JP2015194447A - Monitoring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monitoring device for highly accurately monitoring, with a simple configuration, a presence or absence of abnormality in current supplied to an electric motor from a commercial power supply.SOLUTION: A monitoring device 100 monitors a presence or absence of abnormality in an input current inputted in a control device 20 or an output current outputted from the control device 20, and is provided with: a reception unit 110 that receives an output AC current measured by current sensors 40, 50 for measuring the output AC current outputted from the control device 20; and a monitoring unit 120 that executes Fourier transformation on the output AC current received by the reception unit 110, and monitors a presence or absence of abnormality in the input current or the output current on the basis of a result of the execution.

Description

  The present invention relates to a monitoring device.

  2. Description of the Related Art Conventionally, a technique for monitoring the presence or absence of an abnormality such as an open phase or reverse phase of current supplied from a commercial power source to an electric motor is known. For example, when a three-phase three-wire power source is supplied to an electric motor, the phase loss detection method of the prior art obtains the amplitude value or effective current value of each phase by a current sensor attached to each of the three phases. The phase loss is detected from the ratio of the measured values.

  There is also known a method in which a current sensor is attached to two of the three phases to detect a missing phase. In this method, the amplitude value or effective current value of two phases is obtained, and the missing phase is detected from the ratio of the obtained values. Further, in this method, for the phase where the current sensor is not provided, the missing phase is detected by utilizing the property that the phase difference between the two phases provided with the current sensor changes when the phase is missing.

JP 2005-227073 A Japanese Patent Laid-Open No. 10-62470 JP 2001-309669 A

  However, the method of detecting a phase failure by attaching three current sensors increases the cost for one current sensor, and increases the size of a control device for controlling the power supplied to the motor. .

  Further, in a method of detecting a phase loss by attaching two current sensors, a hardware comparator circuit may be provided in order to obtain a phase difference between the two phases. Therefore, this method also increases the cost and the size of the control device. When measuring the phase difference between two phases only with software, for example, the time from the measurement start point when one phase crosses zero to the measurement end point when another phase crosses zero Although it is necessary to measure, since the measurement start point and the measurement end point are instantaneous, there is a possibility that the zero cross cannot be accurately detected due to the influence of current distortion or noise. For this purpose, it is conceivable to use a moving average. However, the sampling period is shortened accordingly, and a load is applied to the arithmetic unit. In addition, even if a moving average is used, zero crossing may not be detected with high accuracy, so a hardware comparator must be prepared to ensure completeness.

  Accordingly, an object of the present invention is to accurately monitor the presence or absence of abnormality in the current supplied from the commercial power source to the electric motor with a simple configuration.

A monitoring device according to an aspect of the present invention is a monitoring device that monitors whether there is an abnormality in an input current input to a control device that controls electric power supplied to an electric motor or an output current output from the control device, A receiving unit that receives an input AC current or an output AC current measured by a current sensor that measures an input AC current that is input to the control device or an output AC current that is output from the control device; and that is received by the receiving unit. And a monitoring unit that executes Fourier transform on the input AC current or output AC current and monitors whether there is an abnormality in the input current or output current based on the execution result.

  Further, in the monitoring device according to one aspect, the receiving unit outputs a current value of two phases of a three-phase three-wire commercial frequency input AC current input from a commercial power source to the control device, or output from the control device. Receiving the input AC current or the output AC current measured by the current sensor that measures the current value of the two phases of the output AC current of any frequency of the three-phase three-wire type, and the monitoring unit receives the reception By subtracting the direct current component from the current values of the two phases received by the unit at the same time and adding the value obtained by multiplying the instantaneous alternating current value of the two phases by minus 1 as the instantaneous alternating current value, The instantaneous alternating current value of the third phase that is not attached can be obtained.

  Further, in the monitoring apparatus according to one aspect, the monitoring unit compares the input alternating current or the output alternating current obtained by executing the Fourier transform with amplitudes of three-phase fundamental frequencies. The presence / absence of an AC current or a three-phase open state of the output AC current can be monitored.

  Moreover, in the monitoring apparatus according to one aspect, the monitoring unit monitors the presence or absence of a three-phase open state of the input alternating current or the output alternating current. By comparing the phase of the three-phase fundamental frequency of the input AC current or the output AC current obtained by executing Fourier transform, the three-phase negative phase state of the input AC current or the output AC current You can monitor the presence or absence.

  Further, in the monitoring apparatus according to one aspect, the monitoring unit performs an arctangent function operation using a Fourier cosine coefficient and a Fourier sine coefficient obtained by executing the Fourier transform, thereby calculating the input alternating current or the The phase of the three phases of the output alternating current can be obtained, and the obtained phase can be corrected based on the positive / negative relationship between the Fourier cosine coefficient and the Fourier sine coefficient.

  Further, in one aspect of the monitoring apparatus, a value of a sine function and a value of a cosine function corresponding to the number of data sampled when the Fourier transform is performed on the input AC current or the output AC current are stored. The monitor further includes a sine function value and a cosine function value corresponding to each sampling number read from the memory, and the read sine function value when the Fourier transform is performed. By using the value of the cosine function, the Fourier cosine coefficient and the Fourier sine coefficient can be obtained.

  According to this invention of this application, the presence or absence of abnormality of the current supplied to the electric motor can be accurately monitored with a simple configuration.

FIG. 1 is a diagram illustrating a configuration of the monitoring device according to the first embodiment. FIG. 2 is a diagram illustrating the orthogonal coordinates of the Fourier cosine coefficient (a _k ) on the horizontal axis and the Fourier sine coefficient (b _k ) on the vertical axis. FIG. 3 is a diagram illustrating a configuration of the monitoring device according to the second embodiment.

  Hereinafter, a monitoring device according to an embodiment of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a diagram illustrating a configuration of the monitoring device according to the first embodiment. As shown in FIG. 1, the monitoring system includes a control device 20, a motor (electric motor) 30, current sensors 40 and 50, DC superposition circuits 60 and 70, and a monitoring device 100.

  The control device 20 is supplied with electric power of a three-phase three-wire commercial frequency of R phase, S phase, and T phase output from the commercial power source 10. The control device 20 includes a switch 22 formed by an electromagnetic contactor, a relay, a triac, or the like. The switch 22 can be turned on / off by an external signal. The switch 22 switches and outputs the electric power of each phase supplied from the commercial power supply 10. The control device 20 controls the power supplied to the motor 30 by switching the power of each phase supplied from the commercial power supply 10 by the switch 22. Note that when the switch 22 is on, the monitoring device 100 can monitor whether there is an abnormality in the output alternating current from the control device 20.

  The current sensor 40 is a sensor such as a current transformer that measures an R-phase output AC current output from the control device 20 to the motor 30. The current sensor 50 measures an output AC current having an arbitrary frequency in the T phase that is output from the control device 20 to the motor 30. That is, in this embodiment, the current value of the two-phase output AC current among the three-phase output AC currents is measured. The monitoring device 100 can detect not only the presence / absence of an abnormality in the output AC current but also the presence / absence of an abnormality in the input AC current by detecting the current value of the two-phase output AC current from the control device 20. it can.

  The DC superimposing circuit 60 is a circuit that superimposes a DC voltage on the output AC current measured by the current sensor 40 (applies a DC bias). The DC superimposing circuit 70 is a circuit that superimposes a DC voltage on the output AC current measured by the current sensor 50 (applies a DC bias). For example, when the AD input range of the AD input port of the monitoring device 100 (microcomputer) is from 0 V to 5 V, the DC superimposing circuits 60 and 70 superimpose half DC 2.5 V on the current signal. For this reason, when the input port of the monitoring apparatus 100 is a port that does not require a DC voltage to be superimposed, the DC superimposing circuits 60 and 70 may not be provided.

  The monitoring device 100 is a device for monitoring whether there is an abnormality in the output current output from the control device 20. The monitoring device 100 can be realized by, for example, a microcomputer. The monitoring device 100 includes a receiving unit 110 and a monitoring unit 120.

  The receiving unit 110 receives the output alternating current measured by the current sensors 40 and 50.

<First aspect of abnormality monitoring>
The monitoring unit 120 performs a Fourier transform on the output alternating current received by the receiving unit 110, and monitors whether there is an abnormality in the output current based on the execution result.

That is, if an arbitrary alternating current waveform at time t is i (t), a direct current component is I ₀ , an amplitude at order n is I _n , a phase is θ _n , and 2πf _n = ω _n , i (t ) Is expressed by the following equation (1).

In Equation 1, a _k is called a Fourier cosine coefficient, and b _k is called a Fourier sine coefficient. The Fourier cosine coefficient and the Fourier sine coefficient are obtained by Fourier transform. The relationship between the amplitude I _k , the phase θ _K , the Fourier cosine coefficient a _k , and the Fourier sine coefficient b _k is expressed by the following equation (2).

Further, when the arbitrary order is n and the number of data acquired during the basic period is m, the Fourier cosine coefficient a _n and the Fourier sine coefficient b _n of the order n are obtained by the following equation (3).

  Therefore, the monitoring unit 120 performs the Fourier transform on the output AC current received by the reception unit 110, thereby the amplitude value or effective current of the output AC current of each of the two phases (R phase and T phase). The value can be determined. The monitoring unit 120 can detect an open phase of the R phase or the T phase from the ratio of the obtained values.

  Further, the monitoring unit 120 can obtain the phases of the output AC currents of the two phases (R phase and T phase) by performing Fourier transform on the output AC current received by the receiving unit 110. . Therefore, the monitoring unit 120 can obtain the phase difference between the output AC currents of the two phases (R phase and T phase). The monitoring unit 120 can detect an open phase using the property that the phase difference between the obtained two-phase output AC currents changes for the S phase in which no current sensor is provided.

According to the first embodiment, it is possible to accurately monitor whether there is an abnormality in the current supplied from the commercial power source to the electric motor with a simple configuration. That is, conventionally, Fourier transform has been frequently used in a high frequency region such as processing of image data and audio data. Further, since the frequency to be handled is high, a high-speed and expensive calculation value is required. However, in order to Fourier-transform a current or voltage at a commercial frequency with the control device 20 that controls the power for driving the motor 30, even a recent inexpensive microcomputer such as the monitoring device 100 can obtain sufficient performance. It is done.

  Therefore, in the present embodiment, Fourier transformation is performed on the output alternating current from the control device 20. By executing the Fourier transform, the sampling period can be made relatively long (in the sampling theory, it is explained that the Fourier transform is possible with the number of orders to be obtained × 4 data numbers with respect to the basic period). The phase can be obtained from the integration of one period of the current element. Therefore, in the present embodiment, unlike the conventional technique, it is not necessary to detect the measurement start point where the output AC current of one phase crosses zero and the measurement end point where the output AC current of another phase crosses zero. . As a result, according to the present embodiment, it is possible to accurately monitor the presence / absence of current abnormality using current elements that are not affected by noise or distortion. Further, in the present embodiment, unlike the prior art, it is not necessary to provide a hardware comparator circuit for obtaining the phase difference between the two phases, so that it is possible to monitor the presence or absence of current abnormality with a simple configuration. .

<Second aspect of abnormality monitoring>
The monitoring unit 120 subtracts the DC component from the current values of the two phases (R phase and T phase) received at the same time received by the receiving unit 110 to obtain an instantaneous AC current value that is minus the instantaneous AC current value of the two phases. By adding one multiplied by 1, the instantaneous AC current value of the third phase without the current sensor attached can be obtained.

  That is, since the current value acquired by the conventional current measuring means is immediately converted into an amplitude value or an effective current value, the amplitude value or effective current value of the phase where no current sensor is provided cannot be obtained. On the other hand, in the present embodiment, focusing on the fact that the sum of the instantaneous current values of the three phases is 0, the current values of the two phases (R phase and T phase) in which current sensors are provided as preprocessing. Is measured at the same time, and the current sensor is provided by subtracting the DC component from the measured value and adding the instantaneous AC current value of the two phases multiplied by minus 1 as the instantaneous AC current value. The S-phase instantaneous alternating current value can be obtained. In other words, the instantaneous AC current value obtained by subtracting the DC component from the measured current value of the first phase (R phase) to which the current sensor is attached is I1 (t), and the second phase is attached to the current sensor. If the instantaneous AC current value obtained by subtracting the DC component from the measured current value of (T phase) is I2 (t), the third phase (S phase) instantaneous AC current value I3 (t ) Can be obtained by the following equation (4).

[Equation 4]
I3 (t) = − I1 (t) −I2 (t)

  In this way, after obtaining the instantaneous alternating current value for three phases for one period of the fundamental frequency at a constant sampling period, the fundamental frequency for three phases or the amplitude and phase of any order are obtained by performing Fourier transform. Can be requested.

<Third aspect of abnormality monitoring>
Further, the monitoring unit 120 monitors the presence or absence of a three-phase phase failure state of the output AC current by comparing the amplitudes of the three-phase fundamental frequencies of the output AC current obtained by executing the Fourier transform. Can do.

In other words, in a factory or other site, a three-phase, three-wire power supply has a three-phase unbalanced state, and due to differences in the impedance of each motor phase, The amplitude and phase of are significantly different from the ideal state. Further, the current waveform has a distortion component by driving the motor 30. In addition, when the motor 30 is driven by an inverter, noise is superimposed on the current waveform. The noise includes a spike component when the current flowing through the inductance component is turned on / off, or a triangular ripple current that remains when the switching output of the PWM inverter is converted to a commercial frequency by the RC filter. The amplitude value, effective current value, and phase obtained by the conventional current measuring means are easily affected by the above-described three-phase unbalanced state, current distortion, and noise, and cause erroneous detection of missing phases. In addition, the three-phase input AC current to the circuit having a three-phase rectifier circuit and a smoothing capacitor does not flow until the three-phase line voltage exceeds the smoothing voltage, and when it exceeds the smoothing voltage, the current flows sharply. The current conduction angle is narrow and the current waveform is appropriately distorted. Also, since there is a long period in which no current flows, it is difficult to measure time by detecting a zero crossing of current. Therefore, in order to avoid erroneous detection of phase loss, it is necessary to detect phase loss with high accuracy.

  On the other hand, in the present embodiment, the amplitude value of the “fundamental frequency” is used for the phase loss detection, so that the amplitude of each phase can be compared with a value from which noise and distortion components have been removed. If, as a result of the comparison, the relationship between the amplitudes of the respective phases is different from the relationship between the amplitudes of the respective phases when no phase loss occurs, the presence of phase loss can be detected. As a result, phase loss detection with high accuracy can be performed. When actually tested, when a Fourier transform was performed by sampling 20 data with respect to the basic period using a microcomputer with a clock frequency of 32 MHz, the accuracy of amplitude and phase was 1% or less. Good results were obtained.

<Fourth aspect of abnormality monitoring>
Further, the monitoring unit 120 monitors the presence or absence of a three-phase phase loss state of the alternating current. As a result, after detecting that the phase is not a phase loss state, the monitoring unit 120 performs the Fourier transformation to obtain 3 of the output AC current obtained. By comparing the phases of the fundamental frequencies of the phases, it is possible to monitor the presence or absence of the three-phase reversed phase state of the output alternating current.

  That is, in the conventional current detection means, as described above, the amplitude value, effective current value, and phase obtained by the conventional current measurement means are easily affected by a three-phase unbalanced state, current distortion, and noise. For this reason, in the means for detecting the phase difference by detecting the phase difference, the phase difference is large especially when the phase is lost inside the motor of the delta connection, and whether the phase difference is shifted due to the phase loss. In some cases, it may not be possible to determine whether or not the phase difference is shifted.

  On the other hand, in the present embodiment, first, it is confirmed by checking the amplitude ratio of the fundamental wave that the phase is not open, and then determining the opposite phase by looking at the phase of each phase of the fundamental wave. As a result of the comparison, if the phase relationship of each phase is different from the phase relationship of each phase when the reverse phase state does not occur, the presence of the reverse phase state can be detected. As a result, it is possible to clearly discriminate the difference between the open phase and the reverse phase without being affected by distortion or noise.

<Fifth aspect of abnormality monitoring>
The monitoring unit 120 obtains the three-phase phase of the output alternating current by performing an arctangent function calculation using the Fourier cosine coefficient and the Fourier sine coefficient obtained by executing the Fourier transform, and the obtained phase is determined by the Fourier transform. It can correct | amend based on the positive / negative relationship of a cosine coefficient and a Fourier sine coefficient.

That is, FIG. 2 is a diagram showing orthogonal coordinates of the Fourier cosine coefficient (a _k ) on the horizontal axis and the Fourier sine coefficient (b _k ) on the vertical axis. In FIG. 2, I represents the amplitude when the Fourier cosine coefficient (a _k ) is a and the Fourier sine coefficient (b _k ) is b (see Equation 2). In FIG. 2, θ represents the phase when the Fourier cosine coefficient (a _k ) is a and the Fourier sine coefficient (b _k ) is b (see Equation 2). As shown in FIG. 2, considering the orthogonal coordinates of the Fourier cosine coefficient (a _k ) on the horizontal axis and the Fourier sine coefficient (b _k ) on the vertical axis, the position of the current vector is positive when the Fourier cosine coefficient (a _k ) is positive. When the Fourier sine coefficient (b _k ) is positive, it is in the first quadrant Q1. Similarly, when the Fourier cosine coefficient (a _k ) is negative and the Fourier sine coefficient (b _k ) is positive, it is in the second quadrant Q2, the Fourier cosine coefficient (a _k ) is negative, and the Fourier sine coefficient (b _k ). Is in the third quadrant Q3, the Fourier cosine coefficient (a _k ) is positive, and the Fourier sine coefficient (b _k ) is negative, it is in the fourth quadrant Q4.

  As a result, even if the value of arctangent function (arctangent, Atan ()) is only in the range of −90 degrees (−π / 2) to +90 degrees (π / 2), the above property is used. Thus, the phase can be converted from 0 degrees to 360 degrees from the positive / negative relationship between the Fourier cosine coefficient and the Fourier sine coefficient.

As an example, in order to convert the phase from 0 degrees to 360 degrees, the monitoring unit 120 has a positive Fourier cosine coefficient (a _k ) (for example, a) and a positive Fourier sine coefficient (b _k ) (for example, b). At that time, since the value obtained by Atan (b / a) is a positive value in the first quadrant, nothing is corrected. On the other hand, when the Fourier cosine coefficient (a _k ) is negative (for example, −a) and the Fourier sine coefficient (b _k ) is positive (for example, b), the monitoring unit 120 obtains the value obtained by Atan (b / −a). Is a negative value (fourth quadrant Q4), and is corrected by adding 180 degrees to the obtained value.

Further, the monitoring unit 120 calculates Atan (−b / −a) when the Fourier cosine coefficient (a _k ) is negative (for example, −a) and the Fourier sine coefficient (b _k ) is negative (for example, −b). Since the value becomes a positive value (first quadrant Q1), it is corrected by adding 180 degrees to the obtained value. Further, when the Fourier cosine coefficient (a _k ) is positive (for example, a) and the Fourier sine coefficient (b _k ) is negative (for example, −b), the monitoring unit 120 obtains the value obtained by Atan (−b / a). Since it becomes a negative value (fourth quadrant Q4), it is corrected by adding 360 degrees to the obtained value. In addition, the monitoring unit 120 can obtain a relative phase based on the first phase by subtracting the phase of the first phase from the obtained three phases. The monitoring unit 120 can detect the reverse phase based on the relative phase based on the first phase.

<Sixth aspect of abnormality monitoring>
As shown in FIG. 1, the monitoring apparatus 100 includes a memory 130 that stores a sine function value and a cosine function value corresponding to the number of data to be sampled when the Fourier transform is performed on the output AC current. .

  In this case, the monitoring unit 120 reads out the value of the sine function and the value of the cosine function corresponding to each sampling number from the memory 130, and executes the Fourier transform to read out the value of the sine function and the value of the cosine function. To obtain the Fourier cosine coefficient and the Fourier sine coefficient.

That is, when the Fourier cosine coefficient and the Fourier sine coefficient are obtained by Fourier transform, the values of sin () as a sine function and cos () as a cosine function are necessary, but the number of data to be sampled in the basic period is fixed. If so, the values of sin () and cos () of an arbitrary sampling number are always equal, and it is not necessary to perform sequential calculation. As described above, the Fourier cosine coefficient a _n and the Fourier sine coefficient b _n of the order n, where n is an arbitrary order and m is the number of data acquired during the basic period, are obtained by the following equation (3). . Therefore, if the data number m is fixed, the variables in the parentheses of cos and sin in the equation 3 are only n and k, and the sampling numbers k = 0 to k = m−1. A one-dimensional array constant into which the calculation results of sin () and cos () are substituted is prepared in advance and stored in the memory 130. Then, when the monitoring unit 120 obtains the Fourier cosine coefficient and the Fourier sine coefficient, instead of sequentially calculating sin () and cos (), the monitoring unit 120 refers to the corresponding value from the one-dimensional array constants and performs Fourier transform. Perform conversion.

  When actually testing using a simulation tool, the calculation result of sin () and cos () is multiplied by 10,000 for the one-dimensional array constant of sin () and cos () to avoid floating point arithmetic. Assigned an integer value. Sin () and cos () were sequentially calculated to obtain the amplitude and phase of six fundamental frequencies by Fourier transforming six currents assuming the currents of two three-phase three-wire motors. In this case, the processing time of Fourier transform was 15.4 msec, but when the method was changed to a method of referring to a one-dimensional array constant, the processing time of Fourier transform was improved to 1.9 msec.

Second Embodiment
Next, FIG. 3 is a diagram illustrating a configuration of the monitoring device according to the second embodiment. The second embodiment is different from the first embodiment in that the control device 20 is replaced with a control device 220. The second embodiment is different from the first embodiment in that current sensors 80 and 90 for measuring an input AC current input from the commercial power supply 10 to the control device 220 are provided. The second embodiment is different from the first embodiment in that DC superimposing circuits 65 and 75 are provided corresponding to the current sensors 80 and 90. Since other than these are the same as in the first embodiment, the description of the same parts as in the first embodiment will be omitted.

  Control device 220 includes a three-phase smoothing circuit 222, a smoothing capacitor 224, and a three-phase output inverter 226. The control device 220 smoothes the three-phase three-wire commercial frequency input AC current supplied from the commercial power supply 10 by the three-phase smoothing circuit 222 and the smoothing capacitor 224, and the three-phase output inverter 226 by the three-phase three-wire type. Outputs alternating current of any frequency. Thereby, the control device 220 controls the electric power supplied to the motor 30.

  The current sensor 80 is a sensor such as a current transformer that measures an input AC current of an R-phase commercial frequency input from the commercial power supply 10 to the control device 220. The current sensor 90 is a sensor such as a current transformer that measures the input AC current of the T-phase commercial frequency input from the commercial power supply 10 to the control device 220. That is, in the present embodiment, the current value of the two-phase output AC current among the three-phase input AC current is measured.

  The DC superimposing circuit 65 is a circuit that superimposes a DC voltage on the input AC current measured by the current sensor 80 (applies a DC bias). The DC superimposing circuit 75 is a circuit that superimposes a DC voltage on the input AC current measured by the current sensor 90 (applies a DC bias). For example, when the AD input range of the AD input port of the monitoring device 300 (microcomputer) is from 0 V to 5 V, the DC superimposing circuits 65 and 75 superimpose half DC 2.5 V on the current signal. For this reason, when the input port of the monitoring device 300 is a port that does not require the superimposition of a DC voltage, the DC superimposing circuits 65 and 75 may not be provided.

  The monitoring device 300 is a device for monitoring whether there is an abnormality in the input current input from the commercial power supply 10 to the control device 220 and monitoring the output current output from the control device 220 to the motor 30 for abnormality. It is. The monitoring device 300 can be realized by, for example, a microcomputer.

  The monitoring device 300 includes a receiving unit 310, a monitoring unit 320, and a memory 330. The monitoring device 300 corresponds to the monitoring device 100 in the first embodiment. The receiving unit 310 corresponds to the receiving unit 110 in the first embodiment. The monitoring unit 320 corresponds to the monitoring unit 120 in the first embodiment. The memory 330 corresponds to the memory 130 in the first embodiment. The monitoring device 300 monitors the presence or absence of an abnormality in the input current input from the commercial power supply 10 to the control device 220 in the same manner as in the first to sixth aspects in the first embodiment, and from the control device 220 The presence or absence of abnormality in the output current output to the motor 30 is monitored.

  The second embodiment shows an example in which the presence / absence of both an input current input from the commercial power supply 10 to the control device 220 and an output current output from the control device 220 to the motor 30 are monitored. However, the present invention is not limited to this, and it is possible to monitor only whether there is an abnormality in the input current input from the commercial power supply 10 to the control device 220.

10 Commercial power supply 20, 220 Control device 22 Switch 30 Motor 40, 50, 80, 90 Current sensor 60, 65, 70, 75 DC superimposing circuit 100, 300 Monitoring device 110, 310 Reception unit 120, 320 Monitoring unit 130, 330 Memory 222 Three-phase smoothing circuit 224 Smoothing capacitor 226 Three-phase output inverter

Claims (6)

A monitoring device that monitors whether there is an abnormality in an input current input to a control device that controls electric power supplied to an electric motor or an output current output from the control device,
A receiving unit that receives an input AC current or an output AC current measured by a current sensor that measures an input AC current input to the control device or an output AC current output from the control device;
A monitoring unit that performs Fourier transform on the input alternating current or output alternating current received by the receiving unit, and monitors whether the input current or output current is abnormal based on the execution result;
A monitoring device comprising: The monitoring device according to claim 1.
The receiving unit is a three-phase three-wire type arbitrary current value output from the control device or a two-phase current value of a three-phase three-wire commercial frequency input AC current input from a commercial power source to the control device. Receiving input AC current or output AC current measured by a current sensor that measures current values of two phases of output AC current of a frequency of
The monitoring unit adds a value obtained by subtracting a DC component from the current value of two phases received at the same time by the receiving unit to obtain an instantaneous AC current value by multiplying the instantaneous AC current value of the two phases by minus one. By calculating the instantaneous alternating current value of the third phase with no current sensor attached,
A monitoring device characterized by that. The monitoring device of claim 2,
The monitoring unit compares 3 amplitudes of the input AC current or the output AC current by comparing amplitudes of three-phase fundamental frequencies of the input AC current or the output AC current obtained by executing the Fourier transform. Monitor the phase for open phases,
A monitoring device characterized by that. The monitoring device according to claim 3.
The monitoring unit is obtained by executing the Fourier transform after detecting that the input AC current or the output AC current is not in a phase loss state as a result of monitoring the presence or absence of the phase loss in the three phases. Monitoring the presence or absence of a three-phase reversed state of the input AC current or the output AC current by comparing the phase of the three-phase fundamental frequency of the input AC current or the output AC current;
A monitoring device characterized by that. In the monitoring apparatus of any one of Claims 1-4,
The monitoring unit calculates an arctangent function using a Fourier cosine coefficient and a Fourier sine coefficient obtained by executing the Fourier transform, thereby obtaining a three-phase phase of the input AC current or the output AC current. And correcting the obtained phase based on the positive / negative relationship of the Fourier cosine coefficient and the Fourier sine coefficient,
A monitoring device characterized by that. In the monitoring apparatus of any one of Claims 1-5,
A memory in which a value of a sine function and a value of a cosine function corresponding to the number of data to be sampled when performing the Fourier transform on the input AC current or the output AC current is further provided,
The monitoring unit reads the value of the sine function and the value of the cosine function corresponding to each sampling number from the memory, and obtains the value of the sine function and the value of the cosine function that are read when executing the Fourier transform. To obtain the Fourier cosine coefficient and the Fourier sine coefficient,
A monitoring device characterized by that.

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