A Nonlinear Loop Filter based PLL with Harmonic Filtering Capability for Single-Phase Grid Integrated System with Improved Dynamic Performance

The major concern for the single-phase grid-connected inverter system is the phase and frequency error of the phase-locked loop (PLL) under various grid disturbances. This paper employs an effective cascaded bandpass filter (CBPF) to eliminate the effects of the dc offset and harmonics present in grid voltage. However, the presence of a prefilter slowed the dynamic performance of all-pass filter (APF) based PLL, implied to generate the orthogonal signal in the single-phase system. To improve the dynamic performance along with the harmonics filtering capability, a nonlinear loop filter (LF) based PLL with CBPF is proposed. The nonlinear LF contains a nonlinear function applied in proportional-integral control to improve the dynamic response of the PLL. Under various grid disturbances, the proposed controller has a faster dynamic response with less overshoot. Furthermore, the proposed PLL is capable of eliminating the effects of DC offset and subharmonics. The proposed PLL is compared with different state-of-the-art PLLs to assess the performance under various grid disturbances. The efficacy is validated experimentally as well as through simulation results.