A Novel Power Limiter Based on Newton-Raphson Method for Doubly-Fed Induction Generator under Unbalanced Voltage Drop Conditions

A novel power limiter based on Newton-Raphson method is proposed in this paper for the Doubly-fed Induction Generator (DFIG) under the conditions of unbalanced grid voltage drop. Unlike the existing power limiters, which provide an approximate estimation of the maximal reactive power at the cost of introducing a large error in achieving its control target, ours formulates the design of power limiter into an optimization problem which tries to maximize the DFIG’s reactive power towards its two decisive factors: limited rotor current and rotor side converter’s output voltage. Finally the Newton-Raphson method is exploited to find the global maximum of the proposed optimization problem. Consequently, the proposed power limiter could more accurately determine the DFIG’s maximal reactive power without any loss of the accuracy in achieving its control target. Simulation results on a 1.5MW DFIG shows the efficacy of the proposed power limiter for DFIG under the conditions of unbalanced voltage drop.