Voltage Control of Bipoar DC Distribution Systems Considering the Characteristics of Constant Power Load: A Load-Side Solution

Employing bipolar DC distribution systems introduces the possibility of unbalanced voltage. This increases voltage deviations and power losses at each node due to the presence of the neutral line current. This study proposes a method of mitigating unbalanced voltage caused by constant power loads (CPLs) through DC electric springs (DC-ESs). In the case of the small-signal analysis of CPLs, a linearized model is utilized. On this basis, the coupling relations between positive and negative pole voltages are analyzed. After DC-ESs are introduced, the positive and negative pole voltages and output voltages of DC-ESs are found to be closely related, thereby deteriorating the dynamic performance of the control system and increasing its complexity. Therefore, a feedforward decoupling block diagram is introduced based on the small-signal model analysis of DC-ESs in a single node of the bipolar DC system. This can greatly enhance the rapidity and anti-interference performances of the control system. Simulation and experimental results of the unbalanced-voltage suppression in the bipolar DC system are used to verify the effectiveness of the proposed scheme.