Magnet-less electrical machines are characterized by a high material availability and therefore predestined for a broad application in hybrid and electric cars

摘要

During the last years, the introduced hybrid cars with electrical machines, integrated into transmissions, were mainly based on rear ear magnet excited synchronous machine, because the machine size, compared to other kinds of electrical machines, is normally smaller. Also in electrical axle drives, this kind of machine is dominant at this time with few exceptions e.g. the Tesla electric car (high power induction machine) or the Renault electric car (separately excited synchronous machine). Due to limited global availability of rear ear magnets, especially of dysprosium, the costs of this material are very high. Therefore OEMs and automotive suppliers are pushing the so called "magnet-less" electrical machines. Besides high availability of material, this kind of electrical machines offers, additional advantages for the automotive application: No breaking torque at the machine shaft in case of failure within the power electronic; No dragging torque e.g. if the machine is running in the idle mode; Small temperature sensitivity. Furthermore the magnet-less machines, like induction and synchronous reluctance machines are predestined for high speed applications in connection with a reduction gear, in order to increase the power density (lower need for active material, e.g. copper) of the electrical machines. Also the efficiency, related to a realistic driving cycle, will be comparable to the efficiency of a permanent magnet excited synchronous machine. The magnet-less electrical machines are therefore, especially for hybrid cars (Plug-In-Hybrid, Range Extender) with an electrical drive at the rear- or front axle, a very competitive solution for future developments.