Voltage Balancing at the Point of Common Coupling of DG Unit Using Decoupled Double Synchronous Reference Frame

Voltage unbalance reduces the power quality and causes problems in the customer equipment and in the grids operation, especially in grids including distributed generation sources. In microgrids, use of distributed generation sources controlled by the inverter, has made it possible to compensate voltage unbalance by distributed generation units. To compensate voltage unbalance, usually two control loops are used to control the positive and negative components in the dq rotary frame. Nevertheless, the control loops of the positive and negative sequences are not completely decoupled from each other and there is an oscillatory coupling between them. In this paper, the use of the decoupled double synchronous reference frame in order to eliminate oscillating couplings and for voltage unbalance compensation is proposed. The simulation results show that, using the proposed control method, the voltage unbalance at the point of common coupling is effectively reduced. Also, due to the decoupling of the positive sequence from the negative sequence control loop, the performance of the distributed generation unit in the power injection to the grid is not affected by the voltage unbalance control system.