Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

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

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

This paper presents transformerless multilevel power converters as an application for high-power and/or high-voltage electric motor drives. Multilevel converters: (1) can generate near-sinusoidal voltages with only fundamental frequency switching; (2) have almost no electromagnetic interference or common-mode voltage; and (3) are suitable for large voltampere-rated motor drives and high voltages. The cascade inverter is a natural fit for large automotive all-electric drives because it uses several levels of DC voltage sources, which would be available from batteries or fuel cells. The back-to-back diode-clamped converter is ideal where a source of AC voltage is available, such as in a hybrid electric vehicle. Simulation and experimental results show the superiority of these two converters over two-level pulsewidth-modulation-based drives.

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Multilevel converters for large electric drives

This paper explores the fundamental limitations of the neutral-point voltage balancing problem for different loading conditions of three-level voltage source inverters. A new model in the DQ coordinate frame utilizing current switching functions is developed as a means to investigate theoretical limitations and to offer a more intuitive insight into the problem. The low-frequency ripple of the neutral point caused by certain loading conditions is reported and quantified.

A comprehensive study of neutral-point voltage balancing problem in three-level neutral-point-clamped voltage source PWM inverters

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

A new force commutated three level boost type rectifier is proposed in this paper. The rectifier has the characteristics of drawing nearly sinusoidal current from utility with unity fundamental power factor. High reliability is possible due to its shoot-through free structure. A doubled dc bus voltage compared to a normal two-level rectifier is also possible because of the neutral point clamping. The operating principle, steady state analysis, input current and neutral point voltage control schemes, as well as detailed experimental results are presented in this paper.

Force commutated three level boost type rectifier

The marriage of a three-level voltage source inverter with a force-commutated three-level rectifier is examined in this paper. Three-level inverters are capable of reducing the output current harmonics dramatically compared with typical two-level inverters whereas a three-level rectifier of this type allows nearly sinusoidal input currents at unity fundamental power factor on the utility side of the drive system. The dual capacitor split voltage bus can be regulated from either the inverter or rectifier side with neutral point balance maintained. This paper address the issues of neutral point voltage control and current regulation from both the rectifier and inverter perspectives. >

Current control of a 3-level rectifier/inverter drive system

This paper presents the principles of operation, design and transient analysis of a newly developed single phase doubly salient permanent magnet (DSPM) generator. Design equations, finite element, and dynamic analysis of the new generator are described. The single phase DSPM generator has an extremely simple structure with two permanent magnets and four poles wound equipped with armature windings. The rotor of the variable reluctance machine has six poles and is laminated iron without windings. Both stator and rotor have a salient pole structure. Hence, the machine has the inverse geometry of recently reported three phase DSPM motor topologies. >

A novel doubly salient single phase permanent magnet generator

A new variable reluctance motor is introduced to help solve the energy circulation problems which exist during commutation in conventional variable reluctance motors (VRM's). The new motor design enables the energy stored in the magnetic field to be retained and utilized within the motor, instead of being returned to the source. The operating principles of the motor and associated converters are presented. The analysis shows that by employing both short pitch and full pitch windings, this new motor can eliminate the two problems without extra conductors in the slots. As a result, the new motor has the following important performance advantages over conventional VRM's: (1) It allows a significant improvement in the turn-off process and therefore allows higher speed capacity; (2) it has higher output with the same or higher efficiency with the same output because of the improvement on the turn-off performance and due to the utilization of the trapped energy; (3) the machine can have a higher output with the same power converter because of the improvement of the energy conversion ratio.

Yifan Zhao

Papers

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

Force commutated three level boost type rectifier

Current control of a 3-level rectifier/inverter drive system

A novel doubly salient single phase permanent magnet generator

A doubly salient doubly excited variable reluctance motor