1551-3203 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TII.2015.2443718, IEEE Transactions on Industrial Informatics IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS 1 / 10 A Demodulation Based Technique for Robust Estimation of Single-Phase Grid Voltage Fundamental Parameters Md. Shamim Reza, Student Member, IEEE and Vassilios G. Agelidis, Senior Member, IEEE Abstract-This paper proposes a robust technique for the single-phase grid voltage fundamental amplitude, frequency and phase angle estimation under distorted grid conditions. It is based on a demodulation method tuned at a fixed frequency. It does not have stability issue due to an open loop structure, does not require real-time evaluation of trigonometric and inverse trigonometric functions, and also avoids the use of look-up table. It can provide accurate estimation of the single- phase grid voltage fundamental parameters under DC offset and harmonics. When compared with a frequency adaptive demodulation technique, the proposed one is less affected by DC offset, can provide faster frequency estimation and also avoids interdependent loop, trigonometric and inverse trigonometric functions operation. Simulation and experimental results are presented to verify the performance of the proposed technique. Index Terms-Demodulation, monitoring, parameters estimation, and single-phase voltage system. I. INTRODUCTION The power grid voltage parameters like the amplitude, frequency and phase angle are important information in many areas of power system applications such as grid- connected power converters [1, 2], distributed generations [3-7], microgrids [8-11], active power filters [12-15], control and protection [16-18], power quality analysis [19- 21] and uninterrupted power supply [22]. Such applications require fast and accurate estimation of the grid voltage parameters. For this purpose, a digital signal processing technique is required which should be computationally efficient, robust and stable under generic grid conditions. The discrete Fourier Transform (DFT) is the widely used technique to obtain the parameters of a periodic voltage waveform [23]. However, it suffers from a spectral leakage and picket fence effect during a non-periodic case [24]. Nevertheless, the spectral leakage can be used to obtain the frequency of the non-periodic voltage waveform at a cost of high computational burden due to its requirement of three DFT operations with a large size window under distorted grid conditions [25]. A technique based on Prony method can provide an improved frequency resolution and also does not show spectral leakage [26]. However, it needs a prior knowledge of the number of frequency components present in the voltage waveform, thus it requires handling of large size matrix and rooting of a high-order polynomial function under grid disturbances [26]. A least-square technique necessitates large size window, matrix inversion operation and may suffer from matrix singularities [27]. On the other hand, Kalman filter [28], phase-locked loop [29, 30], frequency-locked loop [1], and artificial neural network [13, 31] based techniques require a trade-off between good dynamics and estimation accuracy under distorted grid conditions. Moreover, they contain interdependent loop, thus tuning is sensitive and reduces the stability margin. On the other side, low-pass filter (LPF) used in a demodulation method tuned at a fixed frequency may attenuate amplitude and introduce phase error during off-nominal frequency condition [32-36]. These errors can be avoided by using a frequency adaptive demodulation method [35, 36]. In this case, a separate frequency estimation algorithm can be used, but it increases the computational burden of the technique [35, 36]. To avoid the separate frequency estimation algorithm, an interdependent loop can be included in the demodulation method for feeding back the estimated frequency [37]. In this approach, a quadrature oscillator is also integrated to reject second harmonic oscillations generated by the demodulation of the fundamental voltage component. However, this technique shows slower response and takes around five fundamental cycles as a settling time. The above mentioned techniques also require evaluation of the trigonometric (sin and cos) and/or inverse trigonometric (arctangent) functions which may increase the computational effort for implementing on a real-time low cost digital signal processor [38, 39]. A look-up table can be used for sin and cos functions [38]. However, to increase the accuracy, the number of elements present in the table has to be increased at a cost of large size memory [38]. On the other hand, the look-up table approach may not be suitable for arctangent function, as it requires considerable memory to provide a decent arctangent accuracy [39]. The objective of this paper is to propose a robust technique for providing the estimation of the single-phase grid voltage fundamental amplitude, frequency and phase angle under distorted grid conditions. The proposed technique relies on a demodulation method tuned at a fixed frequency. It does not suffer from stability issue as it has an open loop structure. It avoids the use of look-up table, trigonometric and inverse trigonometric functions operation. It can also reject the negative effects caused by DC offset and harmonics, and meet the standard requirements. When compared with a frequency adaptive demodulation technique reported in [37], the proposed technique is less sensitive to DC offset, can provide faster frequency estimation, avoids interdependent loop, trigonometric and inverse trigonometric functions operation. Manuscript received January 31, 2015; revised April 26, 2015; accepted May 27, 2015. The authors are with the Australian Energy Research Institute, The University of New South Wales, Sydney, NSW 2052, Australia, and also with the School of Electrical Engineering and Telecommunications, The University of New South Wales, Sydney, NSW 2052, Australia (e-mail: m.reza@unsw.edu.au; vassilios.agelidis@unsw.edu.au). Copyright (c) 2009 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to pubs- permissions@ieee.org.