In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

An introduction to heat transfer

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 investigates diagnostic techniques for electrical machines with special reference to induction machines and to papers published in the last ten years. A comprehensive list of references is reported and examined, and research activities classified into four main topics: 1) electrical faults; 2) mechanical faults; 3) signal processing for analysis and monitoring; and 4) artificial intelligence and decision-making techniques.

Advances in Diagnostic Techniques for Induction Machines

This paper presents the comparative study and optimal design of a transverse flux linear machine with different PM configurations, viz. surface-mounted and consequent-pole, in which the consequent-pole version is firstly proposed. Firstly, the effect of variation of the main design parameters on both topologies are studied. Then, the multi-objective optimization method based on genetic algorithm combined with response surface methodology (RSM) is adopted to realize the optimal design of these two topologies and Pareto front solutions will be obtained. Finally, the characteristics of these two topologies are analyzed and compared, with particular regard to the advantages and disadvantages of the consequent pole topology.

/pdf/comparative-study-and-optimal-design-of-alternative-pm-2txm9djdur.pdf

Comparative study and optimal design of alternative PM configuration transverse flux linear machine

Electrical machine rotor shielding has been proposed for high-speed electrical machines, ie, ≥50krpm, where a smooth current waveform becomes difficult and costly to generate due to the required high switching frequency The rotor shielding is used to suppress the unsynchronized low order high amplitude current harmonics and consequently reduces the induced eddy-current losses in rotor For moderate speed machines, 10–40krpm, generally suited for automotive applications, a smooth current waveform is possible to generate, however, fast switching devices are required that increases the overall drive cost In the paper, a feasibility study of low cost electrical drive is presented The electrical drive consists of low cost, low switching frequency modules to generate a pulse width modulation (PWM) current waveform with a few switching pulses, and a rotor with electromagnetic shield to reduce the losses to an acceptable level The feasibility study includes two permanent magnet machines (PMMs) with different rotors Multi-physics results are obtained and compared to illustrate the feasibility of the proposed drive

/pdf/electrical-machine-rotor-shielding-for-low-cost-electrical-2xiwl5i7q1.pdf

Electrical Machine Rotor Shielding for Low Cost Electrical Drive

This paper compares in detail electrical machine technologies for an electrically-assisted turbocharger used with a high-horsepower marine engine. The machine is required to be used both as a motor to improve engine transient characteristics and as a generator for recovering energy (turbocompounding). The application translates to machine operation at high-power(150kW), and high-speeds with a constant power-speed range (CPSR) of 2 (25–50krpm). In this research Permanent Magnet Machines (PMSM), Induction Machines (IM) and Switched Reluctance Machines are compared in detail over a number of considerations, including the thermal performance, size, torque quality, kVA rating, and cost with the aim of identifying the most appropriate technology. In light of the technical and market requirements, an induction machine including novel materials is proposed and prototyped for the application.

Comparison of electrical machines for use with a high-horsepower marine engine turbocharger

In applications that require a high availability and high performance (for example aerospace),modular power electronics and multi-phase machines represent an advantageous choice. In this framework, a control system able to handle a high number of PWM signals and communication interfaces as well as featuring a high computational power is required. This paper proposes a novel HDL plus soft-core approach to be implemented on System-on-Chip hardware which allows for the efficient and modular implementation of the modern control techniques with strong guarantees in terms of determinism. The proposal lies in the adoption of a very simplified and optimized floating-point soft-core, the femtocore (fCore) and its tool-chain, which allows C-like implementation of complex algorithms in a HDL-design power electronics control framework. Several fCore units can be arranged for parallel processing to handle the time requirements of a complex modular system even with low sampling time (100 kHz or more). The proposed architecture is experimentally validated in a proof-of-concept, six-phase electric machine including a comparison against a traditional method.

/pdf/femtocore-an-application-specific-processor-for-vertically-3nia8ot701.pdf

Femtocore: An Application Specific Processor for Vertically Integrated High Performance Real-Time Controls

The paper reports on the development of a spherical induction actuator with multiple degrees of freedom (DOFs). Based on the previous research, the paper presents the concept design of the multi-DOF spherical induction motor which is applied for the attitude control of microsatellites. The structure and working principle are illustrated in detail, including the designs of the stator and rotor. The rotor can rotate around any axis by the combination of the stators of three DOFs. In order to analyze the three-dimensional distribution of electromagnetic field, a three-dimensional model is built using finite-element analysis tool. Based on the numerical analysis, the influence of different parameters on output torque is also obtained. Moreover, the analyzed results can provide great benefits for the structure optimization.

Chris Gerada

Papers

Comparative study and optimal design of alternative PM configuration transverse flux linear machine

Electrical Machine Rotor Shielding for Low Cost Electrical Drive

Comparison of electrical machines for use with a high-horsepower marine engine turbocharger

Femtocore: An Application Specific Processor for Vertically Integrated High Performance Real-Time Controls

Development and structure of multi-DOF spherical induction motor