High-precision phase-locked loop suitable for complex power grids

A high-precision phase-locked method was proposed by combining traditional phase-locked loops and adaptive algorithms to address the difficulty of accurately locking the voltage frequency and phase of existing grid connected inverters under complex grid voltage conditions. Based on the analysis of the drawbacks of traditional phase-locked loops, the contradiction between the filtering effect and delay when using traditional filters in phase-locked loops was determined. Based on the adaptive filtering characteristics of the minimum mean square algorithm and the coordinate transformation formula in the phase-locked loop, the input, output, and weight matrix of the algorithm were determined, and a minimum mean square algorithm matrix model based on the Parker transform was constructed. High precision filtering was achieved by setting the required voltage positive sequence component as a continuously updated weight matrix, while variable step size control was implemented by introducing mean square instantaneous error and autocorrelation estimation mean. The experimental results show that using an improved phase-locked method based on the minimum mean square algorithm can improve the filtering effect of the phase-locked loop without reducing the dynamic response speed, thereby improving the phase-locked accuracy of the grid connected inverter under grid distortion. © 2024 Editorial Department of Electric Machines and Control. All rights reserved.