Study on LVRT Capability of Three-phase PV Grid-connected Inverter

The PV inverter is the core of solar power generation.The LVRT capability is required to consider the safe operation of system.The research nowadays focus on the control strategies on the balance fault,while the unbalance fault is not going deeply.This paper analyzes LVRT capability of PV inverter under both balanced and unbalanced grid voltage drop conditions.When grid voltage drop is unbalanced,the design of phase-locked loop is improved based on SOGI-QSG for grid synchronization.Component of the positive and negative sequence of grid voltage and current is seperately detected.New control stratagies are proposed for cancellation of negative-sequence current or DC-link voltage ripple.Furthermore,through a series of experiments,LVRT capability of three-phase PV grid-connected inverter is tested.Good control effect under balanced condition is obtained.