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 a comparison between hairpin and random distributed winding in electrical machines for automotive applications. Indeed, the overall performance of an electrical drive system is seriously affected by its winding design. The considered electrical machine has a peak power of 115kW and a maximum operating speed of 12000 rpm. Both cost and manufacturing aspects are here discussed in detail. Two different machine topologies have been investigated and Finite Element Analysis (FEA) results are presented and discussed. Then, the comparison between hairpin and random winding configuration in terms of AC copper losses are presented for the selected geometry. The accurate AC losses estimation can be done by modelling each single conductor. In order to significantly reduce the simulation time, a domain model reduction has been adopted. Based on two different driving cycles, Urban Dynamometer Driving Schedule (UDDS) and Highway Fuel Economy Test (HWFET), the AC losses have been evaluated. It is shown that horizontal pin segmentation can contribute to considerable AC loss reduction.

/pdf/rectangular-and-random-conductors-ac-losses-evaluations-and-295mu2p12d.pdf

Rectangular and Random Conductors: AC Losses Evaluations and Manufacturing Considerations

This paper investigates the accuracy of the subdomain modelling technique for high frequency copper loss calculation in stator windings of synchronous generators. The methodology’s accuracy is studied at a slot level up to 10 kHz against FE model with realistic conductor dimensions. The analysis demonstrates that improper conductor area representation and eddy current reaction negligence causes increasing error with increasing frequencies. A modified subdomain model is then proposed to address these challenges which has proven to show a good match with a corresponding FE model.

Analysis and Modelling of High Frequency Effects on Synchronous Generator’s Armature Conductors

The main purpose of this paper is to investigate the influence of winding location on back electromotive force (EMF) and armature inductance in flux-switching permanent-magnet (FSPM) machines. To obtain an analytical solution, a double-stator-pitch model is built based on the equivalent magnetic circuit method. Then, the open-circuit characteristics in FSPM machines with different winding layouts are analyzed by both the analytical model and finite-element-analysis method. The analysis reveals that winding inductance is easier influenced by the winding location than the permanent-magnet flux linkage and corresponding back EMF. Finally, the analytical and finite-element predictions are verified by experimental results.

The Influence of Winding Location in Flux-Switching Permanent-Magnet Machines

This paper looks at a novel optimisation approach to the design of surface mounted permanent magnet (SMPM) machines with self-sensing capabilities. A methodology will be presented which will look at the use of genetic algorithms (GA) to contemporarily maximise the output torque and the self sensing properties of such machines. A GA optimisation environment has been grafted with a finite element analysis (FEA) environment to enable the designer to account for both geometrical and saturation saliencies for an effective determination of the machine's self sensing characteristics. Satisfactory results were obtained in terms of torque maximization and self sensing capability. In addition sensitivity of the major geometrical parameters of the machine will be discussed in terms torque density and the self-sensing.

Permanent magnet motor design optimisation for sensorless control

This paper presents a design of a short term duty electrical machine working in an extreme environment consisting of 80°C ambient temperature and altitudes of over 30,000m. Higher power density is a key factor in the design wherein the machine's operation is required only for a short duty. The requirement of high power-to-weight and power-to-volume leads to a Permanent Magnet (PM) machine design, which is then optimized. Different slot and pole combinations, with both concentrated and distributed winding arrangements are considered. For the optimization, a Genetic Algorithm (GA) is used where analytical electromagnetic and thermal models are adopted together with Finite Element (FE) methods. It is shown that the adopted thermal model provides sufficient accuracy when predicting temperature rise within the winding. It is also shown that the designs are thermally limited where the pole numbers are limited by volt-amps drawn from the converter. The design consisting of a high slot number allows for improving the heat dissipation from the machine and thus, the weight can be minimized for the given torque production.

/pdf/short-term-duty-electrical-machines-21z4ke9ro9.pdf

Chris Gerada

Papers

Rectangular and Random Conductors: AC Losses Evaluations and Manufacturing Considerations

Analysis and Modelling of High Frequency Effects on Synchronous Generator’s Armature Conductors

The Influence of Winding Location in Flux-Switching Permanent-Magnet Machines

Permanent magnet motor design optimisation for sensorless control

Short term duty electrical machines