Research on low voltage ride through control of PV grid-connected inverter under unbalance fault

In order to solve a series of problems caused by photovoltaic (PV) off-grid, PV must have the low voltage ride through (LVRT) capability ensuring grid-connected operation and outputting reactive power to power grid within a certain time range. At present, the control strategies of PV grid-connected inverter under balance fault have been used effectively. However, the strategy of keeping the inverter stable under unbalance fault is still immature. In view of this situation, the requirement of LVRT is introduced in this paper, and reactive power is firstly output when the power grid is faulty. The negative sequence double current loop control strategy of PV inverter is analyzed to suppress the negative sequence current based on unbalance fault characteristics, and the control strategy is improved combined with LVRT requirements and the constraint of maximum short-circuit current of inverter. Then, a new LVRT control strategy is proposed in this paper, which can not only output reactive power but also suppress negative sequence current. In the end, it was verified that the control strategy proposed in this paper is rational and feasible by PSCAD/EMTDC.