JP2007252164A - Distributed power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent excess current of a converter, while preventing deterioration in load voltage, when an accident occurs even if using a mechanical semiconductor switch or a semiconductor switch that has no self-arc extinction capability as a system interconnection switch. <P>SOLUTION: A commutation circuit 15 is provided with respect to the mechanical semiconductor switch 3 or the semiconductor switch 3, having no self-arc extinction capability, and a current-limiting reactor 16 is connected in series with the mechanical semiconductor switch or the semiconductor switch 3, having no self-arc extinction capability. Consequently, it is possible to achieve sure shutting-off of accident current and maintenance of the load voltage. A load current is detected with a detector 21 and inputted to a current reference generating circuit 7 so that the load voltage will not be reduced, when a load power factor is poor. Accordingly, the converter 4 can be controlled via a converter control circuit 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power converter that is connected in parallel to a load connected to a power system via a grid connection switch, and performs a grid-connected operation with the power system, and a charge / discharge connected to the DC side of the power converter BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed power supply system including a possible DC power supply, and more particularly, to a distributed power supply system using a mechanical or a semiconductor having no self-extinguishing capability as a system interconnection switch.

FIG. 5 shows an example of a distributed power supply system described in Patent Document 1, for example.
In the figure, a load 2 is connected to a power system 1 via a system interconnection switch 3 composed of a mechanical switch. A power converter 4 is connected in parallel with the load 2, and a DC power source 5 that can be charged and discharged is connected to the DC side of the power converter 4.
When the power grid 1 is normal, the grid connection switch 3 is closed (on) and supplies power to the load 2. At the same time, the power converter 4 performs charging or discharging operation of the DC power source 5.

  The power converter control circuit 8 determines the voltage to be output by the power converter 4 so that the current value detected by the converter current detector 6 matches the current set in the current reference generation circuit 7. That is, the power converter control circuit 8 generates a PWM (Pulse Width Modulation) signal from the determined voltage and applies it to the gate drive circuit 9 to operate the power converter 4 and charge / discharge the DC power supply 5. This state is referred to as a connected operation mode.

  On the other hand, when an abnormality such as a voltage drop or a power failure occurs in the power system 1, the system connection switch 3 is opened (off), and power is supplied to the load 2 from the DC power supply 5 through the power converter 4. At this time, the power converter control circuit 8 generates a voltage command value such that the detection value of the load voltage detector 10 matches the voltage value set in the voltage reference generation circuit 11, and the PWM generated based on this voltage command value is generated. By supplying a signal to the gate drive circuit 9, the power converter 4 is operated to supply power to the load 2. This state is called a self-sustaining operation mode.

  By the way, the system voltage abnormality detector 12 detects the abnormality of the power system 1 from the time when the abnormality occurs in the power system 1 in a state where the power supply system as described above is in the interconnection operation mode, and the detection signal is detected. Is input to the interconnection switch control circuit 13 and the time until the system interconnection switch 3 is turned off and the operation mode shifts to the self-sustaining operation mode is referred to as switching time. This switching time is a time that does not affect the load 2. It is required to keep within the range.

Japanese Patent No. 3406835

  As described above, even when a semiconductor switch (for example, a thyristor) without mechanical or self-extinguishing capability is used as a system interconnection switch, the switching time shown in FIG. In order to make it equivalent to the case where it is used, the current flowing through the interconnection switch 3 is detected by detecting the current flowing through the interconnection switch 3 by the interconnection switch current detector 14 and inputting the output to the power converter control circuit 8. The voltage command value of the power converter 4 is controlled so that becomes zero immediately.

  However, in the above method, when a system short circuit accident occurs, the load voltage becomes 0 in principle, so that the current of the grid interconnection switch is set to 0. Therefore, the JEC (The Institute of Electrical Engineers of Japan) shown in FIG. Since the output voltage transient fluctuation characteristic class 2 defined in Electrical Standards Investigation Committee Standard) -2433 cannot be satisfied and only the class 3 shown in FIG. 6 (b) can be satisfied (the voltage fluctuation width of 2 is higher than that of class 3). Therefore, it can be applied to a load that is more sensitive to voltage fluctuation.) There is a problem that the applicable range is limited.

  Therefore, the problem of the present invention is that even when a semiconductor element having no self-extinguishing capability, such as a mechanical type or a thyristor, is used as a grid interconnection switch, which has a large overload capability, is inexpensive and has a small loss during conduction, and the like. An object of the present invention is to satisfy the output voltage transient fluctuation characteristic class 2 when a system fault occurs, which is obtained when a semiconductor element having a self-extinguishing capability such as (insulated gate bipolar transistor) is used.

In order to solve such a problem, in the invention of claim 1, power is supplied to the load from the power system through a system interconnection switch using a semiconductor that does not have a mechanical or self-extinguishing capability in normal times, and at the time of a power failure In a distributed power supply system for supplying power from an energy storage element via a self-excited converter connected in parallel to a load via the switch,
An AC reactor is connected in series to the grid interconnection switch.
In the first aspect of the invention, when a power failure occurs, the current flowing through the grid interconnection switch can be cut off at high speed by a commutation circuit connected in parallel with the grid interconnection switch (invention of claim 2). ).

According to the present invention, in a distributed power system, a short circuit is used in the conventional example, particularly when an inexpensive and overload-resistant semiconductor switch having no self-extinguishing capability such as a mechanical type or a thyristor is used as a system interconnection switch. Although the output voltage transient fluctuation determined by JEC at the time of the occurrence of the accident was class 3, according to the present invention, it can be made class 2, and can be applied to a load having a smaller undervoltage withstand capability.
In the configuration in which the current limiting reactor 16 is simply added, it is necessary for the power converter 4 to output an excessive voltage so that the current flowing through the current limiting reactor 16 can be quickly reduced to zero. When the power converter 4 outputs, the output voltage transient fluctuation class 2 cannot be satisfied.

FIG. 1 is a block diagram showing an embodiment of the present invention. The description of the same components as those in FIG. 5 is omitted, and different portions will be mainly described below.
First, as shown in FIG. 1 as a main circuit configuration, a commutation circuit 15 is connected in parallel to the grid interconnection switch 3, and a current limiting reactor 16 is connected in series.

A specific example of the commutation circuit 15 is shown in FIG.
As shown in the figure, a resonance capacitor 19 charged by the charger 20, a resonance reactor 18, and a closing switch 17 are connected in series. When the sum of the current and the current already flowing to the grid connection switch 3 becomes 0, the grid connection switch 3 is turned off. Reference numeral 22 denotes a closing switch control circuit.

The operation timing of FIG. 2 is shown in FIG.
When a power failure occurs, the grid voltage abnormality detector 12 detects a power failure and outputs a power failure detection signal. Thereby, the interconnection switch control circuit 13 outputs a circuit breaker opening command to the grid interconnection switch 3. Moreover, the making switch control circuit 22 receives the power failure detection signal and outputs a commutation circuit ON command, thereby starting the commutation operation.

  On the other hand, the power converter 4 is switched to the connected operation mode before the power failure and the self-sustaining operation mode after the power failure as in the conventional example, but receives the power failure detection signal without providing any switching time. After that, the normal autonomous operation mode is entered. Accordingly, the circuit state shown in FIG. 4A is equivalent until the grid interconnection switch is turned off, and the circuit state shown in FIG. 4B is obtained until the commutation circuit is turned off. In any of these states, a current-limiting reactor 16 having a sufficient value is used so that the power converter 4 does not enter an overcurrent state exceeding the device specification.

  Note that, when the system is normal, power is supplied to the load via the current-limiting reactor 16, so the load voltage decreases. In order to minimize this voltage drop, in the conventional example, the current reference of the current reference generation circuit 7 is generated for the purpose of charging / discharging the DC power supply 5, but here the output of the load current detector 21 is further converted to the current reference. By inputting to the generating circuit 7, a current reference capable of power factor compensation can be generated and output to the power converter control circuit 8.

Block diagram showing an embodiment of the present invention Block diagram showing a specific example of the commutation circuit of FIG. 1 is an explanatory diagram of the operation. Equivalent circuit diagram showing commutation circuit being turned on and off Block diagram showing a conventional example Characteristic diagram showing output voltage transient characteristics class 2 and 3

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Power system, 2 ... Load, 3 ... System interconnection switch, 4 ... Power converter, 5 ... DC power supply, 6 ... Converter current detector, 7 ... Current reference value generation circuit, 8 ... Converter control circuit, DESCRIPTION OF SYMBOLS 9 ... Gate drive circuit, 10 ... Load voltage detector, 11 ... Voltage command value generation circuit, 12 ... Grid voltage abnormality detector, 13 ... Linkage switch control circuit, 14 ... Linkage switch current detector, 15 ... Commutation Circuit: 16 ... Current-limiting reactor, 17 ... Input switch, 18 ... Resonant reactor, 19 ... Resonant capacitor, 20 ... Capacitor charging circuit, 21 ... Load current detector, 22 ... Input switch control circuit.

Claims (2)

A self-excited conversion device that supplies power to the load from the power system via a grid connection switch using a semiconductor that does not have a mechanical or self-extinguishing capability during normal operation, and is connected in parallel to the load via the switch during a power failure In a distributed power supply system that supplies power from an energy storage element via
An AC reactor is connected in series to the grid interconnection switch.   2. The distributed power supply system according to claim 1, wherein when a power failure occurs, a current flowing through the grid interconnection switch is interrupted at high speed by a commutation circuit connected in parallel with the grid interconnection switch.

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