Implementation and Compatibility Analysis of Dynamic Voltage Support and Unintentional Islanding Capability of Power-Electronic Generators

One reason for the trend towards microgrid operation is the increased security of supply for the island itself. But if more and more generation units disconnect from the grid subsequent to a fault event, the overall grid stability might be weakened because there are less generators that provide dynamic valtage support. In this paper we propose a control strategy that combines a low-voltage ride through capability with a subsequent islanding operation. With the proposed approach, inverters are able to supply a maximum amount of grid support in the first place. If there is a collapse of the grid, the inverter disconnects and switches to islanding operation. The designed valtage and frequency control are implemented in an ordinary grid parallel inverter. Thus the method is suitable for a wide range of inverter units whether they are used in microgrids or not. The proposed control strategy was tested in simulation and experimentally validated. It was shown that the control is robust under all relevant load conditions.