Decoupling Control for DC Electric Spring-Based Unbalanced Voltage Suppression in a Bipolar DC Distribution System

The use of bipolar direct current (dc) distribution systems introduces the possibility of unbalanced voltage (current). This situation increases the voltage deviations and power losses at each node owing to the presence of a neutral line current. This article proposes a method that mitigates the unbalanced voltage caused by constant power loads (CPLs) by dc electric springs (DC-ESs). A linearized model is used in the small-signal analysis of CPLs. On this basis, the coupling relationship between positive and negative pole voltages is analyzed. After DC-ESs are introduced, the positive and negative pole voltages and DC-ES output voltages are found to be closely related, thereby increasing the complexity of the control system. Therefore, a feedforward decoupling control block diagram is introduced on the basis of the small-signal model analysis of DC-ESs in a single node of the bipolar dc system. The control system is simplified, and different control loops can be independently controlled. Thus, the rapidity and anti-interference performance of the control system are greatly enhanced. Simulation and experimental results of the unbalanced voltage suppression in the bipolar dc system are used to verify the effectiveness of the proposed scheme.