Multiphysics Design Optimisation and Analysis of a High-speed (100,000 RPM) Interior Permanent Magnet Machine

High-speed has always been a primary development direction for electric machines because of the constantly growing application area and the fact that high-speed can increase the power density by many folds. The interior permanent magnet synchronous machine (IPMSM) has many desirable characteristics, such as high efficiency, excellent controllability, extensive constant-power speed range (CPSR), additional reluctance torque, and lower risk of demagnetisation. Hence, the increase of the maximum speed of IPMSMs is getting substantial attention from both the industry and academia. However, in terms of the highest possible speed, the development of IPMSM is far behind most other types of electric machines. This is because of the conflicting characteristics between the electromagnetic performances and the mechanical robustness of the IPMSM rotor. The maximum speed achieved in laminated rotor IPMSMs is currently limited at 50,000 rpm and 1.5×105 rpm√kW, which is only 25% of what has been achieved by a laminated rotor induction machine. This research attempts to analyse the causes of the speed limit of IPMSM posed by its rotor mechanical strength. With a thorough understanding of the limits, this project proposes methods to mitigate these limitations via a multiphysics multi-objective optimisation. With the aid of the optimisation process, a novel IPMSM rotor topology capable of breaking the existing speed limit of 50,000 rpm and increasing the rpm√kW to 2.24×105 was developed. The thesis presents the detailed analysis, design optimisation, and development of the prototype high-speed IPMSM. The conventional distributed winding is selected because it allows reduced rotor core loss at high speeds. The feasibility of applying the conventional IPMSM rotor topologies such as the flat-, V-, and spoke-types in the target design was analysed thoroughly using both finite element models (FEM) and the analytical models. In a comprehensive evaluation of their performances considering the major physical aspects, it was found that none of the conventional rotor topologies is ideal to withstand the excessive mechanical stress induced at high speeds. A thorough understanding of the limitations of the conventional rotor topologies has led to the proposal of a novel IPMSM rotor topology. It was developed via a mechanical-strength-oriented evolution process giving considerations to multiphysics domains. Its structure was inspired by a double-tied arch bridge (DAB), and hence, it is named DAB-type rotor topology. Compared to a flat-type rotor optimised for mechanical robustness, the DAB-type rotor can achieve a 40% reduction in the maximum mechanical stress (MMS). In order to optimise the high-speed IPMSM, a fast and accurate multiphysics multi-objective optimisation package was explicitly developed. The package utilises accurate analytical models and computationally efficient techniques in FEM-based calculations resulting in a significant reduction of the total computation time. The proof-of-concept of the novel IPMSM was constructed to verify the predicted high-speed performances experimentally. The measured performances were found to match very well with the predicted values. In order to investigate the practical applicability of the proposed novel high-speed IPMSM, it was compared with an existing surface-type PMSM (SPMSM) developed for the air compressor of a commercial air-conditioner. In addition, in a scale-up study, the potential of the proposed design for other types of high-speed applications was explored