: an inverter including a plurality of switching elements driven by pulse width modulation (pulse width modulation) to control a voltage applied to each of a plurality of coils of the plurality of phases; a smoothing capacitor that smoothes voltages applied to a plurality of coils of the plurality of phases via the inverter; a controller that outputs a pulse width modulation drive signal having a duty ratio set for rotating the electric motor according to a target value to the plurality of switching elements; a detection section that detects a voltage applied to at least one of the plurality of coils; and an abnormality determination section that determines abnormality of the smoothing capacitor for determining a lifetime of the smoothing capacitor when the voltage detected by the detection section exceeds a threshold while the plurality of switching elements are driven by the pulse width modulation.

The smoothing capacitor capacitance decreases sharply as it approaches the end of its life. The electric motor control device of the present disclosure detects a decrease in capacitance of the smoothing capacitor based on the magnitude of switching noise caused by the switching element driven by the pulse width modulation. When the smoothing capacitor capacitance is held at a normal value, a voltage variation when the switching element is turned on or off, that is, a switching noise, can be prevented by the smoothing capacitor. However, when the life of the second smoothing capacitor approaches the end and the capacitance of the second smoothing capacitor decreases, a voltage variation due to switching of the switching element, that is, switching noise increases. In other words, switching noise generated when the switching element is turned on or off increases. This switching noise occurs in the voltage applied to the coil.

Therefore, according to the present disclosure, the electric motor control device includes: an abnormality determination section that determines an abnormality of the smoothing capacitor for determining a lifetime of the smoothing capacitor when the voltage applied to the coil and detected by the detection section exceeds a threshold while the plurality of switching elements are driven by the pulse width modulation. In this way, by determining the smoothing capacitor abnormality including the reduction of the smoothing capacitor capacitance based on the magnitude of the switching noise at the time of PWM driving, the electric motor control device in the present disclosure can determine the smoothing capacitor life with high accuracy without requiring a complicated configuration.

Drawings

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings. In the attached drawings

Fig. 1 is a configuration diagram showing an overall configuration of an electric motor control system including an electric motor control device according to a first embodiment;

fig. 2A is a waveform diagram showing one example of a change in drain-source voltage of the switching element when the capacitance of the smoothing capacitor is normal;

fig. 2B is a waveform diagram showing one example of a change in drain-source voltage of the switching element when the capacitance of the smoothing capacitor is reduced due to lifetime;

fig. 3 is a configuration diagram showing one example of the configuration of the noise detection circuit and the abnormality determination circuit;

fig. 4A is a waveform diagram showing one example of a variation in drain-source voltage of the switching element when the capacitance of the smoothing capacitor is reduced due to the lifetime and one example of the case of switching noise generated by PWM driving when the duty ratio of the PWM driving signal is less than 100%;

fig. 4B is a waveform diagram showing one example of a change in drain-source voltage of the switching element when the capacitance of the smoothing capacitor is reduced due to the lifetime and one example of the case of switching noise generated by PWM driving when the duty ratio of the PWM driving signal is equal to 100%;

fig. 5 is a waveform diagram showing one example of a case where the abnormality determining circuit outputs the abnormality determining signal and the estimated lifetime determining section outputs the lifetime determining signal and thus the lifetime extension control is performed by the smoothing capacitor;

fig. 6 is a configuration diagram showing an overall configuration of an electric motor control system including an electric motor control device according to a second embodiment;

fig. 7A is a waveform diagram showing one example of a change in drain-source voltage of the switching element when the capacitance of the smoothing capacitor is normal;

fig. 7B is a waveform diagram showing one example of a change in the neutral point voltage of the electric motor when the capacitance of the smoothing capacitor is normal;

fig. 8A is a waveform diagram showing one example of a change in drain-source voltage of the switching element when the capacitance of the smoothing capacitor is reduced due to lifetime; and

fig. 8B is a waveform diagram showing one example of a change in the neutral point voltage of the electric motor when the capacitance of the smoothing capacitor is reduced due to the lifetime.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

(first embodiment)

Fig. 1 shows the overall configuration of an electric motor control system including an electric motor control device 10 according to a first embodiment. As shown in fig. 1, the electric motor control system includes a higher-level system 4, an electric motor control device 10, and an electric motor 30. The higher-level system 4 calculates a target value (such as a target rotation speed or a target torque) of the electric motor 30 based on the detection values of the respective sensors, and outputs the target value to the electric motor control device 10. The electric motor control device 10 sets the duty ratio of the PWM drive signal so as to rotate the electric motor 30 according to the target value, and drives each of the

switching elements

20 and 22 forming the inverter (inverter) by the PWM drive signal of the set duty ratio. Thereby, three-phase alternating current corresponding to the duty ratio of the PWM drive signal is supplied to each coil of the U-phase, the V-phase, and the W-phase of the electric motor 30, and the electric motor 30 rotates according to the target value.

The higher-level system 4 and the electric motor control device 10 may be integrated, and the electric motor control device 10 may calculate a target value of the electric motor 30. The electric motor 30 is preferably used as, for example, a motor for various purposes used in a vehicle (e.g., a radiator fan motor, a fan motor of an air conditioner, a motor of a water pump for cooling an engine, etc.).

Next, the configuration of the electric motor control device 10 of the present embodiment will be described in detail. The electric motor control device 10 shown in fig. 1 includes a power supply terminal connected to the positive electrode side of the battery 2 as an external connection terminal, a ground terminal connected to the negative electrode side, and an input terminal and an output terminal for transmitting a signal to the higher-level system 4 and receiving a signal from the higher-level system 4. The power supply terminal is connected to a high potential power supply line in the electric motor control device 10, and the ground terminal is connected to a low potential power supply line. The electric motor control device 10 obtains direct current supplied from the battery 2 as a direct current power supply via a power supply terminal and a ground terminal.

The electric motor control device 10 includes an input-output I/F circuit 12, a control circuit 14, switching

elements

20 and 22, a snubber circuit (snubber circuit)23, a noise detection circuit 24, an abnormality determination circuit 26, an and circuit 28, a first smoothing capacitor C1, an inductor L1, a second smoothing capacitor C2, and the like. In the drawing, the noise detection circuit 24 may also be referred to as "noise detection", and the abnormality determination circuit 26 may also be referred to as "abnormality determination".

The input-output I/F circuit 12 receives a target value from the higher-level system 4 via an input terminal of the electric motor control device 10, and outputs the target value to the control circuit 14. When receiving the determination result that the lifetime of the second smoothing capacitor C2 is approaching the end from the control circuit 14, the input-output I/F circuit 12 outputs the result to the higher-level system 4 via the output terminal.

The first smoothing capacitor C1 is connected in parallel to the battery 2 between the high potential power supply line and the low potential power supply line, and smoothes a Direct Current (DC) voltage supplied from the battery 2. The second smoothing capacitor C2 is connected to the first smoothing capacitor C1 via an inductor L1. The inductor L1 and the second smoothing capacitor C2 form an LC filter, and the LC filter blocks noise from, for example, another device sharing the battery 2. The second smoothing capacitor C2 is connected in parallel to the inverter including the

switching elements

20 and 22 between the high potential power supply line and the low potential power supply line. Therefore, the dc voltage smoothed by the second smoothing capacitor C2 is supplied to the inverter.

For example, electrolytic capacitors having a large capacitance are used as the first smoothing capacitor C1 and the second smoothing capacitor C2. The first smoothing capacitor C1 and the second smoothing capacitor C2 assist in supplying power to the inverter by stabilizing the voltage supplied to the inverter and storing electric charges. In the present embodiment, each of the switching

elements

20 and 22 forming the inverter is driven in accordance with the PWM drive signal output from the driver 15 (see fig. 3) based on the control signal from the control circuit 14. By the PWM driving, each of the switching

elements

20 and 22 is turned on and off. Thereby generating a voltage variation between the drain and the source of the switching

elements

20 and 22, i.e., switching noise. The switching noise occurs in the voltage applied to each coil of the U-phase, V-phase, and W-phase. The second smoothing capacitor C2 also prevents this switching noise.

In the case where the capacitance of the second smoothing capacitor C2 remains normal, the second smoothing capacitor C2 can sufficiently suppress the voltage variation between the drain and the source of the switching

elements

20 and 22, that is, the switching noise. For example, as shown in fig. 2A, the magnitude of the switching noise is suppressed to be about the power supply voltage by the second smoothing capacitor C2. However, when the life of the second smoothing capacitor C2 approaches the end and the capacitance of the second smoothing capacitor C2 decreases, it is difficult to suppress the voltage variation due to the switching of the switching

elements

20 and 22, that is, the switching noise. For example, when the life of the second smoothing capacitor C2 approaches the end, as shown in fig. 2B, the maximum value of the peak of the switching noise may exceed the three times value of the power supply voltage. Then, the electromagnetic noise generated by the switching noise deteriorates EMC performance and may adversely affect other products. For example, when the sensorless control of the electric motor 30 is performed, the induced voltage of the non-energized phase (non-energized phase) cannot be read, and the electric motor 30 cannot be driven.

Semiconductor elements such as MOSFETs or IGBTs may be used as the switching

elements

20 and 22. The switching

elements

20 and 22 have freewheeling diodes (freewheeling diodes) which return current due to the transient high voltage generated at the time of interruption. Although in fig. 1, only the switching

elements

20 and 22 placed in the upper and lower arm circuits for the U-phase coil are shown, the upper and lower arm circuits having the switching elements are provided for each of the V-phase coil and the W-phase coil. Switching elements placed in the upper and lower arm circuits of these phases form an inverter.

A series circuit of the capacitor C3 and the resistor R1 is connected in parallel to the switching element 20. A series circuit of the capacitor C4 and the resistor R2 is connected in parallel to the switching element 22. Each of the series circuits of the capacitor and the resistor functions as an RC snubber circuit that absorbs a transient high voltage generated when the switching

elements

20 and 22 are interrupted. Further, the buffer circuit 23 including the capacitor C4 and the resistor R2 functions as a detection section that divides the voltage applied to the U-phase coil and detects the voltage.

As described above, switching noise at the time of PWM driving of the switching

elements

20 and 22 occurs in the voltage applied to the coil of each phase. When the life of the second smoothing capacitor C2 approaches the end and the capacitance decreases, the switching noise may seriously exceed the power supply voltage supplied from the battery 2. Therefore, by detecting the divided applied voltage of the U-phase coil by the buffer circuit 23, it is possible to accurately detect switching noise exceeding the power supply voltage in the noise detection circuit 24, which will be described later. Further, by using the buffer circuit 23 as the detection section, it is not necessary to add a means for dividing the voltage applied to the U-phase coil and detecting the voltage.

Although fig. 1 shows only a configuration for detecting switching noise from a voltage applied to the U-phase coil, a configuration for detecting switching noise from voltages applied to the V-phase coil and the W-phase coil may be added. By providing the configuration that detects the switching noise for each phase coil, the switching noise indicating that the lifetime of the second smoothing capacitor C2 is close to the end can be accurately detected regardless of the change in the inductance value of each phase coil. However, it is not always necessary to provide a configuration that detects switching noise for all the coils of the three phases. A configuration to detect switching noise may be provided for at least one phase of the coil.

The noise detection circuit 24 detects the magnitude of switching noise occurring in the voltage divided by the buffer circuit 23, detected, and applied to the U-phase coil. For example, the noise detection circuit 24 may be configured as a peak hold circuit as shown in fig. 3. When the input voltage divided by the buffer circuit 23 is higher than the output voltage of the peak hold circuit, the peak hold circuit outputs a high voltage to the amplifier 32. When the amplifier 32 outputs a high voltage, the capacitor C5 charges via the diode D1. The voltage charged in the capacitor C5 becomes the output voltage of the peak hold circuit via the voltage follower formed by the amplifier 34. When the output voltage of the peak hold circuit becomes higher than the input voltage divided by the buffer circuit 23 due to the charging of the capacitor C5, the amplifier 32 stops the output of the high voltage. By such an operation, the voltage corresponding to the maximum value of the peak value of the switching noise is held by the capacitor C5 of the peak hold circuit.

The abnormality determination circuit 26 determines abnormality of the second smoothing capacitor C2 including a decrease in capacitance due to the life of the second smoothing capacitor C2 based on the output voltage of the noise detection circuit 24. For example, as shown in fig. 3, the abnormality determination circuit 26 may be constituted by a comparator 36, the comparator 36 comparing the output voltage of the noise detection circuit 24 with the threshold voltage set by the resistors R4 and R5. When the output voltage of the noise detection circuit 24 becomes higher than the threshold voltage set by the resistors R4 and R5, the abnormality determination circuit 26 outputs an abnormality determination signal indicating abnormality of the second smoothing capacitor C2. The noise detection circuit 24 and the abnormality determination circuit 26 may correspond to an abnormality determination section (abnormality determination section).

The control circuit 14 operates to set the duty ratio in accordance with a target value (such as a target rotational speed or a target torque) given by the higher-stage system 4m, and to output a control signal indicating the duty ratio to the driver 15 (see fig. 3). The driver 15 generates a PWM drive signal of a set duty ratio and outputs the PWM drive signal to the control terminal of the switching element 22. The control circuit 14 and the driver 15 may correspond to a controller.

The control circuit 14 includes an energization time integration section (energization time integration section) 16 as a calculation section that calculates an integrated energization time obtained by integrating the energization time to the electric motor 30. When the control circuit 14 drives the electric motor 30, the energization time integrating portion 16 measures a period from the start to the end as one energization time of the electric motor 30. Once the energization time is measured, the energization time integrating unit 16 updates the integrated energization time by adding the measured energization time to the integrated energization time which is an integrated value of the energization times up to that point. In the drawing, the energization time integrating unit 16 may also be referred to as "EN time integration".

Further, the control circuit 14 includes an estimated life determining portion 18 as a set time determining portion that determines the possibility that the life of the second smoothing capacitor C2 reaches the end based on the integrated time energization time calculated by the energization time integrating portion 16. For example, when the accumulated energization time exceeds a predetermined determination time (such as a time corresponding to the required life of the product), the estimated life determination portion 18 outputs a life determination signal indicating the possibility that the life of the second smoothing capacitor C2 reaches the end.

The and circuit 28 receives the output signal from the estimated lifetime determination section 18 and the output signal from the abnormality determination circuit 26. When receiving the life determining signal from the estimated life determining portion 18 and the abnormality determining signal from the abnormality determining circuit 26, the and circuit 28 outputs an abnormality signal indicating that the life of the second smoothing capacitor C2 is approaching the end to the control circuit 14.

When receiving an abnormal signal indicating that the life of the second smoothing capacitor C2 is approaching the end from the and circuit 28, the control circuit 14 notifies the higher-level system 4 via the input-output I/F circuit 12, and performs life extension control to extend the life of the second smoothing capacitor C2. Then, the control circuit 14 or the higher-level system 4 may display a warning lamp for notifying the user that the life of the second smoothing capacitor C2 is approaching the end, or the like. The control circuit 14 and the and circuit 28 may correspond to an abnormality determination section (abnormality determination section).

In the lifetime extension control, for example, the control circuit 14 outputs a PWM drive signal having a duty ratio of 100%. This life extension control may be performed by instructions from the higher level system 4 or may be performed actively by the control circuit 14. In any case, the higher-level system 4 may apply a target value corresponding to a duty ratio of 100% to the control circuit 14 together with the execution of the life extension control.

As shown in fig. 4A, when the duty ratio of the PWM drive signal is less than 100%, the switching

elements

20 and 22 are turned on and off for each PWM period, with the result that switching noise is generated. The switching noise and the fluctuation of the applied voltage of the coil will continue to apply a load to the second smoothing capacitor C2 whose lifetime is near the end.

On the other hand, as shown in fig. 4B, when the duty ratio of the PWM drive signal is 100%, the switching

elements

20 and 22 are not turned on and off for each PWM period. Therefore, the number of times the applied voltage of the coil fluctuates and noise is generated can be reduced. This can extend the life of the second smoothing capacitor C2 whose life is near the end.

As shown in (d) and (e) of fig. 5, in the electric motor control device 10 of the present embodiment, when the abnormality determination signal is output from the abnormality determination circuit 26 and the life determination signal is output from the estimated life determination portion 18, it is determined that the life of the second smoothing capacitor C2 is close to the end point and abnormality occurs. Therefore, for example, it is possible to prevent a surge voltage (surge voltage) or the like from another device (such as a higher system) sharing the battery 2 from being determined as an increase in switching noise, and to prevent the lifetime of the second smoothing capacitor C2 from being erroneously determined to be near the end and thus an abnormality from occurring.

Further, as shown in (a) to (c) and (f) of fig. 5, in the life extension control, the device driven by the electric motor 30 can be operated at the maximum capacity by setting the duty ratio of the PWM drive signal to 100%. Therefore, a situation in which the target set by the higher-level system 4 cannot be achieved can be avoided. For example, the system can be operated in a safer state because the cooling capacity is maximized when, for example, the electric motor 30 is used as a radiator fan motor, a blower fan motor of an air conditioner, or a motor of a water pump for cooling an engine or the like.

However, the life extension control of the second smoothing capacitor C2 is not limited to the above control in which the duty ratio of the PWM drive signal is set to 100%. For example, in the life prolonging control, when the PWM period (PWM cycle) of the PWM drive signal output to the plurality of switching

elements

20 and 22 forming the inverter may be prolonged, the PWM drive of each of the switching

elements

20 and 22 may be performed based on the PWM drive signal of the duty ratio according to the target value set by the higher-level system 4. By extending the PWM period, the number of switching times per switching

element

20 and 22 can be reduced. Therefore, the life of the second smoothing capacitor C2 can be extended. Further, by setting the duty ratio in accordance with the target value set by the higher-level system 4, the electric motor 30 can be controlled in accordance with the target value set by the higher-level system 4.

As described above, according to the present embodiment, the electric motor control device 10 determines the abnormality of the decrease in the capacitance of the second smoothing capacitor C2 based on the magnitude of the switching noise at the time of PWM driving. Therefore, the lifetime of the second smoothing capacitor C2 can be determined with high accuracy regardless of the tolerance of the variation in capacitance such as the second smoothing capacitor C2. Further, in the electric motor control device 10 of the present embodiment, it is not necessary to add components such as an ambient temperature sensor and a configuration for estimating the ripple current or the internal temperature of the smoothing capacitor. Therefore, a complicated configuration is not required.

(second embodiment)

Next, an electric motor control system including the electric motor control device 10 according to a second embodiment of the present disclosure will be described. Fig. 6 shows the overall configuration of the electric motor control system. As shown in fig. 6, the electric motor control system of the present disclosure is different from that of the first embodiment, and detects a voltage at a neutral point of a three-phase coil of the electric motor 30 as a voltage applied to the coil. Although the buffer circuit described in the first embodiment is omitted in fig. 6, a buffer circuit may be provided for each of the switching

elements

20 and 22.

As shown in fig. 6, the neutral point of the three-phase coil is connected to the low potential power supply line via a neutral point filter 25 formed of capacitors C6 and C7. The neutral point filter 25 suppresses potential fluctuation at the neutral point and reduces radiation noise (radiation noise) from the electric motor 30. In the present embodiment, the voltage at the neutral point is divided and detected by using the neutral point filter 25. That is, as shown in fig. 6, the neutral point voltage of the capacitors C6 and C7 is detected as a voltage applied to the coil, and is input to the noise detection circuit 24. The remaining configuration is similar to that according to the first embodiment, and thus the description will not be repeated.

Fig. 7A and 7B show one example of a change in voltage between the drain and the source of the switching

elements

20 and 22 and a change in neutral point voltage when the capacitance of the second smoothing capacitor C2 is normal. As shown in fig. 7B, switching noise generated when each of the switching

elements

20 and 22 is turned on and off also appears in the neutral point voltage.

Fig. 8A and 8B show one example of a change in voltage between the drain and source of the switching

elements

20 and 22 and a change in neutral point voltage when the capacitance of the second smoothing capacitor C2 is reduced due to the lifetime. As shown in fig. 8A, when the capacitance of the second smoothing capacitor C2 is reduced, the voltage between the drain and source of the switching

elements

20 and 22 varies, i.e., the switching noise, significantly exceeds the power supply voltage. Such switching noise also appears in the neutral point voltage of the electric motor 30, as shown in fig. 8B. Therefore, when the neutral point voltage is detected and the maximum value of the peak value exceeds the threshold voltage, it can be determined that the second smoothing capacitor C2, whose capacitance decreases due to its lifetime, is abnormal.

Embodiments of the present disclosure have been described. However, the present disclosure 3 is not limited to the above embodiments, and various modifications may be made within the spirit and scope of the present disclosure.

For example, fig. 3 shows an example in which the noise detection circuit 24 includes an analog circuit as a peak hold circuit. However, the noise detection circuit 24 may include a digital circuit. For example, the voltage detected by the buffer circuit 23 is sampled and converted into a digital value, and the maximum value at the peak value can be calculated. Alternatively, the maximum value is not calculated, but an average value in a predetermined period may be calculated. Further, the abnormality determination circuit 26 may be provided in a digital configuration, and may determine abnormality of the second smoothing capacitor C2 based on the frequency or the number of times the sampled voltage exceeds the threshold value.

The control circuit 14 and methods described in this disclosure may be implemented by a special purpose computer configured with a memory and a processor programmed to perform one or more specific functions embodied in a computer program in the memory. Alternatively, the control circuit 14 and methods described in this disclosure may be implemented by a special purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control circuit 14 and methods described in this disclosure may be implemented by one or more special purpose computers configured as a combination of a processor and memory that execute a computer program and that are programmed to perform one or more functions, and a processor configured with one or more hardware logic circuits. The computer program may be stored in a tangible, non-transitory computer-readable storage medium as instructions to be executed by a computer.

Claims

1. An electric motor control device configured to control an electric motor (30) having a plurality of coils of a plurality of phases, the electric motor control device comprising:

an inverter including a plurality of switching elements (20, 22) driven by pulse width modulation to control a voltage applied to each of a plurality of coils of the plurality of phases;

a smoothing capacitor (C2) configured to smooth a voltage applied to the plurality of coils of the plurality of phases via the inverter;

a controller (14, 15) configured to output a pulse width modulation drive signal to the plurality of switching elements, the pulse width modulation drive signal having a duty ratio set for rotating the electric motor according to a target value;

a detection section (23, 25) configured to detect a voltage applied to at least one of the plurality of coils; and

an abnormality determination section (24, 26) configured to determine abnormality of the smoothing capacitor for determining a lifetime of the smoothing capacitor when the voltage detected by the detection section exceeds a threshold value while the plurality of switching elements are driven by the pulse width modulation.

2. The electric motor control device according to claim 1, further comprising:

a calculation section (16) configured to calculate an accumulated energization time obtained by accumulating energization times to the electric motor;

a set time determination section (18) configured to determine that the integrated energization time exceeds a set time set as a lifetime time of the smoothing capacitor; and

an abnormality determination section (14, 28) configured to determine that an abnormality of the smoothing capacitor has occurred when the abnormality determination section determines that the smoothing capacitor is abnormal and the set time determination section determines that the integrated energization time exceeds the set time.

3. The electric motor control device according to claim 1, wherein the controller is configured to set a duty ratio of the PWM drive signal output to the plurality of switching elements to 100% when the smoothing capacitor is abnormal.

4. The electric motor control device according to claim 1, wherein the controller is configured to extend a period of the PWM drive signal output to the plurality of switching elements when the smoothing capacitor is abnormal.

5. The electric motor control device according to any one of claims 1 to 4, wherein the detection portion is configured to detect, as the voltage applied to the at least one coil, a voltage divided by a snubber circuit (23) connected in parallel to each of the plurality of switching elements.

6. The electric motor control device according to any one of claims 1 to 4, wherein the detection portion is configured to detect, as the voltage applied to the at least one coil, a voltage divided by a neutral point filter (25) connected to a neutral point of the plurality of switching elements.