Φ Abstract -In this paper, the main aim is to propose and investigate possible methods for extending and improving the torque density capabilities of high performance, electrical machines. This is achieved by combining performance enhancing strategies such as the use of an outer rotor, the use of cobalt iron laminations and the adoption of high performance winding arrangements into a structured methodology that details the potential improvements step by step. A main point of interest of this paper is the permanent magnet demagnetisation analysis, resulting in the adoption of an optimum arrangement of a five stage, full-Halbach array. The above is presented in terms of an electrical machine used as an in-wheel motor in an aircraft traction application.
Index Terms --Aerospace, Halbach arrays, high torque density, permanent magnets, synchronous machines
I. INTRODUCTIONLECTRICAL machines for mobile applications such as the rail, aerospace and automotive industries have strong requirements for power and torque density. On top of this, reliability, cost-effectiveness, efficiency and availability are generally, additional, desirable requirements. This paper will look at methodologies for maximising torque density for a given application. The application considered is that of an in-wheel motor for aircraft traction. The machine is an outer rotor, permanent magnet (PM) machine which will be directly coupled to the aircraft wheel. A feasibility study and an electro-magnetic study of an electrical machine for such an application was presented in a previous paper [1].Considering the high torque density, fault tolerance and reliability requirements associated with such an application, the initial investigations indicate a 36-slot/42-pole, PM synchronous machine (PMSM) with an outer rotor as the most promising technology. In [1], measures to enhance the torque capability of the machine were identified, including measures to improve the winding factor K w , measures to obtain the best possible air-gap flux density B g (i.e. improve the fundamental component B g1 and minimise air-gap, spatial harmonics) and efforts to decrease the copper loss.In the first part of this paper, these torque improving measures are investigated and comparisons in terms of a set of quantifiable, quality indicating (QI) parameters are given. The second part of the paper builds on the methodologies presented in [1] in order to meet the application performance requirements. Design considerations for torque ripple T rip minimisations are presented while PM demagnetisation issues are also addressed.
