JPH09322407A - Control method for reactive power compensator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the voltage of a link point from going up even if there is an omission of ripple load. SOLUTION: This method is one which automatically adjusts the system voltage VL at the linkage point, in a reactive power compensator 1 where the parallel circuit of a thyristor phase control reactor 2 and an LC filter 3 is connected to a system bus 4 and is linked to the system power 5. This is one which forcibly makes a thyristor phase control reactor 2 fully electrically continuous at the point of time when the system voltage VL gets over the reference voltage VDU, by comparing the system voltage VL at the control linkage point with preset reference voltage VDU.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive power compensator, and more particularly, to a reactive power compensator for phase-controlling a thyristor phase control reactor to suppress voltage fluctuations due to load fluctuations in a power system. The present invention relates to a control method for automatically adjusting a system voltage in a vehicle.

[0002]

2. Description of the Related Art For example, in an electric power system in which a variable load such as an electric arc furnace, electric iron load, steel rolling load, etc. is connected to a system power supply,
In order to suppress fluctuations in the system voltage due to load fluctuations, a reactive power compensator (hereinafter referred to as SVC) that compensates reactive power due to load fluctuations is provided between the system power supply and the fluctuating load.

As shown in FIG. 3, the SVC 1 includes a thyristor phase control reactor 2 (hereinafter, referred to as TCR) for generating a variable lagging reactive power and an LC filter 3 for generating a fixed lagging reactive power in parallel. It has a structure in which the circuit is connected to the system bus 4 and is connected to the system power supply 5. In the figure, 6
Is one or more variable loads.

In a power system provided with SVC1, SVC1
By adjusting the current I _T flowing in the TCR2 in the TCR2, the lagging reactive power generated in the TCR2 is increased / decreased in accordance with the change in the system voltage V _S accompanying the load change, and the voltage change is suppressed. The constant advance reactive power generated in 3 suppresses the voltage drop in the system bus 4 uniformly while improving the power factor.

On the other hand, when a capacitor constituting the LC filter 3 is connected to the system bus 4, the system voltage V _L (hereinafter, referred to as a connection point voltage) at the connection point of the SVC 1 on the system bus 4 rises. The phenomenon may occur. Therefore, in the conventional SVC 1, in order to control the interconnection point voltage V _L to a constant voltage, the following control method has been adopted.

As shown in the control block of FIG. 4, the interconnection point voltage V _L is detected by a transformer (not shown), and the effective value V _D of the interconnection point voltage V _L is calculated by the arithmetic circuit 7. on the other hand,
The effective value V _{D of} the interconnection point voltage V _L obtained as described above
Is input to the transfer function circuit 8 and the time constant T of the transfer function is increased to output the long-term average value of the effective value V _D of the interconnection point voltage V _L from the transfer function circuit 8.

[0007] As long voltage average value control command value V _ref of the effective value V _D of the interconnection point voltage V _L, the error between the voltage control command value V _ref and the effective value V _D via the subtraction circuit 9 Input to the voltage control transfer function circuit 10. In this voltage control transfer function circuit 10, the voltage control command value V _ref and the effective value V
PI control that minimizes the error from _D is executed.

The output signal S _T of the voltage control transfer function circuit 10 is input to the thyristor firing arithmetic circuit 11, the thyristor firing arithmetic circuit 11 generates a thyristor firing signal, and based on the thyristor firing signal. Phase control of TCR2. By controlling the phase of the TCR 2 by the thyristor firing signal, the interconnection point voltage V _L is maintained at a substantially constant voltage.

[0009]

By the way, the variable load 6
Is separated from the grid, the interconnection point voltage _VL rises due to the loss of the variable load 6. Therefore, in the voltage control system of the SVC 1, the lagging reactive power of the TCR2 is reduced in order to reduce the interconnection point voltage _VL. It works to increase. However, this type of voltage control system detects the interconnection point voltage V _L and adjusts the current I _T of the TCR 2 based on the detection signal to control the interconnection point voltage V _L described above. Therefore, depending on the control constant and the system condition, the response delay or the impedance of the control circuit and the main circuit cannot be matched, resulting in an unstable state, and the transition point voltage _VL is transiently lowered. There is a possibility that an unstable state occurs in which the interconnection point voltage V _L rises above a permissible value and vibrates.

FIG. 5 is a simulation in which two fluctuating loads 6 are prepared, and one fluctuating load 6 is separated from the system. The system voltage V _S , the interconnection point voltage V _L ,
Effective value V _{D of} interconnection point voltage V _L , voltage control transfer function circuit 1
0 output signal S _T , system current I _S , two load currents I _L1 , I _L2 , LC filter current I _F and TCR current I _T
Each waveform of is shown. As shown in the figure, at the time when one variable load 6 is removed (when the load current I _L2 is lost), the interconnection point voltage V _L rises (a portion in the figure) and an unstable state in which it is oscillating Is apparently occurring.

When the interconnection point voltage V _L rises above the allowable value in this way, the remaining variable loads 6 become overvoltages. When these variable loads 6 use semiconductor elements, etc. There were problems such as element breakdown and load withstand voltage.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to provide reactive power compensation capable of suppressing an increase in the interconnection point voltage even if a variable load is removed. It is to provide a control method of the device.

[0013]

As a technical means for achieving the above object, the present invention relates to an SVC in which a parallel circuit of a TCR and an LC filter is connected to a system bus and is connected to a system power source. A control method for automatically adjusting the interconnection point voltage, in which the interconnection point voltage is compared with a preset predetermined reference voltage, and the TCR is forcibly full when the system voltage becomes equal to or higher than the reference voltage. It is characterized in that it is made conductive.

[0014]

1 and 2 show an embodiment of the present invention.
Will be described. The same parts as those in FIGS. 3 to 5 are designated by the same reference numerals.

The SVC 1 of the present invention, like the conventional one, is variable.
TCR2 that generates lagging reactive power and fixed leading reactive power
A parallel circuit with the LC filter 3 for generating
It has a structure in which it is connected to and connected to the system power supply 5, and the TCR2
Current I flowing through_TBy adjusting its TCR2
Of the lagging reactive power generated in the _S
The voltage fluctuation is suppressed by increasing or decreasing according to the fluctuation of
Due to the constant advanced reactive power generated in the LC filter 3,
Uniformly suppresses the voltage drop on the system bus 4 while improving the power factor.
Control.

Here, in the SVC 1 of the present invention, in order to control the interconnection point voltage V _L to a constant voltage, the following control method is adopted.

[0017] In steady state interconnection point voltage V _L is no omission of variable load 6 is not increased, conventional manner, the interconnection point voltage V _L transformer (shown as indicated by the control block 1 And the effective value V _D of the interconnection point voltage V _L is calculated by the arithmetic circuit 7. On the other hand, by inputting the effective value V _D of the interconnection point voltage V _L obtained as described above into the transfer function circuit 8 and increasing the time constant T of the transfer function,
The transfer function circuit 8 outputs the long-term average value of the effective value V _D of the interconnection point voltage V _L.

[0018] a long time a voltage mean value control command value V _ref of the effective value V _D of the interconnection point voltage V _L, the error between the voltage control command value V _ref and the effective value V _D via the subtraction circuit 9 Input to the voltage control transfer function circuit 10. In this voltage control transfer function circuit 10, the voltage control command value V _ref and the effective value V
PI control that minimizes the error from _D is executed. This time,
The switch 12 is switched to the terminal A, and the voltage control transfer function circuit 10 has the thyristor firing arithmetic circuit 11
Is connected to.

Therefore, the output signal S _{T of the} voltage control transfer function circuit 10 is input to the thyristor firing arithmetic circuit 11 via the switch 12, and the thyristor firing arithmetic circuit 1 is provided.
At 1, the thyristor firing signal is generated, and the TCR 2 is phase-controlled based on the thyristor firing signal. By the phase control of the TCR 2 by this thyristor firing signal, the interconnection point voltage V _L is maintained at a substantially constant voltage.

Meanwhile, if the variable load 6 is separated from the system, when the interconnection point voltage V _L by omission of load fluctuation 6 rises, the effective value V _D of the interconnection point voltage V _L to its raised,
A predetermined reference voltage V set in advance by the comparison circuit 13
Compared to _DU . This comparison circuit 13 causes the interconnection point voltage V
_L result of the comparison between the effective value V _D and the reference voltage V _DU of, when the effective value V _D of the interconnection point voltage V _L is equal to or higher than the reference voltage V _DU, on the basis of the output signal of the comparator circuit 13 Switch 12 is switched from terminal A to terminal B.

The reference voltage V _DU input to one terminal of the comparison circuit 13 is about 110% of the system voltage V _{S when} the allowable range of fluctuation of the interconnection point voltage V _L is about ± 10%. It may be set in advance to a corresponding voltage value.

The terminal B of this switch 12 has a TCR2
Since a signal (1 pu) for fully conducting the thyristor is previously given, the signal is input to the thyristor firing arithmetic circuit 11 via the switch 12, and the thyristor firing arithmetic circuit 11 fully ignites the thyristor firing. Generate a signal,
Based on the thyristor firing signal, the TCR2 is fully turned on.

Due to this forced full conduction of TCR2,
The lagging reactive power generated in the TCR 2 increases and the leading reactive power of the interconnection point voltage V _L can be instantaneously reduced, and the rise of the interconnection point voltage V _L is suppressed. Two variable loads 6
As shown in FIG. 2 which shows a simulation in which one of the fluctuating loads 6 is separated from the system, one fluctuating load 6 is compared with the conventional case (see FIG. 5).
At the time when the load current has passed (when the load current I _L2 has disappeared), T
Due to full conduction of CR2 (b part in the figure), the interconnection point voltage V
The rise of _L is suppressed (part c in the figure), and an unstable state such as vibration does not occur.

[0024]

According to the present invention, there is provided a control method for automatically adjusting the interconnection point voltage in an SVC in which a parallel circuit of a TCR and an LC filter is connected to a system bus and is connected to a system power supply. , The interconnection point voltage is compared with a preset predetermined reference voltage, and the TCR is forcibly brought into full conduction when the system voltage becomes equal to or higher than the reference voltage.
Even if the variable load is pulled out, the rise of the interconnection point voltage can be suppressed instantaneously, a stable interconnection point voltage can be secured, and accidents such as element destruction due to overvoltage can be prevented beforehand. It is possible to provide a highly reliable and highly reliable var compensator.

[Brief description of drawings]

FIG. 1 is a control block diagram showing an embodiment of a method of the present invention.

FIG. 2 is a waveform diagram showing a voltage or current signal in a simulation reproducing a load drop by the method of the present invention.

FIG. 3 is a circuit diagram showing a main circuit in which a reactive power compensator is connected to a grid.

FIG. 4 is a control block diagram for explaining a conventional method.

FIG. 5 is a waveform diagram showing a voltage or current signal in a simulation in which load loss is reproduced by a conventional method.

[Explanation of symbols] 1 Reactive power compensator (SVC) 2 Thyristor phase control reactor (TCR) 3 LC filter 4 System bus 5 System power supply V _L System voltage at interconnection point V _DU reference voltage

Claims (1)

[Claims] 1. In a reactive power compensator in which a parallel circuit of a thyristor phase control reactor and an LC filter is connected to a system bus and is connected to a system power supply, a control method for automatically adjusting a system voltage at the connection point. The system voltage at the interconnection point is compared with a preset reference voltage, and the thyristor phase control reactor is forcibly brought into full conduction when the system voltage becomes equal to or higher than the reference voltage. A method of controlling a reactive power compensator, comprising: