Analysis and Suppression of Unbalanced Voltage in Radiant Bipolar DC Distribution Network

The difference between positive and negative pole voltages in the bipolar DC distribution network will cause unbalanced current in the middle line, which will increase the network power losses and lead to further deviation of the rated bus voltage. In this paper, based on the characteristics of constant-resistive and constant-power load and combined with the network constraint equation, the relationship between the unbalanced power and the neutral current, voltage unbalance factor and positive and negative pole voltages was derived. Moreover, the influence of source, network and load on DC voltage unbalance was further analyzed. On this basis, the unbalanced current interaction characteristic of upstream and downstream nodes was studied. The unbalance current can be reduced by adjusting the polarity of upstream node, which is based on load polarity switching method. Besides, the topology and implementation process of load polarity switching method was presented. Finally, the simulation platform of radial bipolar DC distribution network was built in MATLAB/Simulink, which verified the effectiveness of the DC voltage unbalance analysis method and the inhibition strategy. © 2019 Chin. Soc. for Elec. Eng.