Analysis of Load Unbalance According to Topology of Bipolar Low Voltage DC Distribution System

Abstract

A Low Voltage DC (LVDC) distribution system is a promising topology as a future smart distribution system due to its high efficiency and reliability. It can have two configuration, namely - unipolar and bipolar. Especially, interest in the bipolar system is increasing because various voltage levels offer more flexibility to the customers. However, the bipolar system is prone to cause voltage unbalance problem due to the difference between load capacities connected to each pole. The voltage unbalance causes the unbalance current, which leads to additional power loss and voltage drop on the system. Thus, this paper analyzes load unbalance in bipolar LVDC distribution system according to topology - radial and loop. The analysis of problems such as voltage unbalance and power loss caused by load unbalance is conducted by three stages. At first stage, the power loss which is a function of line current and active power is calculated on each topology using the DistFlow method. Next, the comparison for voltage unbalance and power loss between both topologies is performed. Finally, the analysis results are verified by using ElectroMagnetic Transients Program (EMTP) simulation.