Virtual DC Machine Control Strategy for Stability Improvement in DC Microgrid with Constant Power Loads

With a large number of constant power loads connecting to DC microgrid, the negative damping characteristics of constant power loads reduces the stability of DC microgrid. In order to improve the system stability, a voltage stability control strategy based on virtual DC machine (VDCM) is proposed in this paper. This paper focused on the bidirectional DC/DC converter with droop control strategy. By introducing the VDCM link into the feedback branch of double closed-loop droop control strategy, the VDCM control strategy improves the system stability without affecting the performance of voltage loop and current loop. Then, the small signal model of the system is established to analyze the system stability by using the Middlebrook criterion. The analysis results show that the VDCM control strategy can effectively increase the system damping and improve the system stability. Finally, a simulation model is built by PSCAD/EMTDC to verify the effectiveness of the proposed control strategy.