JPH0352086B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a reactive power control device that controls the opening and closing of a capacitor using a semiconductor switching device such as a thyristor in order to compensate for flickering caused by a load such as a resistance welding machine where the reactive power fluctuates rapidly. It is something.

Generally, a reactive power control device in which a semiconductor switchgear such as a thyristor is connected in series with a capacitor detects the reactive power of the load and controls it accordingly, resulting in a response delay of about 0.5 cycles. For this reason, when the load decreases, the opening delay of the capacitor causes an over-phase state, and the terminal voltage of the capacitor increases.
Since the capacitor is opened while being charged with this terminal voltage, the residual terminal voltage of the capacitor becomes higher than the circuit voltage after the capacitor is opened.
If the load increases in this state and the capacitor is turned on again, an inrush current equivalent to the difference between the residual terminal voltage of the capacitor and the circuit voltage will flow, so for example, the rated surge current of a thyristor will be It had to be large enough to withstand high temperatures, and had the disadvantage of being expensive.

That is, FIG. 3 shows a circuit configuration diagram of a group of conventional reactive power control devices, and the line impedance 2
A series circuit is formed of a thyristor 3 and a capacitor 4 which are connected in antiparallel to a power supply 1 having It is connected.

As shown in the example in Figure 3, the power supply side reactance
A capacitor with a capacity of Q (kVA) is inserted into a circuit of X _B (Ω), and the current rise when the load becomes 0 is ΔE=X _B・Q×10 ³ /E=X _B・I _C becomes. E is the circuit voltage and I _C is the rated current of the capacitor.

In this type of reactive power control device, in order to prevent damage to a semiconductor switchgear such as a thyristor due to inrush current, it is controlled to fire at the timing when the voltage e between the terminals of the semiconductor switchgear is at its minimum. As mentioned above, the terminal voltage of the capacitor is higher than the circuit voltage E by ΔE, so the voltage e between the terminals of the semiconductor switchgear is at least ΔE, and if the semiconductor switchgear is ignited in this state, an inrush current will flow. Become.

The magnitude of this inrush current is determined by the surge impedance Z of the circuit, assuming that the reactance of the capacitor is X _C. Therefore, the transient current component I _S of the inrush current is, It is required as.

Since X _B = ΔE/I _C X _C = E/I _C , becomes.

For example, if the voltage rise is 10%, that is, ΔE/E=0.1, I _S = I _C √0.1=0.321 _C , so if the inrush current including the steady current is I _O , then I _O = I _C + I _S = 1.321 _C , and the inrush current will flow 1.32 times the rated current.

Conventionally, a discharge resistor or a discharge coil is connected in parallel to this capacitor to discharge the residual charge in the capacitor, thereby lowering the capacitor terminal voltage. In order to keep the loss low, a fairly high resistance (high impedance) is set, so the discharge speed is not very fast and it takes time for the terminal voltage of the capacitor to drop. If you wait for the voltage to drop, you will lose the high-speed response required of this type of reactive power control device. When using a discharge coil, it is possible to increase the discharge speed considerably, but in many cases, this type of reactive power control device discharges at a high frequency of once every several dozen cycles, and the discharge energy is The disadvantage was that the discharge coil to prevent overheating was large.

The present invention aims to eliminate the above-mentioned drawbacks and provide a reactive power control device that is compact and capable of high-speed response.

That is, in a reactive power control device in which a capacitor is connected in series with a first semiconductor switchgear that controls reactive power by connecting triacs or thyristors in antiparallel, the residual charge discharge current of the capacitor is controlled by connecting triacs or thyristors in antiparallel. This is a reactive power control device characterized in that a second semiconductor switchgear for controlling a discharge resistor or a discharge coil connected in series is connected in parallel to the first semiconductor switchgear.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the reactive power control device of the present invention shown in FIGS. 1 and 2 will be described below.

FIG. 1 shows a circuit configuration diagram of a group _of reactive power control devices of the present invention, in which a thyristor 3 (a first semiconductor switchgear ) and a capacitor 4, and a resistor 5.
(resistance value is R) and a series circuit of thyristor 6 (second semiconductor switchgear) connected in antiparallel to control it are connected in parallel to thyristor 3 (first semiconductor switchgear) connected in antiparallel. It is composed of 7 is the load.

Next, the operation of this device will be explained with reference to FIG.

Now, if the load becomes 0 just before time point A and the phase becomes over-advanced, and the capacitor is opened with the voltage E rising by ΔE, the capacitor terminal voltage will be charged by e _C = √2 (E + ΔE). It is opened by the thyristor 3 while it remains open. Next, when the anti-parallel connected thyristor 6 is fired, the current i flowing through it is i=√2(E+ΔE)ε− ^γt −√2Esin ωt, if the line impedance is small compared to the resistance R and ignored. /R γ is the discharge time constant of this circuit.

Therefore, i=0 when √2(E+ΔE)ε−γ ^t =√2sin ωt, that is, when the terminal voltage e _C of the capacitor becomes equal to the circuit voltage e _O .

This means that once the thyristor 6 connected in anti-parallel for discharge after opening the capacitor is turned on, the capacitor charging voltage will automatically discharge to the circuit voltage and the arc will be extinguished naturally, so there is no need for a special arc extinguishing circuit. This makes the circuit configuration extremely simple.

Figure 2 is a diagram of the voltage and current waveforms of the capacitor 4, in which i _O is the current of the capacitor 4 when the anti-parallel connected thyristor 3 conducts, e _C is the terminal voltage of the capacitor 4, and i is the anti-parallel connected thyristor 3. The discharge current of capacitor 4 at the time of ignition of 6, e _O indicates the voltage of power supply 1. Also, time point A is when the capacitor 4 is opened by the anti-parallel connected thyristor 3, time B is when the anti-parallel connected thyristor 6 is ignited and discharge of the capacitor 4 is started, and time C is when the capacitor 4 is discharged. This shows the time when the circuit of the anti-parallel connected thyristor 6 is opened.

Immediately before opening and closing capacitor 4 at time A, the power factor becomes leading due to a decrease in load, so capacitor 4
Since the terminal voltage e _C of the capacitor 4 is higher than the voltage e _O of the power supply 1 by an amount e _d , the terminal voltage e _C of the capacitor 4 after opening is higher than the voltage e _O of the power supply 1 by an amount e _d . Time B
When the thyristor 6 of the discharge circuit is ignited, a discharge current i determined by the conditions of the discharge resistor 5, power supply impedance 2, and capacitor 4 flows, and the peak value of the terminal voltage of the capacitor 4 gradually decreases from the residual terminal voltage e _C. , at time C, the peak value of the terminal voltage of capacitor 4 becomes equal to the peak value of voltage e _O of power supply 1 (e _C between times B and C in the figure indicates the change in the peak value of the terminal voltage of capacitor 4. ), e _d =0, so the anti-parallel connected thyristor 6 is extinguished and the discharge current i=0. Even if the anti-parallel connected thyristor 3 is fired in this state, no rush current will flow into the capacitor 4.

Furthermore, according to this device, the energy Q consumed during discharging is Q=1/2C{√2(E+ΔE)} ² -1/2C(√2E), where C is the capacitance of the capacitor.
) ² = CE ² {(1+ΔE/E) ² −1} CE ²・2ΔE/E (because ΔE≪E).

Compared to the conventional discharge resistor or discharge coil connected in parallel to a capacitor as shown in Figure 3, the energy consumed during discharge Q' is Q' = 1/2C {√2 (E + ΔE)} ² CE ² . As a result, energy consumption during discharging is significantly reduced. For example, when ΔE/E = 0.1 (voltage rise is 10%), the energy consumption is 20%, so the discharge resistor or discharge coil can be of small capacity, and even if discharge is performed frequently, the energy consumption will be 20%. There are advantages to not having to do that.

As mentioned above, the reactive power control device of the present invention has the great advantage that it can be made smaller and lighter by significantly reducing the energy consumption of the discharge device. Since no voltage is applied, there is no energy consumption while the capacitor is energized, the impedance of the discharge device can be made low, and the discharge time can be significantly shortened, so there is an advantage that the response time is not delayed due to discharge. The discharge circuit requires an anti-parallel connected thyristor for this purpose, but since it can be self-extinguished, a special extinguishing circuit is not required, and the circuit can be simplified, so it has great practical value. be.

It goes without saying that the same effect can be obtained when a triax is used instead of the anti-parallel connected thyristor. Further, when a discharge coil is used instead of a discharge resistor, the same effect can be obtained by making the discharge coil resistance sufficiently larger than the inductance.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram of a group of reactive power control devices of the present invention, Fig. 2 is a voltage and current waveform diagram of a capacitor of the same reactive power control device, and Fig. 3 is a circuit diagram of a group of conventional reactive power control devices. This is a structural drawing. 1: Power supply, 2: Line impedance, 3: Thyristor connected in anti-parallel (first semiconductor switchgear),
4: capacitor, 5: discharge resistor (or discharge coil), 6: anti-parallel connected thyristor (second semiconductor switchgear), 7: load.

Claims (1)

[Claims] 1. In a reactive power control device in which a first semiconductor switchgear and a capacitor are connected in series to control reactive power by connecting triacs or thyristors in anti-parallel, residual charge discharge current of the capacitor is controlled by connecting triacs or thyristors in anti-parallel. A reactive power control device characterized in that a second semiconductor switchgear to be controlled and a discharge resistor or a discharge coil connected in series are connected in parallel to the first semiconductor switchgear.