Low-pass filtering or gain tuning free simple DC offset rejection technique for single and three-phase systems

This paper aims to address the DC offset rejection problem in grid synchronization algorithm. A simple approach to estimate the unknown grid frequency in the presence of DC offset is proposed for this purpose. Some of the existing techniques available in the literature use either low-pass filter or an additional integrator to eliminate the DC offset. Both approaches require an additional parameter to tune. However, tuning the additional parameter is not straightforward. Moreover, tuning the overall system can be complicated due to the presence of DC offset rejection part. The proposed approach does not require any additional parameter to tune. By considering the orthogonal signal instead of the DC offset as an additional state, the proposed technique can efficiently estimate the unknown frequency of the grid. Application to both single and three-phase grids are provided. Comparative experimental results with DC offset rejection capable second-order generalized integrator (SOGI) phase-locked loop (PLL) (SOGI-PLL) demonstrate the effectiveness and suitability of the proposed technique

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

Quasi Type-1 PLL With Tunable Phase Detector for Unbalanced and Distorted Three-Phase Grid

International audienc

Adaptive Observer-Based Grid-Synchronization and Sequence Extraction Techniques for Renewable Energy Systems: A Comparative Analysis

Various faults and disturbances often make the grid unbalanced and distorted. To make the grid-connected converters resilient to unbalanced and distorted grid, real-time estimation of grid voltage sequences are essential. Adaptive-observer based grid-synchronization techniques are very suitable for this purpose. In this paper, a comparative analysis of three recently proposed adaptive observer-based grid-synchronization technique are presented for frequency estimation and sequence extraction. The considered techniques are: global adaptive observer, gain normalized adaptive observer, and second-order generalized integrator type adaptive observer. Following a fair and systematic gain tuning process, the performances are verified through extensive numerical simulation and experiments. Experimental results demonstrate the merits and demerits of the individual techniques. Academic researchers and industrial practitioners will find the results useful for the selection of adaptive observer-based grid-synchronization and sequence extraction techniques