A distributed reactive power sharing approach in microgrids with improved droop control

Conventional droop control causes frequency and voltage deviations (from rated value) in a inverter-intensive microgrid (MG), and the reactive power sharing cannot be obtained when the communication structure of the MG or load suddenly changes. Compared with a centralized control and droop control scheme, a distributed hierarchical control structure of the MG can overcome the limitation of communication and realize reactive power sharing. In this paper, an improved droop control is adopted, which is based on the hierarchical control structure. The hierarchical control structure consists of zero-level control, primary control and a proposed secondary control. First, the secondary controller is modeled, and the MG system composed of distributed generators (DGs) is considered as a multi-agent system. The secondary controller can make up for the shortcomings of the droop controller and adjust the frequency and voltage to their rated values. Secondly, the reference voltage and frequency of the zero-level control are calculated, and combined with the primary control. The zero-level control and primary control can make the voltage and frequency of the MG run stably and provide reference voltage for the inverter. Finally, the stability of the system is proved by the theory of multi-agent consistency. A simulation system is established in the Matlab/Simulink environment, and the results show the effectiveness of the proposed controller.