JPH099510A - Detecting method of single operation of inverter for system interconnection - Google Patents

Abstract

PURPOSE: To detect surely a state of single operation even in the case when a plurality of inverters are interconnected in an interconnected system, after the system is interrupted. CONSTITUTION: A synchronous signal carried by a distribution line is received by synchronous signal receiving circuits 35 and 36. The phases of periodic minute signals outputted by fluctuation signal generators 31 and 32 are synchronized with this synchronous signal and inverters 12 and 22 for an interconnected system are operated, while the frequency of the system is monitored by a frequency detector 33 and a frequency monitoring circuit 34 so that a state of single operation can be detected without fail.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed power source connected to a power system, for example, a grid-connected inverter used in a solar power generation system, a fuel cell power generation system, etc. The present invention relates to a method for detecting an isolated operation of an inverter for system interconnection, which detects that the inverter is disconnected from the system and becomes an independent operation.

[0002]

2. Description of the Related Art In a photovoltaic power generation system, a fuel cell power generation system or the like as a distributed power source, interconnection operation with an electric power system is performed for the purpose of stably supplying electric power to a load. In particular, in recent years, interconnection operation in the state of supplying power from a distributed power source to the commercial power system (hereinafter also referred to as reverse power flow) has been recognized, so isolated operation that occurs due to system loss such as interruption of the commercial power system (Islanding
ing)) phenomenon must be detected.

In the islanding phenomenon, when the system power is lost due to interruption of the commercial power system or the like, if the load and the power generation amount of the distributed power sources are balanced, the loss of the system power is detected on the distributed power source side. It is difficult to do so, and if this power system is recharged in this state from the commercial power system again, a short circuit condition may occur in the power system.Therefore, this islanding phenomenon can be reliably detected. There has been a demand for the above-mentioned methods of active landing detection (actively giving disturbance to the power system) as shown in the following.

[0004] A periodic minute fluctuation is generated in the reactive power of the distributed power source, and a fluctuation in the system frequency (50/60 Hz) is detected when the islanding phenomenon occurs. . The active power of the distributed generator is periodically changed to detect the fluctuation of the system voltage and frequency when the islanding phenomenon occurs. . An offset is applied to the internal oscillator that determines the output frequency of the grid-connected inverter of the distributed power supply, and the frequency change that appears in the power system when the islanding phenomenon occurs is detected.

.. Impedance is instantaneously and periodically inserted in parallel with the distributed power supply, and a sudden change in voltage or current at the impedance insertion end is detected. Among these methods, in the photovoltaic power generation system, the fuel cell power generation system, etc., the above method is conventionally used, which does not involve fluctuations in active power, and therefore does not cause fluctuations in DC output power of batteries (cells). There is.

[0006]

SUMMARY OF THE INVENTION In the above-mentioned method for detecting the islanding phenomenon, the distributed power sources vary the reactive power to the power system independently of the other distributed power sources. There is a possibility that the distributed power sources may interfere with each other, and as a result, the detection sensitivity at the linkage point may be reduced.

An object of the present invention is to provide a method for detecting an isolated operation of a grid interconnection inverter that solves the above problems.

[0008]

[Means for Solving the Problems] Independent operation for detecting that the inverter for grid interconnection of distributed power supplies connected to a plurality of power grids is disconnected from the power grid and becomes an independent operation during grid interconnection In the detection method according to the first aspect of the present invention, the phase of a periodic minute fluctuation of the reactive power supplied by each grid interconnection inverter is synchronized by a synchronization signal superimposed on a distribution line connecting a distributed power source to a power grid. And detect the islanding state by monitoring the frequency fluctuation at the grid interconnection point,
Disconnect all inverters from the power system or stop them.

In a second aspect based on the first aspect, the synchronizing signal is a rising or falling signal generated from the signal of the periodic minute fluctuations given to the individual grid interconnection inverters. The synchronization signal is transmitted so as to be superimposed on the.

[0010]

According to the present invention, the reactive power supplied by each individual grid interconnection inverter is periodically varied, and the periodic fluctuations of the reactive power of the other grid interconnection inverters and their phases are synchronized to make a plurality of them. This prevents interference such as electric power transfer between the inverters for system interconnection, and ensures the detection of isolated operation.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an independent operation method of a grid interconnection inverter according to the present invention, and is a circuit configuration diagram in the case of two distributed power sources. In FIG. 1, 1 is a power system, 2
Is a load, 10 and 20 are solar power generation systems, and the solar power generation systems 10 and 20 are solar cell main bodies 11 and 21,
Grid interconnection inverters 12, 22, power distribution transformers 13,
23. Also, 3 is a load distribution circuit breaker,
4, 5 are solar power generation systems 10 as distributed power sources,
A distributed power source side circuit breaker 20 and a power receiving point circuit breaker 6 for receiving power from the power system 1.

Further, the islanding operation detecting device 30 includes fluctuation signal generators 31 and 32 which generate, for example, square wave minute signals.
A frequency detection circuit 33 composed of a frequency / voltage converter and the like, a frequency monitoring circuit 34 composed of a comparator and a setter for monitoring minute fluctuations in the output value of the frequency detection circuit 33,
A fluctuation signal generator 31, which demodulates the synchronization signal from the distribution line,
For example, the synchronizing signal receiving circuits 35 and 36 for synchronizing the rising timing of the output of 32 and the fluctuation signal generator 3
For example, the synchronizing signal transmitting circuits 37 and 38 which output a pulse of the outputs of 1 and 32 at a rising timing, modulate the pulse at a predetermined frequency, superimpose the pulse on the distribution line and transmit the signal.

The operation of the islanding operation detector 30 of FIG. 1 will be described below. In the state where the total amount of power generation supplied by the grid interconnection inverters 12 and 22 of the photovoltaic power generation systems 10 and 20 and the amount of power consumed by the load 2 are balanced, a power receiving point due to an accident on the side of the power system 1 When the power system 1 is disconnected by the circuit breaker 6, an islanding phenomenon occurs between the solar power generation systems 10 and 20 and the load 2. In such a state, if the synchronizing signal receiving circuits 35 and 36 provide the photovoltaic power generation systems 10 and 20 with, for example, square wave reactive power fluctuations in which the rising timings of the outputs of the fluctuation signal generators 31 and 32 are synchronized, respectively. A frequency fluctuation occurs at the interconnection point A, which is detected by the frequency detection circuit 33, and the frequency monitoring circuit 34 operates according to the detected value to output an isolated operation signal to the outside.

Details of the operations of the synchronizing signal receiving circuits 35 and 36 and the synchronizing signal transmitting circuits 37 and 38 of FIG. 1 will be described below with reference to the operation explanatory diagram shown in FIG. For distribution lines,
For example, it is assumed that the respective synchronization signals are transmitted to the other side by being carried on a carrier wave by a known power line carrier method.
At time t ₀ shown in FIG. 2C, the photovoltaic power generation system 10 side as the split-type power source, the fluctuation signal of the output of the fluctuation signal generator 31, the synchronization signal transmitted to the partner of the synchronization signal transmission circuit 37, The synchronization signal received by the synchronization signal receiving circuit 35 is in a state as shown in FIG. 2A, and similarly, on the side of the photovoltaic power generation system 20 as the split power source, the fluctuation of the output of the fluctuation signal generator 32. If the signal, the synchronization signal transmitted to the counterpart of the synchronization signal transmission circuit 38, and the synchronization signal received by the synchronization signal reception circuit 36 are in the state shown in FIG. 2B, the solar power generation system 10 side Sync signal receiving circuit 3
5 gradually advances the synchronization signal to be given to the fluctuation signal generator 31 in the direction of the arrow F shown in FIG.
The fluctuation signal generator 32 gradually moves in the direction of arrow S shown in (b).
The synchronizing signal given to the signal is delayed, and at time t ₂ shown in FIG.

In the embodiment of the present invention described above, the configuration in which the number of distributed power sources is two has been described. However, when the number of distributed power sources is three or more, all the remaining synchronizations in the synchronization signal receiving circuit are performed. It suffices to receive a signal and gradually delay or advance the synchronizing signal output from the synchronizing signal receiving circuit by, for example, a majority decision method.

[0016]

According to the present invention, periodic minute fluctuations are generated in synchronism with the reactive power supplied from a plurality of grid interconnection inverters, respectively, and the frequency of the grid is monitored to ensure the isolated operation state. It is possible to detect and improve the detection reliability.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of an independent operation method of a grid interconnection inverter of the present invention.

FIG. 2 is an operation explanatory diagram illustrating the operation of FIG.

[Explanation of symbols]

1 ... Power system, 2 ... Load, 3 ... Load distribution breaker, 4,
5: Distributed power source side circuit breaker, 6 ... Power receiving point circuit breaker, 10, 2
0 ... Solar power generation system 11,21 ... Solar cell body,
12, 22 ... Inverter for grid interconnection, 13, 23 ... Transformer for distribution, 30 ... Independent operation detection device, 31, 32 ... Fluctuation signal generator, 33 ... Frequency detection circuit, 34 ... Frequency monitoring circuit, 35, 36 ... Synchronous signal receiving circuit, 37, 38 ... Synchronous signal receiving circuit, A ... Interconnection point.

Claims (2)

[Claims] 1. An islanding operation detection method for detecting that the inverter for grid interconnection of distributed power sources connected to a plurality of power systems is disconnected from the power system and becomes an islanding operation during grid interconnection. The synchronization signal superimposed on the distribution line that connects the distributed power source to the power system synchronizes the phase of the periodic minute fluctuations of the reactive power supplied by the individual grid-connection inverters, and changes the frequency at the grid connection point. A method for detecting an isolated operation of a grid interconnection inverter, characterized by detecting an isolated operation state by monitoring and disconnecting or stopping all of a plurality of inverters from the power system. 2. The isolated operation detection method for a grid interconnection inverter according to claim 1, wherein the synchronization signal is a rising or rising edge generated from the signal of the periodic minute fluctuation given to each grid interconnection inverter. A method for detecting an isolated operation of a grid interconnection inverter, characterized in that a down signal is sent as a synchronizing signal transmitted so as to be superimposed on the distribution line.