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

The aviation industry is tending towards more electric aircraft, replacing conventional pneumatic, hydraulic, and mechanical systems with electrical solutions. The electrification of actuators is motivated by increased efficiency, reduced maintenance and potential mass savings. Special considerations need to be made when designing an electric drive system with long feeder cables for aerospace. For a given actuation requirement, mass and volume need to be minimized while obeying thermal and reliability constraints. Fast switched high dV/dt voltages applied to a cable with poor machine-cable impedance matching can cause high-amplitude high-frequency voltage oscillations, potentially leading to corona discharge, insulation failure, high common-mode, differential-mode currents, bearing currents, and reduced system lifetime. Mitigation of these voltage oscillations can reduce and/or eliminate the problems associated with it. In this paper, the details of a high-level electric drive system design tool for component sizing and modelling is described. The designed system's mass, volume, reliability, and performance figures are produced. To demonstrate the sizing and design procedure, the results of a hypothetical 3kW fault-tolerant, multilane centralized electric drive system case study is presented. A LC inverter filter is used to mitigate transmission line effects due to long feeder cables.

/pdf/sizing-design-and-modelling-of-aerospace-electric-drive-18vnngctpo.pdf

Sizing, Design, and Modelling of Aerospace Electric Drive System with Long Feeder Cables

This paper investigates the influence of a constant carrier phase shift on the DC-link capacitor harmonic current of cascaded converters used in fuel-cell and mild-hybrid electric vehicles. In these applications, a DC-DC converter can be adopted between the battery and the motor drive inverter in a cascaded structure, where the two converters share the same DC-link. Since the DC-link capacitor of such a system represents a critical component, the optimization of the converter operation to limit the current stress and extend the lifetime of the capacitor is an primary objective. This paper proposes the use of a carrier phase shift between the modulations of the two converters in order to minimize the harmonic current of the DC-link capacitor. By harmonic analysis, an optimal carrier phase shift can be derived depending on the converter configuration. Analytical results are presented and validated by hardware-in-the-loop experiments. The findings show that the pulse width modulation carrier phase shift between the interleaved boost converter and the voltage source motor drive inverter has a significant influence on the DC-link capacitor current and thus on its lifetime. A case study with two-cell and three-cell interleaved boost converters shows a possible DC-link capacitor lifetime extension of up to 390%.

/pdf/common-dc-link-capacitor-harmonic-current-minimization-for-2qh75j5x.pdf

Common DC-Link Capacitor Harmonic Current Minimization for Cascaded Converters by Optimized Phase-Shift Modulation

Test Setup for multistress characterization of insulation degradation mechanisms in electric drives

Dynamic power decoupling for low-voltage ride-through of grid-forming inverters

This paper proposes two new techniques to improve the transient torque response in presence of axial saturation due to skewing of rotor slots in induction motors. The effect of skew is to cause significant air-gap flux path saturation at one axial-end element of the rotor, loss of flux, and, consequently, of drive performance. The induction motor operations with variable q-axis current command during rapid speed changes are studied with a 3 dimensional dynamic magnetic reluctance model (DMRM). The new techniques for compensation of flux loss regard the indirect rotor flux oriented (IRFO) control. The first technique is based on a modified omegaslip calculator, and the second one on a modified adaptive i-omega estimator. The paper proves the effectiveness of the two techniques and also shows the stator flux oriented sliding-mode (SFO-SM) control is low sensitive to the rotor bars skew effect and ensures high performance, without any accurate parameter tuning

Chris Gerada

Papers

Sizing, Design, and Modelling of Aerospace Electric Drive System with Long Feeder Cables

Common DC-Link Capacitor Harmonic Current Minimization for Cascaded Converters by Optimized Phase-Shift Modulation

Test Setup for multistress characterization of insulation degradation mechanisms in electric drives

Dynamic power decoupling for low-voltage ride-through of grid-forming inverters

Transient torque response improvement in presence of axial saturation due to skewing of rotor slots in induction motors