Abstract: Rapid penetration of renewable energy sources connected to the grid and distribution systems with power electronic circuits have changed the expected grid requirements to guarantee an appropriate performance under grid faults. This paper presents the analysis of 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 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. All analytical results are verified using MATLAB software.
Keywords—Grid-connected operation, phase-locked loop (PLL), Band pass filter, Low pass filter, seamless transfer, three-phase inverter, PI regulator, voltage sag detection.
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