Reluctance synchronous (RS) and field-intensified permanent magnet (FI-PM) motors are designed and optimised for a variable-gear electric vehicle (EV) drive in this paper. Recent literature shows that EVs with variable-gear drive trains operate at higher drive-cycle efficiencies than fix-gear EV drive trains. The advantages and design challenges of variable-gear EV drives are discussed in the paper. With variable-gear, the operation field-weakening performance of the electric drive is not important, which makes the RS motor drive, amongst others, very suitable. The FI-PM motor with minimum amount of PM material is also attractive from the performance and positionsensorless-control points of view. It is found that both the optimum designed RS and FI-PM motors perform very well considering the volumetric space available and the required torque-speed specifications. In particular, the performance of the FI-PM motor with the same volume as the RS motor is surprising considering the simple FI-PM rotor structure proposed. The variable gear system was tested and the average efficiency was found to above 80%.

In this paper a per unit scale saliency-and saliency shift equation are used to predict the saliency based position sensorless control performance of synchronous machines for EV drives by means of a finite element package. These equations are used in a comparative study of various types of synchronous machines. The machine drives investigated and compared are a reluctance synchronous machine (RSM) hybrid EV drive and two variable gear RSM EV drives. Also included in the investigation are two field intensified permanent magnet (FI-PM) EV drives with asymmetric rotors, one FI-PM machine with a symmetric rotor and one field weakening interior permanent magnet drive. The saliency shift of the different FI-PM machine rotor topologies are also investigated. Closed loop saliency based position sensorless control shows startup torque capabilities of up to 304 Nm of a 32 kW 6-pole RSM. The RSM EV machine is used to investigate possible design modifications to improve on the saliency ratio and shift of synchronous machines. Index Terms-Position sensorless control, EV drives. NOMENCLATURE AND DEFINITIONS Symbols: u, i, ψ Voltage current and flux linkage r, L Resistance and inductance T m , Θ Mechanical torque and inertia T ripple Torque ripple f Machine frequency φ Current angle θ r , ω r Rotor-angle and speed θ e , ω e Electrical-rotor angle and speed Δ, Σ Difference and sum Indices: s, r Stator and rotor α, β Stator fixed cartesian axes d, q Rotor fixed direct and quadrature axes c Carrier frequencyScalar values are written in normal letters, e.g. R or τ , vector values are written in small bold letters, e.g. i or ψ. Subscripts describe the location of the physical quantity, e.g. r s is the stator resistance. Superscripts specify the reference frame of the quantity, e.g. i r s is the stator current vector in the rotor reference frame. Estimated quantities are indicted with a hat, e.g.θ e . Small signal values are represented with δ.

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