Output impedance comparison of different droop control realizations in DC systems

Droop control is broadly used in source paralleling and distributed dc systems. While the dc droop resistance guarantees static load sharing, the output impedance determines the dynamic performance and is important in stability analysis. In this paper, a general small signal model is established to derive the output impedance of a droop-controlled power source. Using buck converter as an example, the analytical result is verified by switching circuit simulation and hardware measurement. Three different droop control realizations are presented and compared. Though all the realizations achieve the same dc output resistance (i.e. the droop resistance), they have different output impedance control capability. The damping effect on the resonance peak of output impedance is also different. The impact of inserting a low pass filter in the droop loop is also analyzed. A proper droop design requires the consideration of both the output impedance regulation and resonance damping.