Pre-filters based synchronous rotating reference frame phase locked loop (SRF PLL) design for distorted grid conditions

Abstract

In this paper presents the analysis of pre-filters based SRF PLL for distorted grid conditions. An exact detection of phase and fundamental frequency of grid current is essential for the control algorithm of grid connected power converter circuit. A control model of the SRF PLL is developed and is made on tuning the system under distorted grid conditions like harmonics and dc offsets. The SRF PLL can be completely implemented in software with and without pre-filters. The pre-filters are band pass and high pass filters these can be used to reduce harmonics present in the input and high pass filter alone can reduce the dc offset present in the input. The effects of high pass and band pass filters on dc offsets are analyzed. The superior performance of proposed pre-filter-based SRF PLL phase detection system is studied and the obtained results are compared with SRF PLL-based phase detection to confirm the feasibility of the study under different grid environment such as high-harmonic injection and dc offset. All analytical results are verified using MATLAB software.