Voltage stability improvement of a bipolar DC system connected with constant power loads

Abstract The constant power loads (CPLs) in direct current (DC) power system have the potential to degrade the stability of the whole system. This paper proposed a virtual resistance damping method that improves the stability of the bipolar DC system connected with CPLs. At first, a stability criterion for the bipolar system is given. After that, a bipolar DC system based on a half-bridge voltage balancer (HBVB) is introduced and its small-signal model is derived. On this basis, a virtual resistance damping method, Capacitor-Parallel-Damping-Resistance (CPDR), is proposed and analyzed. Moreover, the Lyapunov stability theory is adopted to investigate the impact of unbalanced load on the system stability. It turns out that system stability is determined by the sum of the system output power. This conclusion can significantly reduce the complexity of the bipolar system stability analysis and control loop design. Finally, the simulations and experimentations are performed to verify the proposed idea in this paper.