High fidelity mechanical and loss modelling of an interior permanent magnet traction machine for electrical vehicles

High-performance permanent magnet electrical machines have become the leading machine technology in the electric vehicle market due to their combination of high efficiency and high-power density. However, their design optimisation involves complex and often strongly coupled mechanical, electromagnetic and thermal behaviour. Of the many possible topologies of permanent magnet machines, interior (IPM) machines have become the favoured machine type as they offer advantages in field weakening, a contribution from reluctance torque and the ability to retain the magnets within the rotor core without the need in many cases for a separate containment sleeve. However, the trade-off between electromagnetic and mechanical performance is especially important in IPMs because of the use of thin bridge-sections within the rotor core. This thesis reports on detailed design study into the mechanical and electromagnetic optimisation of an 8-pole, 100kW IPM machine with a base speed of 4,000rpm and an extended speed range up to 12,000rpm and makes extensive use of structural and electromagnetic finite element analysis to identify a preferred design. The other aspect of IPM performance which is investigated in this thesis is the influence of high frequency converter switching on the iron loss in the machine. An analysis methodology is developed and applied to an IPM machine with combines a SIMULINK model with pre-calculated finite element characteristics of the machine to predict detailed localised element-by-element flux density variations in the cores of an IPM machine which includes realistic representation of switching events. The effect of current ripple and the grounding of the star-point is investigated. These high frequency flux density waveforms are then used as the basis for estimating the effect of high frequency current ripple on iron loss. This aspect includes a detailed investigation of the limitations of different analytical and numerical models for solving the diffusion equation with 3D eddy current finite element simulations providing a baseline against which to test various models. This aspect of the research results in a time-stepped finite difference representation of 1D eddy current flow in laminations and is applied at full machine level as post-processing tool. The thesis concludes with some experimental measurements of core loss with switching ripple which demonstrates the value of including lamination level eddy current effects in loss predictions

Development of a Direct Drive Synchronous Reluctance Motor with Finite Element Analysis and Surrogate-Assisted Optimisation

This thesis is concerned about the development and evaluation of reluctance machines used for variable speed Raymond Pulveriser and centrifugal pump applications. The research is carried out through analytical and numerical analysis of two types of reluctance machines Synchronous Reluctance and Switched Reluctance machines, followed by experimental validation on prototype motors. In the synchronous reluctance machine, the rotor is a crucial part in terms of magnetic flux configuration and is a specific focus of this research is on the design, evaluation, and manufacturing of the rotor to improve the motor drive performance. An analytical procedure is firstly proposed for the rotor design. The rotor elements including the ribs and the bridges that maintain the mechanical strength of the rotor as well as the Q-axis insulation ratio (air-to-steel ratio) are studied. A FEM simulation with surrogate optimisation method is adopted, the main parameters of rotor geometry such as flux barrier and flux carrier are designed thoroughly investigated on the square and round shapes. Then, final designs are optimised, prototyped and tested on a test bench. The first machine is 75kW, 105rpm switched reluctance machine designed and prototyped for the direct- drive the application of Raymond Pulveriser. FEM modelling is carried out for 72/48 Switched reluctance motor in Motor Solver Software. The second machine is a 10kW synchronous reluctance motor for the application of Raymond Pulveriser used for mining applications. In order to improve the overall machine performance, a Surrogate assisted optimisation technique is applied with a particle swarm optimisation (PSO) method. FEM models are established by electromagnetic design software (Magnet) for both the stator and rotor. The Surrogate-based optimisation is tested on 24 and 36 stator slots while considering both the square and round shapes. 5 stator variables to generate Latin Hypercube samples are airgap, slot depth, tooth width, number of turns and slot openings. The rotor optimisation variables are flux barrier width, flux carrier width, and edge angle. Three and four flux barriers are tested with square and round shapes. Additionally, design of 10kW Switched reluctance motor for the same application of Raymond Pulveriser is carried out. FEM models are established on Motor Solver machine design software. The SBO is tested on 12/8 SRM on both stator and rotor. The following variables are considered: stator pole arc, stator yoke thickness, air gap, rotor pole arc, number of turns, shaft diameter, and rotor yoke thickness and then the comparison is made between SynRM and SRM. These designs are initially for the machines operating in both directions. However, the applications only require uni-directional rotation of the machine. It is necessary to consider an optimised design for the uni-directional operation. Additionally, the study on the asymmetrical rotor design is also conducted to analyse the machine performance and its merits and drawbacks. Thirdly, a 24-kW synchronous reluctance motor is designed for the centrifugal pump applications. The stator structure is similar to the induction motor but has 36 slots and 4 poles. The research mainly is 3 focused on reducing the power losses and torque ripple, and a new rotor design of motor with different optimisation arrangements of flux barrier shapes have been studied and tested through the FEM. The rotor optimisation is carried out by varying the flux carrier width, flux barrier width, shaft diameter, and barrier edge angle. The simulation carried on different designs and shapes. Finally, a rotor design with 3 V-shaped flux barriers is chosen and is prototyped for testing. Experimental results show the effectiveness of the optimal rotor designs which can provide a required torque profile with low torque ripples and low power losses. The main advantage of the proposed designs is the good thermal performance of the machine which increases motor efficiency. The study shows the benefits of utilizing a reluctance machine