JP2004254428A - Static reactive power compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive static reactive power compensator(TSC: Thyristor Switched Capacitor). <P>SOLUTION: An arm 2 composed of thyristors only, and an arm 3 partially composed of the thyristors (with the number of pieces which can withstand an AC voltage) and the rest of which is composed of diodes (with the number of pieces which can withstand a DC voltage at charge) are connected as shown in Fig., and this compensator controls gate signals supplied to the thyristors so that the signal stop applications of currents 4, 5, and 6 at the zero point of the currents after the application of currents of negative polarity by the arm 3 of each phase after the reception of a TSC stop command. Hereby, the arms 2 and 3 have withstand voltages enough both at the charge and after the discharge of a capacitor 1 after the stoppage of TSC, whereby this can reduce the number of required thyristors using inexpensive diodes. Moreover, a capacitor discharge device 7 becomes unnecessary by giving the gate signals to the thyristors of the arms 2 and 3 thereby discharging them. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a static reactive power compensator that turns a capacitor on and off with a semiconductor element.
[0002]
[Prior art]
In a static reactive power compensator (hereinafter abbreviated as TSC, TSC: Thyristor Switched Capacitor) for controlling reactive power by turning on / off a capacitor, a semiconductor element is used as a switch for turning on / off the capacitor. . Since the TSC performs AC power adjustment, it is necessary to pass current in both directions. Therefore, as shown in FIG. 5, the semiconductor elements are connected in antiparallel as in the arms 2 and 3A. Usually, a thyristor is used as a semiconductor element, and bidirectional energization is performed by a gate signal from a gate generator. Hereinafter, TSC in the case of using a thyristor will be described.
[0003]
A plurality of thyristors are connected in series to withstand a predetermined voltage. As shown in FIG. 3A, the number of thyristors is connected to the DC voltage charged in the capacitor 1 after the TSC is stopped. Designed to withstand the superimposed voltage of AC voltage. The polarity of the DC voltage charged in the capacitor is determined by the direction of the thyristor that was energized immediately before the TSC stopped. Since the thyristor is turned off when the current becomes zero, as shown in FIG. 6, each of the three phases is turned off at the current zero point after receiving the TSC stop command.
[0004]
Then, the DC voltage charged in the capacitor must be the same polarity for two of the three phases and the opposite polarity for the remaining one phase. Depending on the TSC stop command and the energization timing of arm 2 or arm 3A, A waveform in which an AC voltage is superimposed on a DC voltage is applied in either a positive polarity or a negative polarity.
[0005]
Further, in order to discharge the DC voltage charged in the capacitor 1, each capacitor 1 is separately provided with a capacitor discharging device 7 as shown in FIG. After stopping the TSC, the capacitor discharge device 7 is operated to discharge the electric charge charged in the capacitor 1.
[0006]
In the TSC where the capacitor is turned on / off by a pair of anti-parallel thyristors, when the capacitor needs to be initially charged, the technology for soft-starting charging in order to suppress abnormal voltage due to inrush current during charging is Is already known (see, for example, Patent Document 1).
[0007]
[Patent Document 1]
Japanese Utility Model Publication No. 6-75016 (first page, FIG. 1)
[0008]
[Problems to be solved by the invention]
As described above, as the thyristor, it is necessary to determine the series number so that both the positive polarity and the negative polarity of the voltage obtained by superimposing the DC voltage of the capacitor and the AC voltage of the power source are required, and a large number of thyristors are required. Each capacitor required a discharge device.
[0009]
Conventionally, a technique for solving such a problem has not been known, and Patent Document 1 discloses a technique for solving such a problem, that is, a reduction in the number of thyristors and an unnecessary discharge device. Not.
[0010]
Accordingly, an object of the present invention is to provide an inexpensive static reactive power compensator that can reduce the number of necessary thyristors and eliminate the need for a discharge device.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a static reactive power compensator in which a capacitor is turned on / off by a circuit in which a first and a second circuit including a semiconductor element that is conducted by a gate signal are connected in antiparallel. The first circuit is composed of semiconductor elements that are all conductive by a gate signal, and the second circuit is a semiconductor element that is partially conductive by a gate signal and the remaining part is a diode, which is a static invalid When the power compensator is stopped, gate signal supply control means is provided for controlling a gate signal supplied to the semiconductor element so that conduction is stopped on the second circuit side.
[0012]
According to the present invention having such a configuration, since a part of the second circuit is an inexpensive diode, it is not necessary to make all elements of the second circuit conductive semiconductor elements by a gate signal. The reactive power compensator can be made inexpensive, and the number of gate signal transmission paths for supplying gate signals can be reduced.
[0013]
Here, the gate signal supply control means further controls the gate signal for discharging the charge of the capacitor to the semiconductor elements of the first and second circuits after stopping the static reactive power compensator. It can also be.
[0014]
With this configuration, it is not necessary to install a capacitor discharge device.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
(First embodiment)
The TSC according to the first embodiment of the present invention will be described.
[0017]
FIG. 1 is a diagram showing a configuration of a main part of this embodiment, and FIG. 2 is a diagram showing a current waveform of each phase and a signal for controlling a gate for explaining the operation of this embodiment.
[0018]
In FIG. 1, 1 is a capacitor, 2 is an arm in which M semiconductor elements that conduct positive current of FIG. 2 (a) are connected in series, and 3 is a semiconductor element that conducts negative current of FIG. The arms 4, 5, and 6 connected in series indicate currents of three phases. Reference numeral 7 denotes a capacitor discharge device.
[0019]
In FIG. 2 (a), 8, 9, and 10 are current waveforms corresponding to the currents of phases 4, 5, and 6 in FIG. 1, and the current after energization of the negative current of each phase after receiving the TSC stop command. It shows how each of the three phases is turned off at the zero point. 2 (b) to 2 (k) show signals for controlling the gates so that the three phases are turned off at the current zero point after energization of the negative polarity current of each phase after receiving the TSC stop command. It is shown.
[0020]
In order to stop the energization of the current 4 of the arm 2 or the arm 3 by the TSC stop command, control is performed so as to be performed at the current zero point after the negative current by the arm 3 is energized.
[0021]
For example, for the phase of current 4, during operation of the TSC, gate signals (c) and (d) as shown in FIG. 2 are supplied to the thyristors of arm 2 and arm 3 from a gate control device (not shown). However, in the gate control device (not shown), after receiving the gate signal of the TSC stop command, the TSC stop command signal (b) shown in FIG. 2 and the signal (e) corresponding to the negative current conduction period When the AND is established, the supply of the gate signal (c) to the arm 2 thereafter is stopped, and the supply of the gate signal (d) to the arm 3 thereafter is also stopped a little after the AND is established. Control to do. Therefore, the current 4 of the arm 2 or 3 stops at the current zero point after the negative current is applied, as indicated by 8 in FIG.
[0022]
Similarly, for the current 5, the supply of the gate signal (f) to the arm 2 is stopped when the AND of the TSC stop command signal (b) and the signal (h) corresponding to the negative current conduction period is established. Control is performed so that the supply of the gate signal (g) to the arm 3 thereafter is stopped a little after the AND is established. Therefore, the current 5 stops at the current zero point after the negative current is applied, as indicated by 9 in FIG.
[0023]
Further, for the current 6, the supply of the gate signal (i) to the arm 2 thereafter is stopped by the AND of the TSC stop command signal (b) and the signal (k) corresponding to the negative current conduction period. Then, the control is performed so that the supply of the gate signal (j) to the arm 3 thereafter is stopped a little after the AND is established. Accordingly, the current 6 stops at the current zero point after the negative current is applied, as indicated by 10 in FIG.
[0024]
As described above, the current waveform of each phase after receiving the TSC stop command is as shown in FIG. 2A, and the polarity charged in the capacitor 1 is the forward voltage in the arm 2 as shown in FIG. The arm 3 has a reverse voltage. The voltage waveform at this time is shown in FIG. The capacitors are charged in the same direction for all three phases.
[0025]
3A shows a waveform when the capacitor is charged, and FIG. 3B shows a waveform when the capacitor has been discharged. In FIG. 3A when the capacitor is charged, the arm 2 has a waveform in which a DC voltage and an AC voltage are superimposed in the forward direction, and the arm 3 has a waveform in which the DC voltage and the AC voltage are superimposed. It will be applied in the reverse direction. Further, in FIG. 3B when the capacitor has been discharged, the AC voltages equal in the forward direction and the reverse direction are applied to the arms 2 and 3.
[0026]
Therefore, the arm 2 uses all the semiconductor elements as thyristors so as to have a forward withstand voltage even when a waveform in which a DC voltage and an AC voltage are superimposed is applied in the forward direction. After the capacitor 1 is discharged, a voltage is applied to the arm 2 in both the forward and reverse directions. However, since the thyristor also has a reverse withstand voltage, the withstand voltage is sufficient.
[0027]
Subsequently, the arm 3 is configured such that some semiconductor elements are thyristors and some remaining semiconductor elements are diodes (rectifier elements) so as to have a reverse breakdown voltage even when a waveform in which a DC voltage and an AC voltage are superimposed is applied in the reverse direction. And After the capacitor 1 is discharged using the capacitor discharge device 7, a voltage is applied to the arm 3 in both the forward and reverse directions, and the diode cannot block the forward voltage. By using a semiconductor element as a thyristor, it also has a forward withstand voltage and a sufficient withstand voltage.
[0028]
The number M of semiconductor series in the arm 2 described above is a number that can withstand a waveform in which a DC voltage and an AC voltage are superimposed in the forward direction. The semiconductor series number N of the arm 3 is the sum of the thyristor number N1 designed to withstand the AC voltage after discharging the capacitor 1 and the diode number N2 designed to withstand the DC voltage charged in the capacitor 1.
[0029]
In this embodiment configured as described above, a part of the arm 3 is a diode, so that a part of the gate signal circuit of the gate generator (not shown) can be reduced, and the gate from the gate generator to the arm 3 can be reduced. The signal transmission path can be reduced.
[0030]
Furthermore, a cheaper static reactive power compensator can be provided by using a part of the arm 3 as an inexpensive diode.
[0031]
In the above description, the arm 2 is assumed to be a single row in which M thyristors are connected in series. However, the arm 2 is not limited to a single row, and a plurality of M thyristors connected in series is connected in parallel in a plurality of rows. Also good. Further, the arm 3 is not limited to a single row, and a plurality of thyristors N1 and diodes N2 connected in series may be connected in parallel in a plurality of rows.
[0032]
(Second Embodiment)
Next, the TSC according to the second embodiment of the present invention will be described. In the second embodiment, a gate signal is applied to the three-phase arms 2 and 3 to discharge the electric charge of the capacitor 1, and the capacitor discharge device 7 in the first embodiment described above is provided. It is unnecessary.
[0033]
FIG. 4 is a diagram showing a discharge current waveform and a signal for controlling the gate for explaining the operation of this embodiment.
[0034]
In the first embodiment described above, after the TSC is stopped, the capacitor 1 is charged in the same direction in all three phases. Therefore, by applying a gate signal from a gate generator (not shown) to the thyristors of the three-phase arms 2 and 3. The capacitor 1 can be discharged. That is, when the gate signal (b) shown in FIG. 4 is applied to the thyristor of the three-phase arm 2 from the gate generator (not shown), the capacitor 1 is charged in the reverse direction, so that the thyristor of the arm 3 is not shown next. The gate signal (c) shown in FIG. 4 is given from the gate generator. Then, the capacitor 1 is charged in the same direction as after the TSC is stopped.
[0035]
As described above, when the gate signals (b) and (c) are periodically supplied to the arms 2 and 3 from the gate generator (not shown), the discharge current is attenuated by the resistance of the semiconductor element and the resistance of the circuit. The discharge current from 1 becomes a vibration waveform as shown in FIG. 4A, and the charge of the capacitor 1 eventually becomes zero.
[0036]
Instead of providing the gate signals (b) and (c) shown in FIG. 4 to the thyristors of the arms 2 and 3, respectively, the gate signals (d) and (e) shown in FIG.
[0037]
According to the second embodiment, it is possible to discharge the capacitor 1 without providing the discharge device 7 dedicated to the capacitor 1, and it is possible to provide a cheaper static reactive power compensator.
[0038]
【The invention's effect】
According to the present invention configured as described above, a part of the semiconductor element to be used can be an inexpensive diode, and a more inexpensive static reactive power compensator can be provided.
[0039]
Further, it is possible to provide a more inexpensive static reactive power compensator that can discharge a capacitor without providing a capacitor-specific discharge device.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a main part of a TSC according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a current waveform for each phase and a signal for controlling a gate for explaining the operation of the first embodiment;
FIG. 3 is a view showing voltage waveforms applied to each arm in the first embodiment.
FIG. 4 is a diagram showing a discharge current waveform and a signal for controlling a gate for explaining the operation of the second embodiment.
FIG. 5 is a diagram showing a configuration of a main part of a conventional TSC.
FIG. 6 is a diagram showing each phase current waveform of a conventional TSC.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Capacitor 2 ... Positive polarity current conduction arm 3 ... Negative polarity current conduction arm 4, 5, 6 ... Each arm conduction current 7 ... Capacitor discharge device 8, 9, 10 ... Each arm conduction current waveform

Claims (2)

In a static reactive power compensator in which a capacitor is turned on / off by a circuit in which a first and a second circuit including a semiconductor element that is conducted by a gate signal are connected in antiparallel, the first circuit is a gate signal In the case where the second circuit is composed of a semiconductor element that is partly conducted by a gate signal and the remaining part is constituted by a diode, and the static reactive power compensator is stopped, A static reactive power compensator comprising gate signal supply control means for controlling a gate signal supplied to the semiconductor element so that conduction is stopped on the second circuit side. The gate signal supply control means controls to supply a gate signal for discharging the charge of the capacitor to the semiconductor elements of the first and second circuits after the static reactive power compensator stops. The static reactive power compensator according to claim 1, wherein:

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