Analytical Modelling, Optimization and Electromagnetic Performance Analysis of Electrically Excited Flux Switching Motor

Abstract

High torque-density, high efficiency and robust rotor structure are the key features of flux switching motors (FSMs) [1]. Permanent magnet (PM) FSMs are preferred choice, however, these machines consume high amount rare-earth magnet and its resources are depleting with the passage of time. The degradation of performance with increase in temperature and uncontrolled flux are the other concerns with PMFSMs. The flux of electrically excited (EE) FSM can be controlled electronically, performance is not degraded with increase in temperature and overall cost is low. The simple manufacturing process of single phase EEFSM, easy maintenance, longer lifetime and low cost are the main characteristic that prioritized it for high speed applications [2-3]. Authors [4-6] have proposed novel single phase EEFSM designs, they have successfully accomplished their targets in the form of good average torque and efficiency etc. These designs have overlapped windings and segmented or modular rotor. High copper losses are caused by overlapped windings and segmented or modular rotor is not suitable for high speed applications. High power density, torque and efficiency are key factors for motors used in high speed applications. Flux switching motor (FSM) designs with the conventional stator slot have relatively good average torque but high copper losses and low efficiency. This paper has proposed an optimized octane modular stator (OMS) 8slots-6poles (8S-6P) single phase electrically excited (EE) FSM design. The geometric representation of the OMS design is given in Fig.1 (a), Rse, Rre, βsθs, βrθr, and θ are stator outer radius, rotor outer radius, stator slot opening, rotor slot opening and rotor position respectively. The proposed OMS design has high copper slot filling factor and high efficiency than the conventional stator trapezoidal slot [3]. Moreover, the purpose of this paper is to analyze OMS EEFSM design by means of simplified analytical method. For electromagnetic performance investigation numerical based technique finite element analysis (FEA) is powerful tool. But, computational complexity, high computational time and high drive storage compel researchers to model and analyze electric machines and especially FSMs analytically. In this paper, doubly-salient air-gap permeance, magneto-motive force (MMF) and inductance calculation is performed to obtain radial magnetic flux density distribution in the air-gap and electromagnetic torque, accounts the influence of all parts of EEFSM. This simplified approach has reduced the computational time, drive storage and computational complexity. Geometric optimization (GO) is implemented in multiple steps to optimize the initial design. The analytical results are validated via JMAG v18.1 finite element analysis (FEA) simulator. Finally, prototype is fabricated and experimentally tested. Prototype stator without windings and with windings are shown in Fig.1 (b) and (c) respectively. The analytical results has good agreement with FEA and experimental results and the deviancy is from 3 to 4%. Overall GO implementation, average torque of the proposed optimized EEFSM design is enhanced 42.5% and comparison of the electromagnetic performance is plotted in Fig.2. **