Novel droop control design for overvoltage protection of DC microgrids with a constant power load

A novel droop controller for DC microgrid systems, consisting of multiple paralleled sources feeding a constant power load (CPL), is proposed to achieve the desired voltage regulation and accurate load power distribution, while ensuring an overvoltage protection for each source. CPLs are well-known to exhibit negative impedance characteristic due to their nonlinear behaviour, which may cause instability to a DC microgrid if the necessary impedance inequality criteria are not satisfied. In this paper, a new droop control scheme is proposed to limit the voltage of each source below a desired bound, achieve tight voltage regulation and power sharing, and guarantee closed-loop system stability with the existence of a CPL. The upper limit of the voltage of each source is rigorously proven using ultimate boundedness theory, while after a suitable manipulation of the admittance matrix of the microgrid, analytic conditions of stability are obtained to guide the control parameters design. To validate the theoretical design and analysis, a detailed simulation is performed of a DC microgrid equipped with the proposed controller.