JPH0698469A - Control system of voltage detection-type reactive-power compensation apparatus - Google Patents

Abstract

PURPOSE:To control this system at high speed and to restrain a fluctuation in a voltage by a method wherein a detection circuit is installed in order to detect a DC signal in a system voltage and an operation circuit expressed by a specific operation formula is installed. CONSTITUTION:The difference between a detected system voltage VL and a target reference voltage Vref is input to a control-meter circuit 13. Reactive power generated by a thyristor-controlled reactor connected to a system bus 1 is increased or decreased and controlled by its output. The system voltage VL is made to follow the target voltage Vref. Especially a phase voltage VL as the system voltage and a phase voltage VL' delayed by 90 deg. from it are converted respectively into DC signals by squaring devices 17, 18. A voltage detection circuit 16 which finds a DC signal VC in the system voltage by instantaneously adding both and by removing a ripple is provided. The operation and processing of the voltage detection circuit 16 is expressed by a formula of VC={(VL<2>+VL'<2>)/2}<1/2>. Thereby, the system voltage VL can be converted instantaneously into a direct current by the voltage detection circuit 16, and the V control system of a feedback can be achieved at high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls a reactive power compensator (hereinafter referred to as SVC) installed in an AC power system based on a difference between a detected system voltage V _L and a target reference voltage V _ref. The present invention relates to a voltage detection type SVC control system.

[0002]

2. Description of the Related Art SVC suppresses voltage fluctuations due to load fluctuations by increasing or decreasing the reactive power supplied to the power system. In this SVC control, it is preferable to detect a reactive power fluctuation of the load and thereby perform open loop Q control because high speed control is possible. In particular, when it is desired to suppress voltage fluctuations at the flicker level, high-speed response is essential, and a response speed of, for example, 10 msec or less is required.

However, when the installation location of the SVC is limited and the load current cannot be detected easily, the reactive power of the load cannot be detected, so that the Q control method cannot be adopted.

In such a system, a DC signal (effective value) of the system voltage VL is detected, and V which increases / decreases the reactive power generated by the SVC so as to follow the target reference voltage V _ref.
Control (AVR control) is performed. This target reference voltage V
_ref is, for example, a long-period component of the system voltage V _L extracted by a low-pass filter (corresponding to the sending voltage of the substation).
To use.

The V control is a feedback control, requires a controller circuit having a first-order lag element for system stabilization, and has a problem that the response is inferior to the Q control.

FIG. 4 shows the control system of the SVC in which the portion related to the response is represented by a transfer function. In FIG. 4, reference numeral 1 is a system bus, which is connected to the substation power supply E _S by an impedance on the power supply side.
It is connected through dance X _S and supplies the variable load 2 in the distance.

Reference numeral 3 denotes an SVC connected to the system bus 1, which is a thyristor control reactor (hereinafter referred to as TCR) and a filter (hereinafter referred to as FC) connected in parallel. The TCR consists of the anti-parallel connection thyristor 4 and the lagging power Q.
FC is composed of a reactor X _L such as a high impedance transformer that generates _TCR , and FC is a capacitor 5 that generates a constant advance power Q _FC and a small-capacity series reactor that absorbs harmonics with this capacitor 5. 6 and 6.

A PLL circuit 7 receives a system voltage V _L from the system bus 1 via a transformer PT ₁ and produces a power supply synchronizing signal. Reference numeral 8 is a voltage detection circuit, which is composed of a rectifier 9 and a ripple-removing low-pass filter 10, and is provided with a transformer PT ₁
A DC signal V _c is output from the system voltage V _L received via the. The transfer function G ₁ (S) of the low-pass filter 10 is 1 /
(1 + ST ₁ ).

Reference numeral 11 is a reference voltage generating circuit, which is a low-pass filter.
The DC signal V _cTo system voltage V_Lof
Target period voltage V_refTake out as. This biography
Reaching function G₂(S) is 1 / (1 + ST₂).

An adder 12 outputs the difference between the detected DC signal V _c of the system voltage V _L and the target reference voltage V _ref . Thirteen
Is a controller circuit for AVR control, and K _{3 is used} as a transfer function.
Holds / (1 + ST ₃ ).

A pulse generator 14 compares the output of the controller circuit 13 with the power supply synchronizing signal to generate positive and negative trigger pulses. A pulse amplifier 15 outputs a trigger pulse to the gates G ₁ and G ₂ of the thyristor.

The above-mentioned configuration has a system voltage V_LDC signal V
_cAnd the target reference voltage extracted by the reference voltage generation circuit 11.
Pressure V_refDifference with (V_c-V_ref) With a constant response delay
Input the applied controller circuit 13 and output it to the TCR
Control. That is, the system voltage V _LDC signal V_cBut the eyes
Standard reference voltage V_refTCR lagging power Q to approach_TCR
Is increased or decreased to suppress voltage fluctuations.

[0013]

The response speed of the control system will be examined from the transfer function. The transfer function G ₁ (S) of the voltage detection circuit 8 is 1 / (1 + ST ₁ ) of the low pass filter 10.
Is. Further, the transfer function G of the reference voltage generation circuit 11
₂ (S) is 1 / (1 + ST ₂ ), and in parallel with this,
The transfer function G ₂ ′ (S) including the signal line for inputting the voltage detection signal V _c to the adder 12 becomes 1 + 1 / (1 + ST ₂ ). The transfer function of the controller circuit 13 is G ₃ (S) is K ₃ / (1
+ ST ₃ ).

Therefore, the transfer function of the entire control system is G ₀
(S) becomes G ₀ (S) = G ₁ (S) · {(1 + G ₂ (S) · G ₃ (S)}.

Here, since the reference voltage generating circuit 11 extracts the long-period component, ST _{2 is set} to a large value and 1 + G.
₂ (S) ≈ 1 can be considered.

Therefore, the transfer function of the entire control system is G ₀ (S) ≉G ₁ (S) G ₃ (S).

Consider the response speed of the voltage fluctuation suppression by the transfer function G ₀ (S). The system voltage fluctuation ΔV is the reactive power fluctuation Δ of the load 2 in the power supply side impedance X _S.
Occurs according to Q _L (change in flicker) (ΔV = ΔQ _L
・ X _S ). SVC is the change in reactive power of _TCR ΔQ _TCR
Try to suppress this by compensating with (Δ
Q _TCR = -ΔQ _L = -ΔV / X _S ). However, the detected ΔV changes the reactive power Q _{TCR of the} TCR through the transfer function G ₀ (S). This relationship is G ₀ (S) = ΔQ
_{It is TCR} / ΔV.

Here, each first-order lag element S of G ₀ (S)
In the feedback control system, T ₁ and ST ₃ need to be ST ₁ << ST _{3 in} order to stabilize the control. ST ₁ of the low-pass filter 10 for removing the ripple is ST ₁ ≈
Than one cycle (20msec / 50H _Z), it can not be shortened. Since ST ₃ is required to be about 5 times that of ST ₁ , high-speed control of SVC cannot be expected.

The response delay due to the adoption of the V control does not catch up with the response when the voltage fluctuation (flicker) ΔV in which the load fluctuation is abrupt and changes irregularly is suppressed as in the arc furnace, and the response is improved. The effect is significantly reduced.

Therefore, an object of the present invention is to provide a control system capable of high speed control even when V control is adopted.

[0021]

The control system of the voltage detection type SVC provided by the present invention is sufficient for stabilizing the difference between the detected DC signal V _c of the system voltage V _L and the target reference voltage V _ref. Is input to a controller circuit which is an amplifier circuit having a large response delay, and its output controls increase / decrease of reactive power generated by a thyristor control reactor connected to a system bus to set a system voltage V _L to a target voltage V _{L. In} a voltage detection type reactive power compensator that is made to follow _ref , the phase voltage of the system voltage and the phase voltage delayed by 90 ° are each converted into a DC signal by a squarer, and both are instantaneously added. It is characterized in that a voltage detection circuit for determining the DC signal V _c of the system voltage V _L is provided by removing the ripple.

The above arithmetic processing of this voltage detection circuit can be specifically expressed by the following arithmetic expression.

[Equation 1]

[0023]

When the instantaneous value is calculated based on the above formula, the DC signal V _C corresponding to the effective value is obtained for the system voltage V _L at each detection time point.

That is, V _L and V _L ′ have a phase difference of 90 °, and V _L ² = V _l ² · cos ² ωθ, V _L ² ′ = V _l ² · si
It is expressed as n ² ωθ, and from cos ² ωθ + sin ² ωθ = 1, each instantaneous value is squared and instantaneously added to obtain V _L ² with ripples removed at each time point. Since the voltage has been doubled by the addition, the coefficient unit is multiplied by 1/2 and square rooted to obtain the DC signal V _c corresponding to the effective value.

The detection delay of the voltage detection circuit 16 is only the calculation time, and can be obtained in a few msec which is about 1/10 of that when the ripple removing low-pass filter 10 is used. The first-order lag element ST _{3 of the} controller circuit 13 is also
Corresponding to this, the response speed of the control system of the SVC is 1/10 of that of the conventional one because it can be set to about 5 times the same as in the conventional one.
You can speed it up to a certain degree.

As a result, the V control method (feedback control) can ensure the same responsiveness as the Q control method (open loop control), and the SVC performance can be improved.

[0027]

1 shows an embodiment of the present invention. This is because the voltage detection circuit 16 is replaced with the conventional low-pass filter 10
The voltage detecting circuit 8 is replaced with the conventional voltage detecting circuit 8 using the above, and the other parts indicated by the same reference numerals have the same or equivalent configuration as the conventional configuration shown in FIG.

The present invention uses the system voltage V _L and the voltage V _L ′ which is delayed by 90 ° from the system voltage to calculate the control signal V _c obtained by converting the system voltage into a direct current, and calculates the value obtained by squaring the instantaneous value thereof. Instantly add, halve and square root. Therefore, a transformer PT having a Δ-Y connection for extracting a voltage delayed by 90 ° from the system voltage
₂ is added, and squarers 17, 18 for squaring the instantaneous value, an adder 19, a coefficient unit 20, and a switch 21 are provided.

The details of the voltage detecting circuit 16 are shown in FIG. 2 as a three-phase circuit. This voltage detection circuit 16
Corresponding to the SVC provided for three phases, it is provided for each of the U phase, V phase, and W phase.

The transformer PT ₁ takes out the phase voltage by the YY connection without changing the phase. A third circuit with a Δ connection is provided to absorb the third harmonic.

The transformer PT ₂ produces a 90 ° phase difference with the Δ-Y connection. That is, the V'phase on the secondary side is delayed by 90 ° with respect to the U phase on the primary side.

The operation of the U-phase voltage detection circuit 16 _u is shown in the waveform diagram of FIG. That is, the U-phase voltage detection circuit 16 _u receives the U-phase voltage V _u and the V′-phase voltage V _v ′ which is delayed by 90 °. Then, these are squared by the squarers 17 and 18, and added instantaneously by the adder 19. Further, the coefficient unit 20 is halved, and the square rootizer 21 is used to open the square root,
A DC signal _Vcu corresponding to the U-phase effective value is calculated.

The voltages of the primary V phase and the secondary W'phase, and the voltages of the primary W phase and the secondary U'phase also have a phase difference of 90 ° as in the above. Therefore, the operations of the V-phase and W-phase voltage detection circuits 16 _v and 16 _w are similarly performed in response to these voltages, and the V-phase DC signal V _cv and the W-phase DC signal V _cw are respectively calculated. Output.

When the transformers PT ₁ and PT ₂ have an output error in amplitude, as can be seen from the output waveform of the squarer shown in FIG. 3, a ripple of a quadruple cycle of the power supply occurs. In this case, the output levels of the respective squarers 17 and 18 are adjusted.

In the voltage detection circuit 16, the detection delay of the system voltage V _L is determined only by the calculation time, and a circuit of several msec can be realized. ST ₃ of the controller circuit 13 may be determined according to the response speed of the speeded up voltage detection circuit 16, and for example, ST ₃ = 5 · ST ₁ ≈10 msec.

This response speed is close to the time delay of the open loop Q control system, and therefore, the V control system can be expected to have the same flicker improvement effect as the Q control system.

[0037]

According to the present invention, the voltage detection circuit 16
Thus, the DC voltage of the system voltage V _L can be instantly converted, and the response time ST ₃ of the next-stage controller circuit 13 which is set to about 5 times the response time ST ₁ can be shortened to about 1/10 of the conventional one.
As a result, the speedup of the V control method is achieved.

[Brief description of drawings]

FIG. 1 is a control system diagram of a voltage detection type SVC control device showing an embodiment of the present invention.

FIG. 2 is a diagram showing the voltage detection circuit of FIG. 1 as a three-phase circuit.

FIG. 3 is a voltage waveform diagram showing the contents of calculation of the voltage detection circuit of FIG.

FIG. 4 is a control system diagram of a conventional voltage detection type SVC control device.

[Explanation of symbols]

1 system bus 2 load 3 reactive power compensator (SVC) 11 reference voltage generation circuit 12 adder 13 controller circuit 14 pulse generator 15 pulse amplifier 16 voltage detection circuit 17,18 squarer 19 adder 20 coefficient unit 21 switching Transformer PT ₁ Transformer for extracting phase voltage of system voltage without phase difference PT ₂ Transformer for extracting phase voltage with 90 ° phase delay

Claims (1)

[Claims] 1. A detected system voltage V _L and a target reference voltage V
The difference from _ref is input to the controller circuit that has a sufficiently large response delay with respect to the detection time of the system voltage for stabilization, and the output is used to disable the thyristor control reactor connected to the system bus. In the voltage detection type reactive power compensator in which the power is controlled to increase or decrease so that the grid voltage _VL follows the target voltage _Vref , the phase voltage of the grid voltage and the phase voltage delayed by 90 ° are respectively 2 Control of a voltage detection type reactive power compensating device characterized by comprising a voltage detection circuit for converting a direct current signal by a multiplier and instantaneously adding both to remove a ripple to obtain a direct current voltage _VL of a system. method.