JP2921039B2 - Malfunction monitoring device for harmonic suppression device - Google Patents

Description

The present invention relates to a malfunction monitoring device for a harmonic suppression device.

B. Summary of the Invention The present invention monitors the operation of an active filter by comparing a load current with an output current of an active filter that cancels a harmonic current included in the load current in a power supply system to which an active filter is applied. As a result, a malfunction monitoring device for a high-performance harmonic suppression device is obtained.

C. Conventional technology If a rectifier load or an AC variable speed motor (VVVF) is present in the power supply system as a load, the voltage waveform of the power supply is distorted due to the harmonics generated by this load, causing abnormal heating of other equipment connected to the same system. Or an abnormal beat sound.

To prevent this, an active filter has been put to practical use in addition to a conventional LC filter.

D. Problems to be Solved by the Invention The principle of the active filter is to detect the harmonic components contained in the load current, and to apply a harmonic having the opposite phase to this harmonic current to this system by a pulse width modulation inverter (PWM inverter). By flowing the current, the harmonics of the load current cannot be canceled out well unless the magnitude and the phase are different from each other by 180 °. As well,
If the magnitude or phase deviates significantly, it becomes a harmonic generation source.

Conventionally, by increasing the reliability of the active filter, it has been prevented that the active filter becomes a harmonic generation source.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to compare an output current of an active filter that cancels out a harmonic current included in a load current with a load current to be suppressed. The object of the present invention is to provide a highly reliable and high-performance malfunction suppression device for a harmonic suppression device by monitoring the operation of the device.

E. Means and Action for Solving the Problems To achieve the above object, the present invention provides a power supply system to which an active filter is applied, in which a load current to be suppressed by a harmonic and a harmonic current included in the load current are reduced. The operation of the active filter is monitored by comparing the output current of the active filter to be canceled. In addition, as a monitoring circuit, the Fourier series expansion of each waveform is performed by digital processing using a microcomputer, and the absolute value and phase angle of the load current and the output current of the active filter are calculated for each order and each phase, and the absolute value is calculated. If the difference between the value ratio and the phase angle is within a certain value, the active filter is determined to be normal.

F. Embodiment An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 shows a schematic configuration of a malfunction monitoring device for a harmonic suppression device according to an embodiment of the present invention.
Is a load that generates harmonics such as a rectifier load or an AC variable speed motor (VVVF), 30 is an active filter that is a harmonic suppression device, 40 is a monitoring device, 50 is a first current transformer that detects load current, Reference numeral 60 denotes a second current transformer for detecting the output current of the active filter 30.

The detection signal Ii of the first current transformer 50 for detecting the load current becomes an input signal of the active filter 30, and the detection signal Ii of the first current transformer 50 and the active filter provided in the active filter 30 The second output current detector
The detection signal Io of the current transformer 60 becomes an input signal of the monitoring device 40. The number of current detectors is two (for two phases) or three (for three phases) for both load current detection and active filter detection. The current detectors for load current detection and the active filter output current detection are used. The inserted phase of the current detector must be the same. That is, input signals to the monitoring device 40 are 2-3 channels from the load side and 2-3 channels from the active filter side, for a total of 4-6 channels.

FIG. 1 shows the configuration of the monitoring device 40. In FIG. 1, 41
Is a sample and hold circuit, 42 is a multiplexer, 43 is an analog / digital conversion circuit (A / D conversion circuit), and 44 is a microprocessor unit (MP
U) and 45 are random access memories (RAM), and 46 is an interface.

In the monitoring device of FIG. 1, the load current detection signals Ii ₁ , Ii ₁
i ₂ is input to the shift registers S / H ₁ and S / H ₂ of the sample and hold circuit 41, respectively, and the shift register output current detection signals Io ₁ and Io ₂ are input to the shift registers S / H
Input to H ₃ and S / H ₄ . The sample and hold circuit 41
These analog input values are transferred to the microprocessor unit
The instantaneous value is held at regular time intervals based on the command from 44. The multiplexer 42 sequentially switches the data held in each shift register based on a command from the microprocessor unit 44 and sends the data to the A / D conversion circuit 43. The A / D conversion circuit 43 operates according to a command from the microprocessor unit 44, converts analog data into digital data, and sends the digital data to the microprocessor unit 44. The RAM 45 serves as a wave memory for input signals and output currents of the active filter, and the interface circuit 46 outputs alarm information and the like from the microprocessor unit 44 to the outside.

The RAM 45 records the waveforms of the load current and the output current of the active filter in digital quantities from the input signal. From this, it is expanded into a Fourier series by the microprocessor unit 44. The absolute value and the phase angle of each order on the load current side and the active filter output side as a result of Fourier expansion are compared, and if the difference is within a certain range, the operation of the active filter is determined to be normal.

FIG. 3 shows a flow of the above-mentioned monitoring. First, step
At S1, the active filter input / output current waveform is recorded.
The sampling interval for recording the load current waveform and the active filter output current waveform may be 0.1 to 1 msec, and can be handled by a general-purpose microcomputer. In step S2, Fourier series expansion is performed from the recorded waveform.

The calculation time required to expand the Fourier series takes a considerable amount of time with a general-purpose microcomputer, but there is no inconvenience because the purpose is to constantly monitor the active filter.

In step S3, an absolute value and a phase angle for each order of each waveform are obtained from the Fourier expansion result. In step S4, n = 2
The calculation for 13 is repeated, and in step S5, the n-th harmonic current _ILn included in the load current is compared with the basic current _IL1 of the load current.

Next, in step S6, of the respective higher harmonics included in the load current, only the order of a certain value or more (the ratio of the load current to the fundamental wave component is 10% or more, that is, K ≧ 0.1) is compared with the load current and the active current. Nth harmonic current included in the load current only for the same order of the filter output current
I _Ln and the nth harmonic current I _{An of the} active filter output current
Is compared. That is, the absolute values of the harmonics of the same phase and the same order of the load current and the output current of the active filter are compared, and when α ≦ 0.7 to 0.8, it is determined that the active filter is operating normally. If the comparison result is equal to or smaller than α, the process proceeds to step S7, and a difference operation between the phase angle of I _{Ln and} the phase angle of I _An is executed. In this case, the normal operation of the active filter is approximately β <30 °.

If (I _Ln phase angle) − (I _An phase angle) <β, the operations of steps S4 to S7 are repeated. If not less than β, the process proceeds to step S8. In step S8, if the harmonic of the load current exceeds the compensating capacity (capacity) of the active filter and the active filter is overloaded, the output of the active filter is automatically limited and compensation within the rating is performed. So that the above α is
Can be 0.7 or less. Therefore, when α becomes equal to or more than a certain value, an overload is determined, and the process proceeds to step S9 to display an overload. In step S7, (the phase angle of I _Ln ) −
(The phase angle of the L _An) <does not hold beta, or when it is not overloaded in step S8 raise an alarm output process proceeds to step S10. By performing the above operation cyclically,
The active filter is constantly monitored.

G. Effects of the Invention The present invention is as described above, and compares the output current of the active filter for canceling the harmonic current included in the load current to be suppressed with the harmonic current included in the load current. , A commercially available microcomputer can be mainly configured, and the load status can be displayed by software. Therefore, a malfunction monitoring device of a harmonic suppression device which is inexpensive and has a wide applicability can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a monitoring circuit of a malfunction monitoring device of a harmonic suppression device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a schematic configuration of a malfunction monitoring device of the harmonic suppression device according to an embodiment of the present invention. FIG. 3 is a monitoring flowchart of the monitoring circuit of FIG. 10 AC power supply, 20 load, 30 active filter, 40 monitoring circuit, 41 sample-hold circuit,
42 Multiplexer, 43 A / D conversion circuit, 44 Microprocessor unit, 45 RAM, 46 Interface, 50 Current transformer, 60 Current transformer.

Claims (1)

(57) [Claims] In a power supply system for suppressing harmonics contained in a load current using an active filter, a load current for suppressing a harmonic and an output current of an active filter for canceling a harmonic contained in a load current are provided. Monitoring means for comparing and monitoring the operation of the active filter, the monitoring means performs a Fourier series expansion of the load current and the output current waveform of the active filter by digital processing,
Calculating means for calculating the absolute value and phase angle of the load current and the output current of the active filter for each order and each phase; and when the ratio of the absolute value and the phase angle difference are within a predetermined value, the active filter is normal. A malfunction monitoring device for a harmonic suppression device, characterized by comprising a judging means for judging.