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.

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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

Synchronous reluctance (SynRel) machines with improved saliency ratio can be realized using bi-state magnetic material (BSMM) in the rotor. However, a significantly higher number of localized heat treatments are required on the BSMM to maximize its effectiveness on being used in the conventional SynRel rotor structure. The cumbersome manufacturing process and its associated cost renders the conventional SynRel rotor topology as an impracticable solution for exploiting the benefits of BSMM. Therefore, it is essential to identify alternate SynRel rotor structures which can effectively utilize the advantages of BSMM with reduced manufacturing related complexity. Consequently, a 3 kW, 90 krpm high-speed sleeve rotor SynRel machine having a retaining sleeve of BSMM is analysed in this paper. The proposed rotor structure offers 26% more torque with a reduced manufacturing related complexity compared to conventional SynRel rotor with BSMM. Further, 3D simulations are performed to understand the impact of eddy current on the electromagnetic performance of sleeve rotor SynRel machine with BSMM sleeve.

Improving Saliency of High-Speed Synchronous Reluctance Machine Using Rotor Sleeve made of Bi-State Magnetic Material

As one of the most important kinds of distributed generation systems, the micro turbine generation system can be flexibly installed near the end user, and becomes an important trend of development in DGS gradually. The high speed permanent magnetic generator (HSPMG) can be properly applied in a micro turbine generation system and benefits the system from high efficiency, high power density, simple structure, and good reliability [1]. For this kind of machine, to protect and fix the rotor and magnets under a large centrifugal during the high speed operating, a sleeve is often added to rotor outer surface, and metal sleeves are usually implemented [2,3].

A kind of alloy designed for HSPMG rotor sleeve

A permanent magnet conical motor comprises a stator whose inner surface has a cone shape and a rotor having a truncated cone shape where a cone angle of the rotor is the same as a cone angle of the stator. The rotor may have a permanent magnet and rotate axially with respect to the stator. A spring mounted on a shaft of the rotor may negate an axial force produced by the magnet when the motor is not energized. The spring elasticity coefficient may be based on the axial force produced by the magnet when the motor is at no load. The cone angle may be calculated based on torque demand and an axial force required for an axial movement. When energized, a force acting on the rotor has a normal component and a tangential component with respect to a rotor lateral surface, and the tangential component may be proportional to rotor torque and a shear stress produced on the surface. The rotor axial force may be determined according to magnet characteristics at no load, and the magnet characteristics are based on the torque demand.

Permanent magnet conical motors, stators and rotors thereof

Synchronous reluctance machines (SynRel) are becoming very attractive for different applications because of their reluctance nature, easy manufacturability and low cost. Their design still represents a challange because of the many degrees of freedom that their rotor structure presents. Furthermore, in order to obtain a design with defined electromagnetic characteristics and low torque ripple machine geometry is needed to be optimised. In this paper, three different optimisations are performed on 6 poles SynRel motor with three flux barriers per pole. The aim of the work is to show the effect of the objective selection on the optimization process. An automatic procedure has been applied coupling finite element analysis with an optimization algorithm that is working towards the competitive targets of maximazing the torque, while minimizing the torque ripple and losses. The effects of these objectives on the geometrical variables are investigated in detail. The outcome of the analysis show how the problem definition heavily affects the obtained results. This gives useful insights on how to approach SynRel rotor design.

/pdf/influence-of-optimisation-target-functions-on-synchronous-4fbjd2g2js.pdf

Influence of Optimisation Target Functions on Synchronous Reluctance Machines Design

Permanent magnet (PM) less electrical machines are required in electric assisted turbochargers (EATs). Synchronous reluctance (SynRel) machine is a good candidate considering it is rugged and magnet less rotor structure. Saliency of a high-speed SynRel machine is impacted more by q-axis inductance $(L_{q})$ in comparison to d-axis inductance $(L_{d})$. Lq depends on the saturation flux density in addition to other geometrical parameters of the ribs. The impact of saturation flux density on the electromagnetic performance of a 1 kW, 60 krpm high-speed SynRel machine is analysed in this paper by considering 6 different materials. The average torque is found to increase with a reduction in saturation flux density till the decrease in Lq dominates the decrease in Ld. Further, ribs operate at higher values of saturation flux density. Therefore, the average torque is determined by the saturated BH curve of the material in addition to the knee point.

Chris Gerada

Papers

Improving Saliency of High-Speed Synchronous Reluctance Machine Using Rotor Sleeve made of Bi-State Magnetic Material

A kind of alloy designed for HSPMG rotor sleeve

Permanent magnet conical motors, stators and rotors thereof

Influence of Optimisation Target Functions on Synchronous Reluctance Machines Design

Impact of Saturation Flux Density of Rotor Lamination on the Performance of 2-Pole High-Speed Synchronous Reluctance machine