A novel solid state transformer based control topology for interconnected MV and LV hybrid microgrids

Abstract

Hybrid microgrid continues to be an attraction for researchers as it brings the advantages of both ac and dc systems under one roof. The interlinking converter (ILC) of this system regulates the ac frequency and dc voltage while maintaining bidirectional power. This paper proposes a novel solid-state transformer (SST) based topology for interconnected medium voltage (MV) and low voltage (LV) hybrid microgrids. Based on the topology, various control modes are identified and correspondingly, an autonomous power sharing scheme is presented with dc voltage and ac frequency regulation. A linear voltage-frequency control is discussed for ac/dc and dc/ac converters of SST which provides a secondary control mechanism. The dual active bridge (DAB) of the SST operates at voltage control mode while providing electrical isolation and stable system operation. The proposed topology and control scheme is significant in the sense that it allows integration of ac and dc grids with different voltage and frequency levels. In addition, the secondary dc voltage or ac frequency regulation control at any hybrid microgrid automatically regulates the ac frequency and dc voltage in the system which reduces system cost. Various simulated scenarios in PSCAD with load changes highlight the optimal performance of the proposed scheme.