Three-phase photovoltaic inverter control strategy for low voltage grid current unbalance mitigation

Three-phase electrical systems are subject to current imbalance, caused by the presence of single-phase loads with different powers. In addition, the use of photovoltaic solar energy from single-phase inverters increases this problem, because the inverters inject currents of different values, which depend on the generation capacity at a given location. To mitigate the problems caused by current imbalance, solutions that measure and compensate for the current in the neutral conductor are proposed. However, through an adequate control method, the current balance of the distribution network could be achieved by the photovoltaic inverters themselves. Thus, this work proposes to use positively the idle capacity of three-phase photovoltaic inverters to partially compensate for the current imbalances in the low voltage network but in a decentralized way. Therefore, a control method is developed, based on instantaneous symmetric components theory and on the estimation of orthogonal signals using a third-order generalized integrator (TOGI). In turn, through a laboratory prototype, experimental results are presented that demonstrate the feasibility of implementation and the effectiveness of the proposed control technique on current balancing.