The current control of PV inverter for three-phase unbalanced fault with Lagrange multiplier

An unbalanced voltage in a 3-phase system will lead to the 2^nd order harmonic and overcurrent in the output of PV inverters. To solve the problem, this paper adopted a double-loop feed-forward decoupling control on the basis of a well-recognized concept of “symmetrical components”. The paper proposed a Lagrange multiplier- based methodology to improve the control current of 3-phase PV inverters so as to meet the criteria of LVRT. Moreover, the paper introduced a weighting parameter into the set of Lagrange equations to achieve a more adaptive control; that is, any desired ratio of the ripple amplitude in real power to that in reactive power can be reached under fault conditions. The simulation results have justified the feasibility of the proposed control method in suppressing both active and reactive power ripples, meanwhile demonstrating the adaptivity of the method to different control targets.