Control design and small-signal stability analysis of inverter-based microgrids with inherent current limitation under extreme load conditions

A novel droop controller that ensures a desired inverter current limitation and guarantees the stable operation of inverter-based microgrids under extreme load conditions, is proposed in this paper. Opposed to existing framework-based droop controllers that align the output voltage on axis, here the inverter current is aligned on axis in order to achieve two main goals: i) limitation of the RMS value of each inverter current during transients, without a need for saturation units that guarantee only steady-state limitation and require adaptation techniques for adjusting their limits and ii) a rigorous proof of closed-loop system stability for the entire microgrid. In particular, the proposed approach significantly simplifies the stability analysis of the microgrid, since it can be investigated through a Jacobian matrix of reduced size. Simulation results are given to highlight the superiority of the proposed controller when compared to a conventional droop controller under extreme load conditions, while experimental validation in a lab-scale microgrid is also provided.