2015 Tenth International Conference on Ecological Vehicles and Renewable Energies (EVER) Field weakening performance of flux-switching machines for hybrid/electric vehicles Yang Tang Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven, The Netherlands Email: y.tang1@tue.nl Johannes J.H. Paulides Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven, The Netherlands Email: j.j.h.paulides@tue.nl Elena A. Lomonova Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven, The Netherlands Email: e.lomonova@tue.nl Abstract—Flux-switching machines (FSMs) are a viable candidate for electric propulsion of hybrid/electric vehicles. This paper investigates the field weakening performance of FSMs. The investigation starts with general torque and voltage expressions, which reveal the relationships between certain parameters and the produced torque and induced voltage of this machine. Based on the understanding of these relationships, a number of methods for reshaping the torque-speed characteristic of an FSM design are proposed and validated using finite element analysis (FEA). Keywords—hybrid/electric vehicle, flux-switching ma- chine, field weakening I. I NTRODUCTION The fast development of the hybrid/electric vehicle in- dustry creates an urgent requirement of advanced electri- cal machines for electric propulsion. Electrical machines selected for these applications are expected to have a high torque production capability with wide constant power speed range (CPSR) [1], [2], shown in Fig. 1. For this purpose, considerable research has been conducted on investigating novel types of electrical machine in recent years, in which flux-switching machines (FSMs) have been frequently mentioned as a viable candidate [3], [4], [5]. FSMs are double-salient structured machines with both AC windings and pre-biased magnetic excitation sources, i.e. permanent magnets [6] (Fig. 2a) or DC field windings [7], [8] (Fig. 2b), in the stator. They are considered to suit automotive applications because they combine the advantages of switched reluctance machines (SRMs) and brushless AC machines (BLACMs), which allow a robust rotor structure while preserving a rea- sonable torque density. However, in these applications the requirement of a wide CPSR is one of the major challenges for the design of FSMs. In [9] and [10], the so-called hybrid excitation was proposed to extend the speed range of FSMs, in which additional DC coils Y Y /RZ VSHHG 9DULDEOH WRUTXH /RZ WRUTXH 9DULDEOH VSHHG (a) Different traction scenarios 7RUTXH 3RZHU &RQVWDQW SRZHU VSHHG UDQJH &365 6SHHG 6SHHG 0D[ VSHHG 0D[ VSHHG 0D[ WRUTXH 0D[ WRUTXH %DVH VSHHG %DVH VSHHG (b) Required torque-speed profiles Fig. 1. Torque-speed requirements for electric traction motors in automotive applications were adopted to enhance or weaken the magnetic field produced by the permanent magnets. In [11] and [12], mechanical field weakening methods for FSMs were proposed and implemented using a movable piece of ferromagnetic material to partially divert the magnetic flux produced by the permanent magnets, hence reducing the flux linkage in the armature winding. However, these methods complicate the stator structure of FSMs, resulting in a decrease in ruggedness and an increase in the production price. [13] and [14] indicated that the high d-axis inductance presented in FSMs is an advantageous factor for field weakening, suggesting a possibility of extending the CPSR without changing the machine structure. In [15], two methods were proposed to improve the field capability of a flux-switching per- 978-1-4673-6785-1/15/$31.00 c 2015 European Union