Research on Control Strategy for Two-stage Three-phase PV Grid-connected System Under Unbalanced Voltage Conditions

In actual operation, voltage imbalance may occur. According to output characteristics of photovoltaic array and the requirement of grid-connected inverter, two-stage PV grid-connected system is studied, and the mathematical model of unbalanced grid is established to independently control the Boost chopper and the inverter system. In order to restrain the negative sequence component, orthogonal signal generator based on second-order generalized integrator (SOGI) is used to separate the positive-negative sequence component and realize the phase locking of grid voltage. At the same time, a control strategy of suppressing the negative sequence current in dq synchronous rotation reference frame is proposed. In the end, simulation model of PV grid-connected system is established to verify the validity of proposed strategy under the unbalanced grid voltage conditions.