Volume 12, Issue 5

This study proposes several high precision selective harmonics compensation schemes for an active power filter. Harmonic currents are identified and on-line tracked by novel Adaline-based architectures which work in different reference-frames resulting from specific currents or powers decompositions. Adalines are linear and adaptive neural networks which present an appropriate structure to fit and learn a weighted sum of terms. Sinusoidal signals with a frequency multiple of the fundamental frequency are synthesized and used as inputs. Therefore, the amplitude of each harmonic term can be extracted separately from the Adaline weights adjusted with a recursive LMS (Least Mean Squares) algorithm. A first method is based on the modified instantaneous powers, a second method optimizes the active currents, and a third method relies on estimated fundamental currents synchronized with the direct voltage components. By tracking the fluctuating harmonic terms, the Adalines learning process allows the compensation schemes to be well suited for on-line adaptive compensation. Digital implementations of the identification schemes are performed and their effectiveness is verified by experiments.

The acceptability of two hottest-spot temperature models is assessed in this paper. The first model, contained in the IEEE loading guide, is shown not to accurately account for the effects of the top-oil temperature (TOT) variation on the hottest-spot temperature. A new model which accounts for TOT variation is derived. The original and modified models are linearized and fitted to field data using linear regression to obtain optimal parameter estimates. Comparison of the parameter estimates and prediction simulations show that even though the original model is not structurally accurate, it, as well as the modified model, are acceptable for prediction purposes. The method of nonlinear regression is also used in an attempt to find better parameter estimates for the nonlinear modified model. It is shown that parameter estimates for the nonlinear model are inferior to those obtained for the linear models.

This paper presents a high efficiency drive strategy for micro-turbine generator (MTG) in which permanent magnet synchronous generator (PMSG) is used. PMSG operates at maximum efficiency point by optimizing the phase of armature current of PMSG; i.e., an optimum d-axis current in the rotor reference frame is analytically derived from mathematical model of PMSG taking iron loss into account. In addition, in order to use turbine output power effectively, compressor input power is minimized by optimizing revolving speed of PMSG. Simulation results confirm validity of the proposed method.

This paper proposes a phase detection method for harmonics and unbalanced voltage conditions. The proposed method uses harmonics and unbalanced voltage compensation circuit in addition to basic PLL (Phase Locked Loop) circuit. In the harmonic compensation circuit, the harmonic voltage component are eliminated from the input voltages using specific harmonic detection method. Besides, frequency information of power system used in the specific harmonic detection method is estimated by an extended complex Kalman filter. In the unbalanced voltage compensation circuit, the input voltage is normalized after the calculated positive sequence component. By means of the proposed method, excellent phase detection performance can be achieved under harmonics and unbalanced voltage conditions. Moreover, detection of positive sequence voltage component becomes possible under voltage drop conditions due to faults in power systems. The effectiveness of the proposed method is verified by simulation results.

Control strategies for extracting the three-phase reference currents for shunt active power filters are compared, evaluating their performance under different source voltage conditions in MATLAB/Simulink environment and also with Real Time Digital Simulator (RTDS) Hardware. When the supply voltages are balanced and sinusoidal, then all control strategies converge to the same compensation characteristics. However, when the supply voltages are distorted and/or un-balanced sinusoidal, these control strategies result in different degrees of compensation in harmonics. The p-q control strategy unable to yield an adequate solution when source voltages are not ideal. Extensive Simulations are carried out with Fuzzy Controller for both p-q and Id-Iq control strategies for different voltage conditions and adequate results were presented. The 3-ph 4-wire SHAF system is also implemented on a RTDS Hardware to further verify its effectiveness. The detailed simulation and RTDS Hardware results are included.

This paper presents a comprehensive review of power quality improvements made by applying the concept of DC ripple reinjection in current source series connected AC-DC rectifier for HVDC transmission. Recent advances in applying the reinjection concept, their suitability and selection is discussed. The main aim is to present a state of the art on the DC ripple reinjection technique over the years.

This paper presents a simple and generalized steady state model and analysis of six-phase self-excited induction generators. The developed matrix equation is formulated using nodal admittance method based on inspection. This model does not involve any lengthy derivations of nonlinear equations which are followed so far. Also this model is flexible such that inclusion or elimination of any equivalent circuit elements can be carried out easily. Moreover, this model can be used to find any combination of unknown quantities of the equivalent circuit. To determine the steady state performance of six-phase self-excited induction generators, applications of genetic algorithms have been proposed. In addition, the details of winding scheme of the six-phase induction generator which is used as prototype model for the experimental study is also presented. The experimental and theoretical results are found to be in close agreement, which validates the proposed method.

Detection of down conductor faults in an overhead electrical power distribution system is extremely difficult by the conventional over current protection devices. This paper presents a new digital down conductor detection scheme which is based on the combination (AND logic) of the ratio of the negative sequence current to the positive sequence current and the value of under current during an actual down conductor condition. Real time implementation of the proposed scheme has been carried out on an existing Indian 11 kV, 3 –Phase, 50 Hz power distribution system with the help of digital over current relay. At the end, a comparative evaluation of the proposed scheme with the scheme modeled in PSCAD/EMTDC software package is also presented. Both practical and simulation results indicate the effectiveness of the proposed scheme.