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.

/pdf/multiphase-induction-motor-drives-a-technology-status-review-1ir91893ja.pdf

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

Testing the high-power machines in general is not an easy task. One of the standard tests is the full-load test. This test typically requires another machine, of the same or higher power rating, to be coupled to the tested one. For multiphase machines, which are commonly designed for high-power applications, this test can be conducted in a different way. In order to simplify full-load test, this paper proposes a new method that is applicable for multiple three-phase machines with even number of neutral points. The method is based on indirect rotor-field oriented control. It enables evaluation of the efficiency and the thermal design in the case of synchronous machines and the segregation of the constant and stator variable losses for induction machines, without the need for coupling another machine as a load. In the presented method, the full-load test conditions on the stator are obtained by circulating the rated active power flow in a closed loop from one winding set to another. The only power used during the test is to cover machine and converter losses. The proposed control scheme is unique and is based around y -component from the vector space decomposition subspace. It is validated through the simulation and experimental results.

/pdf/regenerative-test-for-multiple-three-phase-machines-with-15edf03vbs.pdf

Regenerative Test for Multiple Three-Phase Machines With Even Number of Neutral Points

This paper investigates an enhanced field-oriented control method for a two-pole surface permanent magnet synchronous machine (PMSM) with a symmetrical nine-phase winding configuration and a single neutral point. Magnets on the rotor are shortened, reducing cost of the machine, but cause production of highly non-sinusoidal back-electromotive force (EMF). FFT analysis of the EMF reveals a high third harmonic component, which is almost equal in magnitude to the fundamental. By investigating possible torque improvements using FEM software simulations, it was shown previously that, if controlled under optimal third harmonic current injection, the electromagnetic torque of the studied PMSM can be improved by up to 36%. The optimal current harmonic injection ratio between the fundamental and the third harmonic is determined first in this paper, using the maximum torque-per-ampere method (MTPA). An enhanced high-performance field-oriented control (FOC) algorithm to control a nine-phase non-sinusoidal back-EMF PM synchronous machine is devised next. The developed improved control algorithm is verified using simulation studies and further validated using an experimental prototype.

Control of a Symmetrical Nine-phase PMSM with Highly Non-Sinusoidal Back-Electromotive Force Using Third harmonic Current Injection

An asymmetrical six-phase induction motor drive can be realised with either one or with two isolated neutral points. Each of the two possibilities has its own merits and shortcomings, which are reviewed in the paper. Further, the performance of these configurations is compared, using waveforms and spectra of the phase voltage and current, obtained by simulations and experimentally. Total harmonic distortion (THD) of the phase voltage and current is also calculated as a function of the modulation index and is used as a figure of merit. It is concluded that the drive with two isolated neutral points offers better phase voltage and current THDs, but is inferior from the point of view of post-fault control.

Performance of an asymmetrical six-phase induction machine in single-and two-neutral point configurations

Finite-control-set model predictive control (FCS-MPC) of a five-phase induction motor is investigated in the paper. The predictive controller is operated in the rotor flux oriented reference frame and the predictive current control scheme includes both d-q flux/torque producing current components and non-flux/torque producing x-y current components in the cost function to minimise additional winding losses. All the available switching states (32 in total) are included in the optimization process. Impact of the x-y currents' weighting factor (W xy ) and stator fundamental frequency on the average values in both the primary and the secondary plane and on the phase current ripple are investigated using simulation. Next, the predictive control scheme is further verified experimentally. It is shown that the FCS-MPC regulates the axis currents instantaneously following reference changes, without any disturbance in other axis currents.

Experimental evaluation of model predictive current control of a five-phase induction motor using all switching states

The paper develops for the first time a space vector PWM technique for a seven-phase, three-level voltage source inverter (VSI), based on vector space decomposition (VSD). The algorithm represents an extension of a recently introduced VSD-based space vector algorithm for a three-level five-phase VSI. However, due to the increase of the phase number from five to seven, which simultaneously increases the number of planes that have to be considered from two to three and the number of switching states from 35 = 243 to 37 = 2187, the development of the space vector PWM is here much more involved. Using the ordering-per-sector law in time domain, the number of switching states that have to be considered is reduced to an acceptable number of 297. Choice of switching sequences and division of sectors into sub-sectors are further done in such a manner that space vector projection cancelation in the second and the third plane is achieved, where the references are zero. Each of the fourteen sectors in the first plane (with non-zero reference) is divided into 18 sub-sectors, meaning that each sector is characterised with 18 specific switching sequences. Developed space vector PWM method requires a lot of preliminary calculations for selection of sequences and for sub-division of sectors, but the algorithm is rather straightforward. Once when the appropriate constants have been established, development of the software for real-time implementation is simple. Validity and implementation simplicity of the proposed algorithm are proved at this stage by simulations.

http://ieeexplore.ieee.org/iel5/6014782/6020091/06020169.pdf

Martin Jones

Papers

Regenerative Test for Multiple Three-Phase Machines With Even Number of Neutral Points

Control of a Symmetrical Nine-phase PMSM with Highly Non-Sinusoidal Back-Electromotive Force Using Third harmonic Current Injection

Performance of an asymmetrical six-phase induction machine in single-and two-neutral point configurations

Experimental evaluation of model predictive current control of a five-phase induction motor using all switching states

A space vector PWM algorithm for a three-level seven-phase voltage source inverter