DC Voltage Control of the DC Micro-Grid for Super High Quality Electric Power Distribution

“DC Micro-grid” is a novel super high quality electric power system with using dc distribution (Fig. 1). The power is distributed through dc distribution line and converted to required ac or dc voltage by converters placed near loads. The load side converters do not need transformers by choosing proper distributed dc voltage (±170 V). The dc distribution line is composed of 3 power lines: +170 V line, neutral line and −170 V line, and the voltages of ±170 V have to be balanced to supply high quality power. In this paper, a voltage balance control method for dc distribution is proposed. Computer simulation results demonstrated that dc micro-grid was able to supply both ac and dc power to loads simultaneously and stably by 3-wire dc distribution and load side converters. 3-wire dc distribution system is adopted in DC micro-grid because one side of single phase 100 V lines become neutral line as same as Japanese standard distribution system, and dc distribution line voltage to ground become low level as ±170 V. Load side dc-dc converter is connected with +170 V line and neutral line. So if there is some dc loads in the system, dc voltage balance control is indispensable. There are some voltage balance control methods. In this paper, we chose a bi-directional chopper