CN1282130A - Electric network reactive-load continuous compensation method and its compensation equipment - Google Patents

Abstract

The present invention relates to an electric network reactive-load continuous compensation method and its compensation equipment. It is characterized by adopting fixed capacitor to series-connect with voltage-variable source, then connected into electric network to substitute traditional capacitor switching mode, and the voltage-variable source is produced by auto-governor or inverter, and directly entered into electric network of passed through transformer and entered into electric network. The capacitor is switched in under the condition of zero corrent, so that it can protect electric network against damage due to impact current and can protect capacitor self-body from damage, and use power factor display circuit, capacitor current and voltage detection circuit to sample and monitor, and utilize regulation of voltage-variable source value to continuously change compensation current value to implement electric network reactive-load continuous compensation.

Description

Power grid reactive power continuous compensation method and compensation device

The invention relates to a technology and a compensation device for reactive power continuous compensation of a power grid, which can be used for single-phase or three-phase reactive power compensation of high and low voltage power grids, and belongs to the technical field of electric power systems.

At present, the reactive power compensation of domestic and foreign power grids mainly adopts the capacitor switching method, that is, the capacitor is directly connected in parallel between the phase line-phase line or phase line-neutral line of the power grid, and the purpose of changing the compensation current is achieved by changing the parallel capacitance value of the power grid. For example, the existing reactive power compensation technology and optimized compensation method introduced by Cui Chi in "Analysis of Reactive Power Compensation for Low-Voltage Distribution Network" (Power Grid Technology, July 2000) also use the capacitor switching method. With these traditional reactive power compensation technologies, since the switching of capacitors is carried out in stages, the compensation current generated is also step-wise, which cannot fully compensate the reactive power of the grid, and the grid is still often under-compensated or over-compensated. In the compensation state, the power factor cannot be close to 1, so the capacity of the power supply equipment cannot be fully utilized, and the line loss of the power supply line cannot be reduced to the minimum. In addition, most of the switching and switching of capacitors currently use mechanical AC contactors, which are prone to arcing and adhesion between contacts, short working life, slow response speed, and also generate impulse voltage and impulse current to the system during the switching process. Although some capacitive switching devices use non-contact solid-state relays, their cost is high, and large additional losses will be generated when large compensation currents flow.

The purpose of the present invention is to avoid the above-mentioned problems existing in the existing grid reactive power compensation technology and devices, and propose a continuous compensation method for grid reactive power, and a reactive power compensation device designed according to this method, so that it can not only effectively realize automatic Continuous compensation reduces line loss and avoids damage to compensation capacitors caused by grid overvoltage and harmonics.

In order to achieve such purpose, the following measures are adopted in the technical solution of the present invention, that is, a single fixed-capacity capacitor C is connected in series with a variable voltage source U _V , and then connected to the phase line of the power grid--the phase line or the phase line- Between the neutral lines, by changing the size of the voltage source U _V , the size of the compensation current is continuously changed to achieve the best compensation of reactive power. The value of the capacitor C can be selected according to the maximum compensation current (ic)max that each branch needs to generate: C=(ic)max/Uω. Where U is the effective value of the grid line voltage or phase voltage connected to the branch, and ω is the angular frequency of the grid. The variable voltage source is a sine wave voltage with the same phase and frequency as the grid voltage, and its voltage effective value range is 0-U. At this time, the actual compensation current ic=(UU _V )/(1/ωc)=(ic)max(1-U _V ／U) produced by each branch. Therefore, when U _V changes continuously from 0-U, the compensation current ic also changes continuously from (ic)max-0, realizing the continuous compensation of the reactive power of the grid.

The variable voltage source U _V can be generated by a single-phase or three-phase autovoltage regulator B or an inverter, and connected to the grid directly or through a transformer.

For the low-voltage power grid, the output terminal of the sliding contact of the auto-transformer B can be directly connected to the power grid with the fixed capacitor C in series. For three-phase reactive power compensation, each phase can be respectively connected to a fixed capacitor C and an auto-coupling voltage regulator B. When the three phases are compensated separately, connect the sliding contact output end of the auto-coupling voltage regulator B to the fixed capacitor C in series, and then connect it between the phase line and the neutral line; After the output terminal of the sliding contact is connected in series with the fixed capacitor C, it is connected between the phase line and the phase line.

For the high-voltage power grid, if there is a low-voltage power supply near the compensation device, connect the autotransformer B to the low-voltage power supply in parallel, and the output voltage of the sliding contact is boosted by a step-up transformer and then connected in series with the capacitor C, and then connected to the power grid . If there is no low-voltage power supply near the compensation device, connect the low-voltage autotransformer B to the high-voltage power grid through a step-down reactor, and the output voltage of the sliding contact is boosted by a step-up transformer and connected in series with the capacitor C, and then connected to power grid.

When it is necessary to quickly and dynamically compensate the reactive power of the grid, the variable voltage source U _V proposed by the present invention will be generated by a transformer, a controller, a DC power supply and an inverter, and the inverter converts the DC power supply into its fundamental wave and the power grid The sine wave voltage with the same frequency and phase is then connected to the power grid through a transformer connected in series with a capacitor C. The controller samples the voltage and current information of the main circuit to keep the output voltage of the inverter synchronized with the power grid and keep changing its amplitude to achieve the best compensation.

In order to better understand the technical solution of the present invention, the technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a principle diagram of the method for continuously compensating reactive power of a power grid according to the present invention.

As shown in the figure, the grid reactive power continuous compensation circuit is composed of a power supply U, a fixed capacitor C and a variable voltage source U _V.

Figure 2 is a diagram of the implementation scheme of continuous compensation of single-phase reactive power in low-voltage power grid.

In the figure, the variable voltage source U _V adopts the auto-coupling voltage regulator B, and the grid reactive power continuous compensation circuit is composed of the power supply U, the fixed capacitor C and the auto-coupling voltage regulator B, and the sliding contact of the auto-coupling voltage regulator B The output end is connected to the power grid after being connected in series with the fixed capacitor C.

Fig. 3 is a diagram of an implementation plan for separate compensation of three-phase reactive power in a low-voltage power grid.

In the figure, each phase of the power grid is connected with a fixed capacitor C and an autovoltage regulator B. The output terminal of the sliding contact of the auto-coupling voltage regulator B is connected in series with the fixed capacitor C and then connected between the phase line and the neutral line of the power grid, that is, the three-phase Y-shaped connection.

Fig. 4 is a diagram of an implementation scheme of synchronous compensation of three-phase reactive power in a low-voltage power grid.

In the figure, each phase of the power grid is connected with a fixed capacitor C and an autovoltage regulator B. The sliding contact output end of the auto-coupling voltage regulator B is connected in series with the fixed capacitor C and then connected between the phase line of the power grid - the phase line, that is, the three-phase forming △ connection method.

As shown in Fig. 2, Fig. 3, Fig. 4, to low-voltage grid compensation, the variable voltage source U _V that the present invention adopts is produced by single-phase or three-phase auto-coupling voltage regulator B, changes the position of its sliding contact, just The value of the variable voltage source U _V connected in series with the capacitor C can be changed. When the contact position is at the uppermost end, U _V = U, and the compensation current ic is zero. When the contact position is at the lower end, U _V = 0, The compensation current ic is the maximum value.

Fig. 5 is a diagram of an implementation scheme of continuous reactive power compensation of a high-voltage power grid with a low-voltage power supply.

As shown in the figure, the autotransformer B is connected in parallel with the low-voltage power supply U/n, and the output voltage of the sliding contact is boosted by the secondary winding of a step-up transformer T1, connected in series with the capacitor C, and then connected to the power grid.

Fig. 6 is a diagram of an implementation scheme of continuous compensation of reactive power in a high-voltage power grid without a low-voltage power supply.

As shown in the figure, if there is no low-voltage power supply near the compensation device, the low-voltage autovoltage regulator B is connected to the high-voltage power grid through a step-down reactor L, and the output voltage of the sliding contact passes through the secondary side of a step-up transformer T1 After the winding is boosted, it is connected in series with the capacitor C and connected to the power grid.

Fig. 7 is a diagram of an implementation scheme of continuous compensation of grid reactive power with fast dynamic response characteristics.

In the figure, when the reactive power of the grid needs to be quickly and dynamically compensated, the variable voltage source U _V proposed by the present invention is generated by the transformer T2, the controller CR, the DC power supply U _D and the inverter IT, and the DC power supply U _D and the inverter IT The inverter IT is connected, the output of the inverter IT is connected to the transformer T2, and the output of the transformer T2 is connected to the power grid after being connected in series with the capacitor C.

The inverter IT converts the DC power supply U _D into a sinusoidal voltage with the same frequency and phase as the fundamental wave of the power grid, and then connects to the power grid through the secondary side of the transformer T2 in series with the capacitor C. The synchronization and magnitude of the AC voltage are controlled by the controller CR, which samples the main circuit voltage and current information to keep the inverter output voltage in sync with the grid and keep changing its amplitude to achieve the best compensation.

Fig. 8 is an implementation block diagram of a continuous reactive power compensation device for a power grid.

What is shown in the circuit is the compensation of the three phases respectively. In addition to the compensation of the fixed capacitor C and the variable voltage source UV using the auto-coupling voltage regulator B, it also includes a circuit breaker ZD, a zero-current input confirmation circuit ZC, an AC contactor CJ, Power factor detection and display circuit PFC, motor forward and reverse control circuit MC, motor M, capacitor current and voltage detection circuit CVD, etc. After the sliding contact of the autotransformer B is connected in series with the fixed capacitor C, it is connected to the power grid through the AC contactor CJ, and connected to the line user YH through the circuit breaker ZD. The AC contactor CJ is controlled by the zero-current input confirmation circuit ZC connected to it, the output of the power factor and display circuit PFC is connected to the motor control circuit MC, the output of the motor control circuit MC is connected to the motor M, the capacitive current in the device and The output of the voltage detection circuit CVD is connected to the motor M, and the output of the motor M is connected to the sliding contact of the autovoltage regulator B.

After the circuit breaker ZD is closed, the device is energized, the motor M rotates, and the sliding contact of the autotransformer B is placed at the uppermost position. Even if the variable voltage source UV reaches the maximum value, after the zero current input confirmation circuit ZC confirms, the AC The contactor CJ closes automatically, so that the compensation fixed capacitor C is connected to the power grid under the condition of zero current, and then the power factor and display circuit PFC detects the power factor of the power grid, and controls the motor M to rotate forward or backward through the motor forward and reverse control circuit MC. Reverse to change the value of the variable voltage source U _V to achieve the best compensation effect. Capacitor current and voltage detection circuit CVD constantly monitors the current flowing through the capacitor and the terminal voltage value. If there is a tendency to exceed the rated value, let the motor M rotate to increase the value of _UV to ensure that the grid voltage is overvoltage or there is a large harmonic To prevent capacitor C from being damaged due to overvoltage or overload when there is a wave voltage component, but it does not affect the compensation function of the device for reactive power of the grid in this case.

In one embodiment of the present invention, the rated line voltage of the power grid is 400V, the maximum capacitive reactive power provided by each phase is 10 Kvar, and a 665 μf capacitor is connected to each phase, and the apparent power of the autovoltage regulator used is 2.5KVA .

Compared with the existing capacitive switching type reactive power compensation device, the present invention has the following outstanding advantages:

1. It can realize the continuous automatic compensation of the reactive power of the power grid, so that the power factor of the power grid is close to 1, so as to achieve the purpose of maximizing the power supply capacity of the power supply equipment and reducing line loss.

2. It can realize the zero-current state input of the compensation capacitor, which completely avoids the impact of the existing device on the power grid when the capacitor is switched, and also avoids the damage to the capacitor itself by the impact current that may occur at the moment of capacitor input, and can greatly extend the capacitor. working life.

3. Replacing multi-stage switching capacitors with a single large-capacity capacitor can further reduce and reduce the cost and size of the device.

4. The capacitor classification delay of 10s-120s is switched to real-time tracking of changes in reactive power of the grid, and the dynamic response time is greatly shortened.

5. Avoid damage to the compensation capacitor caused by grid overvoltage and harmonics, and maintain the normal compensation function of the device under this condition.

Claims (8)

1. A continuous reactive power compensation method for a power grid is characterized in that a fixed capacitor C is connected to the power grid after being connected in series with a variable voltage source U _V , and by changing the size of the voltage source U _V , the size of the compensation current is continuously changed, and the capacitance C The value is selected according to the maximum compensation current (ic) max that each branch needs to generate. The variable voltage source U _V is a sine wave voltage with the same phase and frequency as the grid voltage. The effective value of the voltage varies from 0 to the grid line The effective value U of the voltage or phase voltage. 2. The reactive power continuous compensation method of the power grid as claimed in claim 1, characterized in that said variable voltage source U _V can adopt a single-phase or three-phase auto-coupling voltage regulator B. 3. The reactive power continuous compensation method of the power grid as claimed in claim 2, characterized in that when the three-phase reactive power is compensated separately, the sliding contact output end of the auto-transformer B is connected in series with the fixed capacitor C, and then connected to the Between the phase line and the neutral line. 4. The continuous reactive power compensation method of the power grid as claimed in claim 2, characterized in that when three-phase synchronous reactive power compensation is performed, the sliding contact output terminal of the auto-coupling voltage regulator B is connected in series with the fixed capacitor C, and then connected to the Phase line - between phase lines. 5. The reactive power continuous compensation method of the power grid as claimed in claim 2, characterized in that when compensating the high-voltage power grid with a low-voltage power supply near the compensation device, the autotransformer B and the low-voltage power supply U/n are connected in parallel, and the sliding contact The output voltage is boosted by the step-up transformer T1, connected in series with the capacitor C, and then connected to the power grid. 6. The reactive power continuous compensation method of the power grid as claimed in claim 2, characterized in that when compensating the high-voltage power grid without low-voltage power supply near the compensation device, the low-voltage autotransformer B is connected to the high-voltage power grid through the step-down reactor L, The output voltage of the sliding contact is boosted by the step-up transformer T1, connected in series with the capacitor C, and then connected to the power grid. 7. The reactive power continuous compensation method of the power grid as claimed in claim 1, characterized in that when the reactive power of the power grid is quickly and dynamically compensated, the variable voltage source U _V is composed of a transformer T2, a controller CR, a DC power supply U Generated by _D and inverter IT, DC power supply U _D is connected to inverter IT, the AC voltage output of inverter IT is connected to transformer T2, the output of transformer T2 is connected to the power grid after being connected in series with fixed capacitor C, and the synchronization of AC voltage And the size is controlled by the controller CR. 8. A continuous reactive power compensation device for the power grid, characterized in that after the sliding contact of the auto-coupling voltage regulator B is connected in series with the fixed capacitor C, it is connected to the power grid through the AC contactor CJ, and connected to the user YH through the circuit breaker ZD, The AC contactor CJ is connected to the zero current input confirmation circuit ZC, the output of the power factor and display circuit PFC is connected to the motor control circuit MC, the output of the motor control circuit MC is connected to the motor M, and the output of the capacitor current and voltage detection circuit CVD is connected to the motor M is connected, and the output of motor M is connected to the sliding contact of autovoltage regulator B.

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