Abstract:

Islanded microgrids with mismatched feeder impedances have numerous limitations. For accuracy in power sharing, distributed generations (DGs) use conventional droop-based controls but do not consider the different line impedances connected to the DGs, which will affect the consumed power to the load. As known, the line impedance has effects on real power and reactive power in DGs, and hence line impedance parameters should be considered as part of a robust control mechanism in order to maintain the output voltage at the point of common coupling (PCC), while at the same time giving accurate power sharing. Therefore, this research proposed improved control algorithms combined with an adaptive-virtual-impedance-based decentralized predictive controller to solve these issues. An adaptive virtual impedance loop was added to the droop controller to increase power-sharing efficiency and maintain the voltage at the PCC. An improvement was also made on the inverter switching pattern for the prediction mechanism, where a multi-variable multi-functioned cost function was designed to replace the normally employed pulse-width modulation. The proposed control strategies were tested on an islanded microgrid system, which consisted of two DGs with different types of line impedances and with different rated power values for the loads. MATLAB/Simulink results showed that the proposed control strategies were able to give accurate power sharing based on the load demand and that the voltage at the PCC was maintained even with load changes.

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