Analysis and comparison on the control strategies of multiple voltage source converters in autonomous microgrid

Different from traditional utility grid, a microgrid contains a lot of VSC (voltage source converter) interfaced distributed generators which has more controlled variables than the common used synchronous generator. VSC can be operated in active power reactive power (PQ) mode, active power voltage (PV) mode, voltage frequency mode (Vf), etc. The control strategy selection has large impact on the microgrid system performance. This paper analyzes and compares two typical control schemes (PQ and Vf) of the VSCs. A single bus microgrid contains four VSCs was taken as the example. The dynamic performance and load sharing methods of the two control scheme were discussed from three scenarios: (1) all the VSCs operated in Vf mode, (2) one VSC operated in Vf mode and the other ones in PQ mode, (3) a group of VSCs operated in Vf mode and another group in PQ mode. The performances of the system are simulated in PSCAD software. The difference between the control strategies can be obtained from the simulation results and the effect of the control modes on frequency variation were summarized.