Operation of interleaved voltage-source-converter fed wind energy systems with asymmetrical faults in grid

This paper proposes and designs the control schemes for the voltage-source-converter (VSC) fed wind energy system with asymmetrical grid faults in the wind farm, where several VSC wind turbines are paralleled with the common AC bus. The key is to design the interleaved PWM strategy for the VSC of different wind turbines to reduce the switching harmonic in the total grid current, apply the flexible positive- and negative-sequence control (FPNSC) to generate the grid current references, and adopt the double synchronous reference frame current controller (DSRFC) to track both the positive- and the negative-sequence current references. To estimate the phase angle and frequency of voltage at the point of common point, the dual second order generalized integrator frequency-locked loop (DSOGI-FLL) has been implemented, which has been verified to offer smoother and better transient performance compared to conventional phase-locked loops. The simulation on a low-voltage wind park including four VSC fed wind turbines verify the performance of the proposed operating schemes under asymmetrical faulty conditions.