For the microgrid system with peer-peer control strategies

seamless switching between islanded and grid-connected operation modes remains a technical barrier need to be solved urgently. This paper introduces the basic structure and the operating mode of a microgrid. According to the characteristics of the islanded and the grid-connected operation modes

a virtual synchronous generator(VSG)control strategy is proposed to switch the operation modes. Besides

a paralleled switching method based on the controller state following is proposed to meet grid-connected operation characteristics of the microgrid. Both phase and current instructions of the current-source mode based on PQ control and the voltage-source mode based on VSG control are tracked in real time

and it can lay a foundation for seamless switching between the two modes. Finally

both simulation and experimental platforms are established. They verify the effectiveness of the proposed strategies.This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2015AA050607).