Although the concept of variable-speed drives, based on utilization of multiphase machines, dates back to the late 1960s, it was not until the mid- to late 1990s that multiphase drives became serious contenders for various applications. These include electric ship propulsion, locomotive traction, electric and hybrid electric vehicles, ldquomore-electricrdquo aircraft, and high-power industrial applications. As a consequence, there has been a substantial increase in the interest for such drive systems worldwide, resulting in a huge volume of work published during the last ten years. An attempt is made in this paper to provide a brief review of the current state of the art in the area. After addressing the reasons for potential use of multiphase rather than three-phase drives and the available approaches to multiphase machine designs, various control schemes are surveyed. This is followed by a discussion of the multiphase voltage source inverter control. Various possibilities for the use of additional degrees of freedom that exist in multiphase machines are further elaborated. Finally, multiphase machine applications in electric energy generation are addressed.

Multiphase Electric Machines for Variable-Speed Applications

This paper addresses real and reactive power management strategies of electronically interfaced distributed generation (DG) units in the context of a multiple-DG microgrid system. The emphasis is primarily on electronically interfaced DG (EI-DG) units. DG controls and power management strategies are based on locally measured signals without communications. Based on the reactive power controls adopted, three power management strategies are identified and investigated. These strategies are based on 1) voltage-droop characteristic, 2) voltage regulation, and 3) load reactive power compensation. The real power of each DG unit is controlled based on a frequency-droop characteristic and a complimentary frequency restoration strategy. A systematic approach to develop a small-signal dynamic model of a multiple-DG microgrid, including real and reactive power management strategies, is also presented. The microgrid eigen structure, based on the developed model, is used to 1) investigate the microgrid dynamic behavior, 2) select control parameters of DG units, and 3) incorporate power management strategies in the DG controllers. The model is also used to investigate sensitivity of the design to changes of parameters and operating point and to optimize performance of the microgrid system. The results are used to discuss applications of the proposed power management strategies under various microgrid operating conditions

Power Management Strategies for a Microgrid With Multiple Distributed Generation Units

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operation.

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Multiphase induction motor drives - : a technology status review

The technique of vector space decomposition control of voltage source inverter fed dual three-phase induction machines is presented in this paper. By vector space decomposition, the analytical modeling and control of the machine are accomplished in three two-dimensional orthogonal subspaces and the dynamics of the electromechanical energy conversion related and the nonelectromechanical energy conversion related machine variables are thereby totally decoupled. A space vector PWM technique is also developed based on the vector space decomposition to limit the 5th, 7th, 17th, 19th,... harmonic currents which in such a system would be otherwise difficult to control. The techniques developed in this paper can be generalized for the control of an induction machine with an arbitrary number of phases. >

Space vector PWM control of dual three phase induction machine using vector space decomposition

This paper focuses on direct torque control (DTC) for three-phase AC electric drives. A novel model predictive control scheme is proposed that keeps the motor torque, the stator flux, and (if present) the inverter's neutral point potential within given hysteresis bounds while minimizing the switching frequency of the inverter. Based on an internal model of the drive, the controller predicts several future switch transitions, extrapolates the output trajectories, and chooses the sequence of inverter switch positions (voltage vectors) that minimizes the switching frequency. The advantages of the proposed controller are twofold. First, as underlined by the experimental results in the second part of this paper, it yields a superior performance with respect to the industrial state of the art. Specifically, the switching frequency is reduced by up to 50% while the torque and flux are kept more accurately within their bounds. Moreover, the fast dynamic torque response is inherited from standard DTC. Second, the scheme is applicable to a large class of (three-phase) AC electric machines driven by inverters.

Model Predictive Direct Torque Control—Part I: Concept, Algorithm, and Analysis

Preface.Basic Principles for Electric Machine Analysis.Direct--Current Machines.Reference--Frame Theory.Symmetrical Induction Machines.Synchronous Machines.Theory of Brushless dc Machines.Machine Equations in Operational Impedances and Time Constants.Linearized Machine Equations.Reduced--Order Machine Equations.Symmetrical and Unsymmetrical 2--Phase Induction Machines.Semicontrolled Bridge Converters.dc Machine Drives.Fully Controlled 3--Phase Bridge Converters.Induction Motor Drives.Brushless dc Motor Drives.Appendix: Trigonometric Relations, Constants and Conversion Factors, and Abbreviations.Index.

Analysis of electric machinery and drive systems

Originally published in 1986 by McGraw-Hill. Focusing on the areas of electric power and electric drives, this advanced text and industry reference emphasizes analysis and formulation for control applications and computer simulation. Annotation copyright Book News, Inc. Portland, Or.

Analysis of Electric Machinery

The steps in t he applied voltages of a three-phase, inverter-induction motor drive system cause undesirable pulsations in motortor By using multiple inverters connected to a multiphase machine with appropriate winding displacements, significant improvement in system performance is possible. The winding displacements required, however, are not necessarily the symmetrical displacements used in standard multiphase machines. This paper sets forth an improved method for analyzing many types of unsymmetrical, as well as symmetrical, multiphase induction machines. The simulation of a 7.5-hp induction machine with two three-phase sets of stator windings fed from two six-step inverters illustrates the application of the method of analysis and shows how the machine torque characteristic may be improved by proper spacing of the winding sets.

Induction Machine Analysis for Arbitrary Displacement Between Multiple Winding Sets

PREFACE xi 1 MAGNETIC AND MAGNETICALLY COUPLED CIRCUITS 1 2 ELECTROMECHANICAL ENERGY CONVERSION 49 3 DIRECT-CURRENT MACHINES 97 4 WINDINGS AND ROTATING MAGNETOMOTIVE FORCE 145 5 INTRODUCTION TO REFERENCE-FRAME THEORY 185 6 SYMMETRICAL INDUCTION MACHINES 213 7 SYNCHRONOUS MACHINES 287 8 PERMANENT-MAGNET ac MACHINE 345 9 STEPPER MOTORS 415 10 UNBALANCED OPERATION AND SINGLE-PHASE INDUCTION MOTORS 451 APPENDIX A ABBREVIATIONS, CONSTANTS, CONVERSIONS, AND IDENTITIES 477 APPENDIX B MATRIX ALGEBRA 481 APPENDIX C THREE-PHASE SYSTEMS 489 INDEX 493

Electromechanical motion devices

In this paper, a new control strategy is proposed which is simple in structure and has the straightforward goal of minimizing the stator current amplitude for a given load torque. It is shown that the resulting induction motor efficiency is reasonably close to optimal and that the approach is insensitive to variations in rotor resistance. Although the torque response is not as fast as in field-oriented (FO) control strategies, the response is reasonably fast. In fact, if the mechanical time constant is large relative to the rotor time constant, which is frequently the case, the sacrifice in dynamic performance is insignificant relative to FO strategies.

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Paul C. Krause

Papers

Analysis of electric machinery and drive systems

Analysis of Electric Machinery

Induction Machine Analysis for Arbitrary Displacement Between Multiple Winding Sets

Electromechanical motion devices

A maximum torque per ampere control strategy for induction motor drives