Efficiency improvement of an IPMSM using Maximum Efficiency operating strategy

Interior permanent magnet synchronous machines (IPMSM) are preferably used for traction drives in electric vehicles. These are characterized by high efficiency and high torque as well as power density. The generation of reference currents for the field-oriented control is realized by look up tables (LUT). In these LUT the entire machine characteristic is described. The reference currents are selected on the basis of different operating strategies. The Maximum Torque Per Current (MTPC) method, which minimizes the magnitude of the current at a given torque, is the most common strategy in the constant torque range. It can be proven by measurements on a real motor that the MTPC method deviates considerably from the best efficiency under certain boundary conditions. The use of the Maximum Efficiency (ME) method increases the drive efficiency in comparison to the MTPC up to 0.3% at the same torque level. The ME characteristic however, has to be changed with the machine speed. Using the ME method, the gain of efficiency is small but it can be achieved with minor adaptions of a LUT in the machine control.