JP2011097731A - Method of detecting islanding of distributed power supply, distributed power supply system, and power conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an islanding without canceling active signals at power failure of a power system even if a plurality of power conditioners supply the active signals into the power system. <P>SOLUTION: A distributed power supply system includes a distributed power supply 10 and a power conditioner 20 for converting DC power of the distributed power supply 10 to AC power, and supplies the AC power converted by the power conditioner 20 to a system load 40 in cooperation with a commercial power supply of a power system line. In the distributed power supply system, an islanding detection method includes a first step for supplying the active signals to the power system, and a second step for detecting islanding of the distributed power supply 10 from power change caused by supplying the active signals during islanding. In the first step, a current including harmonics in synchronization with fundamental waves of voltage in the power system is supplied to the power system as the active signals. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a distributed power supply system including a distributed power supply, and a power conditioner that converts DC power of the distributed power supply into AC power and that is connected to a power system and supplies the load to a load. The present invention relates to a single operation detection method, a distributed power supply system, and a power conditioner that detect whether a type power supply is disconnected from a commercial power supply and is operating independently.

  The isolated operation in the distributed power supply system is a state in which power is supplied from the distributed power supply to the system load while the commercial power supply is stopped.

  If a single operation for supplying power to a load using only a distributed power source is performed in this way, it is dangerous when trying to repair the cause of the commercial power source being stopped.

 Therefore, it is necessary to prevent the occurrence of an accident by detecting the isolated operation of the distributed power source.

  As a method of detecting the isolated operation of such a distributed power source, a system that monitors the system voltage and detects a change that appears during an isolated operation in the event of a system power failure, and a variation in the system voltage from the distributed power source side. There is an active method in which a disturbance signal (active signal) is applied to give a change, and a change that appears at the time of a single operation in the case of a system power failure is detected.

  In particular, an active method of applying an active signal that forcibly generates periodic minute fluctuations in reactive power of a distributed power supply has been widely adopted (see Patent Document 1 for the above).

 In the passive method, when the power supplied to the distributed power supply and the power used by the load are balanced, the isolated operation cannot be detected even if the power system fails. For this reason, it is generally recommended that an isolated operation detection apparatus detect an isolated operation by combining a passive method and an active method.

JP 2008-172978 A

  However, in the active method, when multiple power conditioners are connected to the same power system, and the active signals of each power conditioner cancel each other out due to interference at the time of power system power failure, it is impossible to detect isolated operation There is.

  From the above, when the distributed power supply power and the load power usage are not balanced, the isolated operation can be detected by the passive method, while the distributed power supply power and the load power usage are balanced. Then, since there is a possibility that the isolated operation cannot be detected in the passive method, the active method is necessary. In that case, in the active method, when there are multiple power conditioners connected to the same power system, and the disturbance signals of each power conditioner cancel each other out due to interference during a power system power failure, detection of isolated operation May not be possible.

  Therefore, in the present invention, the problem of the active method, that is, the problem that the isolated operation cannot be detected when the active signals of the respective power conditioners cancel each other due to interference at the time of the power system interruption is solved. And combining passive methods with each other, it is an issue to be solved to make the best use of the advantages of each method.

  (1) A method for detecting an isolated operation of a distributed power source according to the present invention includes a distributed power source and a power conditioner that converts DC power of the distributed power source into AC power, and the AC power converted by the power conditioner is In a distributed power supply system that is connected to a commercial power supply of a power system line and supplies a system load, a first step of injecting an active signal into the power system and a power fluctuation caused by injection of the active signal during the single operation An isolated operation detection method including a second step of detecting isolated operation of a distributed power source, wherein a current including a harmonic synchronized with a fundamental wave of a voltage in the power system is used as an active signal in the first step. It is characterized by being injected into.

  In the isolated operation detection, when the power supplied to the distributed power source and the load power are not balanced, the isolated operation can be detected by the passive method. Therefore, in the isolated operation detection method of the present invention, the active method alone is used. It is not limited to driving | running detection, The independent driving | operation detection which combined the passive system and the active system can also be included.

  In the passive method, there is a risk that isolated operation cannot be detected when the power supplied to the distributed power supply and the power used by the load are balanced. In the active method, multiple power conditioners are connected to the same power system. If the disturbance signals of each power conditioner cancel each other out due to interference at the time of power system interruption, it may not be possible to detect an isolated operation.

  In the present invention, on the premise that each of such passive and active systems has a problem, in the present invention, a current including a harmonic synchronized with the fundamental wave of the voltage in the power system is injected into the power system as an active signal. Even if a power system power failure occurs while each conditioner is in operation, the active signals will not cancel each other out due to interference, and it will be possible to reliably detect an isolated operation. It can be said that it is a simple method.

  Preferably, when the isolated operation is detected in the second step, a protection signal is output from the grid interconnection protection device, the output of the inverter unit is stopped, and the disconnection operation of the inverter unit and the commercial power source by the disconnection relay is performed. Includes 3 steps.

  (2) A distributed power system according to the present invention includes a distributed power source and a power conditioner that converts the DC power of the distributed power source into AC power, and the AC power converted by the power conditioner is supplied to the power system line. In a distributed power supply system that is connected to a commercial power supply and supplies a system load, the power conditioner injects an active signal into the power system, and from the power fluctuation caused by the injection of the active signal during the single operation of the distributed power supply. An isolated operation detection device that detects the isolated operation of a distributed power source, and outputs a protection signal in response to the detected independent operation from the isolated operation detection device to stop the output of the inverter unit, and the inverter unit and commercial by a disconnection relay A grid connection protection device that performs a disconnection operation with a power source, and the islanding detection device includes a current including a harmonic synchronized with a fundamental wave of the voltage in the power system. It injected into the power system as an active signal, characterized in that.

  (3) A power conditioner according to the present invention is a power conditioner that converts DC power of a distributed power source into AC power, converts the DC power of the distributed power source into AC power, and passes through a disconnection relay. An inverter that outputs alternating current power, and an independent operation detection device that injects an active signal into the power system and detects the isolated operation of the distributed power source from the power fluctuation caused by the injection of the active signal during the independent operation of the distributed power source; In response to islanding operation detection from the islanding operation detection device, a protection signal is output to stop the output of the inverter unit, and to perform the disconnection operation between the inverter unit and the commercial power source by the relay for disconnection A protection device, and the islanding detection device is configured to inject a current including a harmonic synchronized with a fundamental wave of the voltage in the power system into the power system as an active signal. And wherein the door.

  According to the present invention, since a current including a harmonic current is injected as an active signal at a timing synchronized with a fundamental wave of the power system voltage, even if a plurality of power conditioners inject an active signal into the power system, the power system Independent operation can be detected without canceling each other during a power failure.

FIG. 1 is a diagram showing a distributed power supply system according to an embodiment of the present invention. FIG. 2 is a diagram showing a current waveform forming an active signal injected into the power system.

  Hereinafter, an isolated operation detection method, a distributed power supply system, and a power conditioner according to embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a grid-connected inverter device that implements the isolated operation detection method of the embodiment. This apparatus includes a distributed power source 10, a power conditioner 20, a commercial power source 30, and a system load 40.

  The distributed power source 10 is, for example, a solar cell or a fuel cell.

  The power conditioner 20 converts the DC power output from the distributed power supply 10 into AC power, and supplies the AC power to the system load 40 in conjunction with the commercial power supply 30.

  The power conditioner 20 includes an inverter unit 21, a voltage detection unit 22, a disconnection relay 23, an isolated operation detection device 24, and a grid interconnection protection device 25.

  The inverter unit 21 converts the DC power of the distributed power source 10 into AC power and outputs the AC power via the disconnecting relay 23. For example, the inverter unit 21 includes the DC power of the distributed power source 10. A DC / DC converter for DC / DC conversion and an AC / DC inverter for AC / DC conversion of DC power of the DC / DC converter.

  The voltage detection unit 22 detects a change in the frequency or period of the voltage at the grid connection point, and outputs a detection signal S1 to the isolated operation detection device 24.

  The isolated operation detection device 24 includes an active signal generation / injection unit 24a and an isolated operation determination unit 24b.

  The active signal generator / injector 24a generates a fundamental current i1 and its harmonic current i2 in synchronization with the grid voltage from the voltage at the grid connection point detected by the voltage detector 22, and generates the harmonic current i2 as the harmonic current i2. The included current is output to the inverter unit 21 as the active signal S2 and injected into the system. FIG. 2 shows current waveforms of the fundamental current i1 and the harmonic current i2.

  The isolated operation determination unit 24b determines whether or not the commercial power supply 30 is stopped and the inverter unit 21 is in an isolated operation state from the detection signal S1 of the grid connection point detected by the voltage detection unit 22. The determination signal S3 is output to the grid connection protection device 25.

  When the determination signal S3 that the commercial power supply 30 is stopped and the inverter unit 21 is in the single operation state is input from the single operation determination unit 24b, the grid interconnection protection device 25 uses the protection signal S4 for disconnection. It outputs to the relay 23 and the inverter part 21, opens the disconnection relay 23, disconnects the inverter part 21 and the commercial power supply 30, and stops the output of the inverter part 21.

  In the above distributed power supply system, when some abnormality occurs in the commercial power supply 30 and the power supply from the commercial power supply 30 is stopped, and the inverter unit 21 enters the single operation state, In order to avoid an electric shock or the like of the restoration worker, in the isolated operation detection device 24, the active signal generation / injection unit 24a injects the active signal S2 into the system, and in the isolated operation, the isolated operation determination unit 24b immediately By determining the operation and outputting the determination signal S3 to the grid connection protection device 25, the output of the inverter unit 21 is stopped by the signal S4 from the grid connection protection device 25, and the inverter unit 21 by the disconnection relay 23 A disconnection operation with the commercial power supply 30 is performed.

  The isolated operation determination unit 24b in the isolated operation detection device 24 detects the isolated operation state of the distributed power source 10 by using both the passive method and the active method described above. Here, the passive method is a method for detecting a sudden change in the voltage phase, frequency, etc. at the time of shifting to the single operation, and includes a voltage phase jump detection method, a third harmonic voltage distortion rapid increase detection method, a frequency change rate detection method, and the like. . However, when the output of the inverter unit 21 and the power consumption of the system load 40 are balanced, even if the power supply from the commercial power supply 30 is stopped, the above-described passive method may not be able to detect the single operation state. .

  The inverter unit 21 varies the output of the inverter unit 21 by a small amount every fixed period by the fundamental wave current i1 and the harmonic current i2 which are the active signal S2 generated by the active signal generation / injection unit 24a, and determines the single operation. The unit 24b outputs the determination signal S3 to the grid interconnection protection device 25 when the waveform of the detection signal S1 taken in by the isolated operation detection device 24 is affected by the fluctuation. The grid interconnection protection device 25 outputs the protection signal S4 in response to the input of the determination signal S3, thereby stopping the output of the inverter unit 21 and disconnecting the inverter unit 21 and the commercial power source 30 by the disconnection relay 23. Perform column operation.

  The waveform of the fundamental current i1 shown in FIG. 2 is not limited to a sine waveform, and may be a trapezoidal waveform or a triangular waveform. The harmonic current i2 is a 90-degree delayed current in synchronization with the timing at which the fundamental current i1 becomes level zero every half cycle, and the inverter unit 21 is synchronized with the fundamental wave of the voltage in the power system. The current including the harmonic current i2 is injected into the inverter unit 21 as the active signal S2, but this timing is an example in the description of the embodiment and is not limited to this.

  Thus, since the current including the harmonic current i2 is injected into the power system as the active signal S2 in synchronization with the fundamental wave of the voltage of the power system, a plurality of power conditioners inject the active signal S2 into the same power system. Even in the case of a power system power failure, the power conditioners do not cancel each other, and each power conditioner can detect an isolated operation.

DESCRIPTION OF SYMBOLS 10 Distributed type power supply 20 Power conditioner 21 Inverter part 22 Voltage detection part 23 Disconnection relay 24 Independent operation detection apparatus 24a Active signal generation / injection part 24b Independent operation determination part 25 System interconnection protection apparatus 30 Commercial power supply 40 System load

Claims (4)

  A distributed power source and a power conditioner that converts DC power of the distributed power source into AC power are provided, and AC power converted by the power conditioner is connected to a commercial power source of the power system line and supplied to the system load. In a distributed power system, a single step including a first step of injecting an active signal into the power system and a second step of detecting a single operation of the distributed power source from a power fluctuation caused by injection of the active signal during the single operation. A method for detecting operation, wherein in the first step, a current including a harmonic synchronized with a fundamental wave of the voltage in the power system is injected into the power system as an active signal, and the isolated operation in the distributed power system is characterized in that Detection method.   When the isolated operation is detected in the second step, a protection signal is output from the grid interconnection protection device to stop the output of the inverter unit, and the third step of performing the disconnecting operation between the inverter unit and the commercial power source by the disconnecting relay. The method of claim 1 comprising. A distributed power source and a power conditioner that converts DC power of the distributed power source into AC power are provided, and AC power converted by the power conditioner is connected to a commercial power source of the power system line and supplied to the system load. In a distributed power system
The above inverter is
An independent operation detection device that injects an active signal into the power system and detects the isolated operation of the distributed power source from the power fluctuation caused by the injection of the active signal during the independent operation of the distributed power source,
A grid connection protection device that outputs a protection signal in response to the isolated operation detection from the isolated operation detection device and stops the output of the inverter unit, and performs the disconnection operation of the inverter unit and the commercial power supply by the disconnection relay;
Comprising
The isolated operation detection apparatus injects a current including a harmonic synchronized with a fundamental wave of the voltage in the power system as an active signal into the power system. A power conditioner that converts DC power of a distributed power source into AC power,
An inverter unit that converts the DC power of the distributed power source into AC power and outputs AC power via a disconnecting relay;
An independent operation detection device that injects an active signal into the power system and detects the isolated operation of the distributed power source from the power fluctuation caused by the injection of the active signal during the independent operation of the distributed power source,
System interconnection protection that outputs a protection signal in response to the isolated operation detection from the isolated operation detection device, stops the output of the inverter unit, and disconnects the inverter unit and the commercial power source by the disconnection relay Equipment,
Comprising
The power conditioner is characterized in that the islanding detection device is configured to inject a current including a harmonic synchronized with a fundamental wave of a voltage in the power system into the power system as an active signal.

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