The impact of electromagnetic interference (EMI) is an increasingly important aspect of the performance of switching inverters. The challenges of managing EMI continue to grow with the emergence of wide bandgap (WBG) devices, the trend towards ever-greater integration and higher power rating. This paper reviews suppression methods for the conductive common-mode (CM) EMI in inverter fed motor drives. In order to span EMI suppression across the full system design process, the review considers both mitigation from the sources and suppression along the conduction paths. Furthermore, the shortcomings and merits of the reviewed publications are discussed, and their attenuation frequency range and attenuation level are compared. It is demonstrated that the CM EMI at low frequency is mainly determined by the PWM strategies and can be reduced or even theoretically eliminated through zero common-mode control. On the other hand, the CM EMI at high frequency is markedly influenced by the switching transients of the power devices. Thus, various drive circuits are reviewed which improve the switching behavior. Finally, the deployment of passive and active filters to suppress or compensate for the EMI is discussed.

The market for electric motors is experiencing a step-growth due to their adoption across a range of industrial sectors. This increased demand also highlights the importance of end-of-life management of electric motors and a requirement for appropriate strategies for the high value materials embedded in them. This paper aims to offer a holistic view on the circular economy research for electric motors and the role of Industry 4.0 technologies by presenting the state-of-the-art available in literature and comparing it with the industrial perspective. The literature review revealed the absence of a methodology for selecting the best end-of-life scenario for industrial electric motors. Recycling, which is an end-of-product-life strategy, was found to be the key focus area of research. Reuse, which is a better strategy in terms of waste hierarchy, was the least researched area due to lack of information about the condition and availability of returned products. In order to capture the current landscape within the UK for the repair, remanufacture and recycling of electrical machines, a structured survey of UK based companies was conducted. The survey revealed that nearly half of the companies do not undertake any repair strategies for electrical machine components; however, there was an aspiration from the respondents to migrate their companies towards more sustainable activities. The industry survey and the review of existing literature led to the identification of research trends, challenges and recommendations for future research.

The converter switching in variable-frequency drives can generate high frequency common mode voltage between the machine winding and the converter ground, leading to high frequency parasitic currents which can flow through the machine bearings unless precautions are taken in design and installation. These parasitic and unintended currents in the bearings cause deterioration of the lubrication film and surface damage to the rolling elements of the bearings. These problems will be exacerbated as wide-bandgap semiconductors with faster switching rise times start becoming more widespread in variable-frequency drives. This paper reviews the modelling and mitigation techniques of high frequency bearing currents in inverter fed AC drives. It aims to provide a solid base for the research community to further understanding the bearing currents phenomenon and helping to find novel improved technique for their mitigation and measurement.

A novel asymmetric interior permanent magnet (AIPM) machine is proposed in this paper for electric vehicle application. It has a skewed V-shape permanent magnet (PM) cavity, two PMs with different dimensions and an additional flux barrier outside the V-shape cavity in each pole. This asymmetric rotor topology can inherently utilize the magnetic-field-shifting (MFS) effect to reduce the current angle difference between the maximum PM and reluctance torque components, thereby enhancing the maximum synthetic torque with the same PM usage. The influences of cavity positions in the proposed AIPM and an existing AIPM with extra flux barrier inside the V-shape cavity are compared, which indicates that the proposed structure with outside flux barrier has higher average torque. Both AIPM topologies are designed with the same stator, rotor diameter, and PM usage as the conventional V-shape IPM benchmark for Prius 2010. Electromagnetic, mechanical and steady-state thermal performance of three machines are compared. The results confirm that the proposed AIPM machine can achieve significant torque enhancement due to utilizing MFS effect, compared with the existing AIPM and the IPM benchmark. Finally, a small prototype of the proposed AIPM machine is designed, manufactured and tested to validate the FE analysis.

This paper proposes a novel spoke-type asymmetric interior permanent magnet (AIPM) rotor topology that employs an additional asymmetric flux barrier in each pole of IPM synchronous machines for torque density enhancement and torque pulsating suppression without introducing any extra cost. The proposed AIPM-I machine, an existing spoke-type AIPM-II machine with asymmetric rotor profile and a conventional spoke-type IPM machine are designed and optimized with the same 12-slot/8-pole stator with non-overlapping windings as well as the same rotor diameter and PM dimensions. The effect of asymmetric flux barrier dimensions on the proposed AIMP-I machine is investigated with particular emphasis on torque characteristics. The electromagnetic performance and rotor mechanical strength of final optimal designs of three machines are compared. It confirms that the proposed AIPM-I machine can achieve significant torque enhancement and torque ripple reduction across the wide current range while also shows significantly smaller cogging torque at open-circuit condition, compared with both existing AIPM-II and conventional IPM machines. Finally, a prototype of the proposed AIPM-I machine has been manufactured and measured for validation.

Consequent pole (CP) permanent magnet (PM) machines offer scope for reducing the quantity of PM material and hence cost compared to more conventional PM machine topologies of the same rating. In this type of machine, the rotor pole arc is usually optimized to realize the largest output torque with pole shaping methods used to reduce torque ripple. However, such approaches tend to be limited by constraints imposed on the pole shapes. It is a common practice to adopt similar PM and iron pole shapes, an approach that does not fully account for the different characteristics of PM and iron poles in CPPM machines, often leading to large even order harmonics in the airgap flux density. This article proposes a shaping method with a variable rotor profile and pole arc span being established by means of optimization by Genetic Algorithm. It is demonstrated that for a fixed quantity of PM material, different PM and iron pole shapes in combination with optimal PM and iron pole arc spans are essential for ensuring both maximum output torque and lower torque ripple when the due account is taken of flux leakage. It also demonstrates that since the flux density in the region under a PM pole is governed by the magnetic potential produced by magnets while it is governed by magnetic reluctance under iron pole, different PM pole and iron pole shapes are necessary to reduce the even-order harmonics in a CPPM machine and consequently to reduce torque ripple. The performances of optimized and more conventional CP machines are compared by finite-element method on 12-slot/8-pole prototype motors.