Control device, electrical equipment, and fault detection method

Abstract

The objective is to provide a control device that can detect partial discharges in distinction from noise. [Solution] The control device of the embodiment comprises a control unit and a fault detection unit. The control unit controls the electric motor. The fault detection unit detects faults in the electric motor. The fault detection unit performs frequency analysis of the voltage signal and current signal that drive the electric motor. Based on the results of the frequency analysis, the fault detection unit determines whether the current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the voltage signal. Based on the results of the frequency analysis, the fault detection unit determines whether the odd-order harmonics have a first phase angle that is in opposite phase to the phase angle of the fundamental wave.

Description

Technical Field

[0001] Embodiments of the present invention relate to a control device, an electrical device, and a fault detection method.

Background Art

[0002] When the insulation performance of an electric motor deteriorates, partial discharge, which is a precursor phenomenon of insulation breakdown, occurs. Detecting partial discharge helps prevent the occurrence of insulation breakdown in the electric motor. Since partial discharge is buried in the noise associated with the operation of the electric motor, it is necessary to detect partial discharge separately from the noise.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to detect partial discharge separately from noise.

Means for Solving the Problems

[0005] The control device of the embodiment includes a control unit and a fault detection unit. The control unit controls the electric motor. The fault detection unit detects a fault of the electric motor. The fault detection unit performs frequency analysis on a voltage signal and a current signal for driving the electric motor. The fault detection unit determines whether the current signal includes odd harmonics having a frequency that is an odd multiple of the fundamental wave of the voltage signal based on the result of the frequency analysis. The fault detection unit determines whether the odd harmonics have a first phase angle that is a phase angle opposite to the phase angle of the fundamental wave based on the result of the frequency analysis.

Brief Description of the Drawings

[0006] [Figure 1]A schematic diagram showing an example of the configuration of an electrical device according to the first embodiment. [Figure 2] A functional block diagram showing the function of the fault detection unit in the control device of the first embodiment. [Figure 3] A flowchart showing the fault detection process performed by the fault detection unit of the first embodiment. [Figure 4] A schematic diagram showing an example of the configuration of an electrical device according to the second embodiment. [Figure 5] A functional block diagram showing the function of the fault detection unit in the control device of the second embodiment. [Figure 6] A flowchart showing the fault detection process performed by the fault detection unit of the second embodiment. [Figure 7] This figure shows an example of a waveform when a partial discharge occurs in relation to a 50Hz power fundamental frequency. [Figure 8] This figure shows the waveform of the signal obtained by performing bandpass filtering and envelope filtering on the signal shown in Figure 7. [Figure 9] Figure 7 shows the frequency analysis results of a sinusoidal current signal including a partial discharge signal. [Figure 10] Figure 8 shows the frequency analysis results of the signal shown. [Figure 11] A diagram showing a discharge noise signal with a positive charge. [Figure 12] This figure shows the waveform of the signal obtained by performing bandpass filtering and envelope filtering on the signal shown in Figure 11. [Figure 13] Figure 11 shows the frequency analysis results of a sinusoidal current signal including the discharge noise signal. [Figure 14] Figure 12 shows the frequency analysis results of the signal shown. [Figure 15] This diagram shows the phase angles of each harmonic when a partial discharge signal is included in a sinusoidal current signal. [Figure 16] This diagram shows the phase angles of each harmonic when a discharge noise signal is included in a sinusoidal current signal. [Figure 17] A schematic diagram showing the first modified example of an electrical device. [Figure 18] A diagram schematically showing a second modification of an electric device.

Embodiments for Carrying Out the Invention

[0007] Hereinafter, a control device, an electric device, and a fault detection method according to embodiments will be described with reference to the drawings.

[0008] FIG. 1 is a diagram schematically showing a configuration example of an electric device 1 according to a first embodiment. In FIG. 1, the electric device 1 has a configuration for controlling a three-phase induction motor 11 using a three-phase AC power supply 10.

[0009] As shown in FIG. 1, the electric device 1 includes a three-phase AC power supply 10, a three-phase induction motor 11, a switch 15, a voltage sensor circuit 20, a voltage detection circuit 21, a current sensor circuit 22, a current detection circuit 23, and a control device 30. The three-phase AC power supply 10 is an example of a power supply. The three-phase induction motor 11 is an example of a motor.

[0010] The three-phase AC power supply 10 is connected to the three-phase induction motor 11 by a three-phase connection. The three-phase AC power supply 10 supplies a three-phase AC electrical signal including a U-phase, a V-phase, and a W-phase to the three-phase induction motor 11. The AC electrical signal supplied from the three-phase AC power supply 10 to the three-phase induction motor 11 is an electrical signal for driving the three-phase induction motor 11. The AC electrical signal includes an AC voltage signal and an AC current signal. These AC voltage signal and AC current signal are examples of a voltage signal and a current signal for driving the motor. Note that the three-phase AC power supply 10 may be a component external to the electric device 1.

[0011] The three-phase induction motor 11 is driven by an AC electrical signal from the three-phase AC power supply 10. The three-phase induction motor 11 receives a three-phase AC electrical signal via a three-phase connection and is driven. The three-phase induction motor 11 generates mechanical energy by an AC electrical signal from the three-phase AC power supply 10. For example, the output shaft of the three-phase induction motor 11 is connected to a load device (not shown) and a driving device (not shown).

[0012] The switch 15 is provided between the three-phase AC power supply 10 and the three-phase induction motor 11. The switch 15 controls the supply of the AC electrical signal from the three-phase AC power supply 10 to the three-phase induction motor 11 according to the control from the control device 30. For example, when a failure of the three-phase induction motor 11 is detected, the switch 15 cuts off the supply of the AC electrical signal from the three-phase AC power supply 10 to the three-phase induction motor 11.

[0013] The voltage sensor circuit 20 is connected to the three-phase connection. The voltage sensor circuit 20 senses the voltage supplied to the wiring of each phase forming the three-phase connection. For example, the voltage sensor circuit 20 includes a voltage sensor such as a voltage transformer (VT) as a voltage sensor for detecting the voltage of each phase.

[0014] The voltage detection circuit 21 is connected to the voltage sensor circuit 20. The voltage detection circuit 21 receives a voltage signal corresponding to the sensing result of the voltage of each phase by the voltage sensor circuit 20. The voltage detection circuit 21 detects the voltage state of each phase of the three-phase connection based on the sensing result of the voltage sensor circuit 20. The voltage detection circuit 21 has a function of converting the signal from the voltage sensor circuit 20 into a signal corresponding to the input voltage of the ADC310 of the control device 30 described later.

[0015] The current sensor circuit 22 is connected to the three-phase connection. The current sensor circuit 22 senses the current (phase current) flowing through the wiring of each phase forming the three-phase connection. For example, the current sensor circuit 22 includes a current sensor such as a current transformer (CT) as a current sensor for detecting the phase current.

[0016] The current detection circuit 23 is connected to the current sensor circuit 22. The current detection circuit 23 receives a signal corresponding to the sensing result of the current of each phase by the current sensor circuit 22. The current detection circuit 23 detects the current state of each phase of the three-phase connection based on the sensing result of the current sensor circuit 22. The current detection circuit 23 has a function of performing voltage conversion or impedance matching in order to apply the signal from the current sensor circuit 22 to the input of the ADC310 described later.

[0017] The control device 30 controls the internal operation of the electrical equipment 1. In the electrical equipment 1 of this embodiment, the control device 30 includes an ADC (analog-to-digital converter) 310, a fault detection unit 320, and a control unit 340, etc.

[0018] The ADC310 converts various analog signals (analog values) detected within the electrical equipment 1 into digital signals (digital values). For example, the ADC310 converts signals from the voltage detection circuit 21 and signals from the current detection circuit 23 into digital signals. The signal input to the ADC310 from the voltage detection circuit 21 is substantially the same as the AC voltage signal included in the AC electrical signal that drives the three-phase induction motor 11. Similarly, the signal input to the ADC310 from the current detection circuit 23 is substantially the same as the AC current signal included in the AC electrical signal that drives the three-phase induction motor 11. Therefore, it can be said that the ADC310 converts the AC voltage signal and AC current signal that drives the three-phase induction motor 11 into digital signals.

[0019] The fault detection unit (also called a fault detection circuit) 320 detects malfunctions in the electrical equipment 1, such as a fault in the three-phase induction motor 11 or a failure in the three-phase AC power supply 10, based on various signals detected within the electrical equipment 1.

[0020] The control unit (also called a control circuit) 340 monitors the operating status of each component within the electrical equipment 1 and controls the operation of each component. The control unit 340 controls the function and processing of the fault detection unit 320. The control unit 340 is, for example, a processor.

[0021] The control device 30 may further include a memory 390. The memory 390 stores various types of data. For example, the memory 390 stores digital data indicating the sensing results of the AC voltage signal and AC current signal included in the AC electrical signal that drives the three-phase induction motor 11, and programs (software and applications) for controlling the three-phase induction motor 11.

[0022] The electrical equipment 1 in this embodiment uses a three-phase AC power supply 10 as its driving source. The electrical equipment 1 senses the AC electrical signals supplied from the three-phase AC power supply 10 to the three-phase induction motor 11 and controls the rotation of the three-phase induction motor 11 using a control device 30.

[0023] For example, if a fault such as overcurrent, short circuit, or ground fault occurs in the three-phase induction motor 11, the electrical equipment 1 will, based on instructions from the control device 30, cut off the supply of AC electrical signals from the three-phase AC power supply 10 to the three-phase induction motor 11 using the switch 15. For example, if there is an abnormality in the three-phase AC power supply 10 such as phase loss, unbalance, dip, or swell, the electrical equipment 1 will protect the three-phase induction motor 11 by cutting off the switch 15 based on instructions from the control device 30.

[0024] In this embodiment, the electrical device 1 communicates with a higher-level device 9, such as a PLC (Programmable Logic Controller). The higher-level device 9 communicates with the control devices 30 of multiple electrical devices 1. Based on the results of the communication, the higher-level device 9 monitors the operating status of the electrical devices 1. For example, the higher-level device 9 monitors periodic power consumption and status signals obtained in real time from the fault detection unit 320. Through this, the higher-level device 9 understands the status of the three-phase induction motor 11 and the load device (not shown) in the electrical device 1.

[0025] Figure 2 is a functional block diagram showing the functions of the fault detection unit 320 in the control device 30 of the first embodiment. Note that Figure 2 shows an example of the configuration of the signal calculator for one phase of the three-phase system's AC electrical signal. Substantially the same calculations are performed for the AC electrical signals of the other phases.

[0026] The fault detection unit 320 includes one or more arithmetic units (processors) composed of a microcontroller unit (MCU) or an ASIC (application-specific integrated circuit) within the control device 30. The fault detection unit 320 can utilize the data and programs in the memory 390.

[0027] As shown in Figure 2, the fault detection unit 320 includes, as functional blocks, a first LPF (Low Pass Filter) 321, a first FFT (Fast Fourier Transform) calculator 322, a first amplitude calculator 323, a first phase angle calculator 324, a second LPF 325, a second FFT calculator 326, a second amplitude calculator 327, a second phase angle calculator 328, and an analyzer 329. The functions of the fault detection unit 320 represented by these functional blocks may be functions implemented by hardware, or functions implemented by one or more processors executing programs.

[0028] As already explained, the ADC310 converts the AC voltage signal and AC current signal that drive the three-phase induction motor 11 into digital signals. In the following explanation, the AC voltage signal converted into a digital signal may be referred to as the "first voltage signal V1," and the AC current signal converted into a digital signal may be referred to as the "first current signal C1." The first voltage signal V1 is input to the first LPF321. The first current signal C1 is input to the second LPF325.

[0029] The first LPF321 is a digital low-pass filter that extracts a second voltage signal V2, which contains frequency components below the first cutoff frequency, from the first voltage signal V1. The first LPF321 outputs the second voltage signal V2 to the first FFT calculator 322.

[0030] The second LPF325 is a digital low-pass filter that extracts a second current signal C2 from the first current signal C1, which is a signal containing frequency components below the second cutoff frequency. The second LPF325 outputs the second current signal C2 to the second FFT calculator 326. The second cutoff frequency may be the same as or different from the first cutoff frequency.

[0031] The first LPF321 and the second LPF325 limit the bandwidth of the AC electrical signal processed within the fault detection unit 320 to the bandwidth required for monitoring the state of the three-phase induction motor 11. This makes it possible to block harmonic noise and disturbance noise contained in the AC electrical signal driving the three-phase induction motor 11. In addition, decimation filters may be used as the first LPF321 and the second LPF325 to improve the signal-to-noise ratio of the AC electrical signal processed within the fault detection unit 320.

[0032] The first FFT calculator 322 performs a Fast Fourier Transform based on the second voltage signal V2 output from the first LPF 321. As a result of the Fast Fourier Transform based on the second voltage signal V2, the first FFT calculator 322 generates a list showing the correspondence between the frequencies of multiple sine waves contained in the second voltage signal V2 and the complex numbers that represent these sine waves in polar coordinate form. In the following description, the list generated by the first FFT calculator 322 may be referred to as the "first frequency list L1". The first FFT calculator 322 outputs the first frequency list L1 to the first amplitude calculator 323 and the first phase angle calculator 324.

[0033] The second FFT calculator 326 performs a Fast Fourier Transform based on the second current signal C2 output from the second LPF 325. As a result of the Fast Fourier Transform based on the second current signal C2, the second FFT calculator 326 generates a list showing the correspondence between the frequencies of multiple sine waves contained in the second current signal C2 and the complex numbers that represent these sine waves in polar coordinate form. In the following description, the list generated by the second FFT calculator 326 may be referred to as the "second frequency list L2". The second FFT calculator 326 outputs the second frequency list L2 to the second amplitude calculator 327 and the second phase angle calculator 328.

[0034] The first FFT calculator 322 and the second FFT calculator 326 can be implemented by software or by hardware accelerators. When the three-phase induction motor 11 is driven at commercial frequency, it is desirable to acquire AC electrical signals with 10 to 12 cycles and perform the Fast Fourier Transform.

[0035] The first amplitude calculator 323 calculates the amplitude of each sine wave contained in the second voltage signal V2 based on the first frequency list L1 output from the first FFT calculator 322. As is well known, the amplitude of a sine wave can be calculated by calculating the square root of the sum of the squares of the real and imaginary parts contained in a complex number. The first amplitude calculator 323 outputs the first amplitude list L3 to the analyzer 329, which is a list showing the correspondence between the frequency of each sine wave contained in the second voltage signal V2 and the amplitude of each sine wave.

[0036] The first phase angle calculator 324 calculates the phase angle of each sine wave included in the second voltage signal V2 based on the first frequency list L1 output from the first FFT calculator 322. As is well known, the phase angle of a sine wave can be calculated by calculating the arctangent using the real and imaginary parts included in a complex number. The first phase angle calculator 324 outputs the first phase angle list L4 to the analyzer 329, which is a list showing the correspondence between the frequency of each sine wave included in the second voltage signal V2 and the phase angle of each sine wave.

[0037] The second amplitude calculator 327 calculates the amplitude of each sine wave included in the second current signal C2 based on the second frequency list L2 output from the second FFT calculator 326. The second amplitude calculator 327 outputs a second amplitude list L5 to the analyzer 329, which is a list showing the correspondence between the frequency of each sine wave included in the second current signal C2 and the amplitude of each sine wave.

[0038] The second phase angle calculator 328 calculates the phase angle of each sine wave included in the second current signal C2 based on the second frequency list L2 output from the second FFT calculator 326. The second phase angle calculator 328 outputs a second phase angle list L6 to the analyzer 329, which is a list showing the correspondence between the frequency of each sine wave included in the second current signal C2 and the phase angle of each sine wave.

[0039] The first LPF 321, first FFT calculator 322, first amplitude calculator 323, first phase angle calculator 324, second LPF 325, second FFT calculator 326, second amplitude calculator 327, and second phase angle calculator 328 are functions of the fault detection unit 320 that perform frequency analysis of the AC voltage signal and AC current signal that drive the three-phase induction motor 11. The first amplitude list L3, first phase angle list L4, second amplitude list L5, and second phase angle list L6 are the results of the frequency analysis of the AC voltage signal and AC current signal. In the following description, the first amplitude list L3, first phase angle list L4, second amplitude list L5, and second phase angle list L6 may be referred to as the "first analysis results".

[0040] The analyzer 329 analyzes the state of the three-phase induction motor 11 based on the first analysis result. More specifically, the analyzer 329 determines, based on the first analysis result, whether the AC current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental frequency of the AC voltage signal. For example, in this embodiment, the odd-order harmonics are third-order harmonics having frequencies that are three times the fundamental frequency of the AC voltage signal. For example, the analyzer 329 obtains the frequency associated with the largest amplitude in the first amplitude list L3 as the frequency of the fundamental frequency of the AC voltage signal. Then, in the second amplitude list L5, the analyzer 329 determines that the AC current signal contains third-order harmonics if the amplitude associated with the frequency that is three times the frequency of the fundamental frequency of the AC voltage signal is greater than or equal to a predetermined threshold.

[0041] Furthermore, based on the first analysis result, the analyzer 329 determines whether the odd-order harmonics (third harmonic) included in the AC current signal have a first phase angle, which is a phase angle opposite to the phase angle of the fundamental wave of the AC voltage signal. For example, in this embodiment, the first phase angle is a phase angle of ±90 degrees or more relative to the phase angle of the fundamental wave. For example, the analyzer 329 obtains the phase angle associated with the frequency of the fundamental wave in the first phase angle list L4 as the phase angle of the fundamental wave. Then, in the second phase angle list L6, the analyzer 329 determines that the odd-order harmonics (third harmonic) included in the AC current signal have a first phase angle if the phase angle associated with the frequency three times the frequency of the fundamental wave is a phase angle of ±90 degrees or more relative to the phase angle of the fundamental wave.

[0042] The analyzer 329 outputs a partial discharge detection signal D1 indicating that partial discharge has been detected in the three-phase induction motor 11 when an odd-order harmonic (third harmonic) included in the AC current signal has a first phase angle. The analyzer 329 outputs a noise detection signal D2 indicating that disturbance noise has been detected when the AC current signal does not contain odd-order harmonics or when the odd-order harmonics do not have a first phase angle.

[0043] When a partial discharge occurs in the three-phase induction motor 11, the signal generated due to the partial discharge appears as an odd-order harmonic among the harmonics included in the AC current signal, having a frequency that is an odd multiple of the fundamental wave of the AC voltage signal. Therefore, if the AC current signal contains odd-order harmonics, it can be inferred that a partial discharge has occurred in the three-phase induction motor 11. However, when odd-order harmonic noise generated due to mechanical vibration or odd-order harmonic noise generated from the three-phase AC power supply 10 is mixed into the AC current signal, it is not possible to distinguish whether the odd-order harmonics included in the AC current signal are harmonics caused by the partial discharge or harmonics caused by the aforementioned external disturbance noise. Therefore, in this embodiment, the fault detection unit 320 is provided with a function to determine whether or not the odd-order harmonics included in the AC current signal have a first phase angle, which is a phase angle opposite to the phase angle of the fundamental wave of the AC voltage signal. When a partial discharge occurs in the three-phase induction motor 11, the signal generated due to the partial discharge appears as an odd-order harmonic having a first phase angle that is inversely phase to the phase angle of the fundamental wave of the AC voltage signal. Therefore, the fault detection unit 320 can detect the partial discharge by determining not only whether the AC current signal contains odd-order harmonics, but also whether the odd-order harmonics contained in the AC current signal have a first phase angle, thereby distinguishing it from the aforementioned disturbance noise.

[0044] Figure 3 is a flowchart showing the fault detection process performed by the fault detection unit 320. The fault detection process described below can be implemented by hardware, software, or a combination of hardware and software. Furthermore, the fault detection method of this embodiment is realized when the fault detection unit 320 performs the fault detection process.

[0045] As shown in Figure 3, the fault detection unit 320 performs frequency analysis of the AC voltage signal and AC current signal that drive the three-phase induction motor 11 (step S1). Specifically, in step S1, the fault detection unit 320 performs the following processing.

[0046] The fault detection unit 320 extracts a second voltage signal V2, which contains frequency components below the first cutoff frequency, from a first voltage signal V1, which is an AC voltage signal converted into a digital signal. The fault detection unit 320 also extracts a second current signal C2, which contains frequency components below the second cutoff frequency, from a first current signal C1, which is an AC current signal converted into a digital signal.

[0047] The fault detection unit 320 generates a first frequency list L1 that shows the correspondence between the frequencies of multiple sine waves contained in the second voltage signal V2 and the complex numbers that represent these sine waves in polar coordinate form, by performing a fast Fourier transform based on the second voltage signal V2.

[0048] The fault detection unit 320 generates a second frequency list L2 that shows the correspondence between the frequencies of multiple sine waves contained in the second current signal C2 and the complex numbers that represent these sine waves in polar coordinate form, by performing a fast Fourier transform based on the second current signal C2.

[0049] The fault detection unit 320 calculates the amplitude of each sine wave included in the second voltage signal V2 based on the first frequency list L1, and generates a first amplitude list L3 that shows the correspondence between the frequency of each sine wave included in the second voltage signal V2 and the amplitude of each sine wave.

[0050] The fault detection unit 320 calculates the phase angle of each sine wave included in the second voltage signal V2 based on the first frequency list L1, and generates a first phase angle list L4 that shows the correspondence between the frequency of each sine wave included in the second voltage signal V2 and the phase angle of each sine wave.

[0051] The fault detection unit 320 calculates the amplitude of each sine wave included in the second current signal C2 based on the second frequency list L2, and generates a second amplitude list L5 that shows the correspondence between the frequency of each sine wave included in the second current signal C2 and the amplitude of each sine wave.

[0052] The fault detection unit 320 calculates the phase angle of each sine wave included in the second current signal C2 based on the second frequency list L2, and generates a second phase angle list L6 that shows the correspondence between the frequency of each sine wave included in the second current signal C2 and the phase angle of each sine wave.

[0053] The process in step S1 described above is the same as the process performed by the first LPF 321, the first FFT calculator 322, the first amplitude calculator 323, the first phase angle calculator 324, the second LPF 325, the second FFT calculator 326, the second amplitude calculator 327, and the second phase angle calculator 328, so it will not be explained in detail here. By performing the process in step S1 described above, the fault detection unit 320 obtains the first amplitude list L3, the first phase angle list L4, the second amplitude list L5, and the second phase angle list L6 as the first analysis results.

[0054] Next, the fault detection unit 320 determines, based on the first analysis result, whether the AC current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the AC voltage signal (step S2). As already explained, as an example, in this embodiment, the odd-order harmonics are third-order harmonics having frequencies that are three times the fundamental wave of the AC voltage signal.

[0055] If the AC current signal contains odd-order harmonics (step S2: YES), the fault detection unit 320 determines, based on the first analysis result, whether the odd-order harmonics (third harmonic) contained in the AC current signal have a first phase angle which is the opposite phase angle to the phase angle of the fundamental wave of the AC voltage signal (step S3). As already explained, as an example, in this embodiment, the first phase angle is a phase angle of ±90 degrees or more with respect to the phase angle of the fundamental wave.

[0056] Then, if the fault detection unit 320 detects that an odd-order harmonic (third harmonic) included in the AC current signal has a first phase angle (step S3: YES), it outputs a partial discharge detection signal D1 indicating that a partial discharge has been detected in the three-phase induction motor 11 (step S4).

[0057] On the other hand, if the AC current signal does not contain odd-order harmonics (step S2: NO), the fault detection unit 320 outputs a noise detection signal D2 indicating that disturbance noise has been detected (step S5). Also, even if the AC current signal contains odd-order harmonics, if the odd-order harmonics do not have a first phase angle (step S3: NO), the fault detection unit 320 outputs a noise detection signal D2 (step S5). The processing from steps S2 to S5 is the same as the processing performed by the analyzer 329, so it will not be explained in detail here.

[0058] As described above, the control device 30 of the first embodiment includes a control unit 340 and a fault detection unit 320. The control unit 340 controls the three-phase induction motor 11. The fault detection unit 320 detects faults in the three-phase induction motor 11. The fault detection unit 320 performs frequency analysis of the AC voltage signal and AC current signal that drive the three-phase induction motor 11. Based on the first analysis result, the fault detection unit 320 determines whether the AC current signal contains odd-order harmonics (third harmonic) having frequencies that are odd multiples of the fundamental wave of the AC voltage signal. Based on the first analysis result, the fault detection unit 320 determines whether the odd-order harmonics included in the AC current signal have a first phase angle which is a phase angle that is inverse phase with respect to the phase angle of the fundamental wave. According to the control device 30 of the first embodiment described above, the fault detection unit 320 not only determines whether the AC current signal contains odd-order harmonics, but also determines whether the odd-order harmonics contained in the AC current signal have a first phase angle, thereby enabling the detection of partial discharge in distinction from odd-order harmonic noise mixed into the AC current signal.

[0059] The fault detection method includes: performing frequency analysis of the AC voltage signal and AC current signal driving the three-phase induction motor 11 (step S1); determining, based on the first analysis result, whether the AC current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the AC voltage signal (step S2); and determining, based on the first analysis result, whether the odd-order harmonics contained in the AC current signal have a first phase angle that is inverse phase with respect to the phase angle of the fundamental wave (step S3). According to the fault detection method described above, it is possible to detect partial discharges by distinguishing them from odd-order harmonic noise mixed into the AC current signal, not only by determining whether or not the AC current signal contains odd-order harmonics, but also by determining whether or not the odd-order harmonics contained in the AC current signal have a first phase angle.

[0060] Figure 4 is a schematic diagram showing an example of the configuration of the electrical equipment 1 of the second embodiment. The electrical equipment 1 of the second embodiment differs from the electrical equipment 1 of the first embodiment in that the control device 30 is equipped with a fault detection unit 320A that has additional functions to the fault detection unit 320. Accordingly, the fault detection unit 320A, which is a difference from the first embodiment, will be explained in detail below, and other components will be given the same reference numerals as in the first embodiment, and their explanations will be omitted or simplified.

[0061] Figure 5 is a functional block diagram showing the function of the fault detection unit 320A in the control device 30 of the second embodiment. Note that Figure 5 shows an example of the configuration of the signal calculator for one phase of the AC electrical signal in a three-phase system. Substantially the same calculations are performed for the AC electrical signals of the other phases.

[0062] Similar to the fault detection unit 320 of the first embodiment, the fault detection unit 320A of the second embodiment includes one or more arithmetic units (processors) configured by a microcontroller unit (MCU) or ASIC within the control device 30. The fault detection unit 320A can utilize data and programs in the memory 390.

[0063] As shown in Figure 5, the fault detection unit 320A includes a first LPF 321, a first FFT calculator 322, a first amplitude calculator 323, a first phase angle calculator 324, a second LPF 325, a second FFT calculator 326, a second amplitude calculator 327, and a second phase angle calculator 328 as functional blocks. These functional blocks are the same as those in the first embodiment, so their description is omitted.

[0064] The fault detection unit 320A further includes a Band Pass Filter (BPF) 330, an envelope processor 331, a third FFT calculator 332, a third amplitude calculator 333, and a third phase angle calculator 334 as functional blocks. The fault detection unit 320A also includes an analyzer 329A as a functional block, which is an analyzer 329 with additional functions added. The functions of the fault detection unit 320A represented by these functional blocks may be functions implemented by hardware, or functions implemented by one or more processors executing programs.

[0065] In the fault detection unit 320A, the first current signal C1, which is an AC current signal converted into a digital signal, is input not only to the second LPF 325 but also to the BPF 330. The BPF 330 is a digital bandpass filter that extracts a third current signal C3 of the first frequency band from the first current signal C1. As an example, in this embodiment, a BPF 330 with a center frequency of around 100 kHz is used to acquire a low-frequency partial discharge waveform. The BPF 330 outputs the third current signal C3 to the envelope processor 331. The third current signal C3 is an example of the first signal.

[0066] The envelope processor 331 generates a fourth current signal C4 by performing envelope processing on the third current signal C3 output from the BPF 330. The envelope processor 331 outputs the fourth current signal C4 to the third FFT calculator 332. The fourth current signal C4 is an example of the second signal.

[0067] The third FFT calculator 332 performs a Fast Fourier Transform based on the fourth current signal C4 output from the envelope processor 331. As a result of the Fast Fourier Transform based on the fourth current signal C4, the third FFT calculator 332 generates a list showing the correspondence between the frequencies of multiple sine waves contained in the fourth current signal C4 and the complex numbers that represent these sine waves in polar coordinate form. In the following description, the list generated by the third FFT calculator 332 may be referred to as the "third frequency list L7". The third FFT calculator 332 outputs the third frequency list L7 to the third amplitude calculator 333 and the third phase angle calculator 334.

[0068] The third amplitude calculator 333 calculates the amplitude of each sine wave included in the fourth current signal C4 based on the third frequency list L7 output from the third FFT calculator 332. The third amplitude calculator 333 outputs the third amplitude list L8 to the analyzer 329A, which is a list showing the correspondence between the frequency of each sine wave included in the fourth current signal C4 and the amplitude of each sine wave.

[0069] The third phase angle calculator 334 calculates the phase angle of each sine wave included in the fourth current signal C4 based on the third frequency list L7 output from the third FFT calculator 332. The third phase angle calculator 334 outputs the third phase angle list L9 to the analyzer 329A, which is a list showing the correspondence between the frequency of each sine wave included in the fourth current signal C4 and the phase angle of each sine wave.

[0070] The third FFT calculator 332, the third amplitude calculator 333, and the third phase angle calculator 334 are functions of the fault detection unit 320A that perform frequency analysis of the fourth current signal C4 (second signal). The third amplitude list L8 and the third phase angle list L9 are the results of the frequency analysis of the fourth current signal C4. In the following description, the third amplitude list L8 and the third phase angle list L9 may be referred to as the "second analysis results."

[0071] The analyzer 329A analyzes the state of the three-phase induction motor 11 based on the first and second analysis results. More specifically, similar to the analyzer 329 in the first embodiment, the analyzer 329A determines, based on the first analysis result, whether the AC current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the AC voltage signal. As an example, in this embodiment, the odd-order harmonics are third-order harmonics having a frequency three times that of the fundamental wave of the AC voltage signal.

[0072] Furthermore, similar to the analyzer 329 of the first embodiment, the analyzer 329A determines, based on the first analysis result, whether the odd-order harmonics (third-order harmonics) included in the AC current signal have a first phase angle which is the opposite phase angle to the phase angle of the fundamental wave of the AC voltage signal. As an example, the first phase angle in this embodiment is a phase angle of ±90 degrees or more with respect to the phase angle of the fundamental wave.

[0073] Based on the second analysis result, analyzer 329A determines whether the fourth current signal C4 contains even-order harmonics having frequencies that are even multiples of the fundamental frequency of the AC voltage signal. For example, in this embodiment, an even-order harmonic is a second-order harmonic having a frequency twice that of the fundamental frequency of the AC voltage signal. For instance, analyzer 329A determines that the fourth current signal C4 contains a second-order harmonic if, in the third amplitude list L8, the amplitude associated with a frequency twice that of the fundamental frequency of the AC voltage signal is greater than or equal to a predetermined threshold.

[0074] Based on the second analysis result, analyzer 329A determines whether the even-order harmonic (second harmonic) contained in the fourth current signal C4 has a second phase angle, which is a phase angle that is in phase with respect to the phase angle of the fundamental wave of the AC voltage signal. For example, in this embodiment, the second phase angle is a phase angle of less than ±90 degrees with respect to the phase angle of the fundamental wave. For example, analyzer 329A determines that the even-order harmonic (second harmonic) contained in the fourth current signal C4 has a second phase angle if, in the third phase angle list L9, the phase angle associated with twice the frequency of the fundamental wave is a phase angle of less than ±90 degrees with respect to the phase angle of the fundamental wave.

[0075] The analyzer 329A outputs a partial discharge detection signal D1 indicating that partial discharge has been detected in the three-phase induction motor 11 when an odd-order harmonic (third harmonic) in the AC current signal has a first phase angle and an even-order harmonic (second harmonic) in the fourth current signal C4 has a second phase angle. In all other cases, the analyzer 329A outputs a noise detection signal D2 indicating that disturbance noise has been detected.

[0076] Similar to the first embodiment, the fault detection unit 320A not only determines whether the AC current signal contains odd-order harmonics, but also whether the odd-order harmonics contained in the AC current signal have a first phase angle, thereby enabling the detection of partial discharge in distinction from odd-order harmonic noise mixed into the AC current signal. However, when odd-order harmonic noise with a first phase angle is mixed into the AC current signal, it is not possible to distinguish whether the odd-order harmonics contained in the AC current signal are harmonics caused by partial discharge or harmonics caused by the above-mentioned disturbance noise. Therefore, in this embodiment, the fault detection unit 320A is equipped with a function to determine whether the even-order harmonics contained in the fourth current signal C4 (second signal), obtained by performing bandpass filtering and envelope processing on the AC current signal, have a second phase angle, which is a phase angle in phase with the phase angle of the fundamental wave of the AC voltage signal. When a partial discharge occurs in the three-phase induction motor 11, the signal generated due to the partial discharge appears in the fourth current signal C4 as an even-order harmonic having a second phase angle that is in phase with the fundamental wave of the AC voltage signal. Therefore, the fault detection unit 320A can detect the partial discharge by determining not only whether the odd-order harmonic (third harmonic) included in the AC current signal has a first phase angle, but also whether the even-order harmonic (second harmonic) included in the fourth current signal C4 has a second phase angle, thereby distinguishing it from the aforementioned disturbance noise.

[0077] Figure 6 is a flowchart showing the fault detection process performed by the fault detection unit 320A. The fault detection process described below can be implemented by hardware, software, or a combination of both.

[0078] As shown in Figure 6, the fault detection unit 320A performs frequency analysis of the AC voltage signal and AC current signal that drive the three-phase induction motor 11 (step S11). The processing performed by the fault detection unit 320A in step S11 is the same as the processing performed by the fault detection unit 320 in step S1 of the first embodiment, so a detailed explanation of the processing in step S11 will be omitted. By performing the processing in step S11, the fault detection unit 320A obtains a first amplitude list L3, a first phase angle list L4, a second amplitude list L5, and a second phase angle list L6 as first analysis results.

[0079] Next, the fault detection unit 320A extracts a third current signal C3 (first signal) in the first frequency band from the first current signal C1, which is an AC current signal converted into a digital signal (step S12). The process in step S12 is the same as the process performed by the BPF 330, so it will not be explained in detail here.

[0080] Next, the fault detection unit 320A generates a fourth current signal C4 (second signal) by performing envelope processing on the third current signal C3 (step S13). The processing in step S13 is the same as the processing performed by the envelope processor 331, so it will not be explained in detail here.

[0081] Next, the fault detection unit 320A performs frequency analysis of the fourth current signal C4 (second signal) (step S14). Specifically, in step S14, the fault detection unit 320A performs the following processing.

[0082] The fault detection unit 320A generates a third frequency list L7, which shows the correspondence between the frequencies of multiple sine waves contained in the fourth current signal C4 and the complex numbers that represent these sine waves in polar coordinate form, by performing a fast Fourier transform based on the fourth current signal C4.

[0083] The fault detection unit 320A calculates the amplitude of each sine wave included in the fourth current signal C4 based on the third frequency list L7, and generates a third amplitude list L8 that shows the correspondence between the frequency of each sine wave included in the fourth current signal C4 and the amplitude of each sine wave.

[0084] The fault detection unit 320A calculates the phase angle of each sine wave included in the fourth current signal C4 based on the third frequency list L7, and generates a third phase angle list L9 that shows the correspondence between the frequency of each sine wave included in the fourth current signal C4 and the phase angle of each sine wave.

[0085] The process in step S14 described above is the same as the process performed by the third FFT calculator 332, the third amplitude calculator 333, and the third phase angle calculator 334, so it will not be explained in detail here. By performing the process in step S14 described above, the fault detection unit 320A obtains the third amplitude list L8 and the third phase angle list L9 as the second analysis results.

[0086] Next, the fault detection unit 320A determines, based on the first analysis result, whether the AC current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the AC voltage signal (step S15). As already explained, as an example, in this embodiment, the odd-order harmonics are third-order harmonics having frequencies that are three times the fundamental wave of the AC voltage signal.

[0087] If the AC current signal contains odd-order harmonics (step S15: YES), the fault detection unit 320A determines, based on the first analysis result, whether the odd-order harmonics (third harmonic) contained in the AC current signal have a first phase angle which is the opposite phase angle to the phase angle of the fundamental wave of the AC voltage signal (step S16). As already explained, as an example, in this embodiment, the first phase angle is a phase angle of ±90 degrees or more with respect to the phase angle of the fundamental wave.

[0088] If the odd-order harmonics (third harmonic) included in the AC current signal have a first phase angle (step S16: YES), the fault detection unit 320A determines, based on the second analysis result, whether the fourth current signal C4 (second signal) includes even-order harmonics having an even multiple frequency of the fundamental wave of the AC voltage signal (step S17). As already explained, as an example, in this embodiment, the even-order harmonics are second-order harmonics having twice the frequency of the fundamental wave of the AC voltage signal.

[0089] If the fourth current signal C4 contains even-order harmonics (step S17: YES), the fault detection unit 320A determines, based on the second analysis result, whether the even-order harmonics (second harmonic) contained in the fourth current signal C4 have a second phase angle that is in phase with respect to the phase angle of the fundamental wave of the AC voltage signal (step S18). As already explained, as an example, in this embodiment, the second phase angle is a phase angle of less than ±90 degrees with respect to the phase angle of the fundamental wave.

[0090] Then, if the even-order harmonic (second harmonic) included in the fourth current signal C4 has a second phase angle (step S18: YES), the fault detection unit 320A outputs a partial discharge detection signal D1 indicating that partial discharge has been detected in the three-phase induction motor 11 (step S19).

[0091] On the other hand, if the AC current signal does not contain odd-order harmonics (step S15: NO), the fault detection unit 320A outputs a noise detection signal D2 (step S20). Also, even if the AC current signal contains odd-order harmonics, if the odd-order harmonics do not have a first phase angle (step S16: NO), the fault detection unit 320A outputs a noise detection signal D2 (step S20). Also, even if the AC current signal contains odd-order harmonics that have a first phase angle, if the fourth current signal C4 does not contain even-order harmonics (step S17: NO), the fault detection unit 320A outputs a noise detection signal D2 (step S20). Furthermore, even if the AC current signal contains odd-order harmonics with a first phase angle, and the fourth current signal C4 contains even-order harmonics, if the even-order harmonics do not have a second phase angle (step S18: NO), the fault detection unit 320A outputs a noise detection signal D2 (step S20). The processing from steps S15 to S20 is the same as the processing performed by the analyzer 329A, so it will not be explained in detail here.

[0092] As described above, the control device 30 of the second embodiment includes a control unit 340 and a fault detection unit 320A. The control unit 340 controls the three-phase induction motor 11. The fault detection unit 320A detects faults in the three-phase induction motor 11. The fault detection unit 320A performs frequency analysis of the AC voltage signal and AC current signal that drive the three-phase induction motor 11. Based on the first analysis result, the fault detection unit 320A determines whether the AC current signal contains odd-order harmonics (third harmonic) having frequencies that are odd multiples of the fundamental wave of the AC voltage signal. Based on the first analysis result, the fault detection unit 320A determines whether the odd-order harmonics included in the AC current signal have a first phase angle which is a phase angle that is inversely phase to the phase angle of the fundamental wave. Furthermore, the fault detection unit 320A extracts a first signal (third current signal C3) in a first frequency band from the AC current signal. The fault detection unit 320A generates a second signal (fourth current signal C4) by performing envelope processing on the first signal. The fault detection unit 320A performs frequency analysis on the second signal. Based on the second analysis results, the fault detection unit 320A determines whether the second signal contains even-order harmonics having even multiples of the fundamental wave frequency. Based on the second analysis results, the fault detection unit 320A determines whether the even-order harmonics included in the second signal have a second phase angle that is in phase with the phase angle of the fundamental wave. According to the second embodiment described above, the fault detection unit 320A not only determines whether the odd-order harmonics (third harmonic) included in the AC current signal have a first phase angle, but also determines whether the even-order harmonics (second harmonic) included in the second signal (fourth current signal C4) have a second phase angle, thereby enabling the detection of partial discharge in distinction from odd-order harmonic noise that has a first phase angle.

[0093] Figures 7 to 16 show the results of analysis using simulation waveforms to clarify the effects of the above embodiment. Figure 7 shows an example of a waveform in which partial discharge occurs with respect to a 50 Hz power fundamental wave. The partial discharge waveform simulates a phenomenon in which a partial discharge occurs mainly at positions of 45 degrees and 225 degrees relative to the phase of the power fundamental wave, with a half-width of several microseconds. Figure 8 shows the waveform of the signal obtained by performing bandpass filtering and envelope processing on the signal shown in Figure 7.

[0094] Figure 9 shows the frequency analysis results of a sinusoidal current signal including the partial discharge signal shown in Figure 7. Figure 10 shows the frequency analysis results of the signal shown in Figure 8. As shown in Figure 9, the partial discharge signal appears as odd-order harmonics such as the 3rd and 5th harmonics with respect to the power supply fundamental frequency (50 Hz). On the other hand, as shown in Figure 10, in the signal obtained by bandpass filtering and envelope processing on the sinusoidal current signal, the partial discharge signal appears as even-order harmonics such as the 2nd and 4th harmonics with respect to the power supply fundamental frequency.

[0095] To compare the state of the sinusoidal current waveform including the partial discharge signal shown in Figure 7, a discharge noise signal with a positive charge is shown in Figure 11. The partial discharge signal generates a current relative to the ground potential, but the disturbance noise adds a current with a constant charge. Figure 12 shows the waveform of the signal obtained by performing bandpass filtering and envelope processing on the signal shown in Figure 11.

[0096] Figure 13 shows the frequency analysis results of a sinusoidal current signal including the discharge noise signal shown in Figure 11. Figure 14 shows the frequency analysis results of the signal shown in Figure 12. As shown in Figure 13, the discharge noise signal appears as even-order harmonics such as the second and fourth harmonics with respect to the power supply fundamental frequency (50 Hz). On the other hand, as shown in Figure 14, in the signal obtained by performing bandpass filtering and envelope processing on the sinusoidal current signal including the discharge noise signal, the discharge noise signal appears as even-order harmonics such as the second and fourth harmonics with respect to the power supply fundamental frequency.

[0097] The difference between the sinusoidal current waveforms shown in Figures 7 and 11 lies in the difference between the current signal generated relative to the ground potential and the current signal with a constant potential. Comparing the frequency analysis results shown in Figures 9 and 13, the partial discharge signal appears as odd-order harmonics from the third order onward, while the discharge noise appears as even-order harmonics from the second order onward.

[0098] Figure 15 shows the phase angles of each harmonic when a partial discharge signal is included in a sinusoidal current signal. In Figure 15, θ1 is the phase angle of the third harmonic appearing in the sinusoidal current signal that includes the partial discharge signal. θ2 is the phase angle of the second harmonic appearing in the signal obtained by performing bandpass filtering and envelope processing on the sinusoidal current signal that includes the partial discharge signal. For comparison, Figure 15 also shows the phase angle θ0 of the power supply fundamental wave.

[0099] As shown in Figure 15, the partial discharge signal appears in the sinusoidal current signal as an odd-order harmonic with a phase angle θ1 that is out of phase with respect to the phase angle θ0 of the power supply fundamental wave. The phase angle θ1 is ±90 degrees or more relative to the phase angle θ0 of the power supply fundamental wave. Furthermore, in the signal obtained by bandpass filtering and envelope processing on the sinusoidal current signal, the partial discharge signal appears as an even-order harmonic with a phase angle θ2 that is in phase with respect to the phase angle θ0 of the power supply fundamental wave. The phase angle θ2 is less than ±90 degrees relative to the phase angle θ0 of the power supply fundamental wave.

[0100] Figure 16 shows the phase angles of each harmonic when a discharge noise signal is included in a sinusoidal current signal. In Figure 16, θ3 is the phase angle of the second harmonic appearing in the sinusoidal current signal containing the discharge noise signal. θ4 is the phase angle of the second harmonic appearing in the signal obtained by performing bandpass filtering and envelope processing on the sinusoidal current signal containing the discharge noise signal. For comparison, Figure 16 also shows the phase angle θ0 of the power supply fundamental wave.

[0101] As shown in Figure 16, the discharge noise signal appears in the sinusoidal current signal as an even-order harmonic with a phase angle θ3 that is in phase with the phase angle θ0 of the power supply fundamental wave. Furthermore, in the signal obtained by performing bandpass filtering and envelope processing on the sinusoidal current signal, the discharge noise signal appears as an even-order harmonic with a phase angle θ4 that is in phase with the phase angle θ0 of the power supply fundamental wave.

[0102] As is clear from the simulation analysis results above, the partial discharge signal appears as an odd-order harmonic in the sinusoidal current signal, having a frequency that is an odd multiple of the power supply fundamental wave. Therefore, if the sinusoidal current signal contains odd-order harmonics, it is presumed that a partial discharge has occurred. However, when odd-order harmonic noise is mixed into the sinusoidal current signal as disturbance noise, it is impossible to distinguish whether the odd-order harmonics in the sinusoidal current signal are harmonics caused by the partial discharge or harmonics caused by the aforementioned disturbance noise. On the other hand, the partial discharge signal appears as an odd-order harmonic having a first phase angle, which is a phase angle opposite to the phase angle of the power supply fundamental wave. Therefore, by not only determining whether the sinusoidal current signal contains odd-order harmonics, but also determining whether those odd-order harmonics have a first phase angle, it is possible to detect the partial discharge in distinction from the aforementioned disturbance noise.

[0103] When odd-order harmonic noise with a first phase angle is mixed into a sinusoidal current signal, the above determination alone cannot distinguish whether the odd-order harmonics in the sinusoidal current signal are harmonics caused by partial discharge or harmonics caused by disturbance noise. In the signal obtained by bandpass filtering and envelope processing on the sinusoidal current signal (second signal), the partial discharge signal appears as an even-order harmonic with a second phase angle that is in phase with the phase angle of the power supply fundamental wave. Therefore, by determining not only whether the odd-order harmonics in the sinusoidal current signal have a first phase angle, but also whether the even-order harmonics in the second signal have a second phase angle, it is possible to detect partial discharge in distinction from odd-order harmonic noise with a first phase angle.

[0104] Figure 17 is a schematic diagram showing a first modified version of electrical equipment 1. As shown in Figure 17, the first modified version of electrical equipment 1 includes a power converter 40. The power converter 40 drives a three-phase induction motor 11 by converting power from a three-phase AC power source 10. The power converter 40 includes a rectifier circuit 410, a switching circuit 420, and a smoothing capacitor 430.

[0105] The rectifier circuit 410 rectifies the supplied AC voltage. The rectifier circuit 410 outputs a rectified voltage (DC voltage). The rectifier circuit 410 includes multiple diodes 411. Two diodes 411 are connected in series between the high-potential side node and the low-potential side node of the power converter 40. The two diodes 411 connected in series form a leg. Multiple legs are connected in parallel with each other. The rectifier circuit 410 includes three legs to correspond to the U-phase, V-phase, and W-phase of the three-phase AC power supply 10.

[0106] The smoothing capacitor 430 smooths the voltage (DC voltage) output from the rectifier circuit 410. The smoothing capacitor 430 is connected in parallel to the rectifier circuit 410 and the switching circuit 420 between the high-potential side node and the low-potential side node of the power converter 40.

[0107] The switching circuit 420 converts the supplied DC voltage into AC voltage. The switching circuit 420 includes a plurality of switching elements 421. The switching elements 421 include IGBTs (Insulated gate bipolar transistors) and diodes. Two switching elements 421 are connected in series between the high-potential side node and the low-potential side node of the power converter 40. The two switching elements 421 connected in series form a leg. Multiple legs are connected in parallel with each other. The switching circuit 420 includes three legs to correspond to the U-phase, V-phase, and W-phase of the three-phase induction motor 11.

[0108] The power converter 40 may include other components such as a DC reactor (not shown).

[0109] The three-phase AC power supply 10 is connected to the rectifier circuit 410 of the power converter 40. The wiring for each phase of the three-phase AC power supply 10 is connected to the corresponding one of the three legs of the rectifier circuit 410.

[0110] The three-phase induction motor 11 is connected to the switching circuit 420 of the power converter 40. The wiring for each phase of the three-phase induction motor 11 is connected to the corresponding one of the three legs of the switching circuit 420.

[0111] The voltage sensor circuit 20A senses the state of the voltage signal of each phase of the three-phase AC power supply 10. The voltage sensor circuit 20A monitors the input power supply voltage.

[0112] The voltage sensor circuit 20B senses the state of the DC voltage output from the rectifier circuit 410. The voltage sensor circuit 20B monitors the DC voltage after rectification.

[0113] The voltage detection circuit 21 transmits voltage signals indicating the sensing results of the voltage sensor circuits 20A and 20B to the control device 30. The voltage signals are analog signals.

[0114] The current sensor circuit 22 senses the drive current output from the switching circuit 420. The current sensor circuit 22 monitors the value of the drive current supplied to the three-phase induction motor 11.

[0115] The current detection circuit 23 transmits a current signal indicating the sensing result of the current sensor circuit 22 to the control device 30. The current signal is an analog signal.

[0116] The driver control circuit 25 generates a PWM (pulse width modulation) signal or a PAM (pulse amplitude modulation) signal according to instructions from the control device 30. The driver control circuit 25 sends the PWM signal or PAM signal to each switching element 421 of the switching circuit 420. In this way, the driver control circuit 25 drives the switching elements 421 of the switching circuit 420. The driver control circuit 25 is connected to the gate (control terminal) of each switching element 421.

[0117] The control device 30 converts the analog signals transmitted from the voltage detection circuit 21 and the current detection circuit 23 into digital signals using the ADC 310. The resulting digital signals are used to control the power converter 40.

[0118] The control device 30 generates command signals to control the rotation state of the three-phase induction motor 11 in accordance with commands from the higher-level device 9. The control device 30 transmits the generated command signals to the driver control circuit 25. In this way, the control device 30 controls the operation of the three-phase induction motor 11 via the driver control circuit 25.

[0119] The fault detection unit 320 of the control device 30 acquires digital signals corresponding to the sensing results of the voltage sensor circuits 20A and 20B, and digital signals corresponding to the sensing results of the current sensor circuit 22. This allows the fault detection unit 320 to continuously monitor the status of the power converter 40 and the three-phase induction motor 11.

[0120] Figure 18 schematically shows a second modified example of the electrical device 1. As shown in Figure 18, the host device 9 may perform a process to detect partial discharge instead of the fault detection unit 320. That is, the fault detection unit 320 in the electrical device 1 only has the function of communicating various electrical signals within the electrical device 1 to the host device 9.

[0121] As shown in Figure 18, the host device 9 has a fault detection unit 320X. The host device 9 uses the fault detection unit 320X to perform various processes to detect partial discharge based on signals from the fault detection unit 320 of the electrical equipment 1.

[0122] This allows the higher-level device 9 to understand the fault condition inside the electrical equipment 1 from outside the electrical equipment 1. Therefore, the higher-level device 9 functions as a control device for the three-phase induction motor 11 and the electrical equipment 1. In the higher-level device 9, the various functions implemented as the fault detection unit 320 are implemented and operated by software as algorithms and analysis methods.

[0123] This reduces the computational load on the edge device (electrical device 1) in the system (network) including the electrical device 1 and the higher-level device 9. When the functions for performing various processes to detect partial discharge described above are implemented in an existing system, the higher-level device 9, which is capable of performing partial discharge detection processing as in this modified example, can operate the entire system in a highly scalable state without adding the fault detection unit 320 to the existing electrical device.

[0124] According to at least one embodiment described above, a control unit for controlling an electric motor and a fault detection unit for detecting a fault in the electric motor are provided. The fault detection unit performs frequency analysis of the voltage signal and current signal driving the electric motor, determines whether the current signal contains odd-order harmonics having an odd multiple frequency of the fundamental wave of the voltage signal based on the results of the frequency analysis, and determines whether the odd-order harmonics have a first phase angle which is the opposite phase angle to the phase angle of the fundamental wave based on the results of the frequency analysis. In this way, a control device is provided that can detect partial discharge in distinction from noise.

[0125] The control device, electrical equipment, and fault detection method of the embodiment include the following appended embodiments. (Note 1) A control unit that controls the electric motor, A fault detection unit for detecting a malfunction in the aforementioned electric motor, Equipped with, The fault detection unit, Frequency analysis is performed on the voltage signal and current signal that drive the aforementioned electric motor. Based on the results of the frequency analysis, it is determined whether the current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the voltage signal. Based on the results of the frequency analysis, it is determined whether the odd-order harmonic has a first phase angle which is in opposite phase to the phase angle of the fundamental wave. Control device. (Note 2) The control device according to Appendix 1, wherein the odd-order harmonic is a third harmonic having three times the frequency of the fundamental wave. (Note 3) The control device according to Appendix 1 or 2, wherein the first phase angle is a phase angle of ±90 degrees or more with respect to the phase angle of the fundamental wave. (Note 4) The fault detection unit, When the odd-order harmonic has the first phase angle, a partial discharge detection signal is output to indicate that a partial discharge has been detected in the motor. A control device as described in any one of the appendices 1 to 3. (Note 5) The fault detection unit, A first signal in the first frequency band is extracted from the current signal. A second signal is generated by performing envelope processing on the first signal. Perform a frequency analysis of the second signal described above. Based on the results of the frequency analysis of the second signal, it is determined whether the second signal contains even-order harmonics having even multiples of the frequency of the fundamental wave. Based on the results of the frequency analysis of the second signal, it is determined whether the even-order harmonic has a second phase angle that is in phase with respect to the phase angle of the fundamental wave. A control device as described in any one of the appendices 1 to 3. (Note 6) The control device according to Appendix 5, wherein the even-order harmonic is a second harmonic having twice the frequency of the fundamental wave. (Note 7) The control device according to Appendix 5 or 6, wherein the second phase angle is a phase angle of less than ±90 degrees with respect to the phase angle of the fundamental wave. (Note 8) The fault detection unit, When the odd-order harmonic has the first phase angle and the even-order harmonic has the second phase angle, a partial discharge detection signal is output to indicate that a partial discharge has been detected in the motor. A control device as described in any one of the appendices 5 to 7. (Note 9) An electric motor connected to a power source, A control device according to any one of the appendices 1 to 8 for controlling the aforementioned electric motor, Electrical equipment equipped with the necessary features. (Note 10) To perform frequency analysis of the voltage and current signals that drive the electric motor, Based on the results of the frequency analysis, it is determined whether the current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the voltage signal. Based on the results of the frequency analysis, it is determined whether the odd-order harmonic has a first phase angle which is the opposite phase angle to the phase angle of the fundamental wave. including, Fault detection method.

[0126] The functions of the elements disclosed herein may be implemented using circuits or processing circuitry that include general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), FPGAs (Field Programmable Gate Arrays), conventional circuits, and / or combinations thereof that are programmed using one or more programs stored in one or more memories, or otherwise configured to perform the disclosed functions. A processor is considered processing circuitry or circuitry because it includes transistors and other circuits. A processor may be a programmed processor that executes programs stored in memory. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. Hardware may be any hardware disclosed herein that is programmed or configured to perform the enumerated functions.

[0127] There is memory for storing computer programs that include computer instructions. These computer instructions provide logic and routines that enable hardware (e.g., processing circuitry or circuitry) to perform the methods disclosed herein. This computer program can be implemented in commonly known forms, such as computer-readable storage media, computer program products, memory devices, recording media such as CD-ROMs and DVDs, and / or memory in FPGAs and ASICs.

[0128] 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 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. [Explanation of symbols]

[0129] 1...Electrical equipment, 10...Three-phase AC power supply, 11...Three-phase induction motor, 15...Switch, 20...Voltage sensor circuit, 21...Voltage detection circuit, 22...Current sensor circuit, 23...Current detection circuit, 30...Control device, 310...ADC (Analog-to-Digital Converter), 320, 320A...Fault detection unit, 340...Control unit

Claims

1. A control unit that controls the electric motor, A fault detection unit for detecting a malfunction in the aforementioned electric motor, Equipped with, The fault detection unit, Frequency analysis is performed on the voltage signal and current signal that drive the aforementioned electric motor. Based on the results of the frequency analysis, it is determined whether the current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the voltage signal. Based on the results of the frequency analysis, it is determined whether the odd-order harmonic has a first phase angle which is the opposite phase angle to the phase angle of the fundamental wave. Control device.

2. The control device according to claim 1, wherein the odd-order harmonic is a third harmonic having three times the frequency of the fundamental wave.

3. The control device according to claim 1, wherein the first phase angle is a phase angle of ±90 degrees or more with respect to the phase angle of the fundamental wave.

4. The fault detection unit, When the odd-order harmonic has the first phase angle, a partial discharge detection signal is output to indicate that a partial discharge has been detected in the motor. The control device according to claim 1.

5. The fault detection unit, A first signal in the first frequency band is extracted from the current signal. A second signal is generated by performing envelope processing on the first signal. The frequency analysis of the second signal described above was performed, Based on the results of the frequency analysis of the second signal, it is determined whether the second signal contains even-order harmonics having even multiples of the frequency of the fundamental wave. Based on the results of the frequency analysis of the second signal, it is determined whether the even-order harmonic has a second phase angle that is in phase with respect to the phase angle of the fundamental wave. The control device according to claim 1.

6. The control device according to claim 5, wherein the even-order harmonic is a second harmonic having twice the frequency of the fundamental wave.

7. The control device according to claim 5, wherein the second phase angle is a phase angle of less than ±90 degrees with respect to the phase angle of the fundamental wave.

8. The fault detection unit, When the odd-order harmonic has the first phase angle and the even-order harmonic has the second phase angle, a partial discharge detection signal is output to indicate that a partial discharge has been detected in the motor. The control device according to claim 5.

9. An electric motor connected to a power source, A control device according to claim 1 for controlling the electric motor, Electrical equipment equipped with the necessary features.

10. To perform frequency analysis of the voltage and current signals that drive the electric motor, Based on the results of the frequency analysis, it is determined whether the current signal contains odd-order harmonics having frequencies that are odd multiples of the fundamental wave of the voltage signal. Based on the results of the frequency analysis, it is determined whether the odd-order harmonic has a first phase angle which is the opposite phase angle to the phase angle of the fundamental wave. including, Fault detection method.

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