Optimised damping control of islanded DC power systems using state feedback

Abstract

The voltage oscillation of islanded DC-power systems is probably caused by negative impedance, produced by the converter from conventional power control structure. In this study, the small disturbance linearised state equation of a DC-power grid with constant power load is derived to estimate the damping characteristics of DC voltage. To enhance the transient voltage stability, a novel DC-voltage damping control method is proposed, where both DC voltage and DC current are used as statefeedback variables. Furthermore, two state-feedback control loops are designed to regulate the duty cycle of buck-boost converter added to the energy-storage device. Using the root-locus method, the principle of system pole placement is further discussed to determine the optimal control parameters in the proposed feedback loops, so that the damping characteristics of power system can be optimised. Finally, experimental tests are conducted on a hardware-in-the-loop platform of a typical islanded DC-power system to validate the new control structure. The results demonstrate that the DC-voltage oscillation can be reduced rapidly, which greatly improves the transient stability of DC-power system.