Abstract

The all-pass filter (APF) is an orthogonal signal generator (OSG) structure that is widely adopted in single-phase systems because of its simpler implementation. One of its applications is in the form of synchronous reference frame (SRF) based phase-locked loop (PLL). The APF basically provides unity gain in the whole frequency spectrum while altering its phase according to the frequency. The APF is however devoid of a filtering capability. The DC offset poses a particularly serious challenge and this issue is usually addressed with the integration of additional filetering structures. This paper shows the development of a two-stage modified APF (TSMAPF)-based OSG structure that is capable of suppressing DC offset while maintaining a frequency fixed structure. The proposed OSG relies only on optimized parameter tuning without the need for auxiliary filtering units. The TSMAPF is then combined with a quasi type-1 PLL in order to provide an innovative single-phase PLL with a fast dynamic response and the capacity to reject disturbances. Both simulation and the experimental results verify the effectiveness of the proposed PLL.