JP2725538B2 - Voltage fluctuation suppression device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage fluctuation suppressing device which controls a reactive power of a power system by an inverter connected to a power system having an unbalanced load to suppress a voltage fluctuation at a power receiving point.

[0002]

2. Description of the Related Art Conventionally, as this type of apparatus, for example, "Mitsubishi Electric Technical Report" Vol. 65 No. 6, 1991, P60
There are proposed reactive power compensating devices. FIG.
It is a circuit diagram showing a control circuit of the reactive power compensator,
Reference numeral 1 denotes a power source, 2 denotes a power receiving transformer connected to the power source 1 via system impedances R and X, 3 denotes an AC circuit breaker that connects a load 4 such as an arc furnace to the power receiving transformer 2, and 5 denotes a multiple transformer. An AC circuit breaker that connects the power transformer 6 to the power receiving transformer 2; a self-excited inverter 7 configured by a GTO thyristor or the like that generates and consumes reactive power with the system by changing its output; Is a harmonic filter connected to the system via an AC circuit breaker 9, 10 is a load current detecting current transformer for detecting a load current i _L , 11 is an inverter current detecting current transformer for detecting an output current of the inverter 7. Current transformers 12 and 1 for load current detection and inverter current detection.
1 is a control device that introduces a load current and an inverter output current detected by the control circuit 1 and calculates and outputs a firing signal of the self-excited inverter.

That is, the active power and the reactive power generated by the load 4 such as an arc furnace are determined by the impedance Z _S = R + of the power supply system.
It acts on jX to fluctuate the receiving point voltage, but generally X >>
Because of the relationship of R, the reactive power fluctuation ΔQ _L and the reactance component X of the power supply system act, and the voltage fluctuation ΔV =
Resulting in X · ΔQ _L. In order to suppress the fluctuation of the power receiving point voltage, the output of the self-excited inverter 7 is controlled so as to cancel the reactive power fluctuation generated by the load.

FIG. 5 is a detailed block diagram of a control device 12 for controlling the output of the self-excited inverter 7. Reference numeral 12-1 denotes a load current i _L detected by the load current detecting current transformer 10; This is a three-phase to two-phase conversion circuit that performs phase-to-phase conversion and outputs an effective component i _PA + i _PB and an invalid component i _qA + i _qB . Where i _PA is the positive phase component of the active component current, i _PB is the negative phase component (including the harmonic component) of the active component current, _iqA is the positive phase component of the reactive component current, and _iqB is the reactive component current. It is a negative phase component (including a harmonic component). Reference numeral 12-2 denotes a filter circuit that extracts i _PB and i _qA + i _qB as compensation current components from the active component current and the reactive component current introduced from the three-phase to two-phase conversion circuit, and outputs the extracted components. 12-3 is a two-phase to three-phase conversion circuit for performing two-phase to three-phase conversion of the compensation reference command derived by the filter circuit 12-2;
Is a subtractor that outputs the deviation between the three-phase compensation reference output from the two-phase to three-phase conversion circuit and the inverter output current detected by the inverter current detecting current transformer 11, and 12-5 is the output of the subtractor. A current control circuit 12-6 outputs an inverter voltage reference based on the reference voltage. An inverter firing circuit 12-6 outputs a firing signal to the self-excited inverter 7 according to the voltage reference of the current control circuit.

That is, in order to control the reactive power generated by the self-excited inverter 7, the control device 12 receives the load current i _L from the load current detecting current transformer 10, and controls the three-phase to two-phase converter 1.
Introduce to 2-1. The three-phase to two-phase converter 12-1 converts the introduced three-phase current into two phases, and converts the two-phase converted effective component current i _PA
+ I _PB and the reactive current i _qA + i _qB are filtered by the filter circuit 12.
-2. In the filter circuit 12-2, a change i _PB (a negative phase component + a harmonic component) of a load effective current of a load to be compensated by the self-excited inverter 7 from the output of the three-phase / two-phase converter 12-1, and a reactive current The average value _iqA (positive phase component) and the variation _iqB (negative phase component + harmonic component) are detected. Filter circuit 1
The output of 2-2 is converted to a three-phase compensation current reference by a two-phase to three-phase converter 12-3. The difference between the three-phase compensation current reference and the value detected by the inverter current detection current transformer 11 is calculated by the subtractor 12-4, and is input to the current control circuit 12-5. The current control circuit 12-5 calculates the voltage reference of the self-excited inverter 7 that makes the deviation zero based on the input deviation signal. This voltage reference is the inverter firing circuit 12-6.
And a firing signal of the inverter element based on the voltage reference is derived, and drives and controls the self-excited inverter 7.

As described above, the voltage fluctuation at the receiving point is suppressed by compensating the negative phase component of the active current generated by the load 4 and the positive phase component and the negative phase component of the reactive current by the output of the self-excited inverter 7. Together with the three-phase equilibration. In addition, the harmonic filter 8 is provided to absorb the harmonic components generated by the self-excited inverter 7 and to improve the power factor.

[0007]

Since the conventional voltage fluctuation suppressing device is configured as described above, if the reactive power fluctuation width of the load is known in advance, the inverter capacity is determined according to the fluctuation width. However, if the reactive power fluctuation width changes each time, the maximum possible capacity must be selected, and the inverter capacity becomes large and expensive. Further, as shown in FIG. 6, when the reactive power fluctuation width exceeds the inverter capacity, the fluctuation of the power receiving point voltage cannot be suppressed, and there is a problem that the voltage fluctuation occurs. In FIG. 6, a indicates a variation ΔV of the power receiving point voltage, b indicates a load variation, and c indicates a reactive power output from the inverter to compensate for the load variation. As is clear from the figure, the receiving point voltage is suppressed to a constant value as long as the load fluctuation does not exceed the inverter capacity, but if the load fluctuation exceeds the maximum capacity of the inverter, the receiving point voltage fluctuates by ΔV _1. .

The present invention has been made in view of such a problem, and the value of the reactive power of the load is reduced by the inverter capacity.
Even if it becomes larger than the amount, the fluctuation value (fluctuation range)
It is an object of the present invention to obtain a voltage fluctuation suppressing device capable of suppressing fluctuations in the voltage of the receiving point as long as the voltage is equal to or less than the data capacity .

[0009]

Means for Solving the Problems Voltage fluctuation suppression according to the present invention
The device is connected to a load connected to the
Reactive power compensation inverter and harmonic connected in parallel
A reactive power compensator consisting of a wave filter.
Introducing a load current flowing through the load,
Negative phase of active current to be used as compensation current component from load current
(IpB), positive phase component of reactive current (iqA), reactive current
The first file that selects and extracts and outputs the reverse phase component (iqB) of
Filter means, the filter extracted by the first filter means.
Reactive current flowing from the positive current component to the harmonic filter
Flow positive phase component (iqL) to reduce
The first circuit for deriving the active current positive phase component,
Second filter for deriving the time average of the reactive current positive phase
Means, invalidation of the AC power supply side derived by the first circuit
Subtract the output of the second filter means from the current positive phase component
A second circuit, the output of the second circuit and the first
The effective current negative phase component extracted by the filter means;
The reactive current compensating inverter
With a third circuit for deriving the three-phase compensation current reference of
It is.

Further , the voltage fluctuation suppressing device according to the present invention
Load connected to the
Independent inverter and harmonic filter for reactive power compensation
Voltage fluctuation suppression device composed of a reactive power compensator
And introducing a load current flowing through the load.
From the load current, the positive phase component (ipA) of the effective current and the compensation
Negative phase component (ipB) of active current to be current component and invalid
Positive phase component of current (iqA), negative phase component of reactive current (iqB)
A fourth filter means for selecting and extracting and outputting
4 before the reactive current positive phase component extracted by the filter means 4
Reactive current positive phase component (iqL) flowing through the harmonic filter
To introduce the positive phase of the reactive current flowing to the AC power supply.
The first circuit that generates the positive phase of the reactive current on the AC power supply side
Second filter means for deriving a time average value, the first filter means
From the positive phase of the reactive current on the AC power supply side derived by the circuit
A second circuit for subtracting the output of the second filter means,
The positive current component extracted by the fourth filter means
Invalidation of the compensation inverter obtained by multiplying the specified power factor setting
Derivation of the first circuit from the positive-phase current command value (iq1)
Power factor control is performed by subtracting the
A fifth circuit for obtaining an inverter reactive current command for
The effective current command value is subtracted from the output of the second circuit to
A sixth circuit for obtaining a command for the positive phase component of the barter reactive current,
And the output of the fourth filter means.
Due to the negative phase of the active current and the negative phase of the reactive current,
Deriving a three-phase compensation current reference for an inverter for power compensation
3 is provided.

[0011]

The voltage fluctuation suppressing device according to the first aspect of the present invention subtracts the time average of the reactive current positive phase as the compensation current component from the reactive current reference of the inverter, so that the reactive current reference at the time of load change is positive phase. The current reference for the negative phase component and the negative phase component are used. However, the positive phase component is reduced with the passage of time, and the current reference is used only for the negative phase component. As a result, a large inverter compensation capacity during the next load change can be secured.

In the voltage fluctuation suppressing apparatus according to a second aspect of the present invention, the reactive current positive phase component for obtaining a predetermined power factor is reduced from the reactive current positive phase component reference of the inverter, thereby securing a large inverter compensation capacity. And a power factor can be controlled to a predetermined value.

[0013]

[Embodiment 1] Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a control circuit block diagram of a voltage fluctuation suppressing apparatus according to a first embodiment of the present invention, and the same parts as those in FIG. 4 are denoted by the same reference numerals. In FIG. 1, 13
The subtractor for subtracting the reactive current positive-phase component i _qL harmonic filter 8 from reactive current positive phase component i _qA load extracted from the filter circuit 12-2, 14 calculates a time average of the output of the subtracter 13 Since the low-frequency filter 14 has a long time constant, it can be realized by a ring counter or a PC. Reference numeral 15 denotes a subtractor for subtracting the output of the low-frequency filter 14 from the output of the subtractor 13, and 12-7 denotes a reactive current _{antiphase component iqB} extracted by the filter circuit 12-2 and the subtractor 1.
5 is an adder for adding the outputs of the five.

That is, the filter circuit 1 is operated by the subtractor 13.
The reactive current positive phase component iqL of the harmonic filter 8 is subtracted from the extracted reactive current positive phase component iqA of 2-2 to derive the reactive current positive phase component on the power supply side. This reactive current positive phase component is applied to the low frequency filter 1
4 and its time average is taken. Then, the output of the low-frequency filter 14 is subtracted from the output of the subtractor 13 by the subtractor 15, so that the change in the positive phase of the reactive current during the load change is the magnitude of the change.
While the output of, but to generate an output that this variation is going to decrease with time.

The output of the subtractor 15 is added by the adder 12-7 to the reactive current negative phase component iqB extracted by the filter circuit 12-2 and output to the two-phase to three-phase converter 12-3. 2
The phase-to-phase converter 12-3 also receives the active current negative phase ipB from the filter circuit 12-2, and performs the two-phase
The phase-converted current reference is output. The three-phase two-phase in FIG.
The converter 12-1 and a signal that does not output the active current positive phase component ipA
The filter circuit 12-2 is called first filter means.
U. Also, detection of the reactive current positive phase of the harmonic filter 8
The circuit (not shown) and the subtractor 13 are a first circuit, a low frequency
The filter 14 is a second filter means, and the subtractor 15 is
Second circuit, adder 12-7 and two-phase to three-phase converter 12-3
Is the third circuit.

FIG. 2 is a waveform diagram showing the operation of each part in the first embodiment, where a indicates the voltage fluctuation at the power receiving point, b indicates the load fluctuation, and c indicates the output of the inverter. That is, the self-excited inverter 7 generates an output corresponding to the load change in response to the load change, but the output gradually decreases with a time constant determined by the low frequency filter 14. At this time, voltage fluctuation Δ
V will cause a slow fluctuation. And
Even if a large load change occurs, the self-excited inverter 7
Output without reaching the maximum capacity. this is,
This is because the output of the self-excited inverter 7 is adjusted by always monitoring the positive phase component of the reactive current of the load so that the maximum response can be made to the fluctuation of the load. The voltage fluctuation also fluctuates slowly, and becomes small as the fluctuation defined in unit time.

Embodiment 2 FIG. In the first embodiment, the control circuit is configured to increase the voltage fluctuation tolerance at the expense of the power factor. However, as shown in FIG. And the output of the power factor setting unit 16 are multiplied by a multiplier 17 to calculate a positive-phase command value iq1 of the reactive current. Then, the force by the subtractor 18 subtracts the reactive current positive phase component of the power supply
Inverter reactive current command (reactive power compensation) for rate control
The inverter for power supply to operate for power factor control.
It calculates a reactive current command value) of the order, may be obtained inverter reactive current positive phase component command by further reducing the output of the subtracter 15 by the subtractor 19. By adding such a circuit, the average power factor on the power supply side can be set and controlled. Note that the three-phase to two-phase conversion shown in FIG.
The filter 12-1 and the filter circuit 12-2 are for the active current positive phase.
And this is called the fourth filter means.
U. The power factor setting unit 16, the multiplier 17, and the subtractor 18
The circuit and the subtractor 19 are a sixth circuit.

[0018]

As described above, according to the present invention,
Reactive power compensation connected to the power supply based on the output obtained by subtracting the time-reactive reactive current positive phase component from the power source reactive current positive phase component, and the active current negative phase component and reactive current negative phase component obtained from the load current. Derived the three-phase compensation current reference of the inverter, so that the reactive power value of the load
Exceeds the inverter capacity,
While it is below, fluctuations in the receiving point voltage can be suppressed. Further, the reactive current for obtaining a predetermined power factor from the reactive current positive phase component reference reactive power compensating inverter positive-phase component command value
Since to reduce, it can be performed average power factor constant control.

[Brief description of the drawings]

FIG. 1 is a control circuit block diagram of a voltage fluctuation suppressing device according to a first embodiment of the present invention.

FIG. 2 is a waveform chart showing the operation of each unit according to the first embodiment of the present invention.

FIG. 3 is a control circuit block diagram of a voltage fluctuation suppressing device according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a control circuit of the reactive power compensator.

FIG. 5 is a control circuit block diagram showing a conventional voltage fluctuation suppressing device.

FIG. 6 is a waveform chart showing the operation of each part of the conventional voltage fluctuation suppression device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 4 Load 6 Multiple transformer 7 Self-excited inverter 12 Controller 12-1 Three-phase two-phase converter 12-2 Filter circuit 12-3 Two-phase three-phase converter 12-5 Current control circuit 12-6 Inverter ignition Circuit 14 Low frequency filter 16 Power factor setting device

Claims (2)

(57) [Claims] 1. An AC power supply, a negative power supply connected to the AC power supply.
Load, reactive power compensation connected in parallel to this load
Power Compensation Using Inverter and Harmonic Filter
A voltage fluctuation suppression device configured by a device, wherein a load current flowing through the load is introduced, and
Negative phase component (ipB) of active current to be used as compensation current component
And the positive phase component (iqA) of the reactive current, and the negative phase component (i
qB) to select and extract and output the reactive current positive phase component extracted by the first filter means.
And the reactive current positive phase component (i
qL) to reduce the positive phase of the reactive current flowing on the AC power supply side.
A first circuit for deriving a minute value, for deriving a time average value of the reactive current positive phase on the AC power supply side.
Second filter means for detecting a reactive current on the AC power supply side derived from the first circuit.
A second subtraction of the output of the second filter means from the phase component
Circuit, the output of the second circuit, and the extraction of the first filter means.
And the active current negative phase component and the reactive current negative phase component
The three-phase compensation current before Symbol reactive power compensation for the inverter
A voltage fluctuation suppressing device comprising a third circuit for deriving a reference . 2. An AC power supply, a negative power supply connected to the AC power supply.
Load, reactive power compensation connected in parallel to this load
Power Compensation Using Inverter and Harmonic Filter
A voltage fluctuation suppression device configured by a device, wherein a load current flowing through the load is introduced, and the load current
From the positive phase component (ipA) of the effective current,
Negative phase component (ipB) of active current and positive phase of reactive current
Min (iqA) and the negative phase component (iqB) of the reactive current
Fourth filter means for extracting output, the reactive current positive-phase component extracted in the fourth filter means
And the reactive current positive phase component (i
qL) to reduce the positive phase of the reactive current flowing on the AC power supply side.
A first circuit for deriving a minute value, for deriving a time average value of the reactive current positive phase on the AC power supply side.
Second filter means for detecting a reactive current on the AC power supply side derived from the first circuit.
A second subtraction of the output of the second filter means from the phase component
Circuit, the active current positive phase component extracted by the fourth filter means
Of the compensation inverter obtained by multiplying
From the positive-phase command value (iq1) of the active current, the first circuit
By subtracting the derived reactive current positive phase on the power supply side, the power factor control
Circuit for obtaining an inverter reactive current command for subtracting the reactive current command value from the output of the second circuit.
A sixth circuit for obtaining an inverter reactive current positive phase component command by an inverter, an output of the sixth circuit, and extraction of the fourth filter means.
With the output active current negative phase component and reactive current negative phase component,
Voltage fluctuation suppression device, characterized in that it comprises a third circuit for output guide <br/> the 3-phase compensation current reference before Symbol reactive power compensation inverter.