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 addresses to some of the latest contributions on the application of Finite Control Set Model Predictive Control (FCS-MPC) in Power Electronics. In FCS-MPC , the switching states are directly applied to the power converter, without the need of an additional modulation stage. The paper shows how the use of FCS-MPC provides a simple and efficient computational realization for different control objectives in Power Electronics. Some applications of this technology in drives, active filters, power conditioning, distributed generation and renewable energy are covered. Finally, attention is paid to the discussion of new trends in this technology and to the identification of open questions and future research topics.

State of the Art of Finite Control Set Model Predictive Control in Power Electronics

This paper presents an overview of motor drive technologies used for safety-critical aerospace applications, with a particular focus placed on the choice of candidate machines and their drive topologies. Aircraft applications demand high reliability, high availability, and high power density while aiming to reduce weight, complexity, fuel consumption, operational costs, and environmental impact. New electric driven systems can meet these requirements and also provide significant technical and economic improvements over conventional mechanical, hydraulic, or pneumatic systems. Fault-tolerant motor drives can be achieved by partitioning and redundancy through the use of multichannel three-phase systems or multiple single-phase modules. Analytical methods are adopted to compare caged induction, reluctance, and PM motor technologies and their relative merits. The analysis suggests that the dual (or triple) three-phase PMAC motor drive may be a favored choice for general aerospace applications, striking a balance between necessary redundancy and undue complexity, while maintaining a balanced operation following a failure. The modular single-phase approach offers a good compromise between size and complexity but suffers from high total harmonic distortion of the supply and high torque ripple when faulted. For each specific aircraft application, a parametrical optimization of the suitable motor configuration is needed through a coupled electromagnetic and thermal analysis, and should be verified by finite-element analysis.

Overview of Electric Motor Technologies Used for More Electric Aircraft (MEA)

This paper presents a comprehensive study on the state-of-the-art and emerging wind energy technologies from the electrical engineering perspective. In an attempt to decrease cost of energy, increase the wind energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the electric generators and power electronic converters have emerged in a rigorous manner. From the market based survey, the most successful generator-converter configurations are addressed along with few promising topologies available in the literature. The back-to-back connected converters, passive generator-side converters, converters for multiphase generators, and converters without intermediate dc-link are investigated for high-power wind energy conversion systems (WECS), and presented in low and medium voltage category. The onshore and offshore wind farm configurations are analyzed with respect to the series/parallel connection of wind turbine ac/dc output terminals, and high voltage ac/dc transmission. The fault-ride through compliance methods used in the induction and synchronous generator based WECS are also discussed. The past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory. The important survey results, and technical merits and demerits of various WECS electrical systems are summarized by tables. The list of current and future wind turbines are also provided along with technical details.

High-Power Wind Energy Conversion Systems: State-of-the-Art and Emerging Technologies

Multimotor drives, based on utilization of multiphase machines, have been proposed recently. Independent vector control of all the machines of the group can be achieved while using a single multiphase voltage source inverter supply, provided that the stator windings are connected in series in an appropriate manner. The concept is applicable to any system phase number greater than or equal to five. Detailed theoretical and simulation studies have been reported for multiphase multimotor drive configurations of this type and it has been suggested that the concept is valid regardless of the type of ac machines. This paper examines operation of such a drive system when a five-phase induction machine is connected in series with a five-phase synchronous reluctance machine and provides detailed experimental verification of the possibility of independent control of the two-motor drive comprising five-phase motors of different types. The operating principles of the drive system are at first reviewed and a brief description of the experimental system is then given. An extensive presentation of experimental results, collected from a laboratory setup, is further provided. It is shown that fully independent and decoupled vector control of the two machines results, although a single supply source is used.

Induction Machine/Syn-Rel Two-Motor Five-Phase Series-Connected Drive

Open-end winding variable speed drives with dual-inverter supply have been extensively investigated for various applications, including series hybrid powertrains and propulsion motors. The existing body of work is restricted to the three-phase electric machinery. This paper looks at the possibility of using machines with higher phase numbers in an open-end winding configuration with dual multiphase inverter supply for these applications. Switching states for various phase numbers are considered first. Next, a study of the existing space vectors in a five-phase dual-inverter drive configuration is undertaken. This is followed by the discussion of the possible approaches to PWM control of such a drive system. Some simulation results for one particular PWM technique are finally reported.

A multiphase dual-inverter supplied drive structure for electric and hybrid electric vehicles

This paper studies pulse-width modulation (PWM) techniques suitable for a four-level five-phase open-end winding (OeW) drive. The drive comprises a five-phase induction machine, supplied using two two-level voltage source inverters (VSIs) with isolated and unequal dc-link voltages, in the ratio 2:1. A decoupled carrier based (CB) PWM modulation strategy, based on unequal voltage reference sharing between the two converters, is introduced in this paper. The stability of dc-link voltages in OeW drives is investigated next, using a novel analysis technique. Several modulation methods are analysed and the results show that application of the coupled pulse width modulation technique, with carriers having in-phase disposition (PD), leads to overcharging of the capacitor in the dc-link of the inverter intended to operate with the lower dc-link voltage. On the other hand, the proposed decoupled CB PWM scheme naturally eliminates the dc-link capacitor overcharging problem. These findings are verified experimentally, using open-loop V/f control. Two different decoupled CB modulation methods are compared and the best performing modulation method is selected and incorporated further into an OeW drive with field-oriented control (FOC). The presented steady state and transient experimental results demonstrate that the decoupled CB PWM technique is suitable for high performance variable speed drive applications.

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Decoupled PWM Control of a Dual-Inverter Four-Level Five-Phase Drive

The paper considers on-board battery charging of electrical vehicles (EV) using a three-phase voltage source and a nine-phase propulsion motor. The nine-phase inverter and induction machine are fully integrated into the charging process. The proposed integrated on-board battery charger has an advantage of unity power factor operation with no torque production in the machine during the charging mode. Moreover, there is no need for any hardware reconfiguration between the charging and propulsion mode. The principle of the charging mode operation is based on the additional degrees of freedom that exist in nine-phase machines and that can be conveniently utilized to achieve charging through the machine's stator windings with zero electromagnetic torque. Detailed theoretical analysis is reported for asymmetrical and symmetrical nine-phase systems. For both systems control in the charging mode is discussed, and the theoretical considerations are validated by simulations.

On-board integrated battery chargers for electric vehicles using nine-phase machines

Multilevel drive supply can be realised in two different ways, by using either a conventional multilevel single-sided supply configuration or with a dual-inverter supply topology. The second structure is simpler for practical realisation, since the problem of capacitor voltage balancing does not arise. This paper develops a space vector PWM (SVPWM) algorithm for the dual-inverter six-phase supply, based on two two-level six-phase voltage source inverters (VSIs), feeding a symmetrical six-phase load. In the algorithm, each inverter is controlled using SVPWM technique that was previously developed for a single-sided supply configuration. A multilevel output voltage is produced for a certain range of modulation index. The performance of the algorithm is verified through simulations and experiments.

Martin Jones

Papers

Induction Machine/Syn-Rel Two-Motor Five-Phase Series-Connected Drive

A multiphase dual-inverter supplied drive structure for electric and hybrid electric vehicles

Decoupled PWM Control of a Dual-Inverter Four-Level Five-Phase Drive

On-board integrated battery chargers for electric vehicles using nine-phase machines

A six-phase multilevel space vector PWM algorithm for a dual-inverter supplied drive