Diagnostic device and diagnostic method

Abstract

To provide a diagnostic device for a smoothing capacitor having high diagnostic accuracy regardless of a specific operation condition of a power supply frequency of a power converter and a drive frequency of a rotating machine.SOLUTION: A diagnostic device 1S that diagnoses a state of a power converter 1 that converts power supplied from a power source 10 to drive a rotating machine 2 comprises a measurement unit 4 that measures a drive current flowing from the power converter 1 to the rotating machine 2. The diagnostic device comprises a frequency analysis unit 5 that executes frequency analysis of a time waveform of a drive current measured by the measurement unit 4 and calculates a drive frequency that is a frequency of the drive current based on a result of the frequency analysis. The diagnostic device comprises an amplitude extraction unit 12 that extracts the amplitude of the drive current at a specific frequency based on a power supply frequency, which is the frequency of the power supply, and the drive frequency and a diagnosis unit 7 that diagnoses a state of a power converter based on the amplitude extracted by the amplitude extraction unit.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a diagnostic device and a diagnostic method. [Background technology]

[0002] When a specific piece of equipment in a production facility suddenly breaks down, unplanned repair or replacement work becomes necessary, which can reduce the availability of the production facility or require a review of the production plan. Therefore, if it is possible to check for signs of failure and prepare replacement parts in advance for equipment that is likely to break down, or to plan repairs in advance, it is possible to minimize the reduction in the availability of the production facility or the review of the production plan.

[0003] The same can be said about inverters (hereafter referred to as "power converters") that supply power to production facilities. If it is possible to check for signs of failure in power converters and prepare replacement parts in advance for parts that are likely to fail, or to plan repairs, it will be possible to minimize declines in the operation rate of production facilities and revisions to production plans.

[0004] In a power converter, the degradation of the smoothing capacitor is a typical failure mode, and the degradation of the smoothing capacitor will eventually cause the power converter to fail. Therefore, a method of measuring the capacitance of the smoothing capacitor has been proposed as a method of detecting the degradation of the smoothing capacitor.

[0005] One method for measuring the capacity of a smoothing capacitor is to estimate the capacity from the behavior of the current during charging using an existing current sensor for controlling the power converter. However, this method requires that the power converter be stopped. For devices with high operating rates or devices that require high operating rates, it may be difficult to stop the device, so this method cannot be used for constantly monitoring sudden failures, especially for such devices.

[0006] As an alternative method, a method of adding a current sensor to measure the current flowing through the smoothing capacitor has been devised. However, this method requires the installation of an additional current sensor, and the smoothing capacitor of a power converter is generally connected to the board, and there is often no space to add a current sensor. It is also possible to remove the smoothing capacitor from the board and then modify the board, but this would require modifying the power converter, which may void the manufacturer's warranty or may cause a breakdown.

[0007] Therefore, as a diagnostic technique for a power converter during operation, Patent Document 1 discloses a technique in which a current sensor is installed between the power converter and a motor (hereinafter referred to as a "rotating machine") to which the power converter supplies power, to measure the current, and a decrease in the capacity of the smoothing capacitor is detected from an increase or decrease in the current component of a specific frequency, thereby diagnosing deterioration of the smoothing capacitor. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2004 / 070402 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the conventional technology disclosed in Patent Document 1 had a problem in that when the operating conditions that combine the frequency of the power source that supplies power to the power converter (hereinafter referred to as the "power source frequency") and the frequency of the drive current of the rotating machine (hereinafter referred to as the "drive frequency") are certain conditions, the accuracy of diagnosis decreases, leading to erroneous or missed reports.

[0010] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a smoothing capacitor diagnostic device that has high diagnostic accuracy regardless of the specific operating conditions of the power supply frequency of the power converter and the drive frequency of the rotating machine. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems and achieve the object of the present invention, a diagnostic device that diagnoses the state of a power converter that converts power supplied from a power source to drive a rotating machine is characterized by having a measurement unit that measures a drive current flowing from the power converter to the rotating machine, a frequency analysis unit that performs frequency analysis of a time waveform of the drive current measured by the measurement unit and calculates a drive frequency that is the frequency of the drive current based on a result of the frequency analysis, an amplitude extraction unit that extracts the amplitude of the drive current at a specific frequency based on a power supply frequency that is the frequency of the power source and the drive frequency, and a diagnostic unit that diagnoses the state of the power converter based on the amplitude extracted by the amplitude extraction unit. Effect of the Invention

[0012] According to the present invention, it is possible to provide a smoothing capacitor diagnostic device with high diagnostic accuracy, regardless of the specific operating conditions of the power supply frequency of the power converter and the drive frequency of the rotating machine. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the configuration of a diagnostic device according to the prior art. [Diagram 2] FIG. 1 is a configuration diagram of a diagnostic device according to a first embodiment. [Diagram 3] FIG. 4 is a schematic diagram of a frequency spectrum according to the first embodiment. [Figure 4] FIG. 11 is a configuration diagram of a diagnostic device according to a second embodiment. [Diagram 5] FIG. 11 is a configuration diagram of a diagnostic device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "Examples") will be described with reference to the accompanying drawings. Note that the following is merely an example of an embodiment, and it is not intended that the scope of the present invention be limited to the following Examples.

[0015] Prior to describing the embodiments, the prior art will be described. Fig. 1 is a configuration diagram of a diagnostic device S according to the prior art. The diagnostic device S, an example of the configuration of which is shown in Fig. 1, diagnoses the state of a smoothing capacitor of a power converter 1 based on a sensor signal of a current sensor 9.

[0016] In Fig. 1, a power converter 1 and a rotating machine 2 are electrically connected. Furthermore, the rotating machine 2 and a load device 3 are mechanically connected. Possible mechanical connection methods include a method of directly connecting a rotating shaft, a method of connecting via a gear or a belt, etc. Furthermore, the power converter 1 is electrically connected to a power source 10.

[0017] In the diagnostic device S, the sensor signal of the current sensor 9 is measured by the measurement unit 4, and then the time series waveform (time waveform) of the sensor signal is converted into a frequency domain spectrum by the frequency analysis unit 5. The frequency analysis unit 5 calculates the drive frequency of the drive current at which the peak occurs from the result of the frequency analysis of the sensor signal. The amplitude extraction unit 6 converts the signal into the amplitude of one or more specific frequencies based on the drive frequency of the drive current. Then, in the diagnostic device S, the diagnosis unit 7 diagnoses the state of the device to be diagnosed based on the amplitude information from the amplitude extraction unit 6, and displays the diagnosis result on the display unit 8. Specifically, the diagnosis unit 7 uses the amplitudes of the 5th and 7th order components of the sensor signal of the current sensor 9 (drive frequency of the drive current).

[0018] However, there has been a problem in that the accuracy of diagnosis decreases depending on the combination of the power supply frequency of the power converter 1 and the drive frequency of the rotating machine 2. EXAMPLES

[0019] 2 is a configuration diagram of a diagnostic device 1S according to the embodiment 1. A description of the parts common to the prior art with reference to the above-mentioned FIG.

[0020] The configuration of the diagnostic device 1S of the first embodiment includes a power supply frequency setting unit 11 and an amplitude extraction unit 12 in addition to the configuration of the diagnostic device S of the conventional art. The amplitude extraction unit 12 extracts a current amplitude based on the power supply frequency of the power supply 10 and the drive frequency of the rotating machine 2.

[0021] The power supply frequency setting unit 11 sets the frequency of the power supply 10. For example, if the device is installed in eastern Japan, it is generally driven by a power supply of 50 Hz, and if the device is installed in western Japan, it is generally driven by a power supply of 60 Hz. The power supply frequency setting unit 11 sets these frequencies.

[0022] The amplitude extraction unit 12 sets |first component of the drive frequency of the rotating machine 2±sixth component of the power supply frequency of the power source 10| or |first component of the drive frequency of the rotating machine 2±fourth component of the power supply frequency of the power source 10| as a specific frequency, and extracts the current amplitude of this specific frequency. That is, the amplitude extraction unit 12 extracts the current amplitude of the specific frequency=|first component of the drive frequency of the rotating machine 2±2n×first component of the power supply frequency of the power source 10|. However, n=2 when the power source 10 supplies two-phase AC power, and n=3 when the power source 10 supplies three-phase AC power.

[0023] Note that, when there is a lot of noise in a specific frequency band or when it is desired to suppress the processing capacity, it may be only one of the components. That is, it may be either |1st component of the drive frequency of the rotating machine 2 + 6th component of the power supply frequency of the power supply 10| or |1st component of the drive frequency of the rotating machine 2 - 6th component of the power supply frequency of the power supply 10|. Alternatively, it may be either the current amplitude of |1st component of the drive frequency of the rotating machine 2 + 4th component of the power supply frequency of the power supply 10| or |1st component of the drive frequency of the rotating machine 2 - 4th component of the drive frequency of the power supply 10|.

[0024] Noise is a current of frequency components that are not caused by inverter deterioration, and corresponds to environmental noise, the fundamental wave component of the drive current, and its harmonic components. In addition, they have broad frequency characteristics with a spread of frequencies. Therefore, if the frequency of the fundamental wave component of the drive current and its harmonic components is close to the frequency component caused by inverter deterioration, it will be affected even if it does not match completely. If the noise has a constant amplitude, there is no problem, but the amplitude of the noise component may change. When the inverter operates with multiple frequency components or the frequency component of the power supply changes, the distance on the frequency axis between the frequency of the fundamental wave component of the drive current and its harmonic components of the environmental noise and the frequency component caused by inverter deterioration changes. As shown in the above example, if diagnosis can be made with one of the frequency components, diagnosis with one of the frequency components may be made. In addition, in a specific operating mode, when the frequency of the fundamental wave component of the drive current and its harmonic components is separated from the specific frequency component caused by inverter deterioration by a predetermined distance or more, diagnosis with one or both frequency components can be made without being affected by noise.

[0025] As described above, whether the fourth or sixth frequency component of the power source 10 is used depends on whether the power supplied from the power source 10 to the power converter 1 is three-phase or two-phase. That is, in the three-phase case, diagnosis is performed using the current amplitude of |the first frequency of the current of the rotating machine 2±the sixth frequency of the power source 10|, and in the two-phase case, diagnosis is performed using the current amplitude of |the first frequency of the current of the rotating machine 2±the fourth frequency of the power source 10|.

[0026] Here, we will explain the mechanism by which the deterioration of the smoothing capacitor of the power converter 1 can be diagnosed based on the current amplitude of |the first component of the driving frequency of the rotating machine 2±the sixth component of the power supply frequency of the power source 10| or |the first component of the driving frequency of the rotating machine 2±the fourth component of the power supply frequency of the power source 10|.

[0027] The power converter 1 converts the AC voltage supplied to it into a DC voltage using a smoothing capacitor within the device itself. However, when the smoothing capacitor deteriorates, the smoothing effect decreases, and the voltage output from the power converter 1 oscillates slightly with the fourth or sixth order component of the power supply frequency. When the power supply 10 is three-phase, the sixth order oscillation is observed with the upper and lower diodes (total of two) and three phases. On the other hand, when the power supply 10 is two-phase, the fourth order oscillation is observed with the upper and lower diodes (total of two) and two phases. This voltage fluctuation appears on both sides (when the frequency is low and when the frequency is high) of the fundamental wave component (first order component) of the drive current of the rotating machine 2. When the frequency appears as a negative value, it appears as a reflection of that, so the absolute value is taken.

[0028] In this embodiment, the rotating machine 2 must be in a constant load state, with a constant rotation speed and a constant load on the load device 3 driven by the rotating machine 2. This state is referred to as a steady state in this specification. This steady state does not need to continue all the time, as long as at least the data to be diagnosed is acquired in a steady state. The length of the steady state may be one second or longer.

[0029] However, generally speaking, the longer this steady state is, the higher the frequency resolution and the higher the accuracy of diagnosis. Therefore, the length of the steady state used for diagnosis can be determined according to the required diagnostic accuracy, that is, how small a change you want to capture. Similarly, the sampling speed used for measurement can also be determined according to the accuracy required for diagnosis. Generally, a faster sampling speed will level out noise and increase the accuracy of diagnosis.

[0030] In this embodiment, the relationship between the sensor signal acquired by the current sensor 9 and the operating state of the rotating machine 2 is not specified, but in order to improve the accuracy of diagnosis, it is desirable to use only measurement data of a predetermined specific operating state for diagnosis. An example of the specific operating state is a combination of a specific speed and a specific load. Although there is no particular specification for the method of extracting the operating state of a specific speed and a specific load, an example is a method of checking the transition of the current effective value and frequency and extracting a waveform that transitions over a specific time in a specific effective value and frequency range. A sensor signal not used for diagnosis may be additionally input and used to extract the specific operating state.

[0031] Furthermore, the frequency analysis unit 5 may use a window function. The types of window functions include a Gaussian window, a Hann window, a Hamming window, and a Hanning window, and a window function that is superior in terms of diagnostic accuracy may be used.

[0032] The frequency analysis results in this embodiment will be described in comparison with the conventional technique with reference to Fig. 3. Fig. 3 is a schematic diagram of a frequency spectrum according to the first embodiment.

[0033] The power supply frequency of the power converter 1 is three-phase 60 Hz, and the fundamental wave component A0 of the drive frequency of the rotating machine 2 is three-phase 50 Hz. As the smoothing capacitor of the power converter 1 deteriorates, the components A1 (310 Hz) and A2 (410 Hz) shown by the arrows increase. These frequency components do not match either the fifth or seventh order components of the drive frequency of the rotating machine 2. For this reason, with conventional technology, it has been difficult to detect deterioration of the smoothing capacitor of the power converter 1, leading to false or no report.

[0034] On the other hand, the amplitude extraction unit 12 in this embodiment extracts |the first component of the drive frequency of the rotating machine 2±the sixth component of the power supply frequency of the power supply 10|. |50±60×6|=310 Hz and 410 Hz, which match the components A1 and A2, respectively. Therefore, in this embodiment, it is possible to detect the deterioration of the smoothing capacitor of the power converter 1.

[0035] As a diagnostic method, a method of determining that an abnormality exists when the amplitude of each peak of a specific frequency extracted by the amplitude extraction unit 12 exceeds a predetermined value set in advance can be used. For example, a method of monitoring the change over time of the amplitude of each peak of a specific frequency, statistically calculating an upper limit value at which the amplitude can be considered normal, and determining that an abnormality exists when this upper limit value is exceeded can be used. Alternatively, a method of learning an upper limit value at which the amplitude of each peak of a specific frequency can be considered to be in a normal state using machine learning or the like, and determining that an abnormality exists when the amplitude of each peak of a specific frequency exceeds the learned upper limit value can be used.

[0036] The contents of the diagnosis unit 7 are transmitted to the user via the display unit 8. Methods of transmitting the contents to the user by the display unit 8 include displaying the contents on a display, turning on a lamp, notifying the user by email, and the like.

[0037] In this embodiment, the state of the smoothing capacitor of the power converter 1 is diagnosed based on the amplitude of the drive current at a specific frequency based on the power supply frequency and the drive frequency. Therefore, compared to conventional methods that use the fifth and seventh order components of the drive frequency of the drive current, the accuracy of diagnosing the state of the smoothing capacitor of the power converter 1 can be improved.

[0038] In this embodiment, the amplitude of the drive current at the specific frequency = |first-order component of the drive frequency of the rotating machine 2 ±2n × first-order component of the power supply frequency of the power supply 10| is used. Therefore, the influence of the number of phases of the power supply 10 can be reflected, and the accuracy of diagnosing the state of the smoothing capacitor of the power converter 1 can be improved.

[0039] In this embodiment, the state of the smoothing capacitor of the power converter 1 is diagnosed based on the result of frequency analysis of the time waveform of the drive current when the rotating machine 2 rotates at a constant speed and the load of the load device 3 driven by the rotating machine 2 is a constant load. Therefore, the accuracy of diagnosing the state of the smoothing capacitor of the power converter 1 can be further improved.

[0040] In this embodiment, the state of the power converter 1 is diagnosed based on the amplitude of the drive current extracted from the result of frequency analysis of the time waveform of the drive current measured when the operating state of the rotating machine 2 is in a specific state. This makes it possible to further improve the accuracy of diagnosing the state of the smoothing capacitor of the power converter 1.

[0041] Furthermore, in this embodiment, if the amplitude of the drive current exceeds a predetermined upper limit value based on statistics or machine learning, the smoothing capacitor of the power converter 1 is diagnosed as degraded. Therefore, it is possible to further improve the accuracy of diagnosing the state of the smoothing capacitor of the power converter 1 based on past data, rather than on temporary fluctuations in the current amplitude. EXAMPLES

[0042] 4 is a configuration diagram of a diagnostic device 2S according to the second embodiment. The power converter 1 is supplied with power from a power source 10B, which is different from the first embodiment in that the number of phases of the power source 10B is two. In this case, the amplitude extraction unit 12B can diagnose the deterioration of the smoothing capacitor of the power converter 1 using the components |first-order component of the drive frequency of the rotating machine 2±fourth-order component of the power source frequency of the power source 10B|, as described above in the first embodiment. EXAMPLES

[0043] FIG. 4 is a configuration diagram of a diagnostic device 3S according to a second embodiment. In the first embodiment, the frequency of the power supply 10 is set by the power supply frequency setting unit 11. In this embodiment, in order to automate the setting, the sensor signal of the power supply current sensor 9C based on the power supply current flowing from the power supply 10 to the power converter 1 is measured by the power supply current measurement unit 4C. After that, the power supply current frequency analysis unit 5C converts the time series waveform into a spectrum in the frequency domain, and obtains the frequency to be set in the power supply frequency setting unit 11 from the peak frequency. The frequency calculated in this manner is set in the power supply frequency setting unit 11. This prevents incorrect settings due to manual input, etc., and makes it possible to perform highly accurate diagnosis. In addition, the effort required of the user to set the frequency is reduced.

[0044] Although the embodiments of the present disclosure have been described above in detail, the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present disclosure is not necessarily limited to those having all of the configurations described. In addition, it is possible to add, delete, or replace part of the configuration of the above-described embodiments with other configurations.

[0045] Furthermore, the above-mentioned configurations, functional units, processing units, etc. may be realized in part or in whole by hardware, for example, by designing them as integrated circuits. The above-mentioned configurations, functions, etc. may be realized in software by a processor interpreting and executing a program that realizes each function. Information such as the program, table, file, etc. that realizes each function can be stored in a memory, a storage device such as an HDD or SSD, or a recording medium such as an IC card, an SD card, or a DVD.

[0046] In addition, in each of the above figures, the control lines and information lines are shown as those considered necessary for the explanation, and do not necessarily show all the control lines and information lines in the actual implementation. For example, it may be considered that almost all the components are actually connected to each other. [Explanation of symbols]

[0047] 1: power converter, 2: rotating machine, 3: load device, 4: measurement unit, 4C: power supply current measurement unit, 5: frequency analysis unit, 5C: power supply current frequency analysis unit, 6: amplitude extraction unit, 7: diagnosis unit, 8: display unit, 9: current sensor, 9C: power supply current sensor, 10: power supply, 11: power supply frequency setting unit, 12, 12B: amplitude extraction unit.

Claims

1. A diagnostic device for diagnosing a state of a power converter that converts power supplied from a power source to drive a rotating machine, comprising: a measurement unit that measures a drive current flowing from the power converter to the rotating machine; a frequency analysis unit that performs a frequency analysis of the time waveform of the drive current measured by the measurement unit and calculates a drive frequency, which is the frequency of the drive current, based on a result of the frequency analysis; an amplitude extraction unit that extracts an amplitude of the drive current at a specific frequency based on a power supply frequency that is a frequency of the power supply and the drive frequency; a diagnosis unit that diagnoses a state of the power converter based on the amplitude extracted by the amplitude extraction unit; A diagnostic device comprising:

2. 2. The diagnostic device according to claim 1, The amplitude extraction unit A diagnostic device comprising: a first detecting section for detecting a first amplitude at a specific frequency represented by a formula (1). The specific frequency = | the first component of the drive frequency ± 2n × the first component of the power supply frequency | ・・・（１） (However, n=2 when the power source supplies two-phase AC power, and n=3 when the power source supplies three-phase AC power.)

3. 2. The diagnostic device according to claim 1, A diagnostic device, characterized in that the time waveform of the drive current is a waveform obtained when the rotating machine rotates at a constant speed and the load of a load device driven by the rotating machine is a constant load.

4. 2. The diagnostic device according to claim 1, The diagnosis unit includes: a diagnosing device for diagnosing a state of the power converter based on the amplitude extracted from a result of a frequency analysis performed by the frequency analysis unit for a time waveform of the drive current measured by the measurement unit when the operating state of the rotating machine is in a specific state.

5. 2. The diagnostic device according to claim 1, The diagnosis unit includes: A diagnostic device characterized by diagnosing the state of the power converter after confirming that the frequencies of the fundamental wave component and the harmonic components of the fundamental wave component of the drive current are separated from the specific frequency by a predetermined amount or more.

6. 2. The diagnostic device according to claim 1, a power supply current measuring unit that measures a power supply current flowing from the power supply to the power converter; a power supply current frequency analysis unit that executes a frequency analysis of a time waveform of the power supply current measured by the power supply current measurement unit and calculates the power supply frequency based on a result of the frequency analysis; A diagnostic device comprising:

7. A diagnostic method executed by a diagnostic device that diagnoses a state of a power converter that converts power supplied from a power source to drive a rotating machine, comprising: measuring a drive current flowing from the power converter to the rotating machine; Executing a frequency analysis of the measured time waveform of the driving current; Calculating a drive frequency, which is a frequency of the drive current, based on a result of the frequency analysis; extracting an amplitude of the drive current at a specific frequency based on a power supply frequency that is a frequency of the power supply and the drive frequency; A state of the power converter is diagnosed based on the extracted amplitude. A diagnostic method comprising each of the treatments.

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