A Dynamic Consensus Algorithm to Adjust Virtual Impedance Loops for Discharge Rate Balancing of AC Microgrid Energy Storage Units

A dynamic consensus algorithm (DCA)-based coordinated secondary control with an autonomous current sharing control strategy is proposed in this paper for balancing the discharge rate of energy storage systems (ESSs) in an islanded ac microgrid. The DCA is applied for information sharing between distributed generation (DC) units to regulate the output power of DGs according to the ESS capacities and state-of-charge (SoC). Power regulation is achieved by adjusting the virtual resistances of voltage-controlled inverters with an autonomous current-sharing controller. Compared with existing methods, the proposed approach can provide higher system reliability, expandability, and flexibility due to its distributed control architecture. The proposed controller can effectively prevent operation failure caused by over-current and unintentional outage of DGs by means of balanced discharge rate control. It can also provide fast response and accurate current sharing performance. A generalizable linearized state-space model for n-DG network in the z-domain is also derived and proposed in this paper; the model includes electrical, controller, and communication parts. The system stability and parameter sensitivity have been analyzed based on this model. To verify the effectiveness of the proposed control approach, this paper presents simulation results from a ten-node network and a comparison between experimental results obtained from the conventional power sharing control and the DCA-based SoC coordinated control in a setup with three 2.2 kW DC units.