Frequency Adaptive Parameter Estimation of Unbalanced and Distorted Power Grid

Hafiz Ahmed,Mominul Ahsan,Alhussein Albarbar,Mohamed Benbouzid,Mohammad Shahjalal

doi:10.1109/access.2020.2964058

Abstract

Grid synchronization plays an important role in the grid integration of renewable energy sources. To achieve grid synchronization, accurate information of the grid voltage signal parameters are needed. Motivated by this important practical application, this paper proposes a state observer-based approach for the parameter estimation of unbalanced three-phase grid voltage signal. The proposed technique can extract the frequency of the distorted grid voltage signal and is able to quantify the grid unbalances. First, a dynamical model of the grid voltage signal is developed considering the disturbances. In the model, frequency of the grid is considered as a constant and/or slowly-varying but unknown quantity. Based on the developed dynamical model, a state observer is proposed. Then using Lyapunov function-based approach, a frequency adaptation law is proposed. The chosen frequency adaptation law guarantees the global convergence of the estimation error dynamics and as a consequence, ensures the global asymptotic convergence of the estimated parameters in the fundamental frequency case. Gain tuning of the proposed state observer is very simple and can be done using Matlab commands. Some guidelines are also provided in this regard. Matlab/Simulink based numerical simulation results and dSPACE 1104 board-based experimental results are provided. Test results demonstrate the superiority and effectiveness of the proposed approach over another state-of-the art technique.

Highlights

Recent years have seen an exponential growth in the grid integration of renewable energy sources e.g. wind, solar
The frequency estimation error took ≈ 1 cycle to converge by the proposed technique while it is at least two time more for the SOGI-frequency-locked loop (FLL) both techniques have similar peak overshoot
WORKS This paper has proposed a state observer-based parameter estimation approach for three-phase grid voltage signal subject to unbalanced faults and harmonics

Summary

INTRODUCTION

Recent years have seen an exponential growth in the grid integration of renewable energy sources e.g. wind, solar. In observer-based approach, using parameterized dynamical model, Luenberger observers are used to estimate the parameters of the grid voltage signal. Using this type of approach, the design process can be very complex e.g. In this paper, following the directions of [33], a frequency adaptive state observer for three-phase system is proposed that is globally convergent for the fundamental frequency component and robust to unbalance and harmonics. The problem being considered in this paper is to estimate the grid frequency, phase and amplitude of positive and negative sequence voltages from the available measurement Vα and Vβ. Since both state and output matrices are the same for α and β dynamics, instead of writing everything separately in α and β coordinates, α/β notation would be used on for compact representation

STATE OBSERVER DESIGN

TEST-III

CONCLUSION AND FUTURE WORKS