A Combined Bus Port Impedance Based Stability Criterion for DC Distribution Power Systems

The impedance-based criteria are well known to assess the stability of DC systems by impedance measurement method. However, these criteria apply to the DC systems with the precondition of the interconnected converters or subsystems having no right-half-plane (RHP) poles, which is hard to guarantee and verify in a complicated DC distribution power system (DPS) with multiple parallel connected converters. To solve it, this paper proposes a combined bus port impedance based stability criterion for the DC DPS, where the number of RHP poles of the combined bus port impedance are proven zero definitely. Thus, the DC DPS is judged stable if and only if the trajectory of the proposed combined bus port impedance does not encircle the origin (0, 0), which is easily and feasibly determined by measuring port impedance of individual converter, without acquiring its inner information. Specifically, the oscillation frequency can be observed intuitively from the Bode plot of the combined bus port impedance. Three experimental systems are provided to validate the proposed stability criterion.