Stator abnormal current detection device, stator abnormal current detection method, and electric motor

Abstract

A stator abnormal current detection device according to an embodiment of the present invention comprises: a current smoothing unit (21) that smooths an input current detection signal corresponding to the current of each phase of a stator coil of a three-phase motor to be subjected to abnormality detection and outputs a smoothed current signal; an envelope detection unit (22) that detects the envelope of the smoothed current signal; a first smoothing unit (23) that smooths the envelope in a first section of the envelope and outputs a first smoothed envelope; a second smoothing unit (24) that smooths the envelope in a second section of the envelope longer than the first section and outputs a second smoothed envelope; and an abnormality detection unit (25) that obtains a difference value between the first smoothed envelope and the second smoothed envelope, and detects, as an abnormal value, a value of the difference value that deviates from a standard deviation σ by aｋ×σ section (k: a real number that exceeds 1) with respect to the first smoothed envelope. Thus, it is possible to detect an event that occurs in a very early stage of an insulation deterioration event (layer short, ground fault) of the stator coil, and to detect insulation deterioration of the stator coil at an early stage.

Description

Stator Abnormal Current Detection Device, Stator Abnormal Current Detection Method, and Electric Motor 【0001】 An embodiment of the present invention relates to a stator abnormal current detection device, a stator abnormal current detection method, and an electric motor. 【0002】 Conventionally, stator coils of electric motors operated with three-phase alternating current were mainly composed of iron cores and windings. Also, coil strand insulation was provided between the windings, and main insulation was provided between the iron core and the strands. In the above configuration, the insulation is fixedly configured with a structure for increasing the varnish or the static rigidity of the winding itself. By the way, in the above-mentioned stator including an electric motor, when it deteriorates, a rare short event or a ground fault event occurs. Even in a device with a low-voltage insulation system or a device with a high-voltage insulation system, the insulation system may deteriorate due to heat, mechanical, environmental, applied voltage, etc. For this reason, as a conventional method for detecting a rare short circuit in a stator winding, calculating the reverse-phase current may be used as a means for detecting a sign of a rare short event, and calculating the zero-phase current may be used as a means for detecting a sign of a ground fault event. 【0003】 International Publication No. 2024 / 013809 【0004】 However, the conventional method for detecting a rare short circuit in a stator winding has a problem that it cannot be determined unless the rare short circuit has progressed to a certain extent and cannot be applied in the initial stage. 【0005】 The present invention has been made in view of the above, and an object thereof is to provide a stator abnormal current detection device, a stator abnormal current detection method, and an electric motor capable of detecting an event occurring in an extremely early stage of an insulation deterioration event (rare short circuit, ground fault) of a stator coil and detecting the insulation deterioration of the stator coil at an early stage. 【0006】The stator abnormal current detection device of the embodiment includes: a current smoothing unit that smooths current detection signals corresponding to the currents of each phase of the stator coils of a three-phase motor to be abnormally detected and outputs smoothed current signals; an envelope detection unit that detects the envelope of the smoothed current signals; a first smoothing unit that smooths the envelope in a first section and outputs a first smoothed envelope; a second smoothing unit that smooths the envelope in a second section longer than the first section and outputs a second smoothed envelope; and an abnormality detection unit that finds the difference between the first smoothed envelope and the second smoothed envelope, and detects as an abnormal value any difference value that falls outside the k × σ interval (k: a real number greater than 1) with respect to the standard deviation σ of the first smoothed envelope. 【0007】 According to this embodiment, a stator abnormal current detection device, a stator abnormal current detection method, and an electric motor can be provided that can detect insulation deterioration of the stator coil at an early stage. 【0008】 Figure 1 is a schematic block diagram of the stator abnormal current detection system according to the embodiment. Figure 2 is a functional block diagram of the stator abnormal current detection device. Figure 3 is a processing flowchart of the embodiment. Figure 4 is an explanatory diagram of an example of the detection results of U-phase current, V-phase current, and W-phase current. Figure 5 is an explanatory diagram of the smoothed U-phase current, smoothed V-phase current, and smoothed W-phase current. Figure 6 is an explanatory diagram (part 1) of an example of the first smoothed envelope and the second smoothed envelope. Figure 7 is an explanatory diagram (part 2) of an example of the first smoothed envelope and the second smoothed envelope. 【0009】Figure 1 is a schematic block diagram of the stator abnormal current detection system according to an embodiment. The stator abnormal current detection system 10 comprises a three-phase AC power supply 11, a three-phase motor 12, a stator abnormal current detection device 13, a U-phase current detector 14U, a V-phase current detector 14V, and a W-phase current detector 14W. The three-phase AC power supply 11 is a three-phase AC power supply having a U-phase as the first phase, a V-phase as the second phase, and a W-phase as the third phase. The three-phase AC power supply 11 supplies three-phase AC power to the three-phase motor 12. The three-phase motor 12 is driven based on the supplied three-phase AC power. The stator abnormal current detection device 13 detects stator abnormal currents of the three-phase motor 12 based on the U-phase current IU, V-phase current IV, and W-phase current IW supplied from the three-phase AC power supply 11 to the three-phase motor 12, and detects insulation deterioration (rare short circuit, ground fault) of the stator coils at an early stage (initial stage of insulation deterioration), and notifies the operator accordingly. The U-phase current detector 14U is configured as a current transformer and detects the U-phase current IU flowing through the U-phase current line and outputs it to the stator abnormal current detection device 13 as a U-phase current detection signal SIU. The U-phase current detector 14U is an example of a first-phase current detector. The V-phase current detector 14V is configured as a current transformer and detects the V-phase current IV flowing through the V-phase current line and outputs it to the stator abnormal current detection device 13 as a V-phase current detection signal SIV. The V-phase current detector 14V is an example of a second-phase current detector. The W-phase current detector 14W is configured as a current transformer and detects the W-phase current IW flowing through the W-phase current line, outputting it as a W-phase current detection signal SIW to the stator abnormal current detection device 13. The W-phase current detector 14W is an example of a third-phase current detector. 【0010】 Here, the stator abnormal current detection device 13 will be described in detail. Figure 2 is a functional configuration block diagram of the stator abnormal current detection device. The stator abnormal current detection device 13 includes a current smoothing unit 21, an envelope detection unit 22, a first smoothing unit 23, a second smoothing unit 24, and an abnormality detection unit 25. 【0011】The current smoothing unit 21 corresponds to the current of each phase of the stator coil of the three-phase motor 12 that is subject to abnormality detection. It smooths the U-phase current detection signal SIU detected by the U-phase current detector 14U, the V-phase current detection signal SIV detected by the V-phase current detector 14V, and the W-phase current detection signal SIW detected by the W-phase current detector 14W, respectively, and outputs the smoothed current signals SSIU, SSIV, and SSIW to the envelope detection unit 22. 【0012】 The envelope detection unit 22 detects the envelopes ENU, ENV, and ENW of each phase of the three-phase AC current waveform using the Hilbert transform method based on the input smoothing current signals SSIU, SSIV, and SSIW, and outputs them to the first smoothing unit 23 and the second smoothing unit 24. 【0013】 The first smoothing unit 23 calculates a moving average over a first interval (first window width w1) for the envelope of the input three-phase AC current waveform to smooth the envelope, and outputs the first smoothed envelopes SENU1, SENV1, and SENW1 to the anomaly detection unit 25. 【0014】 These first smoothing envelopes, SENU1, SENV1, and SENW1, are used to detect relatively short-term fluctuations in the three-phase current waveform. 【0015】 The second smoothing unit 24 calculates a moving average over a second section longer than the first section (a second window width w2 longer than the first window width w1) for the envelopes ENU, ENV, and ENW of the input three-phase AC current waveform, smooths the envelopes ENU, ENV, and ENW, and outputs the second smoothed envelopes SENU2, SENV2, and SENW2 to the anomaly detection unit 25. 【0016】 These second smoothing envelopes, SENU2, SENV2, and SENW2, are used as waveforms corresponding to low-order steady fluctuations (circular fluctuations, voltage fluctuations). 【0017】The anomaly detection unit 25 calculates the difference value between the first smoothing envelopes SENU1, SENV1, SENW1 and the second smoothing envelopes SENU2, SENV2, SENW2 for each phase. Then, based on the calculated difference value and the first smoothing envelopes SENU1, SENV1, SENW1, the anomaly detection unit 25 detects anomalies at the sampling points of the first smoothing envelopes SENU1, SENV1, SENW1. 【0018】 Furthermore, the abnormality detection unit 25 detects insulation deterioration of the stator coil (rare short circuit, ground fault) based on the count of detected abnormal values, the count of abnormal values ​​under normal conditions, and the count of abnormal values ​​in the other phases of the three phases. 【0019】 Next, the operation of the embodiment will be described. Figure 3 is a processing flowchart of the embodiment. First, the U-phase current detector 14U detects the U-phase current IU flowing through the U-phase current line LU and outputs it as a U-phase current detection signal SIU to the current smoothing unit 21 of the stator abnormal current detection device 13. 【0020】 Furthermore, the V-phase current detector 14V detects the V-phase current IV flowing through the V-phase current line LV and outputs it as a V-phase current detection signal SIV to the current smoothing unit 21 of the stator abnormal current detection device 13. Also, the W-phase current detector 14W detects the W-phase current IW flowing through the W-phase current line LW and outputs it as a W-phase current detection signal SIW to the current smoothing unit 21 of the stator abnormal current detection device 13 (step S11). 【0021】 Figure 4 is an explanatory diagram illustrating an example of the detection results for U-phase current, V-phase current, and W-phase current. In Figure 4, the vertical axis represents current (A), and the horizontal axis represents time (s). Figure 4 also shows a case where a current anomaly occurs in the U-phase current IU. 【0022】 The U-phase current IU, V-phase current IV, and W-phase current IW supplied from the three-phase AC power supply 11 to the three-phase motor 12 are usually superimposed with noise components. Therefore, the U-phase current detection signal SIU, V-phase current detection signal SIV, and W-phase current detection signal SIW detected by the U-phase current detector 14U, V-phase current detector 14V, and W-phase current detector 14W contain noise and do not have a clean sinusoidal waveform as shown in Figure 4. 【0023】 Therefore, the current smoothing unit 21 corresponds to the current of each phase of the stator coil of the three-phase motor 12 to be abnormally detected, and based on the U-phase current detection signal SIU detected by the U-phase current detector 14U, the V-phase current detection signal SIV detected by the V-phase current detector 14V, and the W-phase current detection signal SIW detected by the W-phase current detector 14W, it smooths the detected U-phase current IU, V-phase current IV, and W-phase current IW, respectively, to generate smoothed current signals SSIU, SSIV, and SSIW, which are output to the envelope detection unit 22 (step S12). 【0024】 Figure 5 is an explanatory diagram of the smoothed U-phase current, smoothed V-phase current, and smoothed W-phase current. As shown in Figure 5, the smoothed U-phase current detection signal SSIU, the smoothed V-phase current detection signal SSIV, and the smoothed W-phase current detection signal SSIW, smoothed by the current smoothing unit 21, have waveforms that are closer to a clean sinusoidal waveform compared to Figure 4. 【0025】 Returning to Figure 3, the explanation continues. The envelope detection unit 22 generates envelopes ENU, ENV, and ENW for each phase of the three-phase AC current waveform using the Hilbert transform method for the input smoothed current signals SSIU, SSIV, and SSIW, and outputs them to the first smoothing unit 23 and the second smoothing unit 24, respectively (step S13). 【0026】 As a result, the first smoothing unit 23 calculates a moving average of multiple current data constituting the envelopes ENU, ENV, and ENW for each phase in the first section (first window width w1) for the envelopes ENU, ENV, and ENW of the input three-phase AC current waveform, smooths the envelopes ENU, ENV, and ENW for each phase, generates first smoothed envelopes SENU1, SENV1, and SENW1 for each phase, and outputs them to the anomaly detection unit 25 (step S14). 【0027】 Here, the window width defines the number of time-consecutive data points among multiple data points arranged in a time series. For example, if the window width w1 = 7, then 7 data points are included within the window. Moving average is the process of calculating the average value of the data included within the window width while shifting the position of the window over time. 【0028】 More specifically, if we have 15 current data points D1 to D15 arranged in time series, and the window width is 7, then to find the moving average corresponding to the acquisition timing of current data point D4, we would calculate the average value of current data points D1 to D3, D4, and D5 to D7. Then, to find the moving average corresponding to the acquisition timing of the next current data point D5, we would calculate the average value of current data points D2 to D4, D5, and D6 to D8. In this way, calculating the average value while sequentially shifting the calculation interval over time constitutes calculating a moving average. 【0029】 Meanwhile, the second smoothing unit 24 calculates a moving average of multiple current data constituting the envelopes ENU, ENV, and ENW for each phase in a second interval (second window width w2 > first window width w1) for the envelopes ENU, ENV, and ENW of the input three-phase AC current waveform, smooths the envelopes ENU, ENV, and ENW for each phase, generates second smoothed envelopes SENU2, SENV2, and SENW2 for each phase, and outputs them to the anomaly detection unit 25 (step S15). 【0030】 In the above explanation, the processing in the first smoothing unit 23 and the processing in the second smoothing unit 24 were described as being performed sequentially in chronological order. However, it is also possible to configure the system to process the processing in the first smoothing unit 23 and the processing in the second smoothing unit 24 in parallel. 【0031】 Furthermore, although the processing in the first smoothing unit 23 and the second smoothing unit 24 were performed by arithmetic processing in the above description, it is also possible to configure them using an analog filter or a digital filter that functions as a low-pass filter. 【0032】 In this case, the low-pass filter used in the processing of the first smoothing unit 23 smooths the envelope using a low-pass filter having a first cutoff frequency corresponding to the first section, and the second smoothing unit 24 smooths the envelope using a low-pass filter having a second cutoff frequency lower than the first cutoff frequency and corresponding to the second section. 【0033】The anomaly detection unit 25 receives the first smoothing envelopes SENU1, SENV1, and SENW1 from the first smoothing unit 23 and the second smoothing envelopes SENU2, SENV2, and SENW2 from the second smoothing unit 24, and calculates the difference between the first smoothing envelopes SENU1, SENV1, and SENW1 and the second smoothing envelopes SENU2, SENV2, and SENW2 for each phase (step S16). 【0034】 In this case, the reason for calculating the difference between the first smoothed envelopes SENU1, SENV1, SENW1 and the second smoothed envelopes SENU2, SENV2, SENW2 is that the first smoothed envelopes SENU1, SENV1, SENW1 contain low-order steady fluctuations for each phase of the three-phase current waveform. By calculating the difference for each phase between the first smoothed envelopes SENU1, SENV1, SENW1 and the second smoothed envelopes SENU2, SENV2, SENW2, the low-order steady fluctuations of the three-phase current waveform are removed, so that they are not detected as abnormal values ​​of low-order steady fluctuations in the three-phase current waveform. 【0035】 In other words, the second smoothing envelopes SENU2, SENV2, and SENW2 are thought to correspond to the low-order steady-state fluctuation components of the three-phase current waveform. By taking the difference for each phase between these envelopes and the first smoothing envelopes SENU1, SENV1, and SENW1, which contain the low-order steady-state fluctuation components of the three-phase current waveform, the low-order steady-state fluctuation components of the three-phase current waveform can be removed. 【0036】 Figure 6 is an explanatory diagram (part 1) of an example of the first and second smoothing envelopes. In Figure 6, the first smoothing envelope SENU1, the second smoothing envelope SENU2, and the smoothing U-phase current detection signal SSIU are shown. Furthermore, as shown in Figure 4, the U-phase current detection signal SIU, which detects the U-phase current IU corresponding to the smoothing U-phase current detection signal SSIU, is assumed to show signs of insulation degradation events (rare short circuit, ground fault) in the stator coil. 【0037】 The anomaly detection unit 25 calculates the difference between the first smoothed envelope and the second smoothed envelope for each phase, assuming the first smoothed envelope is the standard average value for each phase. If the calculated difference value exceeds a predetermined variation range of the average value, the unit detects the sampling point of the first smoothed envelope for that phase as an anomaly. 【0038】 More specifically, the anomaly detection unit 25 detects a sampling point of the first smoothing envelope SENU1 as an anomaly if the difference between the first smoothing envelope SENU1 and the second smoothing envelope SENU2 exceeds, for example, k times the standard deviation (k: a real number greater than or equal to 1, e.g., k=2), where σ is the standard deviation of the first smoothing envelope SENU1, and plots it as a black circle on the first smoothing envelope SENU1 (step S17). The result of the processing in step S17 is as shown in Figure 6. 【0039】 Next, the abnormality detection unit 25 acquires the number of abnormal values ​​within a predetermined time (the number of plotted black circles in Figure 6), compares it with the past counts of the same phase (when insulation is normal) and the counts of other phases where signs of insulation deterioration have not yet occurred, and determines the level of insulation deterioration (step S18). 【0040】 Figure 7 is an explanatory diagram (part 2) of an example of the first and second smoothing envelopes. In Figure 7, the first smoothing envelope SENV1, the second smoothing envelope SENV2, and the smoothing V-phase current detection signal SSIV are shown. 【0041】 Furthermore, as shown in Figure 4, the V-phase current detection signal SIV, which detects the V-phase current IV corresponding to the smoothed V-phase current detection signal SSIV, is assumed to be in a normal state with no signs of insulation degradation events (rare short circuit, ground fault) in the stator coil. 【0042】 In this case as well, the anomaly detection unit 25 will detect sampling points of the first smoothing envelope SENV1 as an anomaly if the difference value obtained between the first smoothing envelope SENV1 and the second smoothing envelope SENV2 exceeds a predetermined variation range of the average value, assuming the first smoothing envelope SENV1 is a standard average value. However, in the example of Figure 7, when the standard deviation of the first smoothing envelope SENV1 is σ, it did not exceed, for example, twice the standard deviation (2σ) when k=2, so no anomalies were detected. 【0043】Then, the abnormality detection unit 25 compares the number of sampling points (number of plots) of the first smoothed envelope line SENV1 detected as an abnormal value during the normal operation of the stator coil, and if a difference in the number of counts (number of plots) equal to or greater than a predetermined threshold is detected, it determines that a sign of insulation degradation has occurred. Similarly, although not shown, when the abnormality detection unit 25 regards the first smoothed envelope line SENW1 as a standard average value, the difference value obtained between the first smoothed envelope line SENW1 and the second smoothed envelope line SENW2 exceeds a predetermined variation range of the average value, and the sampling points of the first smoothed envelope line SENW1 are detected as abnormal values. 【0044】 Returning to FIG. 3 again for explanation. Subsequently, if the abnormality detection unit 25 determines that a sign of insulation degradation has occurred as a result of the determination in step S18, it notifies this fact and ends the process (step S19). 【0045】 As described above, according to this embodiment, it is possible to detect an event that occurs at a very early stage of an insulation degradation event (rare short circuit, ground fault) of the stator coil and detect the insulation degradation of the stator coil at an early stage. 【0046】 The following describes a modification of the embodiment. In the above embodiment, in order to remove the noise of the detected current waveform, the detected current waveform was smoothed. However, it is also possible to extract the basic components (for example, third-order component, fifth-order component, seventh-order component,...) that make up the detected current waveform using FFT or a band-pass filter and remove them from the detected current waveform, so as to extract only the harmonic components. In this case, when large noise such as the carrier frequency during inverter drive is included in the detected current waveform, in order to separate the unspecified current peak generated by insulation degradation and the peak of the carrier, the above-described envelope detection process and smoothed envelope calculation process are performed, and data that deviates from k times (k is a constant) of the standard deviation σ of the obtained waveform is counted as abnormal data, and the presence or absence of a sign of insulation degradation is determined by comparing with the number of abnormal data counts during normal operation. 【0047】In the above description, the window width is set to calculate the moving average for smoothing the envelope, but it is also possible to smooth the envelope using an analog filter (low-pass filter) or a digital filter. 【0048】 In the above description, the case of a three-phase motor has been described as the motor, but it is similarly applicable even if it is a single-phase motor. 【0049】 The abnormality detection device of each embodiment includes a control device such as an MPU, a storage device such as a ROM (Read Only Memory) and a RAM, an external storage device configured as a semiconductor memory device such as an SSD and a USB memory, a display device such as a display device, and an input device such as an operation panel and an operation switch, and has a hardware configuration using an ordinary computer. 【0050】 The program executed by the abnormality detection device of the present embodiment is provided by being recorded in a semiconductor memory device such as an SSD and a USB memory, or a computer-readable recording medium such as a DVD (Digital Versatile Disk) in an installable format or an executable format file. 【0051】 Further, the abnormality detection device of the present embodiment may be configured to store the program executed by it on a computer connected to a network such as the Internet and provide it by downloading it via the network. Further, the program executed by the control circuit of the rotating rectifier of the present embodiment may be provided or distributed via a network such as the Internet. 【0052】 Further, the program of the abnormality detection device of the present embodiment may be configured to be provided by being pre-embedded in a ROM or the like. 【0053】While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. 【0054】 Furthermore, this disclosure also includes the following embodiments: (1) First Embodiment The first embodiment of the first embodiment is a stator abnormal current detection device comprising: a current smoothing unit that smooths current detection signals corresponding to the currents of each phase of the stator coils of a three-phase motor to be abnormally detected and outputs a smoothed current signal; an envelope detection unit that detects the envelope of the smoothed current signal; a first smoothing unit that smooths the envelope in a first section and outputs a first smoothed envelope; a second smoothing unit that smooths the envelope in a second section longer than the first section and outputs a second smoothed envelope; and an abnormality detection unit that finds the difference between the first smoothed envelope and the second smoothed envelope and detects as an abnormal value a value in which the difference is outside the k × σ interval (k: a real number greater than 1) with respect to the standard deviation σ of the first smoothed envelope. According to this embodiment, it is possible to detect events that occur in the very early stages of insulation degradation of the stator coil (rare short circuit, ground fault), and to detect insulation degradation of the stator coil at an early stage. 【0055】 (2) Second Embodiment The second embodiment of the embodiment is as follows: In the first embodiment, the first smoothing unit calculates a moving average over the envelope over the first section and smooths the envelope; and the second smoothing unit calculates a moving average over the envelope over the second section and smooths the envelope. According to this embodiment, it is possible to detect events that occur in the very early stages of insulation degradation events (rare shorts, ground faults) of the stator coil with a simple process. 【0056】(3) Third Embodiment The third embodiment is, in the first embodiment, the first smoothing unit smooths the envelope with a low-pass filter having a first cutoff frequency, and the second smoothing unit smooths the envelope with a low-pass filter having a second cutoff frequency lower than the first cutoff frequency. According to this embodiment, with a simple configuration, it is possible to detect events that occur in the very early stages of insulation degradation events (rare shorts, ground faults) of the stator coil. 【0057】 (4) Fourth Embodiment The fourth embodiment is that, in the first embodiment, the value of k is a real number of 2 or more. According to this embodiment, it is possible to reduce the frequency of false detections and reliably detect events that occur in the very early stages of insulation degradation events (rare shorts, ground faults) of the stator coil. 【0058】 (5) Fifth Embodiment The fifth embodiment of the first embodiment includes a current detection unit that detects the current of each phase of the three-phase motor and outputs a current detection signal. According to this embodiment, even existing three-phase motors can be easily accommodated and events that occur in the very early stages of insulation deterioration events (rare short circuits, ground faults) of the stator coils can be detected. 【0059】 (6) Sixth Embodiment The sixth embodiment of the stator abnormal current detection method comprises: a process of smoothing current detection signals corresponding to the currents of each phase of the stator coils of a three-phase motor to be abnormally detected, and outputting smoothed current signals; a process of detecting the envelope of the smoothed current signals; a process of smoothing the envelope in a first section and outputting a first smoothed envelope; a process of smoothing the envelope in a second section longer than the first section and outputting a second smoothed envelope; and a process of determining the difference between the first smoothed envelope and the second smoothed envelope, and detecting as an abnormal value a value in which the difference value falls outside the k × σ interval (k: a real number greater than 1) with respect to the standard deviation σ of the first smoothed envelope. According to this embodiment, it is possible to detect events that occur in the very early stages of insulation deterioration events (rare shorts, ground faults) of the stator coils, and to detect insulation deterioration of the stator coils at an early stage. 【0060】 (7) The seventh embodiment of the seventh embodiment comprises, in the sixth embodiment, a process of calculating a moving average over a first section on the envelope and smoothing the envelope, and a process of calculating a moving average over a second section longer than the first section on the envelope and smoothing the envelope. According to this embodiment, it is possible to detect events that occur in the very early stages of insulation degradation events (rare shorts, ground faults) of the stator coil with a simple process. 【0061】 (8) Eighth Embodiment The eighth embodiment is, in the sixth embodiment, smoothing of the envelope with a low-pass filter having a first cutoff frequency, and smoothing of the envelope with a low-pass filter having a second cutoff frequency lower than the first cutoff frequency. According to this embodiment, it is possible to detect events that occur in the very early stages of insulation degradation events (rare shorts, ground faults) of the stator coil with a simple configuration. 【0062】 (9) The ninth embodiment of the ninth embodiment is the sixth embodiment in which the value of k is a real number of 2 or more. According to this embodiment, it is possible to reduce the frequency of false detections and reliably detect events that occur in the very early stages of insulation degradation events (rare shorts, ground faults) of the stator coil. 【0063】 (10) The tenth embodiment of the tenth aspect is an electric motor comprising: a stator to which an AC power supply is provided; a rotor that rotates in electromagnetic coupling with the stator; a first-phase current detector that detects the first-phase current flowing through the stator from the AC power supply; a second-phase current detector that detects the second-phase current flowing through the stator from the AC power supply; a third-phase current detector that detects the third-phase current flowing through the stator from the AC power supply; and a stator abnormal current detection device as described in any one of (1) to (3). According to this aspect, even existing three-phase electric motors can be easily adapted to detect events that occur in the very early stages of insulation degradation events (rare short circuits, ground faults) of the stator coils. 【0064】10 Stator abnormal current detection system 11 Three-phase AC power supply 12 Three-phase motor 13 Stator abnormal current detection device 14U U-phase current detector (first phase current detector) 14V V-phase current detector (second phase current detector) 14W W-phase current detector (third phase current detector) 21 Current smoothing unit 22 Envelope detection unit 23 First smoothing unit 24 Second smoothing unit 25 Abnormal detection unit ENU Envelope IU U-phase current (first phase current) IV V-phase current (second phase current) IW W-phase current (third phase current) LU U-phase current line LV V-phase current line LW W-phase current line SENU1 First smoothed envelope SENU2 Second smoothed envelope SENV1 First smoothed envelope SENV2 Second smoothed envelope SIU U-phase current detection signal SIV V-phase current detection signal SIW W-phase current detection signal SSIU Smoothing current signal w1 First window width (first section) w2 Second window width (second section)

Claims

1. A stator abnormal current detection device comprising: a current smoothing unit that smooths current detection signals corresponding to the currents of each phase of the stator coils of a three-phase motor targeted for abnormal detection and outputs smoothed current signals; an envelope detection unit that detects the envelope of the smoothed current signals; a first smoothing unit that smooths the envelope in a first section and outputs a first smoothed envelope; a second smoothing unit that smooths the envelope in a second section longer than the first section and outputs a second smoothed envelope; and an abnormality detection unit that calculates the difference between the first smoothed envelope and the second smoothed envelope and detects as an abnormal value any value where the difference falls outside the k × σ interval (k: a real number greater than 1) with respect to the standard deviation σ of the first smoothed envelope.

2. The stator abnormal current detection device according to claim 1, wherein the first smoothing unit calculates a moving average over the first section with respect to the envelope and smooths the envelope, and the second smoothing unit calculates a moving average over the second section with respect to the envelope and smooths the envelope.

3. The stator abnormal current detection device according to claim 1, wherein the first smoothing unit smooths the envelope using a low-pass filter having a first cutoff frequency, and the second smoothing unit smooths the envelope using a low-pass filter having a second cutoff frequency lower than the first cutoff frequency.

4. The stator abnormal current detection device according to claim 1, wherein the value of k is a real number of 2 or more.

5. The stator abnormal current detection device according to claim 1, further comprising a current detection unit that detects the current of each phase of the three-phase motor and outputs a current detection signal.

6. A stator abnormal current detection method comprising: a process of smoothing current detection signals corresponding to the currents of each phase of the stator coils of a three-phase motor to be abnormally detected, and outputting smoothed current signals; a process of detecting the envelope of the smoothed current signals; a process of calculating a moving average over a first interval on the envelope, smoothing the envelope, and outputting a first smoothed envelope; a process of calculating a moving average over a second interval longer than the first interval on the envelope, smoothing the envelope, and outputting a second smoothed envelope; and a process of determining the difference between the first smoothed envelope and the second smoothed envelope, and detecting a value in which the difference falls outside the k × σ interval (k: a real number greater than 1) with respect to the standard deviation σ of the first smoothed envelope as an abnormal value.

7. An electric motor comprising: a stator to which an AC power supply is provided; a rotor that rotates in electromagnetic coupling with the stator; a first-phase current detector for detecting a first-phase current flowing through the stator from the AC power supply; a second-phase current detector for detecting a second-phase current flowing through the stator from the AC power supply; a third-phase current detector for detecting a third-phase current flowing through the stator from the AC power supply; and a stator abnormal current detection device according to any one of claims 1 to 5.

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