Power sharing in hybrid microgrids with multiple DC subgrids

摘要

Control strategies are prominent for the efficient and stable operation of emerging hybrid microgrids (HMGs), where bidirectional dc/dc converters (BDCs) are used to connect multiple dc subgrids to a common dc bus, and bidirectional interlinking converters (BICs) are used to exchange power between the dc and ac sides. Conventional droop controls may not be able to provide accurate power sharing in such sophisticated HMGs. In this paper, a framework is proposed for accurate power sharing among BDCs and BICs using existing harmonics at dc networks and a multi-dimensional droop control. In particular, we employ the frequency of available harmonics as global variables at the dc subgrids and the common dc bus to design a droop control approach for accurate power sharing among BDCs. It outperforms the existing voltage-based droop approaches when practical situations of HMGs, such as different cable resistance of BDCs, are considered. For the BICs, we propose a multidimensional droop as an integrated control strategy to adjust the power exchanged between dc and ac sides as well as the power of the BIC's energy storage system. As a result, not only the converters are operated in a more economical and flexible manner, but also their overstressing and spurious loading are avoided resulting in better maintenance and more robust operation. An HMG with different types of converters and subgrids is used to evaluate the proposed features.