In view of the grid condition that the voltage at the grid connection point is unbalanced and contains fifth- and seventh-order harmonics

this paper presents an improved control strategy for a doubly-fed wind power system with series grid-side converter (SGSC) by coordinated control of the SGSC and parallel grid-side converter (PGSC). A proportional-integral double frequency resonance (PI-DFR) controller in the positive synchronous rotating reference frame during network unbalance and fifth- and seventh-order harmonics distortion is investigated. With the proposed control strategy

the stator and rotor currents are balanced distortion free and the generator’s output power and electromagnetic torque pulsation free. While two-fold and six-fold frequency pulsations in the total active power output of the doubly-fed wind power system can be restrained. In addition

the allocation principles of the reference currents in the PGSC are studied when considering the current capacity of PGSC. Finally

simulation results of a 2 MW doubly-fed wind power system with SGSC under unbalanced and distorted grid voltage condition are used to verify the proposed control strategy and allocation principles of PGSC’s reference currents.