Unbalanced Voltage Analysis and Suppression Method in a Radial Bipolar DC Distribution Network

The difference between positive and negative pole dc loads in a bipolar dc distribution network causes unbalanced current in the neutral line. This unbalanced current increases the power losses in the network and leads to unbalanced voltage in each node. An automatic commutation switch (ACS)-based method is developed in this study to suppress unbalanced current and voltage. Expressions of the unbalanced voltage and current of a single node and multiple nodes are derived. The equations indicate that the unbalanced power between positive and negative poles can be reduced by adjusting the power supply polarity (PSP) of the dc load. The PSP of the dc load and the corresponding switching command is determined by comparing the amplitude and polarity of the neutral line current. Afterwards, the switching command is implemented through ACS. The topology of ACS and the implementation of the switching command are presented. In addition, a simulation platform of a radial bipolar dc distribution network is built in MATLAB/Simulink. The platform verifies the effectiveness of the unbalanced voltage analysis method and the proposed suppression strategy. The proposed method is also validated using a scaled-down hardware setup in the laboratory.