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Abstract
Many high performance drive applications require wide Constant Power Speed Range (CPSR) for efficient use of energy. The examples of such applications are the starter alternator system of automobiles proposed for the 42V PowerNet, traction in the hybrid/electric vehicle, wind power generator etc. The Permanent Magnet (PM) machine is the natural choice of such niche applications because of their higher efficiency and compact size. However, the Surface Permanent Magnet (SPM) machine with sine distributed winding and radially-laminated Interior Permanent Magnet (IPM) machine with conventional structure has very limited or zero flux-weakening capability. The flux-weakening capability of the SPM machine can be improved by using concentrated, fractional-slot stator but here well-known advantages of the sine distributed winding are needed to be compromised. In the IPM machine, fluxweakening was improved using axial lamination and more than two magnet layers per pole. However, the construction of such IPM machine is complicated and expensive. This thesis presents design and analysis of a new type of the Interior Permanent Magnet (IPM) machine that have a very wide Constant Power Speed Range (CPSR) without compromising simplicity of construction and advantages of the distribution winding. In the new IPM machine, the magnet poles were segmented in the radially direction and the iron bridges between magnet segments provide for additional paths of flux-canalization to give the rotor an inherent capability of fluxweakening. Consequently, a very wide constant power speed range can be achieved in such machines. The proposed IPM machine of this work was referred as the Segmented IPM machine.
The thesis focuses on the optimization of the Segmented IPM machine in a 42V environment of the automobile. First, for the conceptual evaluation a 4 pole, 550W Segmented Magnet IPM machine was optimized using finite element analysis. The parameters were calculated for prediction of the steady-state and transient performances. The torque- and power-speed capability were estimated using time-step, circuit-coupled finite element analysis. The cogging torque and variation of iron loss with frequency were also investigated during the design process. A prototype machine was constructed on the basis of the optimized design. The steady-state and transient performances of the prototype machine were measured and compared with the predicted results for experimental verification. The measured performance analysis was found to match very well with the predicted results. The measured torque- and power-speed capability of the Segmented IPM machine was also compared to those of a conventional, non-segmented IPM machine of similar rating and size. The thesis also presents the optimized design of a 6kW, 12 pole Segmented Magnet IPM machine for application in the Integrated Starter Alternator (ISA) of the electric/hybrid vehicle. It can be concluded from the predicted steady-state analysis of the 6 kW, 12 pole Segmented Magnet IPM machine that it should be able to satisfy most of the required criteria of an ISA with appropriate design optimization.