To solve the problems of low control accuracy and frequency instability existing in the conventional V/f droop control during the grid connection/disconnection process of microgrid

an improved V/δ droop control method considering the influence of equivalent resistance on microgrid control is proposed based on the theoretical analysis of droop control. Based on this method

a coordinated multi-microgrid hierarchical control system is designed by taking the microgrid central controller as the core. Then the transient-state control strategy and process during the grid connection/disconnection process of multi-microgrid is put forward. Finally

by taking an off-network wind/photovoltaic/diesel/energy-storage project as an example

the control strategy and the process are verified through the EMTDC/PSCAD simulation and the test in an actual system. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2012AA050208).