DC-bus voltage control for three-phase bi-directional inverter in DC microgrid applications

This paper presents dc-bus voltage control for a three-phase bi-directional inverter in dc-microgrid applications. The bi-directional inverter can fulfill both grid connection and rectification modes with power factor correction. The proposed control includes two approaches, one line-cycle regulation approach (OLCRA) and one-sixth line-cycle regulation approach (OSLCRA), which take into account dc-bus capacitance and regulate dc-bus voltage to track a linear relationship between dc-bus voltage and inverter inductor current. With the OLCRA, the inverter can tune the dc-bus voltage to the desired voltage accurately every line cycle, which can reduce the frequency of operation mode change and current distortion. The OSLCRA adjusts current command every one-sixth line cycle to adapt to abrupt dc-bus voltage variation. The two approaches together can prevent dc-bus voltage from dramatic change and improve the availability of the dc-microgrid without increasing dc-bus capacitance. Determination of dc-bus capacitance is also presented in this paper. Experimental results measured from a 10 kVA three-phase bidirectional inverter have verified the feasibility of the discussed control approaches.