Control strategy of DC microgrid under unbalanced grid voltage

Abstract

When the grid voltage is unbalanced, second order pulsation component will appear in the DC bus voltage, which will affect the voltage quality of DC microgrid. In this paper, a control method to eliminate the DC voltage pulsation component is proposed. Firstly, the voltage fluctuation degrees of each node in DC microgrid under unbalanced grid voltage and three-phase unbalanced load were analyzed, and the rule that the pulsation elimination should be conducted by the fault point was obtained. Then, depending on the mathematical model of the grid-connected system, a control strategy of DC microgrid under unbalanced grid voltage implemented on the stationary coordinate was proposed based on the sliding mode control (SMC). Current reference instructions were calculated by using the DC voltage and power directly without phase-locked loop and sequence component decomposition, which simplifies the control structure. And the SMC can achieve precise tracking of the instructions. Finally, simulations were carried out to verify the effectiveness of the proposed control strategy.