Control Strategy of Seamless Switching Between Grid-connected and Islanding Operation for Weak-connected Microgrid

Abstract

A control strategy of seamless switching is proposed for the high-capacity microgrid, which is at the end of long-distance transmission. Firstly, the control modes of energy storage and diesel generator set under grid-connected conditions and islanding conditions are analyzed. Meanwhile, the seamless switching strategy for the microgrid, in which energy storage or diesel generator sets can be taken as the main power source adaptively, is proposed. During the switching from the grid-connected condition to the islanding condition, the connection line power is optimized according to the respective operational characteristics of the energy storage and diesel generator sets. And the interaction of the power step control with voltage blocking and the regulation characteristics of the line voltage regulator is utilized to effectively suppress the fluctuation of system voltage and frequency. Finally, the combination of auto-synchronization control and multiple synchronization control improves the success rate of switching from the islanding condition to the grid-connected condition. The on-site test results of an actual microgrid project verify the effectiveness of the proposed control strategy.