Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Electrical and Computer Engineering

Supervisor

Dr. M.R.D. Zadeh

Abstract

This thesis proposes a phase-angle tracking method, i.e., based on discrete Fourier transform for synchronization of three-phase and single-phase power-electronic converters under distorted and variable-frequency conditions. The proposed methods are designed based on fixed sampling rate and, thus, they can simply be employed for control applications. For three-phase applications, first, analytical analysis are presented to determine the errors associated with the phasor estimation using standard full-cycle discrete Fourier transform in a variable-frequency environment. Then, a robust phase-angle estimation technique is proposed, which is based on a combination of estimated positive and negative sequences, tracked frequency, and two proposed compensation coefficients. The proposed method has one cycle transient response and is immune to harmonics, noises, voltage imbalances, and grid frequency variations. An effective approximation technique is proposed to simplify the computation of the compensation coefficients. The effectiveness of the proposed method is verified through a comprehensive set of simulations in Matlab software. Simulation results show the robust and accurate performance of the proposed method in various abnormal operating conditions. For single-phase applications, an accurate phasor-estimation method is proposed to track the phase-angle of fundamental frequency component of voltage or current signals. This method can be used in three-phase applications as well. The proposed method is based on a fixed sampling frequency and, thus, it can simply be integrated in control applications of the grid-connected converters. Full-cycle discrete Fourier transform (DFT) is adopted as a base for phasor estimation. Two procedures are taken to effectiveness reduce the phasor estimation error using DFT during o - nominal frequency operation. First, adaptive window length (AWL) is applied to match the window-length of the DFT with respect to the input signal frequency. As AWL can partially reduce the error if sampling rate is not high, phasor compensation is employed to compensate the remaining error in the estimated phasor. Both procedures require system frequency, thus, an effective frequency-estimation technique is proposed to obtain fast and accurate performance. The proposed method has one cycle transient response and is immune to harmonics, noises, and grid frequency variations. The effectiveness of the proposed method is verified through a comprehensive set of simulations in Matlab and hardware implementation test using real-time digital signal processor data acquisition system.

Certificate of Examination.pdf (107 kB)
Certificate of Examination


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