Grid frequency estimation using Rife-Vincent Class I Window based Discrete Fourier Transform

This paper presents the performance analysis of the frequency estimation technique based on the Discrete Fourier Transform (DFT) for single-phase grid voltage waveform under distorted grid conditions. Time varying fundamental frequency estimation requires three DFT operations. In this work, different types of fixed size windows by utilizing a special type of window function called Rife-Vincent window of class I are used for the DFT operations. The fixed size window based DFT operations are implemented as finite impulse response (FIR) filters. The frequency responses of the FIR filters using different windows are shown in this paper. Matlab/Simulink software is considered for the simulations. All the simulation results show that the presented technique does not have stability issue as it is an open loop based technique, and it can successfully estimate the grid fundamental frequency.

I. Introduction

The nominal frequency of the grid voltage waveform is 50 Hz according to the specification of the European standard EN-50160 for low and medium voltage networks [1]. Due to various reasons the frequency starts to drift. If the frequency falls below the tolerance limit, the power system faces instability issues, and in the worst case scenario, blackout occurs. So, it is very important to maintain the frequency up to the tolerance limit. To maintain the desired frequency, we need a suitable and robust technique to determine the grid operating frequency with utmost precision even though the grid is loaded with a wide range of non-linear loads producing noise and harmonics [2]–[4]. In power system, the most common devices and sources that are responsible for the generation of harmonics are mainly due to the presence of nonlinear loads such as rectifiers, variable frequency drives etc. Harmonics distort the grid voltage waveform[26]. These undesired harmonics cause many problems including generation of heat, communication interference, solid state device malfunction, introducing ripple to the torque produced by an electric motor, reduce the lifetime of transformer, flicker and voltage sag and the degradation of power factor [5]–[7].