A pre-filter based PLL for three-phase grid connected applications

This paper proposes a phase estimator based on a pre-filter based phase locked loop (PF-PLL), which overcomes serious limitations of existing PLL routines under frequency variation, distorted power grid conditions and measurement errors. This is achieved by a chain of pre-filters, which systematically attenuates all distortion components and extracts the fundamental, positive-sequence signal. The reported PF-PLL is capable of fast and precise phase estimation, even with unbalanced and highly distorted threephase electrical variables, which may be measured with low-cost transducers of reduced accuracy. Consequently, it is appropriate for control of all grid connected equipment, including the dynamic voltage restorer (DVR), where it is often required to synchronize with line currents, which experience much higher levels of harmonic distortion than voltages. This paper presents a detailed analysis of the PF-PLL, its evaluation through simulation and experiments, using a fixed-point DSP based laboratory prototype.