Fractional frequency transmission system (FFTS) is a promising solution for integrating large-scale wind energy into power systems. In FFTS, the grid frequency is much less than the typical 50 Hz or 60 Hz. Therefore, the phase-locked-loop (PLL) designed for power converters used in traditional systems could not be suitable in FFTS. This paper proposes the design of dual second-order generalized integrator (DSOGI) based PLL, so as to achieve satisfactory dynamic and steady-state performance. The accurate small-signal model is firstly built. Then the optimal parameters are obtained to achieve fast dynamic responses with small transient oscillations. Simulation results have verified the superior performance of the designed DSOGI-PLL.

Fractional Frequency Transmission System (FFTS); Phase Locked Loop (PLL); Dual Second-Order Generalized Integrator (DSOGI)