Abstract
To improve the performance of the frequency lock loop (FLL) under the conditions of a distorted power grid and unexpected noise, a new type of frequency locked loop (Al-FLL) is proposed, in which the AL-FLL prefilter is formed by fusing two first-order low-pass filters (LPFs) with an improved active noise cancellation (ANC) method. Firstly, the improved S function variable step size least mean square algorithm (I-SVSLMS) is discussed and its performance is verified under different signal to noise ratio conditions. Secondly, the function and parameter selection method of LPFs are described. Finally, the stability of the whole system is analyzed. In addition, the denoising work is completed in the synchronous reference frame and the output frequency of the FLL is fed back to the Park transform as the rotation frequency, which further improves the dynamic response and steady state performance of the FLL. The results of simulation and experiment verify the effectiveness and reliability of the proposed method. Compared with the FLL based on second-order generalized integrator (SOGI-FLL), the Comb Filter based on FLL (COMB-FLL), and the AL-FLL without frequency feedback (AL-NF-FLL), the AL-FLL has the advantages of small computation, fast response speed, and small steady-state errors, etc., and it is fully competent to work under the conditions of power grid distortion and unexpected noise.
Highlights
Signal synchronization is a key factor in the control of power electronic devices, so the accurate detection of voltage signal frequency and phase in the grid synchronization is essential [1], such as the three-phase grid inverter [2], shunt active power filter [3], and island detection [4], etc
To address the issues mentioned above, this paper creatively introduces the active noise cancellation (ANC), and proposes an enhanced three-phase frequency locked loop (FLL) based on the improved ANC fusion low-pass filters (AL-FLL)
The purpose of this paper is to propose a new structure of AL-FLL to solve the problem of second-order generalized integrator (SOGI)-based FLLs descending in the case of noise
Summary
Signal synchronization is a key factor in the control of power electronic devices, so the accurate detection of voltage signal frequency and phase in the grid synchronization is essential [1], such as the three-phase grid inverter [2], shunt active power filter [3], and island detection [4], etc. In order to comprehensively improve the harmonic suppression capability of SOGI-FLL under distorted grid conditions, a Comb Filter based FLL (COMB-FLL) is proposed [13], and it can completely eliminate harmonics and DC offset problems under adverse grid conditions. This advantage comes at the expense of high memory requirements at high sampling frequencies. Chilipi et al [25] propose an algorithm for basic frequency synchronization using single-phase PLL from ANC It is suitable for a grid-connected converter used in distributed generation. The effectiveness of the AL-FLL is further verified by comparative simulation experiments
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