Research on a New Synchronous Phase-Locked Method for Renewable Energy Grid-connected Converters

Abstract

Background:: The phase-locked loop (PLL) is widely used to estimate synchronization information such as magnitude and phase angle of the grid voltage, which is essential for gridconnected power generation from distributed renewable energy sources. However, the harmonics in the grid often affect the accurate extraction of fundamental positive sequence, resulting in phase deviations. Methods:: A dual extended novel third-order generalized integrator (DENTOGI) is proposed and placed into the control outer loop of the PLL. This approach can be applied in the condition of the grid with DC offset voltage (DCOV). Additionally, the PLL is proposed by introducing moving average filter (MAF) and eliminating the proportional controller of the integration link to suppress high-frequency harmonics and speed up the response. Results:: A comparative experiment using Matlab/Simulink is conducted to evaluate the proposed PLL against the conventional PLLs. The experimental results confirm that the proposed PLL exhibits superior filtering performance for DC offset and harmonic components when compared to the conventional PLL. Additionally, the proposed PLL demonstrates better dynamic adjustment capabilities. Conclusion:: The main contribution of this paper is to propose a phase-locked method that can eliminate DCOV and harmonic components, which can be applied in non-ideal power grid conditions. The proposed PLL based on DENTOGI and MAF can lock the grid phase stably without errors under the grid fault involving DCOV and harmonic disturbance, it also exhibits the characteristics of fast response.