JP3019063B2 - Inverter internal capacitor abnormality detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting an abnormality of a capacitor for smoothing a voltage fluctuation on a DC side of an inverter for converting DC power to AC power.

[0002]

2. Description of the Related Art When an AC motor is driven by a DC power supply,
For example, when driving a motor of an electric vehicle, power conversion means for converting DC power supplied from a battery or the like to AC power is required, and an inverter is used as the power conversion means. On the input side of the inverter, that is, on the DC power supply side, power storage means (generally, a capacitor, hereinafter, referred to as a smoothing capacitor) for smoothing the output of the DC power supply is provided.

[0003] The smoothing capacitor repeats charging and discharging at all times during operation of the motor, whereby thermal stress due to electric load fluctuation is applied to the smoothing capacitor, and the life thereof may be shortened. This reduction in life becomes remarkable when there is no enough capacity for the capacitor to charge and discharge electricity. In the case of parallel connection, if some capacitors are damaged, the deterioration of other capacitors is accelerated.

Therefore, in conventional electric vehicles, the smoothing capacitor is provided with a capacitor having a sufficient margin more than required for obtaining desired electric characteristics, thereby providing a practically sufficient life of the capacitor. It is designed so that capacitor failure does not become a problem.

[0005]

However, a large-capacity capacitor as described above is large in size and weight, and expensive. For this reason, there is a problem that the size and weight of the electric vehicle are hindered from being reduced in cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. By detecting deterioration of a smoothing capacitor at an early stage, it is possible to prevent the destruction of the smoothing capacitor and a serious situation such as the inability to run an electric vehicle. It is an object of the present invention to make it possible to use a smoothing capacitor having a small capacity margin and a smaller and lighter weight than a conventional capacitor.

[0007]

The capacitor abnormality detecting device according to the present invention comprises a converter for converting DC power into AC power and supplying the AC power to a motor, and a smoothing capacitor provided on the DC side of the converter. A voltage sensor that is used in the inverter that has a DC voltage applied to the input terminal of the conversion unit, and monitors the output of the voltage sensor, and controls the DC side of the conversion unit according to the inverter control operation of the conversion unit. based on a voltage fluctuation appearing in, that having a and abnormality determination processing unit for detecting an abnormality of the smoothing capacitor.

According to the present invention, by monitoring the voltage fluctuation on the input side of the inverter, the deterioration of the smoothing characteristic due to the deterioration of the smoothing capacitor is detected. That is, the voltage sensor measures the DC voltage applied to the conversion unit input terminal,
The abnormality determination processing unit detects a voltage change included in the DC voltage measured by the voltage sensor, and determines deterioration of the smoothing capacitor based on the voltage change.

[0009] In this onset Ming, the abnormality determination processing section, based on the voltage change is greater than a predetermined determination reference value, detects that the smoothing capacitor is deteriorated,
It determined to be abnormal.

The voltage fluctuation occurs due to the DC-to-AC conversion operation (inverter operation) in the conversion unit, and the fluctuation width is the same as that of the same smoothing capacitor even if the degree of deterioration is the same. It may vary depending on the frequency and the amount of output current to the motor. For example, there may be a tendency that the faster the control cycle of the inverter operation, the smaller the voltage fluctuation width, and the larger the output current to the motor, the larger the voltage fluctuation width. The present invention is the determination reference value in abnormality determination processing section, which is determined according to the output current to the frequency and the motor inverter control operation, this
This makes it possible to appropriately detect the deterioration of the smoothing capacitor.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a system configuration of an electric vehicle according to an embodiment of the present invention. The driving power of the motor 2 for driving the vehicle of the electric vehicle is an inverter 4
From the battery 6. That is, the discharge power of the battery 6 is converted into three-phase AC by the inverter 4 and supplied to each phase winding (coil) of the motor 2. The inverter 4 includes a plurality of switching elements (for example, IGBTs) for converting power from DC to three-phase AC.
The smoothing capacitor 10 is provided in parallel with the battery 6 on the DC side of the conversion unit 8 including.

The smoothing capacitor 10 is provided for smoothing the power supplied from the battery 6 to the converter 8. That is, the battery 6 stores a large amount of electricity, but does not have a high transient response. Therefore, if the battery 6 is directly driven by the battery 6, it cannot follow the inverter operation in the converter 8. In addition, the power supplied to the converter 8 fluctuates. On the other hand, the smoothing capacitor 10 cannot store the amount of electricity as much as the battery 6 but has a high transient response. Therefore, the smoothing capacitor 10 is interposed between the battery 6 and the converter 8 and supplied from the battery 6 to the converter 8. Power to be applied can be smoothed.

A voltage sensor 12 is provided on the DC side of the converter 8 in parallel with the battery 6. In the conventional system, such a voltage sensor is required and provided for monitoring the voltage of the battery 6. In the present invention, a voltage sensor is required to monitor the voltage fluctuation on the DC side of the conversion unit 8 as described later, and the voltage sensor for that is basically the same as that for the conventional battery voltage monitoring. Since the configuration is the same as that of the first embodiment and can be shared with the configuration, it is not necessary to separately provide a voltage sensor therefor. That is, as will be described later, information on both the battery voltage 6 and the voltage fluctuation on the DC side of the converter 8 is obtained from the measured voltage of the voltage sensor 12.

The operation of the inverter 4 is controlled by an electronic control unit (hereinafter referred to as ECU) 20. EC
The main part of the U20 is constituted by a microprocessing unit (MPU), and an analog signal input to the ECU 20 is converted into a digital signal by an A / D (analog-to-degital) conversion circuit and then input to the MPU. You. An accelerator signal, a brake signal, a shift position signal, and the like are supplied from each circuit to the ECU 20, a feedback signal of each phase current supplied from the inverter 4 to the motor 2, and a voltage measured by the above-described voltage sensor 12. Is also input.

The ECU 20 includes a motor control processing unit 22 for controlling the motor 2 and a voltage fluctuation monitoring processing unit 24, and starts operating when the ignition switch is turned on.

The motor control processor 22 controls the driving of the motor 2 which has been performed conventionally. For example,
The motor control processing unit 22 calculates a torque command based on an accelerator signal, a brake signal, a shift position signal, and the like. In the ECU 20, a carrier frequency of pulse width modulation (PWM) is set and stored as a parameter.
The motor control processing unit 22 generates a PWM signal based on the calculated torque command and the PWM carrier frequency, and controls a switching operation of each switching element included in the conversion unit 8 of the inverter 4 based on the generated PWM signal.
Further, the motor control processing unit 22 performs, for example, a battery voltage monitoring process for detecting whether or not the voltage of the battery 6 is sufficient for running the vehicle, based on the voltage signal from the voltage sensor 12. In this battery voltage monitoring process, a slight change in the voltage signal from the voltage sensor 12 may cause an error, and it is not preferable that the change is taken into the motor control processing unit 22. Therefore, the motor control processing unit 22 is provided with a low-pass filter 24 for a signal from the voltage sensor 12, and removes a small change at a high frequency. Specifically, the processing of the motor control processing unit 22 is MP
The low-pass filter 24 is implemented by a program operating on the U, and the low-pass filter 24 is also configured by a digital filter implemented by software in the MPU.

On the other hand, the voltage fluctuation monitoring processor 30, which is a characteristic component of the present invention, performs an abnormality determination process for the smoothing capacitor 10. When an abnormality such as deterioration or breakage occurs in the smoothing capacitor 10, the function of the converter 8 for smoothing the power on the DC side is reduced. That is, the smoothing capacitor 1
When an abnormality occurs in 0, the voltage fluctuation range generated at both ends of the voltage sensor 12 increases. This voltage fluctuation is caused by P
It accompanies the WM operation and has a frequency corresponding to the PWM carrier frequency. Incidentally, this frequency takes a value of, for example, up to about 10 kHz, which is a high frequency as compared with the rotation speed of the motor or the frequency of each phase current, which is up to about several hundred Hz.

The voltage fluctuation monitoring processing unit 30 includes a voltage sensor 1
2 to extract a voltage fluctuation component corresponding to the PWM carrier frequency included in the signal from
have. The band-pass filter 32 is a digital filter like the low-pass filter 24, and is realized by the MPU performing a calculation process on the digital signal of the voltage sensor 12 based on the PWM carrier frequency set in the ECU 20.

FIG. 2 is a schematic graph showing the relationship between the voltage fluctuation δV with respect to the PWM carrier frequency fc and the current I0 used for driving the motor. The voltage fluctuation δV on the DC side of the converter 8 is inversely proportional to fc and has a property of increasing in accordance with I0.

The voltage fluctuation monitoring processing section 30 includes an abnormality determination processing section 34 for detecting an abnormality of the smoothing capacitor 10 based on the voltage fluctuation component extracted by the band pass filter 32. The abnormality determination processing unit 34 is also realized by a program executed by the MPU. FIG. 3 is a schematic processing flowchart of the processing of the abnormality determination processing unit 34. E
When the CU 20 is activated, the abnormality determination processing unit 34 also starts processing (S50). The abnormality determination processing unit 34 is provided by the ECU 2
Based on the digital value of each phase current of the motor input to 0, for example, a waveform in real time and an effective value determined by calculating an average of its absolute value are monitored, and I0 is determined based on the monitored value. (S55). Further, the PWM carrier frequency fc stored in the ECU 20 is extracted (S6).
0). Then, based on these I0 and fc, a voltage determination reference value serving as a reference for determining deterioration or abnormality of the smoothing capacitor 10 is determined from a mathematical expression or a table representing the relationship shown in FIG. 2 (S65). This voltage determination reference value is, for example,
An abnormality determination reference value Th1 which is a reference value indicating an abnormality such as breakage of the smoothing capacitor 10, and a deterioration determination reference value Th2 which is a reference value indicating that the deterioration of the smoothing capacitor 10 is not progressing but is progressing. Can be set. As is clear from this definition, there is a relationship of “abnormality determination reference value Th1> deterioration determination reference value Th2”.

The abnormality determination processing section 34 generates an amplitude (p−p) based on the voltage fluctuation waveform extracted from the output waveform of the voltage sensor 12 by the calculation in the bandpass filter 32.
The measured value of the voltage fluctuation value according to the (p value) is obtained (S7).
0). If the voltage fluctuation value is equal to or greater than the abnormality determination reference value Th1 (that is, if “the abnormality determination reference value Th1 ≦ voltage fluctuation value”), it is determined that the smoothing capacitor 10 is abnormal (S75). Then, abnormal measures such as stopping the vehicle and notifying the driver are performed (S80).

If it is determined in step S80 that the voltage fluctuation value is not greater than the abnormality determination reference value Th1, it is further determined whether the voltage fluctuation value exceeds the deterioration determination reference value Th2 (step S80). S85). If the deterioration determination reference value T
h2 (that is, the “abnormality determination reference value Th1
> Voltage fluctuation value and voltage fluctuation value> Deterioration determination reference value Th
In the case of "2"), it is determined that the deterioration of the smoothing capacitor 10 has progressed to some extent (S85), and a measure for avoiding destruction of the smoothing capacitor 10 such as limiting the current I0,
A message prompting the driver to check and repair is displayed (S
90). If it is determined in step S85 that the voltage fluctuation value has not reached any of the two voltage determination reference values, the process returns to step S55, and the above-described step S55 and subsequent steps are repeated.

When the smoothing capacitor 10 is formed by connecting a plurality of capacitors in parallel, the abnormality determination reference value T
For example, h1 can be set to a value that can detect a voltage fluctuation value generated when one of them is damaged. Further, the deterioration determination reference value Th2 can be set based on experiments and experiences, or can be more easily set as a percentage of the abnormality determination reference value Th1.

The deterioration determination reference value Th2 is determined by the processing S
It can also be linked to the current limit at 90. For example, when the deterioration determination reference value Th2 is set for the purpose of avoiding a situation such as vehicle stoppage and securing time for inspection and repair, the deterioration determination reference value Th Th2 may be set to a value close to the abnormality determination reference value Th1, and the current I0 may be greatly limited to extend the time until the vehicle stops due to the damage of the smoothing capacitor 10. Conversely, if the purpose is to extend the life of the smoothing capacitor 10,
The limit amount of the current I0 may be suppressed to a level that does not hinder normal running, while the deterioration determination reference value Th2 may be set to a small value to start the current limit from an early stage of deterioration. As described above, the deterioration determination reference value Th2 can be variously set according to the purpose of the process S90. Further, in the present apparatus, only one deterioration determination reference value Th2 is set. However, a plurality of different deterioration determination reference values are set and measures such as current limiting are performed stepwise according to the degree of progress of deterioration. Forms are also possible.

In the above description, the voltage fluctuation value
Although the pp value, that is, the full width of the voltage fluctuation is adopted, it is free to use the amplitude or the effective value of one side instead.

[0026]

By using the abnormality detecting device for the capacitor inside the inverter according to the present invention, it is possible to detect the deterioration of the smoothing capacitor inside the inverter. Therefore, the possibility of damaging the capacitor is detected in advance, and necessary countermeasures are taken. Can take. Therefore, when determining the capacity of the smoothing capacitor, it is not necessary to provide a large margin for securing the life. In other words, the capacity of the smoothing capacitor can be set smaller than before, based solely on the electrical characteristic of power smoothing, which is a function originally required. Accordingly, the size and weight of the smoothing capacitor can be reduced, and the effect of reducing the size, weight, and cost of an electric vehicle equipped with an inverter using the present invention can be obtained.

Further, since it is possible to take a countermeasure before the smoothing capacitor is damaged, it is possible to obtain an effect that adverse effects on other parts of the electric vehicle due to the damage can be avoided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a system configuration of an electric vehicle according to an embodiment of the present invention.

FIG. 2 is a schematic graph showing a relationship between a voltage fluctuation δV with respect to a PWM carrier frequency fc and a current I0 used for driving a motor.

FIG. 3 is a schematic processing flowchart of the processing of an abnormality determination processing unit.

[Explanation of symbols]

2 motors, 4 inverters, 6 batteries, 8 converters, 10 smoothing capacitors, 12 voltage sensors, 20
ECU, 22 motor control processing unit, 24 low-pass filter, 30 voltage fluctuation monitoring processing unit, 32 band-pass filter, 34 abnormality determination processing unit.

Continued on the front page (72) Inventor Katsuya Shikata 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Takahisa Yamakawa 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) Reference Document JP-A-9-294375 (JP, A) JP-A-7-222436 (JP, A) JP-A-10-14097 (JP, A) JP-A 4-270 (JP, A) JP-A 64-64 91064 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M ⁷ /42-7/98 H02H 7/16

Claims (2)

(57) [Claims] 1. An inverter having a converter for converting DC power to AC power and supplying the AC power to a motor, and a smoothing capacitor provided on the DC side of the converter,
A voltage sensor that acquires a DC voltage applied to an input terminal of the conversion unit, and monitors an output of the voltage sensor, and a voltage fluctuation that appears on the DC side of the conversion unit along with an inverter control operation of the conversion unit is a predetermined value. An abnormality detection device for an internal capacitor of the inverter having an abnormality determination processing unit that detects an abnormality of the smoothing capacitor based on being larger than a determination reference value, wherein the determination reference value is determined according to a frequency of the inverter control operation. Abnormality detecting device. 2. An inverter having a converter for converting DC power into AC power and supplying the AC power to a motor, and a smoothing capacitor provided on a DC side of the converter,
A voltage sensor that acquires a DC voltage applied to an input terminal of the conversion unit, and monitors an output of the voltage sensor, and a voltage fluctuation that appears on the DC side of the conversion unit along with an inverter control operation of the conversion unit is a predetermined value. An abnormality detection device for an internal capacitor of the inverter having an abnormality determination processing unit for detecting an abnormality of the smoothing capacitor based on a value greater than a determination reference value, wherein the determination reference value is determined according to an output current to the motor. Abnormality detecting device.