The reluctance synchronous motor (RSM) is identified to be well suited for the variable-gear (VG) electric vehicle (EV) drive. It is shown in this paper, however, that the RSM drive's position-sensorless capability is limited at zero or very small current magnitudes due to a limited saliency magnitude. In this paper, a novel epoxy-resin-casted rotor with no iron ribs is proposed to increase the saliency of the RSM at zero reference current. This rotor RSM is simulated in finite-element (FE) analysis, built, evaluated, and compared with conventional flux barrier rotor RSMs. The effect of rotor skewing on the position-sensorless control (PSC) capability of the RSM is also evaluated by means of FE analysis and measurements. Other performance aspects are also considered in this paper. It is concluded that, overall, the skewed epoxy-resin-casted rotor RSM drive has no PSC problems in the entire load and speed regions and is well suited for VG EV drives.
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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