JP4877092B2 - Distributed power system - Google Patents

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 that is 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 direct current 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. 6 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 that the power converter 4 should output so that the current value detected by the converter current detector 6 matches the current set in the current reference value 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 (GDU) 9 to operate the power converter 4 and charge / discharge the DC power supply 5. Let 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 command value generation circuit 11, and generated based on this voltage command value. By supplying a PWM 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.

  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) 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. 11 (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 applicant has previously filed an application as described below (Japanese Patent Application No. 2006-076172: also called a proposed method).
FIG. 7 is a block diagram showing the proposed method. As shown in the figure, a commutation circuit 15 is connected in parallel to the grid interconnection switch 3 and a current limiting reactor 16 is connected in series. For example, as shown in FIG. 8, the commutation circuit includes a series circuit of a resonant capacitor 19 charged by a charger 20, a resonant reactor 18, and a closing switch 17, and when the grid connection switch 3 is turned off, the closing switch 17 is turned on. When the resonance current is generated by turning on, and when the sum of the current and the current that has already flowed through the grid connection switch 3 becomes 0, the grid connection switch 3 is turned off.

The operation timing of FIGS. 7 and 8 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. In addition, the closing switch control circuit 22 receives a power failure detection signal and outputs a commutation circuit ON command, thereby starting a commutation operation.

  On the other hand, the power converter 4 is switched to the interconnected operation mode before the power failure and the independent operation mode after the power failure, as in the conventional example, but after receiving the power failure detection signal without providing any switching time. Enters the normal autonomous mode. Accordingly, the circuit state shown in FIG. 10A is equivalent until the system interconnection switch is turned off, and the circuit state shown in FIG. 10B 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.

Japanese Patent No. 3406835

In the proposed method, when the direct operation mode is switched directly to the autonomous operation mode, the current output from the power converter 4 increases in the circuit state shown in FIG. In order to prevent an electric current, an excessive reactor is required, and there is a problem that disadvantages increase in terms of loss and cost.
Accordingly, an object of the present invention is to reduce the size of the current limiting reactor while satisfying the output voltage transient fluctuation characteristic class 2 when a system fault occurs in a distributed power supply system using a current limiting reactor.

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 and a commutation circuit is connected in parallel. When a power failure occurs, the grid interconnection switch is shut off by the commutation circuit, and power is supplied from the energy storage element. In the process of time-varying the output voltage of the self-excited converter to the constant value including the rated value with the voltage detection value based on the grid connection point voltage as the initial value, the current of the self-excited converter exceeds a certain limit value In order to change the voltage of the self-excited converter according to the excess amount, the difference between the value of the current of the self-excited converter and the current of the self-excited converter is input to the regulator. The output voltage of the self-excited conversion device is changed according to the output .

In the first aspect of the present invention, the current limiting operation can be enabled for a certain period from the time when the power failure is detected, and thereafter can be disabled (the second aspect of the invention).

  According to the present invention, in the distributed power supply system, the short circuit is proposed in the proposed method, particularly when a low-cost and overload-resistant semiconductor switch having no self-extinguishing capability such as a mechanical or thyristor is used as a system interconnection switch. A very large current limiting reactor is required to make the output voltage transient fluctuation determined by JEC Class 2 when an accident occurs, but according to the present invention, not only can this reactor be downsized, but also overcurrent can be suppressed. A highly efficient, low-cost and stable system can be realized.

FIG. 1 is a block diagram showing an embodiment of the present invention. The description of the same components as those in FIGS. 6 and 7 will be omitted, and portions different from these will be mainly described below.
The difference from the proposed method shown in FIG. 7 is that a system voltage detector 23 is provided, and its output is input to the voltage command value generation circuit 11, and the output of the converter current detector 6 is input to the voltage command value generation circuit 11. It is in the point which was made to do. Therefore, the internal configuration of the voltage command value generation circuit 11 is also different from the proposed method. The voltage amplitude command 31 generated by the voltage command value generation circuit 11 is input to the control circuit 8.

  As shown in FIG. 2, the voltage command value generation circuit 11 includes a three-phase two-phase converter 25, a square calculator 26, a square root calculator 27, a change rate limiter 29, a maximum and minimum value limiter 30, and a sample hold circuit. 32 or the like. Reference numeral 24 denotes a system voltage value that is an output of the voltage detector 23, 28 denotes a power failure detection signal, and 31 denotes a voltage amplitude command that is an output of the voltage command value generation circuit 11.

The system voltage value 24 is input to the three-phase / two-phase converter 25, and the α-phase component and β-phase component are squared by the square calculator 26, added, and then input to the square root calculator 27. , Get the voltage amplitude instantaneous value. This instantaneous value is sampled and held by the sample and hold circuit 32 when the power failure detection signal 28 becomes active.
On the other hand, the power failure detection signal 28 is a signal that becomes “1” at the time of detection. By inputting this to the change rate limiter 29, a signal that changes from 0 to 1 having a certain slope can be obtained. The voltage amplitude command 31 can be obtained by adding the output of the sample hold circuit 32 to this signal and inputting it to the maximum and minimum value limiter 30.

As shown in FIG. 3, the voltage amplitude command 31 decreases as the system voltage decreases due to a power failure before the power failure is detected, and increases with a certain slope after the power failure is detected. 100% which is a constant value).
The voltage amplitude command 31 is further multiplied by a sine wave signal 33 as shown in FIG. 4, and a new voltage command is obtained by adding a current suppression term thereto.

  The current suppression term is obtained by inputting the difference between the value input to the current limiter 34 that limits the converter current 6 to the upper and lower limits and the converter current 6 to the regulator 35. This suppression term is added to the new voltage command after being multiplied by the output of the current suppression hold circuit 36 that operates according to the power failure detection signal 28 as shown in FIG. The converter control circuit 8 calculates the voltage command value during the self-sustaining operation using the voltage amplitude command thus obtained and the voltage phase information similar to the conventional example. As a result, as shown in FIG. 5, the current limiting operation is enabled for a certain time from the time when the power failure is detected, and then disabled.

Block diagram showing an embodiment of the present invention The block diagram which shows the detail of the voltage command value generation circuit of FIG. Explanatory drawing explaining the voltage command change in FIG. Block diagram showing a new voltage amplitude command calculation circuit Output characteristic diagram of current limiter hold circuit Block diagram showing a conventional example Block diagram showing the proposed method The block diagram which shows the specific example of the commutation circuit of FIG. Explanation of operation of FIGS. Equivalent circuit diagram showing commutation circuit being turned on and off 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 (GDU), 10 ... Load voltage detector, 11 ... Voltage command value generation circuit, 12 ... System voltage abnormality detector, 13 ... Connection switch control circuit, 14 ... Connection switch current detector, 15 DESCRIPTION OF SYMBOLS ... 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, 23 ... System voltage Detector: 25 ... 3-phase to 2-phase converter, 26 ... square computing unit, 27 ... square root computing unit, 29 ... change rate limiting limiter, 30 ... maximum and minimum value limiting limiter, 32 ... sample hold circuit, 34 ... current Re Jitter, 35 ... current limiter control, 36 ... current limiter hold circuit.

Claims (2)

A self-excited converter 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 and a commutation circuit is connected in parallel. When a power failure occurs, the grid interconnection switch is shut off by the commutation circuit, and power is supplied from the energy storage element. In the process of time-varying the output voltage of the self-excited converter to the constant value including the rated value with the voltage detection value based on the grid connection point voltage as the initial value, the current of the self-excited converter exceeds a certain limit value In order to change the voltage of the self-excited converter according to the excess amount, the difference between the value of the current of the self-excited converter and the current of the self-excited converter is input to the regulator. A distributed power supply system characterized in that the output voltage of the self-excited converter is changed according to the output . 2. The distributed power supply system according to claim 1 , wherein the current limiting operation is enabled for a predetermined time from the time when a power failure is detected, and then disabled.

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