JPS597967B2 - Unusual situation - Google Patents

Description

[Detailed description of the invention] The present invention relates to a reactive current compensator.

As is well known, the voltage fluctuates due to loads such as arc furnaces and welding machines that fluctuate rapidly in very short cycles, causing flickering in lights and television screens, causing problems.

This is because the voltage drop changes rapidly and sharply due to the impedance of the power transmission and distribution line due to the current flowing through the load that changes rapidly in a very short period. Normally, with a stable load, the voltage drop will be stable and no flickering will occur. That is, flickering is related to voltage fluctuations, and ultimately due to fluctuations in the current flowing through the load. Voltage fluctuation Δe is generally expressed by the following formula.

△eL-R△1w+X△IQ・・・・・・・・・・・・
... (1) R: Resistance of power transmission and distribution path It is sufficient to make it constant, but making the change in Δ1w constant means making the power consumption constant, which is impossible.

On the other hand, the resistance component in the impedance of the power transmission and distribution line is 0.1 to 0.
．． It is a ratio of 3, and most of it is related to X. Also arc furnace,
Welding machines and the like have a relatively poor power factor, so there is a lot of reactive current.
Therefore, if ΔIQ is compensated, a certain effect can be obtained.)Next, the fluctuation of the reactive current is improved by a compensation device.

If the current is ΔIQ', then Δe'-RΔ1w+X(
△IQ+△IQ')・・・・・・・・・(2) and (1)
Expressions can be expressed.

If we set △e=0 to eliminate this voltage fluctuation, then 6IQ
'=-(Rc・△1w+△IQ)・・・・・・・・・
(3), and in order to accurately improve the voltage fluctuation, it is necessary to use a compensator to compensate so that ΔIQ' of the above equation (3) is satisfied.

The present invention seeks to provide a reactive current compensator that compensates for varying reactive currents in order to improve voltage fluctuations.

FIG. 1 is a block diagram of a reactive current compensator according to the present invention.

A variable load 3 is connected between line terminals 1 and 2, and the voltage on the secondary side of a transformer 4 that detects line voltage is applied to a sampling rectifier circuit 8 via a phase shifter 5 that shifts the phase by π/2. It will be done. Further, the voltage on the secondary side is directly applied to the sampling rectifier circuit 9. Each of the sampling rectifier circuits 8 and 9 samples a voltage proportional to the current at the timing of the zero point of the input voltage using a shunt resistor 7 on the secondary side of the current transformer 6 that detects the load current. FIG. 2 is an oscillographic waveform showing the operation of the reactive current compensator of the present invention shown in FIG.

In FIG. 2a, is the waveform of the secondary voltage obtained by transforming the line voltage by the transformer 4, and V' is the waveform of the voltage obtained by shifting the phase of the secondary voltage waveform by π/2. Further, IL is the waveform of the current flowing through the load 3, which flows, changes in magnitude, changes phase, or stops. FIG. 2b shows a situation in which the load current 1L is sampled at the timing of the zero point of the waveform of the voltage V'.

This thick line has the following relationship. However, v=VmsinO
)t. Therefore, the timing of 7=0 is as shown in (4) above.
Since Sin(ωt-π/2)=0, (ωt-π
/2) -0 or (ωt-π/2) = π Therefore, ωt-π/2, and since it is the same timing, substitute it into equation (5) to find ILW (1) at that timing , and the information is proportional to the effective current.

This ILO) is information proportional to ΔIw in equation (3) above, and is corrected to the size shown by hatching in relation to the value of R/X. The resulting information is the output signal of the sampling rectifier circuit 8.

FIG. 2 1 shows a situation where the load current 1L is sampled at the timing of the zero point of the secondary voltage.

This thick line has the following relationship. Therefore, since the timing of =0 is Sinωt-0 in the above equation (7), ωt-0
or ωt−π.

Therefore, since the timing is the same, substituting it into the above equation (5Y equation) to find ILQ(t) at that timing, we get: This becomes information proportional to the reactive current and becomes the output of the sampling rectifier circuit 9.

2d is a composite signal of the outputs of the suplink rectifier circuits 8 and 9, which becomes an input signal to the conduction angle control circuit 10 of FIG.

d in the same figure compares the triangular waveform lightning pressure generated in synchronization with the voltage 7 in the conduction angle control circuit 10 with the input signal, and outputs the ignition signal at the timing when the triangular waveform voltage becomes larger than the input signal. It is generated as a signal for semiconductor switches 12 and 13. FIG. 2e shows a situation where the conduction angle of the current 1Q flowing through the reactor 11 is adjusted by the semiconductor switches 12 and 13 in response to the ignition signal.

When the current 1L flowing through the load 3 disappears, the current 1Q' increases, and the fact that the direction of change is opposite to the load as shown in equation (3) above means that the voltage fluctuation is reduced. In the reactive current compensator of the present invention, even if there is no sampling rectifier circuit 8 that produces information related to the active current, it is possible to improve the R/X of the power transmission and distribution line to some extent.
It is economical because the sampling rectifier circuit 8 can be omitted depending on the value of .

Next, FIG. 3 shows an embodiment of a sampling rectifier circuit employed in the reactive current compensator of the present invention. The operating principle of this circuit is that the lightning pressure generated across the shunt resistor 7 on the secondary side of the current transformer 6 shown in FIG.
5 and diodes 15, 16 on the secondary side of the transformer 14.
A capacitor 20 is connected in series with transistors 18 and 19 connected in opposite directions. Furthermore, diodes 21 and 22 are connected between the base and emitter of the transistor in the same direction as the conduction direction of the transistor, and are connected to the secondary coil of a pulse transformer 23. Now, the primary side terminals 24, 2 of the transformer 14
5, voltage i=KILrnSin(ω
t-θ).

When this is rectified, i=KILrrlSin(ωt-θ)
becomes. Then, at the timing of 2O, the pulse transformer 23
When a pulse wave is applied to terminals 26 and 27 of , both transistors 18 and 19 become conductive. But capacitor 2
0 is not charged first, the capacitor 20 from the transistor 18 is C=Ik′IL]T)Sin(-θ
) is charged. Further, when the current 1L is not flowing in the next period, when a pulse wave is applied, the voltage charged in the capacitor 20 is discharged from the transistor 19 via the resistor 17. Until this discharge, the voltage C={k'
ILrnSin(-θ) {continue. This voltage (signal) becomes the output voltage of the sampling rectifier circuit. The transformer 14 of the sampling rectifier circuit in FIG. 3 is a current transformer, and the first
It is equally possible to remove the shunt resistor 7 shown and connect the sampling rectifier circuit in series to operate as a current input.

Since the reactive current compensator of this invention adopts a sampling rectification method, the semiconductor switch performs compensation using new information every half cycle, so the response speed is fast, and compensation is performed by including compensation information based on active power. , it can prevent voltage fluctuations and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the reactive current compensator of the present invention.
FIG. 2 is an oscillographic waveform diagram showing the operation of the reactive current compensator of the present invention shown in FIG. 1, and FIG. 3 is a sampling rectifier circuit diagram employed in the reactive current compensator of the present invention. 1, 2: line terminal, 3: load, 4: transformer, 5: phase shifter, 7: shunt resistor, 8, 9: sampling circuit, 10: conduction angle control circuit, 11: reactor, 12, 13: Semiconductor switch, 14: Transformer, 15, 16: Diode, 1
7: Resistor, 18, 19: Transistor, 20: Capacitor, 21, 217, 22, 22': Diode, 23:
Pulse transformer, V: Secondary voltage of line, ′: [ヮ沒dpressure V
Voltage with phase shift of π/2, IL: Load current, ILW (1)
: Effective current obtained by sampling 1L of load current at the timing of the zero point of the voltage V/ waveform, ILQ (1): Load current 1
IQ' is a reactive current obtained by sampling L at the timing of the zero point of the voltage waveform; IQ': current flowing through the reactor 11;

Claims (1)

[Claims] 1. A semiconductor switch that can adjust the conduction angle of the current flowing through a reactor connected in parallel to a power transmission line that supplies power to a fluctuating load is used to sample and rectify the fluctuating load current at the zero point of the voltage of the circuit. The line constant of the power transmission line, that is, the line resistance R and a reactive current compensator that multiplies the inductive reactance X of the line by a value proportional to R/X, and adjusts the conduction angle of the semiconductor switch using a signal obtained by adding these two voltage signals. .