Three-time-scale control for discharging rate consensus and large-signal stability analysis in AC-bus microgrids

A distributed control scheme for islanded AC-bus microgrids is proposed, based on multi-agent system and singular perturbation theory. The goal is to achieve a balanced State Of Charge (SOC) for each Battery Energy Storage System (BESS) in discharging mode, ensuring stability properties of a large-signal model that considers the primary and secondary control loop dynamics. The power inverters are controlled through a voltage and current loop. Moreover, a droop control and consensus algorithm are proposed to ensure that the SOC of these BESSs are balanced. Furthermore, large-signal stability analysis is assessed for the complete network system by using singular perturbation theory. Indeed, through an appropriate selection of the parameters, the dynamics exhibit three-time-scale separation to fit each control goal (power converter control, droop control and consensus control). Experimental results on an Imperix power test bench validate the proposed control scheme, and verify the reliability and robustness with respect to any connection/disconnection event or communication failure through different scenarios.