Two-sample PLL with harmonic filtering capability applicable to single-phase grid-connected converters

Abstract

The two-sample phase locked loop (2S PLL) in single-phase digitally controlled grid-connected power converters provide synchronization with a minimal computational burden. However, the distortion of the grid voltage deteriorates the performance of the 2S quadrature signal generator. To solve this issue, this article introduces a harmonic filtering (HF) structure based on observers of the input voltage for the fundamental and selected harmonics. The stability and sensitivity of the 2S PLL with HF is analyzed. In comparison with second-order generalized integrator (SOGI)-based HF, the observers provide a narrower bandpass, and the subsequent deterioration of the response time is compensated by adapting the filter gains dynamically. The results obtained, both in simulation and experimentally, validate the proposal and compare its performance with other widely adopted PLLs providing harmonic rejection capability. The computational burden is analyzed and in the case of the proposals depends on the number of observers and the use or not of the adaptive strategy based on steepest descent.