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

A stator comprises an inner stator component 10 comprising an annular base portion 12 and a plurality of teeth 14 extending radially outwards and defining slots for stator windings 24. An outer stator component 20, which may form a back iron, is arranged to surround the inner stator component 10. The stator is assembled by first inserting the stator windings into the slots in the inner stator component, and then inserting the inner stator component with the stator windings in place into the outer stator component. The teeth of the inner stator may engage slots in the outer stator to prevent relative rotation between the stator parts. The windings may be preformed and comprise concentrated or distributed windings. The teeth may have parallel or divergent sides and may extend at an angle to the radius and may be straight or curved.

Two part stator for an electrical machine

This paper first identifies and quantifies the saliency components in symmetric permanent magnet synchronous machines. The saliency component dependence on the geometry and operating regime of the machine will be investigated in an effort to set out guidelines for machine and control design of these type of machines.

Permanent Magnet Synchronous machines for Saliency-based, Self-Sensored Motion Control

The increasing demand for high speed, direct drive systems is driving a significant research effort on high speed electrical machines. Thermal management becomes a significant aspect to deal with as power loss per cooling surface area reduces as speed increases. Solid rotor induction machines are often considered at the high end of the speed spectrum as they offer a mechanically robust rotor structure. The current density distribution within their rotor structure typically results in high rotor losses and a significant portion of the total machine losses. In such machines the current distribution in the rotor itself is highly dependent on the rotor resistance and hence on the rotor temperature distribution. This paper will detail an effective model coupling both the electromagnetic and thermal domains to simulate operation of solid rotor induction machines.

Thermal-electromagnetic analysis of solid rotor induction machine

This paper presents an analytical tool to generate torque vs speed characteristics of the surface-mounted permanent magnet machines to minimize the computation time and efforts. The paper also derives an expression of d-axis current in the field weakening region while the stator resistance effect takes into account in order to evaluate the phase advance angles for the motor control. Finally, the results of the analytical tool have been compared with the MotorCAD software which gives less than 1% discrepancies in the results.

/pdf/analytical-tool-to-generate-torque-speed-characteristics-for-5bwuk0t9ce.pdf

Analytical Tool to Generate Torque-Speed Characteristics for Surface Mounted PM Machines in Constant Torque and Field Weakening Regions

In recent years, the field-metric method for measuring the joule losses set up in an electrical steel laminate when subjected to a rotating field has gained popularity. The ideal geometry of the magnetiser required to set up such a field is still however the subject of much debate. The work presented in this paper aims at providing some useful guidelines which might be considered when undertaking the construction of the simplest of such magnetizing setups having four salient poles excited by a two phase system and using a square sample. A 3D model for this rotational power loss tester was simulated for different pole geometries with the induction uniformity being assessed for every alteration.

/pdf/an-investigation-into-the-geometric-parameters-affecting-47yh91nqlo.pdf

Chris Gerada

Papers

Two part stator for an electrical machine

Permanent Magnet Synchronous machines for Saliency-based, Self-Sensored Motion Control

Thermal-electromagnetic analysis of solid rotor induction machine

Analytical Tool to Generate Torque-Speed Characteristics for Surface Mounted PM Machines in Constant Torque and Field Weakening Regions

An investigation into the geometric parameters affecting field uniformity in four pole magnetisers