Partial discharge detector

Abstract

To provide a partial discharge detection device that detects partial discharge in a rotary motor without adding a sensor for detecting partial discharge.SOLUTION: A partial discharge detection device 10 for a rotary motor 1 including a thermistor 2 extracts a high frequency component corresponding to a partial discharge from a voltage output generated by the thermistor 2 included in the rotary motor 1 and detects a partial discharge occurring within the rotary motor 1 based on the high frequency component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a partial discharge detection device for a rotating electric motor. [Background technology]

[0002] The motor system that powers EVs and HEVs consists of a battery, inverter, motor controller, and motor, and the motor is driven by the inverter. The inverter generates the sinusoidal current required to drive the motor by repeatedly switching between inverters at high speeds. During this process, a surge voltage exceeding the battery voltage is generated at the inverter's output terminals with each switching operation. This surge voltage propagates through the cable between the inverter and motor and into the motor, momentarily applying a voltage higher than the battery voltage across the motor coils. This surge voltage varies depending on the motor cable routing, cable length, and operating conditions, and can reach 1.3 times or more the operating voltage. When this surge voltage is applied across the motor coils, it is known to generate minute discharges called partial discharges through the coil coating. If this partial discharge continues, the erosion of the coil coating will progress, eventually leading to insulation breakdown. Monitoring partial discharges is important for determining whether the coil windings are deteriorating and whether there is a high risk of winding damage.

[0003] Against this background, it has become necessary to monitor the insulation performance of motors online.Patent Document 1 describes a partial discharge detection device that uses an antenna-type sensor to detect the current flowing in the ground wire of equipment to which an AC power supply voltage is applied, removes low-frequency components from the detected current, converts it into an envelope signal, and uses this signal, along with the power supply current detected by a current sensor, as inputs to determine whether or not a partial discharge has occurred.Patent Document 2 describes a partial discharge detection device that uses a narrow-band filter to filter a detection signal from a partial discharge sensor installed in the frame of a rotating electric machine, and measures and displays the intensity of the maximum partial discharge level that stably occurs in each cycle of the voltage frequency applied to the stator winding of the peak-detecting rotating electric machine. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-90693 A [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-71742 Summary of the Invention [Problem to be solved by the invention]

[0005] The partial discharge detection devices described in Patent Documents 1 and 2 require the use of a high-frequency current sensor or an RF antenna to detect partial discharges that occur between the coils of a rotating motor, but both methods require the sensor to be installed separately inside or near the rotating motor, which increases costs. Furthermore, in order to achieve stable sensitivity, installation locations are limited and installation requires additional machining of the rotating motor housing.

[0006] An object of the present invention is to provide a partial discharge detection device that can detect partial discharge in a rotating electric motor without adding a sensor for detecting partial discharge. [Means for solving the problem]

[0007] The partial discharge detection device according to the present invention is a partial discharge detection device for a rotating motor, characterized in that the rotating motor is equipped with a thermistor for detecting temperature, high-frequency components corresponding to partial discharges are extracted from the voltage output by the thermistor, and partial discharges occurring in the rotating motor are detected based on the high-frequency components.

[0008] Here, it is preferable that the partial discharge detection device includes a high-pass filter that extracts high-frequency components corresponding to partial discharge from the voltage output by the thermistor, and a pulse converter that outputs a pulse signal when the output voltage of the high-pass filter is equal to or greater than a predetermined reference value.

[0009] Here, it is preferable that the partial discharge detection device includes a partial discharge discriminator that determines that a partial discharge has occurred in the rotating motor when the rotation of the rotating motor is controlled by an inverter and a pulse signal is output from the pulse converter within a predetermined period from the rising or falling edge of the inverter control signal of the inverter.

[0010] In addition, it is preferable that the partial discharge device includes a high-pass filter that extracts high-frequency components corresponding to partial discharge from the voltage output by the thermistor, an envelope detection circuit that detects the peak value of the output voltage of the high-pass filter, and a comparator that determines whether the output voltage of the envelope detection circuit is equal to or greater than a predetermined reference value.

[0011] Here, it is preferable that the partial discharge device is provided with a rotating motor whose rotation is controlled by an inverter, a comparator which outputs a pulse signal when the output voltage of the envelope detection circuit is equal to or higher than a reference value, and a partial discharge discriminator which determines that a partial discharge has occurred in the rotating motor when a pulse signal is output from the comparator within a predetermined period from the rising or falling edge of the inverter control signal of the inverter.

[0012] In addition, the partial discharge device preferably includes an insulation deterioration level determiner that, when a partial discharge that has occurred in the rotating motor is detected, determines the insulation deterioration level of the rotating motor depending on the frequency of partial discharge occurrence.

[0013] In addition, it is preferable that the partial discharge device includes an insulation deterioration level determiner that determines the insulation deterioration level of the rotating motor depending on the rate of change of the motor current flowing through the rotating motor when a partial discharge that has occurred in the rotating motor is detected.

[0014] Furthermore, it is preferable that the partial discharge device limits the drive voltage of the rotary motor when it detects a partial discharge occurring in the rotary motor. [Effects of the Invention]

[0015] The partial discharge detection device according to the present invention uses a thermistor for measuring temperature provided in a rotary motor to detect partial discharge from high-frequency voltage components generated in the thermistor by electromagnetic waves emitted during partial discharge, making it possible to detect partial discharge in a rotary motor without adding a separate sensor. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows the basic configuration of a partial discharge detection device for a rotary electric motor according to the present invention. [Figure 2] 1 is a diagram showing an example of waveforms of an inverter output voltage in a rotary motor and a current flowing through the rotary motor. [Figure 3] FIG. 2 is an enlarged waveform diagram of an inverter output voltage in a rotary motor. [Figure 4] This shows the output voltage waveforms of the RF antenna and the thermistor when a partial discharge occurs during the falling edge of the pulse voltage. [Figure 5] 1 is a configuration diagram of a partial discharge detection device according to an embodiment; [Figure 6] FIG. 10 is a configuration diagram of a partial discharge detection device according to another embodiment. [Figure 7] FIG. 10 is a configuration diagram of a partial discharge detection device according to still another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, specific shapes, materials, directions, numerical values, etc. are examples for facilitating understanding of the present invention, and can be appropriately changed according to the application, purpose, specifications, etc. Furthermore, it is originally anticipated that the components of the embodiments and modifications described below can be selectively combined.

[0018] <Basic configuration> 1 shows the basic configuration of a partial discharge detection device 10 for a rotary electric motor 1 according to the present invention. The partial discharge detection device 10 is applied to a rotary electric motor 1 that has multiple coils wound around it and can be driven by an inverter 3 and a motor controller 4.

[0019] The rotary motor 1 includes a plurality of coils. The rotary motor 1 is driven by the output voltage of an inverter 3. The output voltage of the inverter 3 is controlled by, but not limited to, PWM control or one-pulse control.

[0020] The inverter 3 is configured, for example, as a three-phase inverter circuit in which three arms, each having a power switching element connected in series, are connected in parallel. The inverter 3 is controlled to turn on and off by an inverter control signal output from a motor controller 4. When the switching elements constituting the inverter 3 turn on and off, a voltage is applied to the coil of the rotary motor 1, causing a sinusoidal current to flow through the coil.

[0021] The motor controller 4 outputs an inverter control signal to the inverter 3. The inverter control signal is, for example, a PWM control signal. As will be described later, the motor controller 4 receives outputs from the temperature detection circuit 5 and the partial discharge detection device 10 and controls the output of the rotary motor 1.

[0022] The rotary motor 1 is provided with a thermistor 2 inside the housing. The thermistor 2 is used to detect the temperature inside the housing. The thermistor 2 outputs a voltage signal proportional to the internal temperature of the rotary motor 1. The thermistor 2 is connected to a temperature detection circuit 5, and the signal after high-frequency components have been removed is output to a motor controller 4. The motor controller 4 receives the detection voltage from the temperature detection circuit 5 and modulates the control signal for the inverter 3. For example, if the temperature exceeds a predetermined value, the motor controller 4 generates an inverter 3 control signal to reduce the rotation speed of the rotary motor 1. However, the control of the motor controller 4 is not limited to this.

[0023] The partial discharge detection device 10 has a high-pass filter 11, a pulse converter 12, and a partial discharge discriminator 13. The partial discharge detection device 10 is a device that detects the occurrence of partial discharge based on a voltage signal detected in a high frequency range from the voltage signal of the thermistor 2 separately from that used for temperature detection, and on an inverter 3 control signal from the motor controller 4.

[0024] The output voltage of thermistor 2 is input to high-pass filter 11. High-pass filter 11 extracts high-frequency components, for example, tens of MHz to several tens of MHz, that are caused by partial discharge and are included in the voltage output by thermistor 2. In other words, high-pass filter 11 extracts high-frequency components of electromagnetic waves caused by partial discharge from the voltage signal of thermistor 2.

[0025] When a partial discharge occurs, electromagnetic waves generated in the coil propagate to thermistor 2. Thermistor 2 generates a high-frequency voltage change due to a resistance change caused by heat generated when absorbing the electromagnetic waves. High-pass filter 11 passes the high-frequency components specific to partial discharges contained in the output voltage of thermistor 2 and outputs the signal to pulse converter 12 in the downstream stage.

[0026] The pulse converter 12 is a circuit that extracts the output voltage of the high-pass filter 11 that is equal to or greater than a predetermined value, and outputs it as a pulse signal.

[0027] The partial discharge determiner 13 receives the pulse signal from the pulse converter 12 and the inverter control signal from the motor controller 4. The partial discharge determiner 13 detects the rising or falling timing of the drive voltage of the inverter 3 from the inverter control signal. The rising or falling timing of the inverter drive voltage coincides with the phase inversion (voltage inversion) of the inverter control signal. Therefore, the rising and falling timing of the output voltage of the inverter 3 can be detected based on the phase inversion of the inverter control signal.

[0028] Furthermore, the partial discharge determiner 13 determines whether a partial discharge has occurred based on whether a pulse signal is present from the pulse converter 12 within a predetermined period from the timing of phase reversal of the inverter control signal. The partial discharge determiner 13 determines that a partial discharge has occurred when a pulse signal is detected within a predetermined period from the timing of phase reversal of the inverter control signal. The process of determining the occurrence of a partial discharge will be described in detail later.

[0029] <Partial discharge detection principle> Figure 2 shows the waveforms of the output voltage of the inverter 3 and the current flowing through the rotary motor 1 in a PWM-controlled rotary motor 1. The output current of the rotary motor 1 is controlled by modulating the output voltage width (pulse width). A surge voltage may occur at each rising and falling edge of the pulse in the output voltage waveform of the inverter 3. The greater the absolute value of the surge voltage and the voltage change rate, the more likely partial discharges are to occur.

[0030] The occurrence of partial discharge and the principle of partial discharge detection according to the present invention will be explained with reference to Figures 3 and 4. Figure 3 shows an enlarged waveform of one pulse of the output voltage of the inverter 3. It can be seen that a surge voltage is superimposed at the rising and falling timing of the output voltage of the inverter 3.

[0031] Figure 4 shows the output voltage waveform after the high-pass filter of the RF antenna and thermistor 2 at the falling edge of the voltage when the voltage waveform shown in Figure 3 is applied to the rectangular wire. The voltage waveform from the RF antenna was observed for comparison with the conventional method.

[0032] As shown in Figure 4, the RF antenna output voltage waveform exhibits a large amplitude voltage near the peak of the surge voltage. In other words, with conventional methods, partial discharges can be detected because a large output voltage is observed at the RF antenna. On the other hand, the output voltage waveform of thermistor 2 exhibits a voltage with a superimposed high frequency that synchronizes with the ringing of the surge voltage. Similar to the output voltage of the RF antenna, this high-frequency voltage has the largest amplitude near the peak value of the surge voltage. Therefore, partial discharges can be detected by extracting high-frequency components higher than the ringing frequency from the output voltage of thermistor 2.

[0033] As described above, the partial discharge detection device 10 detects the heat generated when electromagnetic waves are absorbed as a change in resistance of the thermistor 2, out of the high-frequency voltage, current, light, sound waves, and electromagnetic waves that are generated when partial discharge occurs between the coils of the rotating motor 1, and extracts the high-frequency components that correspond to the electromagnetic waves during partial discharge from a frequency range higher than the frequency range that corresponds to the temperature signal of the rotating motor 1. This enables the partial discharge detection device 10 to detect partial discharge without the need to add a separate RF antenna, high-frequency current sensor, or the like.

[0034] First Embodiment Fig. 5 is a configuration diagram of the partial discharge detection device 10 of the first embodiment. The partial discharge detection device 10 of this embodiment further includes an envelope detection circuit 14 and a comparator 15 after the high-pass filter 11, in addition to the basic configuration of the partial discharge detection device 10 shown in Fig. 1.

[0035] 1, the output voltage of thermistor 2 is input to high-pass filter 11. High-pass filter 11 extracts the frequency band components caused by partial discharge from the output voltage of thermistor 2 and outputs the extracted components.

[0036] The envelope detection circuit 14 continuously detects the peak voltage of the voltage value extracted by the high-pass filter 11 .

[0037] Comparator 15 compares the signal obtained by envelope detection circuit 14 with a predetermined signal strength threshold Vth. Signal strength threshold Vth is set to a value that can detect the voltage generated in thermistor 2 when a partial discharge occurs. For example, as shown by the dashed line in FIG. 4, signal strength threshold Vth is set to a value that can detect the first peak voltage (negative voltage) of the surge voltage. Comparator 15 outputs a pulse signal that goes high when the signal output from envelope detection circuit 14 is equal to or greater than signal strength threshold Vth.

[0038] The partial discharge pulse detector 17 receives the pulse signal output from the comparator 15 and the inverter control signal from the motor controller 4. The partial discharge pulse detector 17 detects the timing of the pulse rise or fall of the drive voltage of the inverter 3 from the timing of the phase inversion of the inverter control signal. The partial discharge pulse detector 17 detects the occurrence of a partial discharge when the pulse signal from the comparator 15 is at a high level within a predetermined reference time from the timing of the pulse rise or fall of the drive voltage. The partial discharge pulse detector 17 outputs a pulse signal when it detects a partial discharge.

[0039] Here, the reference time is preferably set to approximately the time it takes for the surge voltage generated by partial discharge to go from its initial peak voltage to zero voltage, as shown by Δt in Figure 4. The ringing frequency of the surge voltage is several MHz to several MHz, and it repeats about three times, so a time equivalent to one-quarter of that cycle (about several tens of nanoseconds) is preferable. Partial discharges are more likely to occur as the absolute value and rate of change of the voltage value of the pulse voltage applied to the coil increase. Therefore, voltage changes in thermistor 2 corresponding to partial discharges are more likely to occur during the period from the initial rise or fall of the surge voltage to the peak voltage.

[0040] According to this embodiment, partial discharge can be detected simultaneously with temperature measurement of the rotary motor 1 using the thermistor 2 for measuring coil temperature, without using a separate partial discharge detection sensor such as a high-frequency antenna or current sensor. This reduces the cost of partial discharge detection. Furthermore, since the configuration uses the voltage of the thermistor 2 for measuring coil temperature and the inverter control signal of the motor controller 4, it can be easily added to an existing control system for the rotary motor 1.

[0041] <Second embodiment> 6 shows a configuration diagram of a partial discharge detection device 10 according to the second embodiment. The partial discharge detection device 10 of this embodiment further includes a partial discharge current detector 18, an insulation degradation level determiner 19, and a memory 20 in addition to the components of the partial discharge detection device 10 of the first embodiment.

[0042] The partial discharge pulse detector 17 outputs a pulse voltage when it detects a partial discharge. That is, the partial discharge pulse detector 17 outputs a pulse voltage when the pulse signal from the comparator 15 becomes high level within a predetermined time from the timing of phase inversion of the inverter control signal. The pulse width of the pulse voltage output from the partial discharge pulse detector 17 may be configured to be approximately the same as the period during which the pulse signal input from the comparator 15 is high level, for example.

[0043] The partial discharge current detector 18 receives as input the pulse voltage from the partial discharge pulse detector 17 and the motor current value obtained from the inverter 3. The partial discharge current detector 18 stores the motor current value when the pulse voltage is input from the partial discharge pulse detector 17 in the memory 20. That is, the partial discharge current detector 18 stores the current value flowing through the rotating motor 1 when a partial discharge is occurring in the memory 20. Furthermore, when the pulse voltage is input from the partial discharge pulse detector 17, the partial discharge current detector 18 outputs a discharge detection signal and a signal indicating the value of the current flowing through the rotating motor 1 at that time to the insulation degradation level determiner 19.

[0044] The insulation degradation level determiner 19 determines the insulation degradation level of the rotating motor 1 based on the motor current value data stored in the memory 20 when a discharge detection signal is input from the partial discharge current detector 18 or at predetermined intervals. The insulation degradation level of the rotating motor 1 can be determined, for example, based on the frequency of partial discharge occurrence or the rate of change of the motor current when a partial discharge occurs. Specifically, the higher the frequency of partial discharge occurrence, the more advanced the insulation degradation of the rotating motor 1 can be determined. Furthermore, the smaller the variation in the motor current value when a partial discharge occurs, the more advanced the insulation degradation of the rotating motor 1 can be determined. The partial discharge occurrence frequency and the rate of change of the motor current when a partial discharge occurs may be calculated each time a signal is input from the partial discharge current detector 18, or the calculated values ​​may be stored in the memory 20 and updated each time a partial discharge is detected. The insulation degradation level may be determined as a result of whether or not a predetermined degradation threshold is exceeded, or may be a result indicating the degree of insulation degradation at multiple levels.

[0045] The partial discharge detection device 10 of the second embodiment can determine the degree of insulation degradation based on the frequency of partial discharge occurrence and the rate of change of the motor current value when a partial discharge occurs, thereby making it possible to determine whether the degree of insulation degradation is within an acceptable level.

[0046] Furthermore, if it is determined that the insulation deterioration has exceeded the allowable level, a configuration may be adopted in which a warning signal is output to notify that the insulation deterioration has exceeded the allowable range, or the motor output is restricted. For example, it is preferable to configure the device to notify that the insulation performance of the motor coil in the rotary electric motor 1 has deteriorated. As an example of the notification, in the case of an EV or HEV, an alarm indicating the insulation deterioration of the motor coil may be displayed on the front panel, or information may be transmitted from the EV or HEV itself to a dealer via a wireless network. The user or dealer who receives the notification can take the necessary measures. However, examples of the notification are not limited to these.

[0047] <Third embodiment> 7 shows a configuration diagram of a partial discharge detection device 10 of the third embodiment. The partial discharge detection device 10 of this embodiment further includes a motor drive upper limit voltage setter 21 in addition to the components of the partial discharge detection device 10 of the second embodiment.

[0048] Motor drive upper limit voltage setter 21 receives the insulation degradation level output from insulation degradation level determiner 19 and sets a motor drive upper limit voltage for motor controller 4. For example, if insulation degradation level determiner 19 determines that insulation degradation has progressed, it outputs a degradation level determination signal to motor drive upper limit voltage setter 21. Upon receiving the degradation level determination signal, motor drive upper limit voltage setter 21 outputs a voltage limit signal to motor controller 4. Upon receiving the voltage limit signal from motor drive upper limit voltage setter 21, motor controller 4 controls inverter 3 to limit the upper limit of the motor drive voltage to the motor drive upper limit voltage indicated by the voltage limit signal. This makes it possible to suppress the occurrence of partial discharge in rotary electric motor 1.

[0049] Furthermore, if insulation deterioration level determiner 19 determines the degree of insulation deterioration at multiple levels, motor drive upper limit voltage setter 21 may output a voltage limit signal so that the motor drive upper limit voltage corresponds to the level of the insulation deterioration level. Note that the operation of insulation deterioration level determiner 19 is an example, and does not limit the method of setting the motor drive upper limit voltage according to the degree of insulation deterioration. [Explanation of symbols]

[0050] 1 Rotating motor, 2 Thermistor, 3 Inverter, 4 Motor controller, 5 Temperature detection circuit, 10 Partial discharge detector, 11 High-pass filter, 12 Pulse converter, 13 Partial discharge discriminator, 14 Envelope detector, 15 Comparator, 17 Partial discharge pulse detector, 18 Partial discharge current detector, 19 Insulation deterioration level discriminator, 20 Memory, 21 Motor drive upper limit voltage setter

Claims

1. A partial discharge detection device for a rotary electric motor, comprising: the rotary motor is provided with a thermistor for detecting temperature; extracting a high-frequency component corresponding to a partial discharge from the voltage output by the thermistor, and detecting a partial discharge occurring in the rotary electric motor based on the high-frequency component; a high-pass filter that extracts the high-frequency component corresponding to partial discharge from the voltage output by the thermistor; an envelope detection circuit that detects the peak value of the output voltage of the high-pass filter; a comparator that determines whether the output voltage of the envelope detection circuit is equal to or greater than a predetermined reference value.

2. The partial discharge detection device according to claim 1, The rotation of the rotary motor is controlled by an inverter, the comparator outputs a pulse signal when the output voltage of the envelope detection circuit is equal to or greater than the reference value; a partial discharge detector that determines that a partial discharge has occurred in the rotating motor when the pulse signal is output from the comparator within a predetermined period from the rising or falling edge of an inverter control signal of the inverter.

3. The partial discharge detection device according to claim 1 or 2, a partial discharge detection device comprising an insulation deterioration level determiner that, when a partial discharge that has occurred in the rotary motor is detected, determines the insulation deterioration level of the rotary motor depending on the frequency of partial discharge occurrences.

4. A partial discharge detection device for a rotating electric motor, comprising: the rotary motor is provided with a thermistor for detecting temperature; extracting a high-frequency component corresponding to a partial discharge from the voltage output by the thermistor, and detecting a partial discharge occurring in the rotary electric motor based on the high-frequency component; A partial discharge detection device characterized by comprising an insulation deterioration degree determiner that, when a partial discharge generated in the rotary motor is detected, determines the insulation deterioration degree of the rotary motor according to the rate of change of the motor current flowing through the rotary motor.

5. The partial discharge detection device according to any one of claims 1 to 4, a partial discharge detection device that limits a drive voltage of the rotary motor when a partial discharge that has occurred in the rotary motor is detected;

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