In electrical machine design, thermal management plays a key role in improving performance and reducing size. End-windings are commonly identified as the machine hot-spot. Hence, lowering and predicting end-windings temperature are crucial tasks in thermal management of electrical machines. This paper proposes and investigates a non invasive but effective cooling method that aims for a uniform cooling of a machine's winding by implementing direct cooling on its end-windings. Modelling and experimental results show that a 25% hot-spot temperature reduction on a particular application can be achieved. To analyse the proposed technique in detail, an accurate but computationally-economic lumped parameter thermal network is developed. Comparison between a ‘standard’ thermal network and its simplified equivalent (with less nodes) is presented where the models are developed and fine tuned based on experimental data. All the above is used to investigate the potential of the proposed end winding cooling method with different configurations of the methodology.

Synchronous reluctance (Syn-Rel) machines with embedded permanent magnets (PMs) are research hotspots in variable speed motor drives due to their robust rotor structure and wide constant power speed range (CPSR). In this paper, the potential of PM-assisted Syn-Rel machine to be next generation heavy duty traction motor solution has been investigated, with special attention put on one key geometric parameter, i.e., airgap length. Careful machine design and optimization has been conducted based on geometric parametrization including airgap length variation, for 15000rpm peak speed and 350kW peak power output. In low speed operations, the influence of airgap length on different torque components has been analyzed in detail based on the frozen permeability method. In field weakening region, the variation trend of several key parameters such as output power, torque ripple, and power losses have been investigated along with airgap length. It is found that with high electric and magnetic loading, reducing the electromagnetic airgap length is not always beneficial. There exists a suitable airgap length value to comprehensively balance torque/power density, cooling capability, efficiency and reliability. Numerical FEA and experimental tests of the prototype are combined to verify the conclusions.

Automotive applications require electrical machines designed for high torque density, wide speed range and low cost. NdFeB magnets can achieve the high torque density and wide speed range, however, they have a high cost. Therefore, this paper explores the capability of rare-earth-free design through a PM-assisted synchronous reluctance motor (PM-SynRel). A PM-SynRel design with NdFeB has been used in this study where the NdFeB magnets have been replaced with ferrite magnets. Then, several modifications on the rotor have been made to ensure mechanical safety. Thermal analysis has been conducted last to evaluate the temperatures in the different machine parts to avoid exceeding the required limits. Finally, a prototype has been made and tested to validate the simulation results.

A close functional and structural integration of passive elements is required to improve the power density of motor drives. Such power dense motor drives are prerequisite in aerospace and automotive applications. This paper presents a permanent magnet motor with integrated filter inductor, which not only eliminates inductor losses but also removes its associated weight and volume. The motor with integrated filter uses motor's inherent magnetics in order to use it as a filter inductance instead of adopting an external inductor option, which is traditionally placed outside the motor. A vector-controlled model, taking modulation and switching effect into account, has been developed by using MATLAB/Simulink tool. To experimentally validate the concept of the motor with integrated filter inductor, the winding connections of an existing motor are modified. The comparative analysis, between the traditional and integrated motor drive systems, is carried out in terms of magnitude of switching component, total system losses, weight and volume. The total losses in the motor with integrated filter are reduced by 34.2% at 2100rpm and 3Nm load, when compared to the motor with traditional filter inductor, whereas, its weight and volume in the motor with integrated filter inductor is eliminated completely.

This paper presents design optimization of a short-term duty electrical machine for extreme environments of high temperature and high altitudes. For such extreme environmental conditions of above 80°C and altitudes of 30 km, thermal loading limits are a critical consideration in machines, especially if high power density and high efficiency are to be achieved. The influence of different material on the performance of such machines is investigated. Also, the effect of different slot and pole combinations are studied for machines used for such extreme operating conditions but with short duty. In the research, a nondominated sorting genetic algorithm (NSGAII) considering an analytical electromagnetic model, structural and thermal model together with finite element methods are used to optimize the design of the machine for such environments achieving high efficiencies and high power density with relatively minimal computational time. The adopted thermal model is then validated through experiments and then implemented within the genetic algorithm. It is shown that, generally, 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 current loading and thus, significant weight reduction can be achieved.