An enhanced phase-locked loop for non-ideal grids combining linear active disturbance controller with moving average filter

Abstract

Aiming at the accuracy deterioration of the synchronous reference frame phase-locked loop (SRF-PLL) caused by the non-ideal grid conditions and the limitation of phase-locked loop based on the linear active disturbance rejection controller (LADRC-PLL), this paper proposes an enhanced three-phase phase-locked loop combining the improved moving average filter and linear active disturbance rejection controller (IMAF-LADRC-PLL). First, a linear extended state observer (LESO) is presented to estimate all uncertainties and disturbances of SRF-PLL. On this basis, an improved moving average filter (IMAF) with phase-lead compensator is used to further enhance the harmonic suppression property. By combining the LESO and IMAF in a specific control structure, the proposed IMAF-LADRC-PLL has satisfactory steady-state accuracy without sacrificing the dynamic performance. To ensure the phase-locked accuracy against frequency fluctuation, a frequency-adaptive implementation is suggested. Furthermore, the parameter tuning and performance analysis of IMAF-LADRC-PLL are also presented in this paper. Experimental results show that the proposed IMAF-LADRC-PLL can achieve better dynamic performance on frequency step response and maintain the phase-locked accuracy in the presence of grid harmonics, voltage unbalances and direct current offsets, compared with the traditional LADRC-PLL or PID-type IMAF-PLL strategy.