The Control Method of Bidirectional AC/DC Converter with Unbalanced Voltage in Hybrid Micro-Grid

Three phase AC/DC converter based on the traditional double loop control may act as a link bridge in hybrid micro-grid due to its bidirectional power flow with unit power factor on AC side. When the AC/DC converter works on the condition of unbalanced voltage on the AC side, a second order ripple voltage will be generated in the DC-link and some amount of third harmonic current will exist in the AC side, which could deteriorate the operation of the micro-grid. By analyzing of the power flow under unbalanced voltage conditions, a three-phase AC/DC converter system, based on super capacitor compensation, is presented. The system can guarantee the AC current sinusoidal and symmetrical, and can keep DC-link voltage fluctuating lightly around rating during the super capacitor working. As an energy buffer, the super capacitor mitigates the active power ripple. Simulation and experimental results are provided to verify the feasibility of the control system.