JP5854609B2 - Converter device and control method thereof - Google Patents

Description

  The present invention relates to a converter device that protects equipment from overvoltage when a line of a power system is interrupted, and a control method thereof.

  If the electric circuit is released during the operation of the PWM converter due to a voltage drop in the power system, a power failure, power interruption, or the like, stable current control cannot be performed. For this reason, there exists a danger that the voltage of a period abnormality may be applied to the circuit connected to the same system | strain. Conventionally, measures to prevent this have been studied. For example, in Patent Document 1, when the power is shut off during the regeneration mode operation, the power source connected to the PWM converter is detected by detecting the power cutoff by the output of the input voltage waveform detection circuit and stopping the PWM converter operation. Abnormal voltage is prevented from being applied to the system.

JP-A-7-322626

  Usually, the converter has a built-in sine wave filter connected to the power system, and power is transferred to and from the power system via a circuit breaker (breaker). If the breaker is cut off during operation of the converter and the electric circuit is released, the control system of the interconnection inverter becomes unstable and voltage oscillation occurs in the sine wave filter portion. At this time, if the sine wave filter resonates due to voltage oscillation, an overvoltage is generated, and there is a risk that a high voltage is applied to an accessory device such as a sine wave filter. The frequency due to this voltage oscillation is around 1 kHz, which is considerably higher than the frequency of a normal system (50/60 Hz).

  This situation will be described with reference to FIG. 3. FIG. 3 (a) shows that the vibration component overlaps the sine wave simultaneously with the occurrence of the voltage vibration, and FIG. 3 (b) shows the frequency due to the voltage vibration. Is shown to rise.

  Usually, since the output voltage in the converter is detected after being taken in through the low-pass filter, the high frequency band due to the voltage oscillation is cut by the low-pass filter and the detection gain becomes small, and there is a possibility that the overvoltage cannot be detected.

  In Patent Document 1, the operation of the PWM converter is stopped using the fact that the PWM switching frequency component is detected at the time of a power failure. However, when voltage detection including the low-pass filter as described above is performed, it is difficult to detect a high frequency such as PWM switching, and it may be impossible to detect the occurrence of a power failure.

  The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a converter device that does not give an overvoltage to an accessory device when an electric circuit of a power system is released, and a control method therefor.

In order to solve the above-described problems, the present invention is connected to a DC power supply unit that outputs DC power, and a PWM command calculation unit for performing current control, and DC power from the PWM command from the PWM command calculation unit. In a converter device comprising a converter for converting into a filter and a filter connected between the converter and an external power system,
The PWM command calculation unit includes a frequency calculation unit that calculates a frequency based on a voltage on the power system side of the filter, a comparison calculation unit that generates a block signal when the calculated frequency exceeds a threshold, and the block signal A gate is provided that shuts off the output of the PWM command to the converter when generated.

  Further, in the converter device described above, the threshold value is a preset threshold frequency, and the comparison operation unit generates a block signal when the calculated frequency is higher than the threshold frequency. To do.

  Further, in the converter device described above, the threshold frequency is set to a frequency higher than a steady frequency of AC power output from the converter.

  Further, in the converter device described above, the PWM command calculation unit further includes a phase calculation unit that calculates a phase from the frequency output from the frequency calculation unit, a current command and the AC power converted by the converter. It has a voltage calculating part which calculates a voltage command value based on the electric current side voltage of the current, the filter, and the phase calculated by the phase calculating part.

  In the converter device described above, the PWM command calculation unit further includes a low-pass filter that receives a voltage on the power system side of the filter and removes a high-frequency component, and outputs the output from the low-pass filter to the frequency calculation unit. Is input.

In order to solve the above-described problems, the present invention is connected to a DC power supply unit that outputs DC power, and a PWM command calculation unit for performing current control, and DC power from the PWM command from the PWM command calculation unit. In a control method of a converter device comprising a converter for converting to a converter, a filter connected between the converter and an external power system, and controlling a PWM command based on the converted AC voltage,
The PWM command calculation unit calculates a frequency based on a voltage on the power system side of the filter, generates a block signal when the calculated frequency exceeds a threshold value, and outputs a block command to the converter by the block signal. The output is cut off.

  According to the present invention, by monitoring the frequency, even when the control system is unstable, the PWM output can be quickly cut off to protect the attached device from overvoltage.

It is a block diagram of the converter apparatus of this invention Example. It is a block diagram explaining the PWM command calculation part of the converter apparatus of this invention Example. It is explanatory drawing of a voltage waveform when a circuit breaker is interrupted | blocked during the converter apparatus driving | operation of this invention Example.

  Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, an example of a converter device during regeneration will be described.

  FIG. 1 is an example of a regenerative converter 108 connected to an inverter 105 that controls a motor (IM). Reference numeral 100 denotes a power converter, which includes a converter 101, a smoothing capacitor 102, a current detector 103, and a PWM command calculation unit 104. Reference numeral 103 denotes a current detector that detects current from the AC output of the converter 101, 107 denotes a sine wave filter connected to the current detector 103 and an external power system 200, and 106 denotes a power system side of the sine wave filter 107. Is a voltage detector for detecting the voltage of The regenerative converter 108 is configured by the above-described units.

  Reference numeral 201 denotes a circuit breaker installed between the regenerative converter 108 and the power system 200.

  During the regenerative operation, the inverter 105 serves as a DC power source, generates DC power, and supplies it to the converter 101 while being smoothed by the smoothing capacitor 102. The DC power is converted into AC power by the power conversion device 100 and supplied to the external power system 200 via the sine wave filter 107 and the circuit breaker 201.

  In order to perform current control, the power conversion device 100 uses a PWM command calculation unit 104 to generate a PWM command (command value) from a current detection value (current signal) of the current detector 103 and a voltage detection value (voltage signal) of the voltage detector 107. ) Is calculated. The converter 101 converts DC power into AC power based on the PWM command value and outputs it. This AC power is supplied to the power system 200 via 107 sine wave filters provided outside and a circuit breaker 201.

  Here, the breaker 201 is in the on state during normal operation, and the electric circuit of the regenerative converter 108 and the power system 200 is in the connected state. The sine wave filter 107 is composed of L (inductance) and C (capacitor) and has a resonance frequency. However, L and C may be connected via a resistor R for resonance suppression. This resonance frequency is normally set to about 1 kHz or more in order to remove PWM ripple.

  The current detector 103 is composed of, for example, a shunt resistor or a hall CT, and is arranged at an AC output unit of the converter to detect an AC current. A voltage detector 106 is arranged on the power system side of the filter 107 to detect an AC voltage. The AC voltage may be the output of a transformer such as PT, or may be a voltage signal divided by a resistor or the like. In addition, the voltage signal and current signal on the AC side are usually three-phase signals, but if no zero-phase current flows, detection for two phases may be performed, and the remaining one phase can be determined by calculation. It is.

  FIG. 2 is an example of a block diagram for explaining the PWM command calculation unit 104 provided in the power conversion apparatus 100.

  The PWM command calculation unit 104 may be constructed by software such as a microcomputer, or part or all may be constructed by an analog circuit. D99 is a low-pass filter (LPF) that removes high-frequency components contained in the voltage signal from the voltage detector 106 and outputs the result. D100 is a frequency calculation unit that calculates and outputs the frequency included in the voltage signal from which the high frequency component has been removed. D101 is a phase calculator that calculates the phase from the frequency output from the frequency calculator D100.

  D102 is a voltage calculation unit that calculates and outputs a voltage command value based on the current command (current command value), the detected AC power current signal, the voltage signal, and the phase from the phase calculation unit D101. . D103 is a PWM signal generation unit that generates a PWM command (PWM command signal) from the voltage command value calculated above.

  D104 is a comparison calculation unit that compares a threshold frequency preset and stored with the calculation frequency output from the frequency calculation unit D100, and generates a gate block signal (level 0) when the calculation frequency is equal to or higher than the threshold frequency. When the frequency is lower than the threshold frequency, no gate block signal is generated (level 1). Here, when the stationary frequency output in the regenerative operation is 50 Hz, the threshold frequency is set to 60 Hz, which is 20% higher than the stationary frequency (power supply frequency).

  D105 is a gate that receives the output of the comparison operation unit D104 and the output of the PWM signal generation unit D103. The gate is closed when the gate block signal (level 0) is generated, and the PWM command signal from the PWM signal generation unit D103 is received. Blocked. When the PWM command signal is interrupted, converter 101 stops the conversion operation from DC power to AC power, and the output of AC power is stopped. When the block signal is not generated (level 1), the PWM command signal from the PWM signal generation unit D103 is output through the gate D105 and supplied to the converter 104.

  Next, the operation of the regenerative converter when the electric circuit is interrupted during the regenerative operation in the above configuration will be described. FIG. 3 is an explanatory diagram showing an increase in voltage waveform and frequency when the breaker 201 is suddenly interrupted during regenerative converter operation.

  If the circuit breaker 201 is suddenly interrupted during the regenerative operation, the current in the electric circuit to the power system 200 is interrupted, so that the current signal detected by the current detector 103 is reduced. When the current signal input to the PWM command calculation unit 104 decreases, the deviation from the current command value (set to a constant value) increases. Therefore, the voltage calculation unit D102 increases the voltage command value in order to reduce the deviation. To control. When the voltage command value increases, the converter 101 is controlled to increase the alternating current by the PWM command.

  However, since the electric path to the electric power system 200 is interrupted by the circuit breaker 201 and no current flows, the above control for increasing the alternating current is repeated and diverges, resulting in the resonance frequency of the sine wave filter 107. Vibrations occur in the output voltage of the converter 101.

  FIG. 3A shows the output voltage of the power conversion device 100 when the electric circuit is interrupted 0.01 seconds after the start, and has a waveform in which the resonance frequency overlaps the sine wave. FIG. 3B shows a tendency of frequency increase due to the voltage oscillation. In normal regenerative operation, it operates at a frequency of 50 Hz, but the frequency tends to increase with the interruption of the electric circuit.

  As described above, when the sine wave filter resonates due to voltage oscillation, an overvoltage is generated, and there is a risk that a high voltage is applied to an accessory device such as a sine wave filter. Since this overvoltage has a higher frequency than 50 Hz or 60 Hz, which is the frequency of the power system, it is filtered by the low-pass filter D99 and the gain at the time of detection is lowered. Therefore, there is a risk that an overvoltage due to resonance cannot be detected.

  In the embodiment of the present invention, for example, when the steady frequency output in the regenerative operation is 50 Hz, the threshold frequency is set to 60 Hz, which is 20% higher than the steady frequency, which is higher than the steady frequency (power supply frequency). When the circuit breaker 201 is shut off, the frequency calculated by the frequency calculation unit D100 rises toward the resonance frequency while vibrating. When the output frequency of the frequency calculation unit D100 reaches 60 Hz at the timing t1 shown in FIG. 3B, a gate block signal (level 0) is generated from the comparison calculation unit D104. This gate block signal closes the gate D10, and the PWM command output from the PWM signal generator D103 is cut off. When the PWM command is interrupted, converter 101 stops the conversion operation from DC power to AC power, and the output is stopped. Therefore, the output can be stopped before the occurrence of the overvoltage based on the oscillation of the output voltage of the converter 101.

  As described above, according to this embodiment, the frequency of the AC voltage output from the power converter 100 is monitored, and when this frequency exceeds a threshold frequency higher than a preset power supply frequency, a gate block signal is generated. By doing so, it is possible to prevent in advance the occurrence of overvoltage due to frequency increase. Therefore, it is possible to protect an accessory device such as a sine wave filter connected from the overvoltage to the output side of the power converter 100 from the overvoltage.

DESCRIPTION OF SYMBOLS 100 Power converter 101 Converter 102 Smoothing capacitor 103 Current detector 104 PWM command calculating part 105 Inverter (DC power supply part)
106 Voltage detector 107 Sine wave filter 108 Regenerative converter 200 Power system 201 Circuit breaker D99 Low pass filter (LPF)
D100 Frequency calculation unit D101 Phase calculation unit D102 Voltage calculation unit D103 PWM signal generation unit D104 Comparison calculation unit D105 Gate.

Claims (8)

A PWM command calculation unit for performing current control connected to a DC power supply unit that outputs DC power, a converter that converts DC power into AC power from a PWM command from the PWM command calculation unit, and the converter and the external In a converter device having a filter connected between the power systems of
The PWM command calculation unit includes a frequency calculation unit that calculates a frequency based on a voltage on the power system side of the filter, a comparison calculation unit that compares the calculated frequency with a threshold value, and a comparison result by the comparison calculation unit. On the basis of a gate for cutting off the output of the PWM command to the converter,
When the connection between the external power system and the filter is cut off and the current of the electric circuit to the power system of the converter device is cut off , the comparison calculation unit has the frequency calculated by the frequency calculation unit. When the threshold value is exceeded, the converter device outputs a block signal that closes the gate and shuts off the output of the PWM command . The converter device according to claim 1,
The threshold value is a preset threshold frequency, and when the connection between the external power system and the filter is interrupted, the comparison operation unit is configured to block when the calculated frequency is higher than the threshold frequency. A converter device for generating a signal. The converter device according to claim 2,
The converter device according to claim 1, wherein the threshold frequency is set to a frequency higher than a stationary frequency of the AC power output from the converter. In the converter apparatus in any one of Claims 1-3,
The PWM command calculation unit further includes a phase calculation unit for calculating a phase from the frequency output from the frequency calculation unit, a current command, a current of AC power converted by the converter, and a voltage on the power system side of the filter. And a voltage calculator that calculates a voltage command value based on the phase calculated by the phase calculator. In the converter apparatus in any one of Claims 1-4,
The PWM command calculation unit further includes a low-pass filter that receives a voltage on the power system side of the filter and removes a high-frequency component, and an output from the low-pass filter is input to the frequency calculation unit. . A PWM command calculation unit for performing current control connected to a DC power supply unit that outputs DC power, a converter that converts DC power into AC power from a PWM command from the PWM command calculation unit, and the converter and the external In the control method of the converter device comprising a filter connected between the power systems of the control system for controlling the PWM command based on the converted AC voltage,
The connection between the external power system the filter is blocked, when the current path to the power system of the converter device is cut off, the PWM command computation unit, the voltage of the electric power system side of the filter A method for controlling a converter device, comprising: calculating a frequency based on the block frequency; generating a block signal when the calculated frequency exceeds a threshold; and cutting off an output of a PWM command to the converter by the block signal. In the control method of the converter device according to claim 6,
The threshold is a preset threshold frequency, and when the connection between the external power system and the filter is interrupted, a block signal is generated when the calculated frequency is higher than the threshold frequency. A control method for a converter device. In the control method of the converter device according to claim 7,
The control method of a converter device, wherein the threshold frequency is set to a frequency higher than a steady frequency of AC power output from the converter.

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