Soft phase-locked loop design for wind power generation

In wind power generation, phase angle of grid voltage is an important variable for decouple control of inverter connected to grid. When grid fault occurred which seriously affect wind turbine operating performance, such as grid voltage unbalance, voltage drop and so on, it is crucial to lock the phase angle as quickly and correctly as possible for the control. In this paper, a soft phase-locked loop (SPLL) is proposed in which decoupled double synchronous reference frame (DSRF SPLL) and variable parameter PI are used and d-q transformation and decoupling calculation are adopted to diminish the negative sequence and zero sequence component of the unbalanced grid voltage. By appropriate changing the parameters of PI controller, the system dynamic performance is improved without affecting the steady-state performance. In order to verify the effectiveness of the soft PLL, simulation module is built in Labview platform. The simulation result shows that proposed soft PLL not only has a fast dynamic performance and good steady-state performance, but also has a strong inhibiting effect for voltage distortion.