A distributed control architecture for hybrid AC/DC microgrid economic operation

Abstract

A distributed control architecture is proposed in this paper to realize economic operation in a hybrid AC/DC microgrid (MG). The entire system operation cost can be minimized when distributed generators (DGs) that induce costs have the same incremental costs (ICs). The architecture consists of two levels. In the first level, the AC frequency-IC (fac-IC) droop and the DC bus voltage-IC (Vdc-IC) droop are employed in the AC and DC subgrids respectively. With the synchronization offac and Vdc, DG ICs in each subgrid will be equalized. However, the droops will cause deviations of fac and Vdc. To restore fac and Vdc to their nominal values, a novel distributed controller is proposed in the second level to provide a generalized method for fac and Vdc recovery. The controller allows DGs in each subgrid to only communicate with their neighbors. Normally, the variations of fac and Vdc directly indicate the loading conditions of AC and DC subgrids. However, fac and Vdc fluctuations are invisible due to the existence of the distributed control scheme. To solve this problem, a relative loading index (RLI) is proposed to extract the hidden loading condition of each subgrid even though fac and Vdc are clamped as constants. By using RLI, the power reference of the bidirectional interlinking converter (BIC) can be easily defined. All DG ICs in the hybrid AC/DC MG will converge to the same value in the steady state, thus saving the total operation cost. The feasibility and effectiveness of the proposed control architecture are verified by simulations.