The dc symmetrical component method is introduced for the analysis and control of bipolar dc distribution systems under asymmetrical operation. This method is an extension of the classical symmetrical component theory in three-phase ac power systems. The asymmetrical voltage and current in the positive and negative poles are decomposed into symmetrical components in common and differential modes.
The equivalent circuit for each mode is derived, which forms decoupled modenetworks. Consequently, it allows for independent investigation of each mode, and provides an insightful view of the static and dynamic behavior of a bipolar dc power system. The dc symmetrical component method is a general approach which is applicable to different aspects of system design. As an example, an enhanced common-mode voltage regulation scheme is described. It suppresses common-mode LC resonance by adding active damping control, and reduces common-mode impedance to improve power quality and voltage stability. The major theoretical conclusions are verified by experimental results.