JP2006197792A - Momentary voltage drop compensation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a momentary voltage drop compensation device that provides voltage compensation, at a high speed. <P>SOLUTION: A semiconductor switch, connected in parallel with a series transformer, is composed of self-arc-extinguishing elements. Further, a control circuit is provided for causing an electric current equal to a load current to flow through the transformer in series, when a detected voltage has come to be not greater than a predetermined value, and for turning the semiconductor switch to an off state via a self-arc-extinguishing element controller, after an electric current flowing via the semiconductor switch has become low. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to instantaneous voltage drop compensation caused by a power system accident or the like, and more particularly to an instantaneous voltage drop compensation device that compensates at high speed with a simple configuration.

A series compensation system as shown in FIG. 10 is known as a device for compensating for an instantaneous voltage drop of the power system caused by an accident such as galloping on the power system side, three jumps, reverse flashover due to lightning, and the like. In the figure, 1 is an AC power source, 2 is a transformer, and has a capacity matched to the load 4. 3 is a series transformer, and its secondary winding is connected in series with the transformer 2 and the load 4. Reference numeral 5 denotes a DC power source, which uses an electrolytic capacitor, a storage battery, an electric double layer capacitor, and the like. 6 is an inverter, 7 is an inductance, and the voltage generated in the inverter 6 is applied to the primary winding of the series transformer 3 through this inductance. 8 is a current transformer for detecting load current, 9 is a voltage transformer, and the voltage and current of the power system detected by this voltage transformer and current transformer are controlled by an inverter not shown. Output to the circuit. Reference numeral 10 denotes a high-speed switch configured by connecting semiconductor elements in anti-parallel, and is connected in parallel with the secondary winding of the transformer 3. When the power system is normal, the on-state is maintained and the load 4 is connected via this switch. Is supplied with power.
The instantaneous voltage drop compensation device shown in FIG. 10 supplies power to a load via a high-speed switch when the power supply is normal. When the control circuit of the inverter detects that the power supply voltage has dropped for some reason, the control circuit opens the high-speed switch 10, and the inverter 6 based on the current and voltage detected by the current transformer 8 and the transformer 9. The inverter 6 generates a voltage commensurate with the amount of decrease in the power supply voltage and superimposes it on the primary winding of the series transformer 3 to keep the load voltage at a predetermined value. The inverter power is supplied from the energy stored in the DC power source 5.

Patent Document 1, Patent Document 2, and the like are known as means for compensating the system voltage through such an instantaneous voltage drop compensation device. In each patent document, when the system voltage is normal, power is supplied to the load through a high-speed switch composed of a thyristor, and when an instantaneous voltage drop of the system voltage is detected, the inverter generates a voltage to the thyristor. The current that was flowing is commutated to the inverter side.
Japanese Patent No. 2773214 Utility Model Registration No. 2578802

  In the conventional instantaneous voltage drop compensator, the load is normally energized through a thyristor connected in antiparallel. Therefore, as a control circuit for the inverter 5, the direction of the load current detected by the instrument current transformer 8 is monitored, and the inverter is directed to forcibly commutate the thyristor of the energized high-speed switch 10 to the series transformer side. Controls to generate voltage. However, the load current is an alternating current, and it becomes difficult to determine the direction of the current in the vicinity of zero current where the current is small, and a detection error of the current direction occurs, and the thyristor that is conducting as shown in FIG. However, there is a problem that a short-circuit phenomenon occurs by generating an inverter voltage in the forward direction. Techniques for preventing such a short-circuit phenomenon are also disclosed in each of the above-mentioned patent documents. However, these conventional devices have a long time until forced commutation and require a high-speed voltage compensation. Is unsatisfactory.

That is, at the time t1 when the thyristor 10B is conducting and the current flows from the power source 1 to the load 4 side as in the load current shown in FIG. Assume that it is erroneously detected that the current flows from the load 4 side to the power source 1 side. In this case, since the control device acts to extinguish the thyristor 10A, the output voltage of the inverter 6 generates a voltage at which the B point becomes positive with respect to the A point. However, since the conductive thyristor is 10B, the current flowing through the thyristor B increases, and an overcurrent flows through the inverter 6 at time t2 as shown in FIG. 12B. It is determined that the direction of is opposite. As a result, the control device generates a voltage that makes the inverter voltage positive with respect to the point B, extinguishes the thyristor 10B, and commutates the load current to the inverter side. The time when the commutation is completed is t3, and the compensation voltage is generated as the instantaneous voltage drop compensator from time t3 shown in FIG. That is, it takes t3-t1 time until the compensation voltage is generated.
Therefore, an object of the present invention is to provide an instantaneous voltage drop compensator capable of voltage compensation at high speed.

A first aspect of the present invention is to connect a secondary side winding of a series transformer to a power system, connect a semiconductor switch configured to be capable of bidirectional flow in parallel with the secondary side winding, and connect the series transformer. In the instantaneous voltage drop compensator that connects the inverter to the primary side of the power supply and compensates for the instantaneous voltage drop of the power system,
The semiconductor switch is configured with a self-extinguishing element, and a voltage drop is detected by introducing a voltage of the power system, and the semiconductor switch is turned off via a self-extinguishing element control unit when the voltage is below a predetermined value. A voltage detection unit, an inverter compensation voltage generation unit that generates a compensation voltage by introducing a voltage of the power system, and generates a PWM signal based on an output signal of the voltage detection unit and an output voltage from the inverter compensation voltage generation unit And a PWM signal generating unit.

  According to a second aspect of the present invention, there is provided a current transformer for an instrument for detecting a load current flowing through the semiconductor switch, and a direction determination unit for determining a detected load current direction and a current level, respectively, and a current level determination unit And, based on the determination signal from each determination unit and the signal input from the voltage detection unit, outputs an off signal to the switch element in which the load current of the semiconductor switch does not flow, and In other words, a control circuit is provided for controlling to output the signal from the inverter compensation voltage generator to the inverter while the ON signal is continued.

  A third aspect of the present invention introduces a direction determination unit and a current level determination unit for determining a load current direction and a current level, a determination signal from each determination unit, and a signal from the voltage detection unit, and a current value. And a control circuit having a function of calculating the commutation operation end timing from a known constant of the device and outputting the off signal of the semiconductor switch by using the known constant of the device, and the inverter at the time of the semiconductor switch off signal by the control circuit A control circuit that controls to output a signal from the compensation voltage generator to the inverter is provided.

A fourth aspect of the present invention is characterized in that the commutation operation end timing time t1 in the control circuit is obtained by the following equation.
t1 = -L / R.In (1-IL0R / E)
Where E: DC voltage of inverter, L: sum of inverter circuit inductance and series transformer inductance, R: sum of inverter circuit resistance and series transformer resistance, IL0: before commutation start In the fifth aspect of the present invention, the control circuit should predetermine a time until the current flowing through the semiconductor switch is sufficiently reduced, and output the inverter from the known inductance, capacitance, and resistance of the inverter circuit. The voltage is calculated, and the semiconductor switch is turned off after the predetermined time has elapsed.

As described above, according to the present invention, since the semiconductor switch connected in parallel with the series transformer is composed of a self-extinguishing element, there is no risk of commutation failure such as inverter overcurrent at the start of compensation, and it is ensured. In addition, the current can be cut off even when the current is flowing. When the semiconductor switch is turned off, current flows from the power source to the load through the series transformer. At this time, since the series transformer has an impedance, a voltage is generated at both ends of the series transformer due to a rapid current change, resulting in a decrease in the load voltage, and high speed switching cannot be performed as it is. In the present invention, it is possible to perform switching at high speed and reliably by flowing a current equivalent to a load current through a series transformer with an inverter in advance and performing forced commutation to reduce the flow through the semiconductor switch.

  FIG. 1 is a block diagram of a control device showing a first embodiment of the present invention. 2 to 5 show main circuits constituting the present invention. That is, the present invention uses a self-extinguishing semiconductor element as a semiconductor switch, and FIG. 2 shows a case where a GTO is used as a single self-extinguishing element. In the figure, 12 is a GTO, 13 is a snubber circuit, and is composed of a diode D, a capacitor C, and a resistor R and is connected in parallel with the GTO to constitute a single switch body 11. In FIG. 2, GTO is used as a self-extinguishing type semiconductor element, but it goes without saying that an IGBT or the like may be used.

3 shows the semiconductor switch 14. The switch body 11 shown in FIG. 2 is connected in antiparallel, and if necessary, the arrester LA is connected in parallel to form the semiconductor switch 14. The semiconductor switch shown in FIG. Used as an alternative to 10. FIG. 4 shows an application example when the circuit voltage is large. A plurality of semiconductor switches 14 are connected in series, and an arrester LA is connected in parallel with the series body. R1 to Rn are resistors, which are voltage dividing resistors for equalizing the voltage sharing when the semiconductor switch 14 is turned off.
FIG. 5 shows an application example when the rated current is large, and a plurality of semiconductor switches 14 and arresters LA are configured in parallel. The other main circuit as the instantaneous voltage drop compensator is configured in the same manner as in FIG.

FIG. 1 is a configuration diagram of the control device 20 when the semiconductor switch of the instantaneous voltage drop compensation device is configured as shown in FIG. In the figure, reference numeral 21 denotes a voltage detector, which detects the instantaneous voltage drop by introducing the secondary voltage of the instrument transformer 6. Reference numeral 22 denotes a control unit of a self-extinguishing element such as GTO or IGBT, which outputs an off signal to the semiconductor switch 14. Reference numeral 23 denotes an inverter compensation voltage generation circuit. The inverter compensation voltage generation circuit 23 introduces a secondary voltage of the instrument transformer 6 to generate a reference waveform, and an output of the generation unit 23a. It has a compensation voltage signal section 23b that generates a compensation voltage signal by introducing a deviation signal from the secondary voltage output of the instrument transformer 6. Reference numeral 24 denotes a PWM signal generator for generating a PWM signal. A PWM signal is generated based on the signal from the compensation voltage signal unit 23 b and the signal from the voltage detector, and the switching element of the inverter 6 is connected via the gate circuit 25. Output to the gate.
In the configuration as described above, when the value detected by the instrument transformer 9 is higher than the threshold value and the power supply voltage is normal, the semiconductor switch 14 is in the on state. Power is supplied to the load via When the power supply voltage drops instantaneously for some reason, the voltage detection unit 21 detects this via the instrument transformer 9 and outputs it to the control unit 22. The control unit 22 calculates and compares the deviation between the input detection value and a preset threshold value. As a result, when it is determined that the instantaneous voltage drop has occurred, the semiconductor switch 14 is opened.
On the other hand, the secondary voltage of the instrument transformer 6 is also applied to the reference waveform generator 23a to generate a voltage corresponding to the input voltage, and compensates after the deviation from the output of the instrument transformer 9 is obtained in the adder. It is output to the voltage signal generator 23b. The compensation voltage signal generator 23 b generates a compensation signal corresponding to the input signal and outputs it to the PWM signal generator 24. The PWM signal generator 24 receives a detection signal from the voltage detector 21, generates a PWM signal based on the detection signal and the compensation voltage signal, and outputs the PWM signal to the inverter gate circuit. Therefore, a voltage corresponding to the amount of decrease in the power supply voltage is superposed on the secondary winding via the primary winding of the series transformer 3 from the inverter 6 to maintain the load voltage at a predetermined value.

  Therefore, according to this embodiment, by using the self-extinguishing element for the semiconductor switch 14 connected in parallel with the series transformer 3, the semiconductor switch is turned off regardless of the direction of the load current and the load current is cut off. Therefore, the inverter can immediately generate a compensation voltage, and the load voltage can obtain an AC waveform that is not interrupted.

  FIG. 6 is a block diagram of the control device showing the second embodiment. This control device is an embodiment in the case where an instrumental current transformer 15 for detecting the direction of the current flowing through the semiconductor switch 14 is installed as shown in FIG. In FIG. 6, reference numeral 26 denotes a direction determination unit for determining the flow direction of the load current, and the current detected by the current transformer 15 is input. A current level determination unit 27 determines the level of current flowing through the semiconductor switch 14. Reference numeral 28 denotes a control circuit, to which a signal from the direction determination unit 26 and current and voltage values from the current level determination unit 27 and the voltage detection unit 21 are input. Reference numeral 29 denotes a switching unit.

  In the embodiment of FIG. 6, when the instantaneous voltage drops, the voltage detector 21 detects this via the instrument transformer 9 as in the first embodiment, and notifies the control circuit 28 that the voltage has dropped. At this time, the direction signal of the current flowing through the semiconductor switch 14 and the magnitude thereof are input to the control circuit 28 via the direction determination unit 26 and the current level determination unit 27, and the direction of the load current is corrected without error. If it is large enough to be detected, the control circuit 28 immediately passes through the self-extinguishing element control unit 22 to the switch body 11 on the side of the switch body 11 constituting the semiconductor switch 14 where no current flows. The gate signal of the element is turned off, and the switching unit 29 is switched to the control circuit 28 side while the gate signal of the switch body 11 in the energized direction remains on. As a result, the current flowing through the semiconductor switch 14 is forcibly commutated by the inverter voltage controlled by the signal output from the control circuit 28, and the current level determination unit 27 determines when the current has sufficiently decreased. Then, an OFF command is output to the switch body 11, and the switching unit 29 switches to the inverter guarantee voltage generating unit 28 side almost simultaneously. At the time of switching, the current flowing through the semiconductor switch flows from the power source to the load through the series transformer because the semiconductor switch is turned off. Since the series transformer has impedance, a voltage is generated at both ends of the series transformer due to an abrupt current change, resulting in a decrease in the load voltage, which cannot be switched at high speed as it is. Switching can be performed at high speed and reliably by passing a current equivalent to the load current through the series transformer with the inverter and performing forced commutation to reduce the flow through the semiconductor switch.

Since the inverter compensation voltage generator 23 is configured in the same manner as in the first embodiment, it generates a compensation voltage corresponding to the input voltage, and an element constituting the inverter via the PWM signal generator not shown. The inverter 6 generates a voltage commensurate with the amount of decrease in the power supply voltage, and superimposes the voltage from the inverter on the secondary winding of the series transformer 3, thereby setting the load voltage to a predetermined value. maintain.
The control circuit 28 turns off the gate signal of the semiconductor switch via the self-extinguishing element control unit 22 regardless of the conduction state of the semiconductor switch 14 when the load current is small in the above-mentioned operating place. Turn off the load current.

  According to this embodiment, at the start of compensation, the inverter can be switched at high speed and reliably without generating current, and switching control with suppressed load voltage oscillation is possible as shown in FIG. is there.

  FIG. 9 is a block diagram of the control apparatus showing the third embodiment. The difference from the second embodiment shown in FIG. 6 is that the control circuit 28 is provided with a timing calculation section 28a and a comparison section 28b. Other than that, the current detection is obtained from the current transformer 8 instead of the current transformer 15. The timing calculation unit 28a calculates the timing at which the current flowing through the semiconductor switch 14 becomes sufficiently small due to the commutation operation in which the inverter voltage is applied to the series transformer side, and an inductance value that is a known constant in the device, The current value is calculated from the resistance value and the DC voltage value of the circuit. The control unit 28b is composed of a table such as a ROM, and the current value is obtained in advance as a variable and stored as a table. The timing calculation unit 28a refers to the table at the time of the calculation, determines the timing when the current is almost commutated, and instructs the self-extinguishing element control unit 22 to turn off the gate signal.

  The timing calculation of commutation end by the timing calculation unit 28a is executed as follows.

E = Ldi (t) / dt + Ri (t) (1)
Where E: DC voltage of inverter, L: sum of inverter circuit inductance and series transformer inductance, R: sum of inverter circuit resistance and series transformer resistance, i: commutation flows When the inverter current (1) equation is expanded,
i = E / R. (1-exp (-R / Lt)) (2)
Assuming that the load current before the start of commutation is IL (t = 0) = IL0, the time t1 until commutation ends is
t1 = -L / R.In (1-IL0R / E) (3)
It becomes.

Also in the embodiment of FIG. 9, the voltage detector 21 detects an instantaneous voltage drop via the instrument transformer 9 and notifies the control circuit 28 that the voltage has dropped. When the control circuit 28 turns off the non-energized switch body of the semiconductor switch 14 and, at the same time, the current from the current level determination unit 27 is larger than the erroneous recognition level, the current flowing through the semiconductor switch 14 decreases. The current is commutated to the inverter side through the DC transformer 3. Further, the control circuit 28 calculates the time until the current flowing through the semiconductor switch 14 becomes sufficiently small by the above-described means, and when the time comes, the semiconductor switch 14 is turned off and the switching unit 29 is switched to the inverter compensation voltage. Switching to the generation unit 23 side is executed.

  According to the third embodiment, switching for high-speed compensation control can be performed while suppressing vibration of the load voltage without installing the instrument current transformer 15.

If the time until the load current flowing through the semiconductor switch sufficiently decreases can be fixed in advance, the semiconductor switch may be turned off as follows.
That is, the inverter voltage E can be varied from the DC voltage of the inverter of the embodiment shown in FIG. 9 and the inverter switching pattern such as PWM control. From this, the timing at which the current is commutated to the series transformer is determined in advance, and the voltage generated by the inverter at this time is calculated from the inductance value, capacitance value, resistance value, and circuit DC voltage, which are known constants of the device. And ask. Alternatively, the calculation result is obtained from the comparison table of the table, the inverter voltage is output, the commutation operation is executed, and the semiconductor switch is turned off after a predetermined time has elapsed.

  According to this embodiment, compared with the third embodiment, the control unit for generating an arbitrary voltage such as the existing PWM control can be used as it is, and each phase independent control like a three-phase inverter can be performed. Even if it is not possible, it has an effect that can be applied.

The block diagram of the control apparatus which shows the 1st Example of this invention. The block diagram of the switch body which uses a self-extinguishing element. The block diagram of a semiconductor switch. The other block diagram of a semiconductor switch. The other block diagram of a semiconductor switch. The block diagram of the control apparatus which shows the 2nd Example of this invention. The block diagram of the main circuit used for the 2nd Example of this invention. The wave form diagram of the load voltage by this invention. The block diagram of the control apparatus which shows the 3rd Example of this invention. The block diagram of the conventional instantaneous voltage drop compensation apparatus. Operation | movement explanatory drawing of the conventional instantaneous voltage drop compensation apparatus. It is an operation waveform diagram, (a) is a received voltage and load current, (b) is an explanatory diagram of occurrence of overcurrent, (c) waveform diagram after compensation operation.

Explanation of symbols

1 ... Power supply
2 ... Transformer
3 Series transformer
4 ... Load
5 ... DC power supply
6 ... Inverter
7 ... Inductance
DESCRIPTION OF SYMBOLS 8,15 ... Current transformer for instrument 9 ... Transformer for instrument 10, 14 ... Semiconductor switch 21 ... Voltage detection part 22 ... Self-extinguishing element control part 23 ... Inverter compensation voltage generation part 26 ... Direction determination part 27 ... Current Level determination unit 28 ... control circuit 29 ... switching unit

Claims (5)

Connect the secondary side winding of the series transformer to the power system, connect a semiconductor switch configured to allow bidirectional flow in parallel with the secondary side winding, and connect an inverter to the primary side of the series transformer In the instantaneous voltage drop compensation device that compensates for the instantaneous voltage drop of the power system,
The semiconductor switch is configured with a self-extinguishing element, and a voltage drop is detected by introducing a voltage of the power system, and the semiconductor switch is turned off via a self-extinguishing element control unit when the voltage is below a predetermined value. A voltage detection unit, an inverter compensation voltage generation unit that generates a compensation voltage by introducing a voltage of the power system, and generates a PWM signal based on an output signal of the voltage detection unit and an output voltage from the inverter compensation voltage generation unit An instantaneous voltage drop compensator characterized by comprising a PWM signal generating unit. A current transformer for an instrument for detecting a load current flowing through the semiconductor switch is provided, a direction determination unit for determining a direction and a current level of the detected load current, a current level determination unit, and a determination from each determination unit Based on the determination signal and the signal input from the voltage detection unit, an off signal is output to the switch element in which the load current of the semiconductor switch does not flow, and the on signal is continued to the switch element that is conducting. 2. The instantaneous voltage drop compensator according to claim 1, further comprising a control circuit that controls to output a signal from the inverter compensation voltage generator to the inverter. A direction determination unit that determines the direction of the load current and the current level, a current level determination unit, a determination signal from each determination unit, and a signal from the voltage detection unit, and a known value of the device using the current value as a variable A control circuit having a function of calculating a commutation operation end timing from a constant and outputting an OFF signal of the semiconductor switch is provided, and when the semiconductor switch is OFF signal by the control circuit, the signal from the inverter compensation voltage generating unit is an inverter The instantaneous voltage drop compensator according to claim 1, further comprising a control circuit that controls to output to the output. 4. The instantaneous voltage drop compensator according to claim 3, wherein the commutation operation end timing time t1 in the control circuit is obtained by the following equation.
t1 = -L / R.In (1-IL0R / E)
Where E: DC voltage of inverter, L: sum of inverter circuit inductance and series transformer inductance, R: sum of inverter circuit resistance and series transformer resistance, IL0: before commutation start Load current The control circuit predetermines a time until the current flowing through the semiconductor switch sufficiently decreases, calculates a voltage to be output from the inverter from the inductance, capacitance, and resistance of the known inverter circuit, and determines the predetermined time. 5. The instantaneous voltage drop compensator according to claim 3, wherein the semiconductor switch is turned off after elapse of time.

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