A Strategy for Unbalanced Voltage Suppression in Bipolar DC Distribution Systems Based on Flexible ZIP Load Regulation

In bipolar DC distribution systems, various types of imbalances can lead to unbalanced voltage and current distributions. Unbalanced voltages reduce the power supply quality, while unbalanced currents increase system losses. To address this issue, this paper introduces a control strategy based on the utilization of the DC electric spring (DC-ES) to suppress unbalanced voltages in bipolar DC distribution grids. Firstly, the paper investigates the coupling relationship between positive and negative pole voltages and derives the coupling matrix between the bipolar voltages and the DC-ES output voltage. Furthermore, the small signal model of the bipolar DC distribution grid containing DC-ES is derived, simplifying the control system through decoupling and improving the suppression capability. Finally, a bipolar DC distribution grid system is constructed on the MATLAB/Simulink simulation platform to validate the effectiveness of the proposed unbalanced voltage suppression strategy.