An improved synchronous reference frame phase-locked loop for stand-alone variable speed constant frequency power generation systems

The phase-locked loop (PLL) based on conventional synchronous reference frame, i.e. dqPLL, is usually employed in grid-connected variable speed constant frequency (VSCF) power generation systems (PGSs). However, the voltage amplitude drop of stand-alone PGSs is often greater than that of the grid-connected PGSs when loads are added drastically, which makes the response of dqPLL deteriorated. This paper presents an improved dqPLL (IdqPLL) for stand-alone VSCF PGSs. The simulation results verify the dynamic performance of the IdqPLL.