JPH07212977A - Reactive power compensator - Google Patents

Abstract

PURPOSE:To keep a high conversion efficiency by connecting a large-capacity rectangular wave inverter and a small-capacity high-frequency PWM inverter in series and generating compensating current which negates reactive current based on the output voltage of the small-capacity high-frequency PWM inverter. CONSTITUTION:Out of the composite output voltages VI which increase and decrease following the fluctuation of reactive current of a load, the base voltage V which is equal to the system voltage Vs is taken charge of by a large- capacity rectangular wave inverter 11 whose capacity is large and has a high conversion efficiency and has a 120 deg. conduction width and a voltage component DELTAV which generates compensating current which negates the fluctuation of the reactive current of the load is taken charge of by a small-capacity high-frequency PWM inverter 12 which has a good responsibility. Since the small- capacity high-frequency PWM inverter 12 has a high switching frequency, the conversion efficiency is low. However, it requires the voltage component DELTAV which is only about 10% of the system voltage Vs and therefore it needs only a small capacity. By this method, a high conversion efficiency can be maintained.

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 specifically, it detects a reactive current of a fluctuating load connected to a system power supply and generates a compensating current for canceling a reactive current of a fluctuating load by an inverter, The present invention relates to a reactive power compensator that suppresses a voltage fluctuation of a system power supply due to a load fluctuation by the compensation current.

[0002]

2. Description of the Related Art In a power system, a system power supply 1 and an inverter 2 are interconnected via a transformer impedance 3, and a reactive power compensator for compensating the reactive power of a variable load connected to a system bus 4 thereof. Are generally provided on the same bus bar [see FIG. 5].

This reactive power compensator is shown in FIG.
Is installed on the system bus 4 between the system power supply 1 and the variable load 5.
The load current I by the current transformer 6 and the transformer 7._L, System power
Pressure V _SIs detected, and the reactive current detector 8 detects the load current I_LIn
Detects reactive current. Control is performed based on the detection of this reactive current.
The control circuit 9 drives and controls the inverter 2. That is, the system
Inverter 2 connected to main bus 4 via transformer 3
Output voltage V while synchronizing with system power supply 1_IThe amplitude of
System voltage V_SThe reactive current
Generates a compensation current that cancels the
The voltage fluctuation of the power supply 1 is suppressed.

As the above-mentioned inverter, it is usual to use either a one-pulse, three-pulse, etc. rectangular wave inverter for switching by a rectangular wave signal or a small capacity high frequency PWM inverter for switching by a pulse signal. Is. In these inverters, as shown in FIG.
As shown in (b), while compensating with the system power supply 1, the amplitude of the output voltage V _I is made to follow the system voltage V _S to be increased or decreased to generate a compensation current that cancels the reactive current. Incidentally, FIGS. 6 (a) is smaller than the inverter output voltage V _I is the system voltage V _S, shows the reactor operation flows lagging phase current to the system power supply, FIG. (B) the inverter output voltage V _I is the system voltage V _A capacitor operation that is larger than _{S and} has a phase-advancing current flowing through the system power supply.

[0005]

By the way, in the conventional reactive power compensator, either the rectangular wave inverter or the high frequency PWM inverter is used as the inverter 2 (see FIG. 5) for generating the compensation current for canceling the reactive current as described above. One of them is used, and in general, a GTO inverter is used to reduce the capacity.

Since this GTO inverter requires a snubber circuit with a large loss, there is a problem that the loss increases when the switching frequency is increased for the purpose of improving the response. On the other hand, the rectangular wave inverter has a low switching frequency and thus has a good conversion efficiency, but has a poor responsiveness to a load change. In addition, the high frequency PWM inverter
Contrary to the above-mentioned rectangular wave inverter, the switching frequency is high, so the response is good, but the conversion efficiency is poor.

Therefore, the present invention has been proposed in view of the above problems, and an object thereof is to provide a reactive power compensator having a large capacity, good conversion efficiency, and high-speed response. is there.

[0008]

As a technical means for achieving the above object, the present invention detects a reactive current of a fluctuating load connected to a system power supply, and outputs the same while an inverter synchronizes with the system power supply. In a reactive power compensator that generates a compensating current that cancels the fluctuation of the reactive current of the load by increasing and decreasing the amplitude of the voltage following the fluctuation of the load and suppressing the voltage fluctuation of the system power supply by the compensating current, it is equal to the system voltage. A 120 ° energization width large-capacity rectangular wave inverter that generates a base voltage and a small-capacity high-frequency PWM inverter that generates only a voltage component for generating a compensating current are connected in series via a transformer, respectively, and mainly a small capacity is provided. High frequency P
It is characterized in that a compensation current for canceling the reactive current is generated based on the output voltage of the WM inverter.

[0009]

In the reactive power compensator of the present invention, a large-capacity rectangular wave inverter having a 120 ° conduction width for generating a base voltage equal to the system voltage and a small-capacity high-frequency PWM for generating only a voltage component for generating a compensation current. By including the inverter, when both inverters increase and decrease the output voltage amplitude in synchronization with the system power supply by following the load fluctuation, the large-capacity rectangular wave inverter uses the Since it only generates a base voltage equal to the voltage, there is no need to immediately respond to load fluctuations, the switching frequency of the inverter can be lowered, and conversion efficiency is high. On the other hand, a small-capacity high-frequency PWM inverter has a low conversion efficiency because the switching frequency of the inverter is high, but the required voltage component is sufficiently smaller than the system voltage, so a small capacity can be used, and the effect on the overall conversion efficiency is small. In addition to maintaining high speed response, the entire device can maintain high conversion efficiency.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a reactive power compensator according to the present invention will be described with reference to FIGS. The same parts as those in FIGS. 5 to 7 are designated by the same reference numerals, and a duplicate description will be omitted.

A feature of the present invention is that it produces a base voltage V equal to the system voltage V _S , as shown schematically in FIG.
A large-capacity rectangular wave inverter 11 having a conduction width and a small-capacity high-frequency PWM inverter 12 that generates only a voltage component ΔV for generating a compensation current are connected in series to a system bus 4 via a transformer. This is because the compensating current for canceling the reactive current is generated via the combined impedance 3 of the transformer based on the combined output voltage V _I of 12.

In this reactive power compensator, the system voltage V_S
120 ° energization width for generating a base voltage V equal to
Square wave inverter 11 for generating a compensation current
Small capacity high frequency PWM inverter that generates only voltage component ΔV
And the inverter 12, both inverters 11,
12 is synchronized with the system power supply 1 and its combined output voltage V _I
A large-capacity rectangle
The wave inverter 11 increases and decreases the combined output voltage V_IAmplitude of
Of which, the system voltage V_SGenerate a base voltage V equal to
Since there is no need to immediately respond to load changes,
The conversion frequency is high because the etching frequency is low. On the other hand, small contents
The high-frequency PWM inverter 12 increases and decreases the combined output power.
Pressure V_IOf the voltage amplitude to generate the compensation current.
Since only ΔV is generated, the switching frequency is high.
And fast response is achieved.

As shown in FIG. 2, of the combined output voltage V _I of the inverter that increases and decreases in accordance with the fluctuation of the reactive current of the load, the base voltage V equal to the system voltage V _S has a large capacity and high conversion efficiency. Large capacity rectangular wave inverter with energizing width 1
1, the small-capacity high-frequency PWM inverter 12 having good responsiveness takes charge of the voltage component ΔV for generating the compensating current for canceling the fluctuation of the reactive current of the load, whereby the two inverters 11 and 12 share the roles. The small-capacity high-frequency PWM inverter 12 has a high switching frequency and thus has low conversion efficiency. However, since the required voltage component ΔV is about 10% of the system voltage V _S , a small capacity can be used.
The effect on the overall conversion efficiency is small, and high conversion efficiency can be maintained.

Next, the circuit configuration of the reactive power compensator of the present invention is shown in FIG. 3, and the specific configurations of the reactive current detector 13 and the control circuits 14 and 15 in FIG. 3 will be described in detail with reference to FIG. .

First, as shown in FIG. 3, the large-capacity rectangular wave inverter 11 connected to the system bus 4 between the system power supply 1 and the variable load 5 via the transformer 16 has only the capacitor 17 in its DC circuit section. provided, the base voltage V corresponding with the system voltage V _S, that is, the control circuit 14 such that the voltage output phase is synchronized with the system voltage V _S in the three-phase average value of the output amplitude system voltage V _S is generated Controlled. On the other hand, the load current I _L and the system voltage V _S are detected by the current transformer 6 and the transformer 7 provided in the system bus 4, and the reactive current detection unit 13 is detected.
Detects the reactive current in the load current I _L. The small-capacity high-frequency PWM inverter 12 connected to the system bus 4 via the transformer 18 includes a rectifier (not shown) in its DC circuit section, and a reactive current command based on the detection output of the reactive current detection section 13 described above. The control circuit 15 controls to generate a voltage component ΔV for generating a compensation current that follows the value. At this time, the small capacity high frequency PWM inverter 12
Of the voltage component Δ so as to correct the error between the reactive current command value and the output current of the small-capacity high-frequency PWM inverter 12 based on the detected signal.
Adjusting V.

As described above, the combined output voltage V _I of the inverter is converted into a large-capacity rectangular wave inverter 11 of 120 ° conduction width for generating a base voltage V equal to the system voltage V _S and a compensation current for canceling the reactive current of the load. A small-capacity high-frequency PWM inverter 12 that generates a voltage component ΔV to generate the electric current has a shared role, and both inverters 11 and 12 synchronize with the system power supply 1 and the amplitude of the combined output voltage V _I follows the load fluctuation. A compensating current that cancels the reactive current is generated by increasing and decreasing it, and the voltage fluctuation of the system power supply 1 is suppressed by the compensating current.

The reactive current detecting section 13 described above includes the load current detecting circuit 2 via the current transformer 6 as specifically shown in FIG.
The load current I _L is detected by 0, and the system voltage V _S is detected by the system voltage detection circuit 21 via the transformer 7. The synchronization signal synchronized with this detection voltage is supplied to the phase synchronization circuit 2
2 and the reference sine wave generating circuits 23 and 24 generate the reference sine wave a having the same phase as the system voltage V _S and the reference sine wave b having the 90 ° phase based on the generated voltage. The reactive power component of the load 5 is calculated by multiplying the 90 ° phase reference sine wave b and the load current detection signal, and the reactive power component is output as a DC voltage by the average value circuit 25, and the output voltage The reactive current command value is obtained by multiplying the 90 ° phase reference sine wave b.

Also, a small capacity high frequency PWM inverter 12
The control circuit 15 includes a compensation current control unit 26 and a gate signal generation unit 27. In the compensation current control unit 26, the output current of the inverter 12 is detected by the current transformer 19 and invalidated based on the detection signal. The error from the reactive current command value output from the current detector 13 is error-amplified and corrected by the current control circuit 28. On the other hand, in the gate signal generation unit 27, the correction signal output from the current control circuit 28 is modulated by the carrier wave generation circuit 29 with the triangular wave carrier signal to modulate the circuit 3.
The pulse width modulation [PWM] is performed by 0, and the small capacity high frequency PW is used as a gate signal through the inverter driving amplifier 31.
It is sent to the M inverter 12.

Further, the control circuit 14 of the large-capacity rectangular wave inverter 11 having a 120 ° conduction width is composed of a DC voltage control unit 32 and a gate signal generation unit 33, and the DC voltage control unit 32 is provided.
Then, the DC voltage corresponding to the three-phase average value of the system voltage V _S is set, while the DC voltage in the DC circuit unit of the large-capacity rectangular wave inverter 11 having a 120 ° conduction width is set to the DC voltage detection circuit 3
4, the detected value is compared with the above-mentioned set value for error amplification, and the output is multiplied by the system voltage V _S and the 90 ° phase reference sine wave b to generate a DC voltage control signal.
Then, by controlling the 90 ° phase component with respect to the reference sine wave a having the same phase as the system voltage V _S , active power is exchanged with the system power supply 1 to control the DC voltage. On the other hand, in the gate signal generator 33, a large-capacity rectangular wave inverter 1 having a 120 ° energization width as a gate signal is pulsed through the 120 ° energizing circuit 35 to 120 ° in order to reduce low-order harmonic components.
Send to 1.

[0020]

According to the reactive power compensator of the present invention, a large capacity rectangular wave inverter having a 120 ° conduction width for generating a base voltage equal to the system voltage and a compensating current for canceling the reactive current of the load are generated. A small-capacity high-frequency PWM inverter that generates only a voltage component is provided, and a base voltage equal to the system voltage among the combined output voltages of the inverter that increases and decreases in accordance with load fluctuations has a large capacity and high conversion efficiency.
° A large-capacity rectangular wave inverter with a conduction width is responsible for it, and a small-capacity high-frequency PWM inverter with good response is responsible for the voltage component for generating the compensation current. It is possible to provide a high-performance reactive power compensator having a large capacity, good conversion efficiency, high-speed response, and high performance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an inverter of a reactive power compensator connected to a system bus.

FIG. 2 is an explanatory diagram for explaining an inverter operation of the reactive power compensator of the present invention.

FIG. 3 is a circuit block diagram showing a specific configuration of a reactive power compensator of the present invention.

4 is a circuit block diagram of a reactive power compensator including a specific configuration of a reactive current detection unit and a control circuit of FIG.

FIG. 5 is a schematic diagram showing an inverter of a conventional reactive power compensator connected to a system bus.

FIG. 6 is an explanatory diagram for explaining an inverter operation of a conventional reactive power compensator, in which (a) is a reactor operation;
(B) shows a capacitor operation.

FIG. 7 is a circuit block diagram showing a specific configuration of a conventional reactive power compensator.

[Explanation of symbols]

1 system power supply 5 variable load 11 mass square wave inverter 12 small-capacity high-frequency PWM inverter V _S system voltage V _I output voltage V base voltage ΔV voltage change

Claims (1)

[Claims] 1. The fluctuation of the reactive current of the load is detected by detecting the reactive current of the fluctuating load connected to the system power supply and increasing and decreasing the amplitude of the output voltage of the inverter while following the load fluctuation while synchronizing with the system power supply. In a reactive power compensator that generates a compensating current that cancels the voltage fluctuation and suppresses the voltage fluctuation of the system power supply by the compensating current, a large-capacity rectangular wave inverter of 120 ° conduction width that generates a base voltage equal to the system voltage and the compensating current are generated. A small-capacity high-frequency PWM inverter that generates only a voltage component for generation is connected in series via a transformer, and a compensation current that cancels the reactive current is generated mainly based on the output voltage of the small-capacity high-frequency PWM inverter. A reactive power compensator characterized in that