Nonlinear coordinated control of parallel bidirectional power converters in an AC/DC hybrid microgrid

Abstract

Parallel bidirectional power converters (BPCs) can support each other's power between the ac grid and the dc grid, and they play an important role in maintaining the dynamic power balance in an ac/dc hybrid microgrid. This paper proposes a nonlinear coordinated control strategy for parallel BPCs when the hybrid ac/dc microgrid operates in grid-connected mode. First, taking the minimization of the sum of the power losses of the BPCs as the objective, this strategy can obtain the economically optimal distribution scheme for power transmission among parallel BPCs according to the efficiency curves of the BPCs. Second, distributing the transmission power according to the economically optimal distribution scheme rather than distributing the transmission power equally among parallel BPCs can not only reduce the sum of the power losses of the BPCs but also increase the power margin of the BPC that is used to control the dc bus voltage after a power disturbance. Third, a nonlinear control method that is based on the state-dynamic feedback linearization theory is proposed for the BPC that is used to control the dc bus voltage. This method can quickly re-establish the dc bus voltage if a power disturbance occurs and realize high dynamic voltage quality. Finally, the performance of the proposed control strategy is verified in MATLAB/Simulink.