Inductance tensor calculation method for characterizing synchronous reluctance machines

Abstract

Synchronous reluctance traction machines are becoming more and more important participants of electromobility due to the increasing demand to reduce the amount of the rare-earth materials in the electric vehicle components. With reducing rare earth material consumption, the economic and ecological risks of the future in e-mobility can partially be prevented. Without permanent magnet the electrical motor design requires a disruptive concept, which can compensate the lack of the most efficient type of motor component with good efficiency performance at the operating points. For instance, even the lower torque density and vehicle acceleration requirements of a city car design can be rationally acceptable if the reduced ecological footprint of the traction motor is more dominated than the driving experience as the cognitive engineering prefers the vehicle test cycle of a green driver instead of a racing driver. More innovative engineering cogitation is expected for designing a motor layout of a synchronous reluctance machines, which possesses more significant non-linear behavior and technical challenges regarding the drive control than the permanent magnet synchronous machines. To describe the non-fundamental motor behavior, the inductance tensor of the motor must be determined in a multi-variable parameter-field over the time domain. Since the inductance tensor maps cannot be directly evaluated from the FEA software, therefore this paper presents a novel inductance tensor map postprocessing method of FE analysis based on the differential inductances. The co-energy-based force method coupled with the number of divisions of rotor displacement, prescribes the resolution of required inductance map. The reduction of the non-linear effects by modifying the current profiles via the motor control can be satisfied only with a well-defined tensor mapping method. A properly determined motor model together with the corresponding control compensation method can further improve the efficiency of synchronous reluctance motors and provide the required performance at low speed and partial load domain, where the real operating points of an ordinary used vehicle can be found.