Adaptive Filtering-Based Pseudo Open-Loop Three-Phase Grid-Synchronization Technique

International audienc

A Quasi open-loop robust three-phase grid-synchronization technique for non-ideal grid

Abstract Development of advanced grid‐synchronization technique for unbalanced and distorted grid is considered in this paper. In this context, self‐tuning filter (STF) is considered to extract the fundamental component from the measured unbalanced and distorted voltages. Standard STF considers balanced grid voltages which is not always possible to ensure in the actual power grid. To mitigate this issue, an extended STF is proposed by analyzing the standard STF in the state‐space framework. To make the proposed ESTF grid‐following, a robust open‐loop frequency estimator is also applied. The closed‐loop system enjoys excellent filtering benefit from the extended STF side while taking advantage of the fast convergence speed property of the open‐loop frequency estimation technique. Numerical simulation and experimental results with double second‐order generalized integrator phase‐locked loop are provided to validate the theoretical developments

An improved pre-filtering moving average filter based synchronization algorithm for single-phase V2G application

The performance and overall operation of grid- connected electric vehicle is directly affected by abnormal grid conditions. In this regard, Moving Average Filter (MAF) provide high noise cancellation capability and require less computational resources. However, the conventional in-loop MAF based synchronization suffers from slower dynamic response. In this paper, an improved pre-filtering MAF based PLL (IPMAFPLL) is proposed where MAF is removed from the control-loop and placed in the pre-filtering stage to improve the dynamic response of system. The phase drift provided by MAF under off-nominal frequency is further mitigated by introducing a compensation factor in the pre-filtering stage. The proposed technique is compared with conventional MAF-PLL and non-adaptive MAF- PLL. The simulation and experimental results show that our proposed approach have lower frequency overshoot and improved performance towards compensating grid harmonics under nominal and off-nominal grid frequencies

A single-phase synchronization technique for grid-connected energy storage system under faulty grid conditions

The control of a single-phase grid-connected energy storage system (ESS) requires a very fast and accurate estimation of grid voltage frequency and phase angle. A phase-locked loop (PLL) based synchronization algorithm usually extracts this information. The operation and control of the entire system are directly affected by the performance of PLL. In this article, a novel advanced single-phase PLL (ASϕPLL) technique with reduced complexity is proposed for the fast and accurate extraction of grid information in an ESS under distorted and abnormal grid conditions, including harmonics, interharmonics, dc offset, and grid faults. The proposed method provides a faster dynamic response, lower frequency overshoot, and accurate estimation under off-nominal grid frequencies with reduced computational complexity in comparison with the existing method. The advanced performance of the proposed ASϕPLL is verified through the simulation and experimental results

Enhanced Frequency Adaptive Demodulation Technique For Grid-Connected Converters

This paper presents an enhanced frequency adaptive demodulation technique for grid-synchronization of grid-connected converters (GCC) in variable frequency condition. Demodulation works by generating demodulated voltages which contain undesired double frequency components. As a result, high-order low-pass filters (LPF) with high cutoff frequency are required to eliminate the undesired components. This reduces the dynamic performance. Frequency adaptive demodulation technique enhances the dynamic performance by rejecting the double frequency components as opposed to filtering, however, at the cost of additional computational complexity. This paper overcomes this problem by using double demodulation without recreating the double frequency component for rejection purpose. This reduces the computational complexity significantly. Suitability of proposed method is verified through numerical simulation and experimental study. Comparative study with existing frequency adaptive demodulation and second-order generalized integrator phase-locked loop (SOGI-PLL) techniques demonstrate the validity and performance improvement by the proposed technique

Gain Normalized Adaptive Observer For Three-Phase System

International audienceThis paper proposes the estimation of parameters and symmetrical components of unbalanced grid using adaptive observer framework. Recent adaptive observers proposed in the literature doesn’t employ any gain normalization in their frequency estimation loop. This can be problematic in the presence of large voltage dip. This paper proposes a solution to overcome this limitation using a novel gain normalized - frequency-locked loop (GN-FLL). Technical details of GN-FLL, stability analysis and tuning are provided in this paper. Comparative experimental results with adaptive Luenberger observer, second-order generalized integrator - phase-locked loop (SOGI-PLL) and enhanced PLL (EPLL) are provided to demonstrate the effectiveness the proposed technique in the single-phase case. Comparative experimental results with double SOGI-FLL (DSOGI-FLL) and adaptive notch filter (ANF) are provided to demonstrate the effectiveness the proposed technique in the three-phase case