JP2009278813A - Instantaneous voltage drop compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an instantaneous voltage drop compensator which secures high efficiency by minimizing a failure rate of semiconductors and relatively increasing a DC voltage during a compensation operation to increase output capacitance. <P>SOLUTION: In the instantaneous voltage drop compensator, a DC capacitor 4 is connected between DC output terminals of an inverter circuit 3 connected to a power system, a chopper circuit 6 is connected to the DC capacitor 4, and a super conductive coil 7 is connected to the chopper circuit 6. When an instantaneous voltage drop occurs in the power system, the DC voltage of the DC capacitor 4 and the super conductive coil 7 compensates a load voltage prior to the instantaneous voltage drop. A circuit for setting a DC voltage value during standby lower than that during an instantaneous voltage drop compensation operation is provided to the control circuit 100 of the inverter circuit 3, and a circuit for increasing the DC voltage during the instantaneous voltage drop compensation operation and outputting it to the power supply, is provided to the control circuit 200 of the chopper circuit 6. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an improvement in an instantaneous voltage drop compensator that compensates a load voltage via an inverter using stored energy when an instantaneous voltage drop occurs in a commercial power supply.

In recent years, a failure due to an instantaneous voltage drop (hereinafter simply referred to as “instantaneous drop”) in a power supply system due to lightning strikes has become a problem. For this reason, critical load facilities such as bank online, traffic control, computer control, industrial manufacturing facilities, and power supplies for measurement and control should be detected and supplied to the load facilities quickly. An instantaneous voltage drop compensator for compensating the power supply voltage has been introduced.

In such a sag compensator, there are methods for storing energy, such as those that store chemical energy such as batteries, and those that store mechanical rotational energy such as flywheels. A superconducting energy storage device (hereinafter referred to as SMES) is known.

As a typical device, there is an instantaneous voltage drop compensator that accumulates current energy in a superconducting coil during a period when the power is stable and returns the accumulated power to the power system when a sag occurs (Patent Document 1). As shown in FIG. 8, 1 is an AC input terminal connected to an AC power supply system, 2 is a transformer, 3 is a voltage type inverter circuit, and is connected to the AC power supply system via the transformer 2 as shown in FIG. By controlling the phase difference and voltage difference of the voltage with the AC power supply system, energy is exchanged with the AC power supply system, and AC is converted into DC, or conversely, DC is converted into AC It is comprised by semiconductor switches, such as IGBT.

4 is a DC capacitor connected between DC output terminals of the voltage type inverter circuit 3, 5 is a current detector, 6 is a chopper circuit composed of semiconductor switches 8 and 9 such as IGBTs and diodes 10 and 11. 4 are connected in parallel. A superconducting coil 7 is connected to the chopper circuit 6. 12 is a control circuit of the superconducting coil energy storage circuit, 13 is a coil current detector connected to the superconducting coil 7, and 14 is a voltage detector.

  Next, the operation will be described. First, this circuit operation includes three modes: a first mode in which energy is first stored in the superconducting coil 7, a second mode in which the energy of the superconducting coil 7 is retained, and a third mode in which the energy stored in the superconducting coil 7 is released. -Consists of Table 1 shows the relationship between each mode and each state, voltage type inverter control and chopper control.

Normally, when the current of the superconducting coil 7 is less than the set value without the sag compensation, the first mode in which the current is stored in the superconducting coil 7 is entered, and direct current is generated by opening and closing the semiconductor switches 8 and 9 of the chopper circuit 6. The average level of the terminal voltage of the capacitor 4 is stepped down and controlled so that the current of the superconducting coil 7 becomes a set value.

At this time, the voltage type inverter circuit 3 supplies electric power by controlling the voltage phase difference and the voltage difference with the AC power supply so that the DC voltage is constant by supplying the voltage from the AC power supply to the DC capacitor 4. Next, when the current value of the superconducting coil 7 is within the set range in the state where there is no sag compensation, the second mode in which the energy of the direct current stored in the superconducting coil 7 is returned to the chopper circuit 6 9 is closed. For example, when the semiconductor switch 8 is turned on (closed) and the semiconductor switch 9 is turned off (opened), the current in the superconducting coil 7 circulates through the diode 11 -the semiconductor switch 8.

On the other hand, when the semiconductor switch 9 is turned on (closed) and the semiconductor switch 8 is turned off (opened), the current in the superconducting coil 7 circulates through the semiconductor switch 9-diode 10. That is, in a state where energy is held in the superconducting coil 7, the voltage type inverter circuit 3 is in a mode in which no coil current flows, and the voltage type inverter 3 maintains DC voltage control but does not exchange power with the superconducting coil 7. No state. Further, when a voltage sag occurs in the power supply system, the third mode of voltage sag compensation is entered, and the chopper circuit 6 operates as a step-up chopper circuit, and releases the energy stored in the superconducting coil 7 to the DC capacitor 4, and the DC capacitor. 4 operates to control the DC voltage of 4 to a value corresponding to the operation of the voltage type inverter circuit 3.

In the voltage type inverter circuit 3, the electrical energy stored in the superconducting coil 7 is reversely converted into an alternating current through a direct current capacitor 4 by an inverse conversion operation, and the energy is discharged to the alternating current power supply system. In this third mode, the voltage type inverter circuit 3 converts the DC voltage of the DC capacitor 4 into AC and supplies the voltage to the AC power supply system via the transformer 2, but the charging energy of the DC capacitor 4 is relatively small. For this reason, when energy is released, the DC voltage decreases. In order to prevent this drop in DC voltage, both the semiconductor switches 8 and 9 are turned off (opened), so that the current in the superconducting coil 7 recharges the DC capacitor 4 via the diodes 10 and 11. In this way, the electricity from the AC system is stored in the superconducting coil 7, and the electricity stored in the DC capacitor 4 and the superconducting coil 7 is returned to the AC system again at the time of a sag.

In such a voltage sag compensator, if the DC voltage stored in the DC capacitor 4 is set high, the output capacity discharged to the AC system can be increased, and if the output capacity is the same, the AC output current can be reduced, so that the loss is reduced. The efficiency can be improved by lowering. However, when the DC voltage is increased, semiconductor switches such as IGBTs used in the voltage-type inverter circuit 3 connected to the DC circuit, semiconductors such as IGBTs used in the semiconductor switches 8 and 9, and diodes 10 and 11 are used. The value of the DC voltage applied to is also increased.

For this reason, the DC voltage is usually selected in accordance with the rating of the semiconductor, but it is necessary to increase the DC voltage as much as possible in order to increase the output capacity of the device or increase the efficiency. In this case, it goes without saying that the surge voltage generated during switching of the semiconductors falls within the allowable value. However, if the DC voltage applied when the semiconductors are non-conductive is increased, the failure rate of the semiconductors increases. Will occur. FIG. 9 shows the relationship between these operating voltages and the expected value of the failure rate. Since the vertical axis is the failure rate [FIT] and is a LOG scale, a slight increase in the applied voltage on the horizontal axis indicates the semiconductors. It has been shown to increase the failure rate.

FIT is a unit expressing a failure probability, and the failure rate when one component fails in 1 billion hours is set to 1 FIT. In this example, the failure rate when the overprint voltage is 1800 V is about 50 FIT, but when the overprint voltage is 2200 V, the failure rate is significantly increased to about 1000 FIT. That is, increasing the DC voltage leads to an increase in the efficiency of the converter, but on the other hand, there is a problem of increasing the failure rate of semiconductors and the like.
Japanese Patent No. 2543336

In order to solve the above-mentioned problem, the present invention controls the DC voltage value during the standby time to be lower than the DC voltage value during the instantaneous voltage drop compensation operation to suppress the failure rate of the semiconductors, and at the time of the compensation operation. It is an object of the present invention to provide an instantaneous voltage drop compensator capable of ensuring a high efficiency by increasing the output capacity by relatively increasing the DC voltage.

The instantaneous voltage drop compensator according to claim 1 of the present invention has a DC capacitor connected between DC output terminals of an inverter circuit connected to a power supply system, and a chopper circuit connected to the DC capacitor. Instantaneous voltage drop that compensates for the load voltage before the instantaneous voltage drop by the DC voltage of the DC energy storage part when an instantaneous voltage drop occurs in the commercial power supply that connects the storage unit and supplies power to the load connected to the power supply system In the compensator, the control circuit of the inverter circuit is provided with a circuit for setting the DC voltage value during standby to be lower than the DC voltage value during the instantaneous voltage drop compensation operation, and the control circuit of the chopper circuit has an instantaneous voltage drop Provide a circuit to increase the DC voltage value during compensation operation and output it to the power supply system so that the voltage applied to the semiconductors during standby is kept low. It is characterized in that the.

The instantaneous voltage drop compensator according to claim 2 of the present invention is characterized in that, in claim 1, the DC capacitor and the DC energy storage unit are charged from the power supply system via an inverter circuit. .

The instantaneous voltage drop compensator according to claim 3 of the present invention is characterized in that, in claim 1, a direct current power source for charging the direct current capacitor and the direct current energy storage unit is provided.

The instantaneous voltage drop compensator according to claim 4 of the present invention is characterized in that, in claim 1, 2 or 3, the DC energy storage part is formed of a superconducting coil.

According to the instantaneous voltage drop compensator according to claim 1 of the present invention, the failure rate of the semiconductor is controlled by controlling the DC voltage value during the standby time to be lower than the DC voltage value during the instantaneous voltage drop compensation operation. In addition, the DC voltage during the compensation operation can be made relatively high to increase the output capacity, thereby ensuring high efficiency.

According to the instantaneous voltage drop compensator of the second aspect, the DC capacitor and the DC energy storage unit can be charged from the power supply system via the inverter circuit, respectively.

According to the instantaneous voltage drop compensator of the third aspect, since the direct current power source for charging the direct current capacitor and the direct current energy storage unit is provided, the control is easy.

According to the instantaneous voltage drop compensator of the fourth aspect, since the DC energy storage part is formed of a superconducting coil, the apparatus is small and excellent in durability.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. A voltage type inverter circuit 3 composed of a semiconductor switch such as IGBT is connected to an AC input terminal 1 connected to the AC power supply system via a transformer 2, and further connected between the DC output terminals of the voltage type inverter circuit 3. A chopper circuit 6 including semiconductor switches 8 and 9 such as IGBTs and diodes 10 and 11 is connected via a DC capacitor 4. A superconducting coil 7 is connected to the chopper circuit 6, and a coil current detector 13 is connected thereto. Reference numeral 14 is a voltage detector, and 15 is an AC voltage detection transformer connected to the AC input terminal 1, which is connected to the inverter control circuit 100 of the voltage type inverter circuit 3 so as to input the detected voltage. . Reference numeral 200 denotes a chopper control circuit that controls the chopper circuit 6.

FIG. 2 is a block diagram showing the details of the inverter control circuit 100, where 101 is a DC voltage reference A set to, for example, 1800V. Reference numeral 102 denotes DC voltage feedback, which is an output signal of the voltage detector 14 of FIG. Reference numeral 103 denotes a DC voltage control circuit which controls the DC voltage feedback 102 so that the signal of the DC voltage reference 102 is, for example, 1800V. 104 is an AC voltage reference and is set to 6.6 KV of the power supply system, for example. Reference numeral 105 denotes AC voltage feedback, which is a voltage signal obtained by rectifying the output signal of the transformer 15 in FIG. 106 is an AC voltage control circuit that receives an AC voltage feedback 105 signal and controls the output so that the AC voltage reference is, for example, 6.6 KV. 107 is a control switch, and switches to the AC voltage control side during sag compensation operation. The switch is made to the DC voltage control side except during sag compensation operation. Reference numeral 109 denotes a PWM control circuit that receives a signal from the AC voltage control circuit 106 and generates a PWM signal of the voltage type inverter 3, and 110 denotes a gate drive of a switch element of the voltage type inverter 3.

3 is a block diagram of the chopper control circuit 200 of the chopper circuit 6 shown in FIG. 1, in which 201 indicates a coil current reference, 202 indicates a coil current feedback, and the output signal of the coil current detector 13 shown in FIG. is there. A coil current control circuit 203 receives a signal from the coil current feedback 202 and controls the coil current reference 201 to have a value. Reference numeral 204 denotes a DC voltage reference B set so as to be boosted to, for example, 2200 V at the time of an instantaneous drop, and reference numeral 102 denotes DC voltage feedback, which is an output signal of the voltage detector 14 in FIG. Reference numeral 206 denotes a DC voltage control circuit which controls the DC voltage feedback 102 so that the signal of the DC voltage reference B is, for example, 2200V. A control switch 207 switches to the DC voltage control side during the sag compensation operation, and switches to the coil current control side except during the sag compensation operation. Reference numeral 209 denotes a PWM control circuit that receives a signal from the DC voltage control circuit 206 and generates a PWM signal of the chopper circuit 6. Reference numeral 210 denotes a gate drive of the semiconductor switches 8 and 9 of the chopper circuit 6.

The operation of the above circuit will be described. In the first mode in which energy is first stored in the superconducting coil 7, the voltage type inverter circuit 3 supplies a voltage from the AC power source to the DC capacitor 4 so that the DC voltage becomes constant. Electric power is supplied by controlling the phase difference and voltage difference between the AC power supply and the superconducting coil 7. In the second mode in which the energy of the superconducting coil 7 is maintained, the DC voltage feedback (voltage signal) 102 whose voltage is detected by the voltage detector 14 and the DC voltage reference A 101 that constitutes the inverter control circuit 100 of FIG. For example, the direct current voltage control circuit 103 adjusts the voltage so that the voltage becomes 1800 V by comparing with 1800 V, for example.

In this second mode, when the current value of the superconducting coil 7 detected by the coil current detector 13 is within the set range compared to the coil current reference 201 of the chopper control circuit 200 of FIG. On (closed), the semiconductor switch 8 is turned off (opened), and the current of the superconducting coil 7 recirculates the energy of the direct current stored in the superconducting coil 7 via the semiconductor switch 9-diode 10. In this second mode in which energy is held in the superconducting coil 7, no coil current flows through the voltage type inverter circuit 3, and the voltage type inverter circuit 3 maintains DC voltage control but does not exchange power, or a gate block. It becomes a state.

The AC voltage detection transformer 15 constantly measures the voltage of the power supply system, and uses the AC voltage feedback (voltage signal) 105 of the inverter control circuit 100 and the AC voltage reference 104 set to, for example, 6.6 KV. In comparison, when a voltage sag occurs in the power supply system, the inverter control circuit 100 in FIG. 2 receives the signal of the voltage sag compensation operation 108 and the control switch 107 is turned on, and the AC voltage control circuit 106 changes to 6.6 KV. A signal is output from the PWM control circuit 109 of the voltage type inverter 3 to the gate drive 110 so that the voltage control is performed in the voltage type inverter 3. Inversely converted to current, energy is released to compensate the voltage of the power system.

On the other hand, in the chopper control circuit 200 of FIG. 3, when a sag occurs in the power supply system, the control switch 207 is turned on in response to the signal of the sag compensation operation 108, and the direct current that is the detection voltage of the voltage detector 14 is switched. The voltage feedback 102 and 204 are compared with the voltage set to 2200 V by the DC voltage reference B, and the semiconductor switch 8 of the chopper circuit 6 through the PWM control circuit 209 and the gate drive 210 from the DC voltage control circuit 206, 9 is adjusted to 2200 V, and the electric energy stored in the superconducting coil 7 is reversely converted into an alternating current through the direct current capacitor 4 by an inverse conversion operation, and is discharged to the power supply system.

In this case, in a normally used voltage type inverter circuit of a pulse width control system, the relational expression between the DC voltage Vdc and the AC output voltage Vac is expressed as follows.
Vac = K ・ M ・ Vdc
Here, K is a constant, and M represents a control rate of pulse width control having a value from 0 to 1. In order to obtain a predetermined AC output voltage Vac, the voltage type inverter circuit 3 controls the control rate M according to the DC voltage. For example, even when the DC voltage Vdc changes, the AC output voltage Vac can be controlled to be constant by controlling M in accordance with the change in Vdc. On the other hand, the DC voltage Vdc can be varied by adjusting the OFF section of the semiconductor switches 8 and 9 in the case of the circuit configuration of FIG. As shown in FIG. 4, in the standby mode without the sag compensation operation, the DC voltage reference A is set to 1800V, for example, and during the sag compensation operation, the DC voltage reference B is set to 2200V, for example. To the power system.

In other words, assuming that the DC voltage in the standby mode is 1800V, the DC voltage Vdc can be increased to 2200V by lengthening the OFF section of the semiconductor switches 8 and 9 during a sag. In this way, the instantaneous voltage drop compensator of the present invention sets the DC voltage low during standby, thereby suppressing the failure rate of the semiconductors connected to the DC circuit to a low value, and in the instantaneous voltage compensation mode, the DC voltage is reduced. The output capacity can be increased by increasing the voltage. Normally, the instantaneous voltage drop compensation mode time is as short as 1 second or less, so even if the DC voltage is increased by this time, the influence on the failure rate of the semiconductor is extremely small.

Next, another embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram for explaining the circuit of the instantaneous voltage drop compensator. The same reference numerals as those in FIG. Reference numeral 16 denotes a DC power supply for charging the DC capacitor 4, and the DC capacitor 4 is always charged at 1800 V, for example, via a resistor 17 and a diode 18. Reference numerals 19 and 24 denote diodes, 20 denotes a chopper composed of a semiconductor switch such as IGBT, 21 denotes a semiconductor switch such as IGBT, and 25 denotes a DC power source for charging the superconducting coil 7. Reference numeral 300 denotes an inverter control circuit of the voltage type inverter circuit 3, and 400 denotes a chopper control circuit of the chopper 20.

FIG. 6 is a configuration diagram showing details of the inverter control circuit 300 of the voltage type inverter circuit 3, which is equivalent to a part of the function of the control circuit shown in FIG. 2, but is a first for storing energy in the superconducting coil 7. In the second mode in which the mode and energy are maintained, the gate of the voltage type inverter circuit 3 is stopped.

FIG. 7 is a configuration diagram showing details of the control circuit 400 of the chopper 20, which is equivalent to a part of the function of the control circuit shown in FIG. 2, but the current flowing through the superconducting coil 7 by the on / off control of the chopper 20. In the first mode in which energy is stored in the superconducting coil 7 and the second mode in which energy is held, the ON signal 401 is continuously output to the chopper 20.

The above circuit configuration is different from the case of charging from the external power source in FIG. 1 in that the DC capacitor 4 is charged separately by the DC power source 16 and the superconducting coil 7 is separately charged by the DC power source 25. Therefore, in the first mode for storing energy in the superconducting coil 7 and the second mode for holding energy, the voltage type inverter circuit 3 is in a blocked state. Further, in the semiconductors connected to the DC circuit, in the first mode and the second mode, the power source of the DC power supply 16 is set to be low, for example, 1800 V to protect the semiconductors. Further, in the control circuit 400 of the chopper 20 in FIG. 7, the chopper 20 is continuously turned on to recirculate the current of the superconducting coil 7 through the diode 24.

When a voltage sag occurs in the power supply system, the inverter control circuit 300 of FIG. 6 receives the signal of the voltage sag compensation operation 108 and the control switch 107 is turned on, and the voltage from the AC voltage control circuit 106 is 6.6 KV. In order to control, a signal is output from the PWM control circuit 109 of the voltage type inverter 3 to the gate drive 110, and the electric energy stored in the DC capacitor 4 is converted by the voltage type inverter circuit 3 into an alternating current. The energy is released to compensate the voltage of the power system.

On the other hand, in the chopper control circuit 400 of FIG. 7, when a voltage sag occurs in the power supply system, the control switch 207 is turned on in response to the signal of the voltage sag compensation operation 108, and the DC voltage that is the detection voltage of the voltage detector 14 is switched. The voltage feedback 102 is compared with the voltage set to 2200V by the DC voltage reference B of 204, and the chopper 20 is turned on / off from the gate drive 210 through the PWM control circuit 209 from the DC voltage control circuit 206. By controlling, the electric energy stored in the superconducting coil 7 is reversely converted by the voltage-type inverter circuit 3 via the DC capacitor 4 and reversely converted to 6.6V AC current and released to the power supply system.

As described above, the voltage type inverter circuit 3 and the chopper 20 are operated by the control circuits 300 and 400 depending on whether or not the sag compensation operation is performed, and the DC voltage during the sag compensation operation can be increased as shown in FIG. .

In the above description, the case where a superconducting coil is used as a direct current energy storage unit has been described. However, the superconducting coil is used for a battery that stores chemical energy such as a battery or a mechanical wheel that stores mechanical energy such as a flywheel. Can do.

1 is a circuit diagram of an instantaneous voltage drop compensator according to an embodiment of the present invention. It is a block diagram which shows the inverter control circuit which comprises the instantaneous voltage drop compensation apparatus of FIG. It is a block diagram which shows the control circuit of the chopper which comprises the instantaneous voltage drop compensation apparatus of FIG. It is explanatory drawing explaining the method of control by this invention. It is a circuit diagram of an instantaneous voltage drop compensator according to another embodiment of the present invention. It is a block diagram which shows the inverter control circuit which comprises the instantaneous voltage drop compensation apparatus of FIG. It is a block diagram which shows the control circuit of the chopper which comprises the instantaneous voltage drop compensation apparatus of FIG. It is a circuit diagram of the conventional instantaneous voltage drop compensation apparatus. It is a graph which shows the example of a relationship between the working voltage of a semiconductor, and the expected value of a failure rate.

Explanation of symbols

1 AC input terminal
2 transformers
3 Voltage type inverter circuit
4 DC capacitor
5 Current detector
6 Chopper circuit
7 Superconducting coil
8 Semiconductor switch
9 Semiconductor switch
10 Diode
11 Diode
12 Superconducting coil control circuit
13 Coil current detector
14 Voltage detector
15 Transformer for AC voltage detection
16 DC power supply
17 Resistance
18 Diode
19 Diode
20 Chopper
21 Semiconductor switch
22 Rectifier
23 AC power supply
24 diodes
25 DC power supply
100 Inverter control circuit
101 DC voltage reference A
102 DC voltage feedback
103 DC voltage control circuit
104 AC voltage reference
105 AC voltage feedback
106 AC voltage control circuit
107 Control changer
108 Instantaneous low compensation operation
109 PWM control circuit
110 Gate drive
200 Chopper control circuit
201 Coil current reference
202 Coil current feedback
204 DC voltage reference B
206 DC voltage control circuit
207 Control changer
209 PWM control circuit
210 Gate drive
300 Inverter control circuit
400 Chopper control circuit
401 ON signal

Claims (4)

  Connect a DC capacitor between the DC output terminals of the inverter circuit connected to the power supply system, connect a chopper circuit to this DC capacitor, connect a DC energy storage unit here, and connect it to the load connected to the power supply system. In the instantaneous voltage drop compensator that compensates the load voltage before the instantaneous voltage drop by the DC voltage of the DC energy storage unit when the instantaneous voltage drop occurs in the commercial power supply that supplies power, the control circuit of the inverter circuit has a DC A circuit is provided to set the voltage value lower than the DC voltage value during instantaneous voltage drop compensation operation, and the DC voltage value during instantaneous voltage drop compensation operation is increased and output to the power supply system in the control circuit of the chopper circuit. An instantaneous voltage drop compensator characterized in that a voltage applied to semiconductors during standby is suppressed to a low level by providing a circuit for performing standby.   2. The instantaneous voltage drop compensator according to claim 1, wherein the DC capacitor and the DC energy storage unit are charged from a power supply system through an inverter circuit.   2. The instantaneous voltage drop compensator according to claim 1, wherein a DC power source for charging each of the DC capacitor and the DC energy storage unit is provided.   4. The instantaneous voltage drop compensator according to claim 1, wherein the DC energy storage unit is formed of a superconducting coil.