Development of high performance improved technique for grid synchronization of WECS

In grid-connected wind energy conversion systems (WECSs), phase locked loop (PLL) technique became widely used to enhance the stability and power quality. However, the accuracy of PLL is one of the major aspects that influence the system performance. Conventional synchronous-reference frame PLL (SRF-PLL) techniques have difficulty of low accuracy, frequency fluctuation, power oscillation and poor power quality. To improve these drawbacks, this paper proposes a new improved PLL technique. A comparative study for the conventional techniques and the developed technique is introduced. Two types of current controllers (hysteresis and vector oriented control) are compared. A reconfigurable inverter controller is also proposed here as an effective method that supports both grid-connected and stand-alone operation modes. This provides stable operation under various grid conditions and maintains stable frequency reference during islanding mode. More advantages include voltage unbalance operation capability and robustness under fault conditions. Simulation results are carried out to validate the proposed solution. The results have demonstrated that the proposed technique is more efficient than other conventional techniques to achieve better performance, improved power quality, and enhanced stability under various conditions.