JP2588954B2 - Control circuit for static var compensator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control circuit for a static var compensator.

[Conventional technology]

FIG. 4 shows a conventional control circuit for a static var compensator of this type. In the figure, 1 is a power system, 2 is a reactor, 3 is a thyristor device constituted by an anti-parallel circuit of a thyristor, 4 is a capacitor, 5 is a voltage detection circuit, 6 is an addition point, 7 is a primary delay circuit, and 8 is an addition. point,
9 is a voltage control circuit, 10 is an addition point, 11 is a thyristor firing phase control circuit, 12 is a current transformer, 13 is a current detection circuit, 14 is an addition point, 15 is an integration circuit, 16 is a negative polarity prevention circuit, 17 Is a static var compensator composed of the reactor 2, the thyristor device 3, and the capacitor 4.

In the reactive power compensator 17, the capacitor 4 is connected to the power system 1
And the thyristor device 3 continuously controls the admittance of the reactor 2 connected in parallel with the capacitor 4 to advance the combined reactive power Q ₀ of the capacitor 4 and the reactor 2. It is configured so that the adjustment can be continuously performed from the range to the late phase.

 Next, the operation of the control circuit will be described.

In FIG. 4, an effective value of the voltage of the power system 1 is detected by a voltage detection circuit 5, and a voltage deviation ΔV ₁ between the detected value and a voltage reference value Vref is obtained at an addition point 6. The voltage deviation signal ΔV ₁ is input to the addition point 8 and also to the primary delay circuit 7. At the addition point 8, the above-described first deviation ΔV ₁ (voltage deviation)
And the output of the primary delay circuit 7 to calculate the second deviation Δ
Find V ₂ (voltage deviation). This second deviation ΔV ₂ is input to the next-stage voltage control circuit 9. The voltage control circuit 9 includes:
Usually consists of a first-order lag element, (Where Ty is a time constant and Ky is a gain constant). The output of the voltage control circuit 9 is input to a thyristor firing phase control circuit 11 via an addition point 10. The thyristor firing phase control circuit 11 converts the gate firing signal with the gate firing phase corresponding to the reactive power Q ₀ so that the reactive power compensator 17 can output the required reactive power Q ₀ according to the input signal level. 3 is performed.

When the control circuit performing the above operation reduces the voltage of the power system 1 below the first voltage reference value Vref, the reactive power compensation device
The reactive power compensator 17 outputs the leading reactive power as the reactive power Q ₀ and acts to increase the voltage of the power system 1, and conversely, when the voltage of the power system 1 rises above the voltage reference value Verf. Acts as a reactive power Q ₀ to output the delayed reactive power to lower the voltage of the power system 1. As described above, the voltage increasing operation and the voltage decreasing operation make it possible to keep the voltage of the power system 1 constant.

However, when the voltage of the power system 1 is constantly lower than the voltage reference value Verf and the reactive power compensator 17 is operated so as to increase the voltage in response thereto, Most of the compensating ability it has is spent for steady voltage drop. Therefore,
During a steady voltage drop, for example, even if a new voltage change occurs, there is a problem that the voltage change can no longer be accommodated and the function of the reactive power compensator 17 cannot be fully utilized. To solve the above problems, and added to the first-order lag circuit 7 to the control circuit, for steady variation of the voltage deviation [Delta] V _1, a first deviation [Delta] V ₁ at the summing point 8 first-order delay circuit 7 so that the control circuit does not respond to a steady change in the first deviation ΔV ₁ . For example, when the first deviation ΔV ₁ changes stepwise at time t ₁ as shown in FIG. 5 (a), the second deviation ΔV ₂ becomes only the initial part of the change of the first deviation ΔV _1. It follows and then gradually converges to zero.

On the other hand, when the voltage of the power system 1 rises, the control circuit controls the reactive power output Q ₀ of the reactive power compensator 17 to the lag side,
It acts to suppress the rise in voltage. When suppressing the rise of the voltage, because the must flow leading phase reactive power Q _C or more slow reactive power Q _L of the capacitor 4, a reactor 2 and thyristor device 3 controls the reactive power Q _L = Q _O + Q _C It is necessary to have a sufficient capacity, and a device with a very large rating is required, so that there is a problem that it becomes uneconomical.

Therefore, from an economic point of view, the reactor 2 and the thyristor device 3 are provided with an overload rating for a short period of time, and a relatively small continuous rating device is used for a short period of time to generate several times the delayed reactive power of the continuous rating. It is desirable to control. In the reactive power compensator 17 having such a short-time overload rating, it is necessary to add a constant current control circuit 100 for operating the reactor 2 and the thyristor device 3 within an allowable overload to the control circuit.

The constant current control circuit 100 detects a current I _R flowing through the thyristor device 3 by a current transformer 12 and converts the current I _R into a DC signal corresponding to an effective value of the current I _R by a current detection circuit 13.
When the current I _R is larger than the current setting value Iref, it calculates the deviation signal ΔI by summing point 14 and input to the integrating circuit 15. The result integrated by the integration circuit 15 is input to the negative polarity prevention circuit 16. The negative-polarity blocking circuit 16 allows only the positive-polarity input signal to pass therethrough, and performs the operation of blocking the input signal when the negative-polarity blocking signal is applied. This is to operate the constant current control circuit 100 only when the current I _R of the thyristor device 3 is larger than the current set value Iref. Further, the output of the negative polarity blocking circuit 16 is input to the addition point 10, to suppress the current I _R within the current set value Iref as a current feedback signal, performs the function of preventing the overloading of the thyristor device 3.

As is clear from the above description, the conventional control circuit for a reactive power compensator uses the reactor 2 and the thyristor device 3 in an overload region when the voltage of the power system 1 rises relatively large, and It operates so as to suppress overvoltage of the system 1. That is, as shown in FIG. 6 (a), when the voltage rising period of the power system 1 continues for a relatively long period, the reactor 2 and the thyristor device 3 are used in an overloaded state for the long period. Therefore, in order to keep this state within the allowable overload tolerance, the above-mentioned constant current control circuit 10 is used.
The operation of 0 is started, and the current I _R of the thyristor device 3 is gradually reduced as shown in FIG. 6 (b), and finally acts to keep it within the range of the continuous rated current. In addition to the above operation, in the delay circuit 7 which is a first-order delay circuit, the addition point 8 does not constantly respond to a steady change in the first deviation ΔV ₁ as shown in FIG. The second deviation ΔV ₂
The level of reduced, operates to lower the current I _R of the thyristor device 3.

[Problems to be solved by the invention]

Since the conventional control circuit for a static var compensator is configured as described above, overvoltage of the power system continues for a relatively long time as shown in FIGS. 5 (a) and 6 (a). If, for both the constant current control circuit 100 and a primary delay circuit 7 acts in the direction of decreasing the current I _R of the thyristor device 3 simultaneously, the current I _R seventh FIG synergy by thyristor device 3 for the acting As shown in FIG.
If only, or compared to when only the constant current control circuit 100, the magnitude of the current I _R will be caused to rapidly decrease beyond predetermined. As a result, there has been a problem that the overvoltage suppression function of the reactive power compensator 17 cannot be sufficiently exhibited when the voltage of the power system 1 rises.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a control circuit for a static var compensator capable of sufficiently exhibiting an overvoltage suppression function for a var compensator. I do.

[Means for solving the problem]

The control circuit for a static var compensator according to the first aspect receives, as inputs, a static var compensator that adjusts reactive power of a power system with a thyristor, and an output of a detection circuit that detects a voltage of the power system. A delay circuit for delay control, a voltage control circuit for voltage-controlling the output of the delay circuit, and detecting an energizing current of the thyristor to suppress and control the thyristor to the set value when the current value exceeds the set value. A constant current control circuit, and a thyristor firing phase control circuit that controls the thyristor based on a composite value of an output of the voltage control circuit and an output of the constant current control circuit, and an output signal of the constant current control circuit. The delay circuit is constituted by a first-order lag element having a variable time constant so that the time constant of the delay circuit can be varied according to the magnitude of the delay time.

According to a second aspect of the present invention, there is provided a control circuit for a static var compensator, wherein an input resistance of an operational amplifier including a delay element in a delay circuit and a feedback resistance are changed only in a time constant without changing a steady gain. It is configured to be switched simultaneously by a switch.

The control circuit for a static var compensator according to the third aspect is provided with a switch for changing the size of the feedback capacitor of the operational amplifier including the delay element of the delay circuit, and changing only the time constant without changing the steady-state gain. It is a thing.

[Action]

The control circuit for a static var compensator according to any one of claims 1 to 3, wherein the constant current control circuit for suppressing overload of the static var compensator for adjusting the reactive power of the power system by a thyristor is operating. For example, the time constant can be changed without changing the steady-state gain by changing the input resistance and the feedback resistance of the operational amplifier including the delay element of the primary delay circuit, or the size of the feedback capacitor of the operational amplifier can be changed by the steady-state gain. It is designed to purify its function by changing without changing it.

(Example of the invention)

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention. First, the structure will be described. In the figure, components having the same reference numerals as those in FIG. 4 indicate similar components.

In FIG. 1, 18 is a comparison circuit, 19 is a delay circuit having a first-order delay element with a time constant changeover switch,
Reference numeral 20 denotes a switch control circuit for controlling the time constant changeover switches SW1 and SW2 of the delay circuit 19.

 Next, the operation of the present invention will be described below.

When the reactor 2 and the thyristor device 3 are not operated in the overload region, the current I _R flowing through the thyristor device 3
Is smaller than the current reference Iref of the constant current control circuit 100,
The output S of the integrating circuit 15 becomes zero, and the constant current control circuit 100 does not operate. In the non-operation state, the comparison value Y of the comparison circuit 18 is larger than the output S of the integration circuit 15, so that the comparison circuit 18 does not operate, and the input from the comparison circuit 18 causes the switch control circuit 20 to switch the delay circuit 19 Switch SW1
And SW2 to ON state. In this state, the delay circuit 19
Is represented by the following equation.

Here, since the deviation ΔV ₂ needs to be made zero with respect to the stationary deviation ΔV ₁ , the stationary gain of the delay circuit 19 needs to be 1. Therefore, from the above equation (1), Shall be satisfied. As a result, the above equation (1) becomes Can be expressed as The time constant T _{1 in} this case is Next, T ₁ is chosen to equal to the constant T _R when the first-order lag circuit 7 in the conventional control circuit of Figure 4. Therefore, SW1 and S
When W2 is ON, the operation of the delay circuit 19 is the same as that of the primary delay circuit 7 of the conventional static var compensator control circuit shown in FIG.

Next, the case where the reactor 2 and the thyristor device 3 are operated in the overload region will be described. The current I _R flowing through the thyristor device 3 increases to be equal to or more than the current reference value Iref in the constant current control circuit 100. 15 starts integrating the positive direction, the output S of the negative polarity blocking circuit 16 after the integrating is input to a summing point 10, the constant current control with slow as current I _R is equal to the current reference value Iref Start operation.

On the other hand, the output S of the negative polarity blocking circuit 16 is input to the comparison circuit 18, and when the output S becomes equal to or greater than the comparison value Y of the comparison circuit 18, the switch control circuit 20 is driven, and the switch SW1 of the delay circuit 19 and SW2 is both turned off. In this state, the transfer function of the delay circuit 19 can be expressed by the following equation.

In the above equation (5), it is possible to 1 the constant gain G ₂ while satisfy the expression (2). Therefore, It can be.

 As a result, the above equation (5) can be expressed by the following equation.

The time constant T _{2 in} this case is as follows: T ₂ = R ₃ C (8) In the above equation (4), if R ₂ ≪R ₃ is selected, the above equation (4) becomes approximately T ₁ = R ₂ C (9). Therefore, if the switches SW1 and SW2 are turned on,
Constant T ₁ time of the delay circuit 19 can be selected to a relatively small value, when leaving the switches SW1 and SW2 to OFF, constant T ₂ time of the delay circuit 19 becomes a sufficiently large value as compared to T _1, the delay circuit 19 The effect can be dulled.

As described above, when the operation of the constant current control circuit 100 is started, by setting the time constant of the delay circuit 19 sufficiently large, it is possible to prevent a rapid output drop which is a problem in the conventional control circuit. be able to. This operation will be described below with reference to FIG.

As shown in FIG. 2A, the voltage of the power system 1
Consider the case of relatively large increases stepwise at t _1.
In this case, the reactive power compensator 17 is controlled on the lag side,
The reactor 2 and the thyristor device 3 are controlled in the overload region. As a result, the current I _R flowing through the thyristor device 3 is reduced as shown in FIG.
Integrator 1 to increase beyond the current reference value Iref at 0
5 starts integration in the positive direction, and the output S of the negative polarity blocking circuit 16 is input to the addition point 10. Then S as shown in FIG. 2 (c) operates the comparing circuit 18 at time t ₂ became more than the comparison value Y, the switch of the delay circuit 19 having a first-order lag element by driving the switching control circuit 20 OF both SW1 and SW2
Perform the action to make it F. As a result, by previously chosen as the time constant of the delay circuit 19 is changed from T ₁ to T _2, the constant T ₁ and T ₂ becomes T ₁ <T ₂ time, slowing the operation of the delay circuit 19 Can be done. Therefore, the current I _{R of the} thyristor device 3
Is almost only reduced by the constant current control circuit 100,
Comparison circuit 18 and the output S of the integrating circuit 15 of the constant current control circuit 100 becomes equal to or lower than the set value Y at time t ₃ stops operation,
Operation of the delay circuit 19 time constant is switched to T ₁ from T ₂ again delay circuit 19 by the ON both switches SW1 and SW2 of the delay circuit 19 is restarted. At this point, since the operation of the constant current control circuit 100 has almost stopped, the output of the reactive power compensator does not decrease rapidly even if the delay circuit 19 operates with a relatively short time constant. Problems in the control circuit for the reactive power compensator can be solved.

As the reactive power compensation device in the above embodiment, the case of a method of controlling the reactive power Q _R of the reactor 2 in the thyristor device 3, regardless of its particular type as long as the reactive power compensation device using thyristors The same effects as in the above embodiment can be obtained.

Further, in the above embodiment, a method of simultaneously switching the input resistance and the feedback resistance of the operational amplifier by a switch as the time constant switching means of the delay circuit 19 has been described. However, as shown in FIG. 3, the feedback capacitor may be switched by the switch. good.

In the above embodiment, the first-order delay element is shown as the delay circuit 19. However, the delay circuit is not limited to the first-order delay element, and any configuration may be used as long as the time constant is variable. Play.

〔The invention's effect〕

As described above, according to the first to third aspects of the present invention, the magnitude of the time constant of the delay circuit is increased according to the magnitude of the output signal of the constant current control circuit. It is possible to prevent a rapid decrease in the thyristor current due to the synergistic action of the constant current control circuit and the delay circuit at the time of overvoltage, and to exert an effect of sufficiently suppressing the overvoltage of the power system by the reactive power compensator.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a control circuit for a static var compensator according to one embodiment of the present invention, FIG. 2 is an explanatory diagram showing the operation of FIG. 1, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a block diagram of a control circuit of the conventional static var compensator, and FIGS. 5, 6, and 7 are explanatory diagrams showing the operation of FIG. . DESCRIPTION OF SYMBOLS 1 ... Power system, 2 ... Reactor, 3 ... Thyristor device, 4 ... Capacitor, 5 ... Voltage detection circuit, 6 ...
Addition point 7, 7 Primary delay circuit 8, Addition point 9, Voltage control circuit 11, Thyristor firing phase control circuit 12,
... Current transformer, 13 ... Current detection circuit, 14 ... Addition point, 15
…… Integration circuit, 16… Negative blocking circuit, 17… Static var compensator, 18… Comparison circuit, 19… Delay circuit, 20
... switch control circuit, 100 ... constant current control circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-17426 (JP, A) JP-A-61-122726 (JP, A) JP-A-60-84925 (JP, A)

Claims (3)

(57) [Claims] 1. A static var compensator for adjusting reactive power of a power system by a thyristor, an output of a detection circuit for detecting a voltage of the power system, and a time constant variable by inputting the output. A voltage control circuit that performs voltage control on the output of a delay circuit that performs phase control by a next-delay element; and detects a current flowing through the thyristor and sets the current value to a set value when the current value becomes larger than a set value. A constant current control circuit that performs such suppression control, and a thyristor firing phase control circuit that controls the thyristor with a composite value of the output of the voltage control circuit and the output of the constant current control circuit,
A control circuit for a static var compensator, wherein the time constant of the delay circuit is increased in accordance with the magnitude of the output signal of the constant current control circuit. 2. An input amplifier and a feedback resistor of an operational amplifier including a delay element in a delay circuit are simultaneously switched by a switch so that only a time constant is changed without changing a steady-state gain. A control circuit for a static var compensator according to claim 1. 3. The method according to claim 1, wherein the size of the feedback capacitor of the operational amplifier including a delay element in the delay circuit is switched by a switch to change only the time constant without changing the steady-state gain. 2. A control circuit for a static var compensator according to claim 1.