Intentional islanding describes the condition in which a microgrid or a portion of the power grid, which consists of a load and a distributed generation (DG) system, is isolated from the remainder of the utility system. In this situation, it is important for the microgrid to continue to provide adequate power to the load. Under normal operation, each DG inverter system in the microgrid usually works in constant current control mode in order to provide a preset power to the main grid. When the microgrid is cut off from the main grid, each DG inverter system must detect this islanding situation and must switch to a voltage control mode. In this mode, the microgrid will provide a constant voltage to the local load. This paper describes a control strategy that is used to implement grid-connected and intentional-islanding operations of distributed power generation. This paper proposes an intelligent load-shedding algorithm for intentional islanding and an algorithm of synchronization for grid reconnection.
Distributed generators (DG), such as photovoltaic cells, are low cost, highly reliable and have electronic interfaces and reduced emissions. Even with the mentioned benefits, there are technical limits on the degree to which DG can be connected. One of these technical concerns is the islanding phenomenon. In utility practice at the present time, accidental islanding is an undesirable mode of operation and is not permitted. Therefore, islanding must be detected and the islanded DG units must be disconnected from the rest of the system. This paper presents a survey of the islanding detection methods for grid-connected photovoltaic (PV) systems.
Intentional islanding describes the condition in which a microgrid, which consists of a load and a distributed generation (DG) system, is isolated from the remainder of the utility system. In this situation, it is important for the microgrid to continue to provide adequate power to the load. Under normal operation, each DG inverter system in the microgrid usually works in constant current (or constant power) control mode in order to provide a pre-set power to the main grid. When the microgrid is cut off from the main grid, each DG inverter system must detect this islanding situation and switch to a voltage control mode. In this mode, the microgrid will provide a constant voltage to the local load. This paper describes a control strategy to implement intentional islanding operation of microgrids. The described method proposes two control algorithms, one for gridconnected operation and the other for intentional islanding operation.
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