Optimal Current Trajectory Evaluation for Sensorless Controlled Synchronous Machines based on Finite Element Analysis

The performance of sensorless controlled synchronous drives is strongly depending on the electromagnetic and mechanical design of the synchronous machine itself. This paper discusses a methodology to analyze the self-sensing capability of different synchronous machine types to evaluate an optimized operational strategy by a special current trajectory for low-speed and standstill especially with respect to sensorless operation. A comprehensive analysis of the machine’s differential inductances by using finite element simulation enables the characterization of achievable sensorless rotor position accuracy by the help of statistical properties. A sensorless error angle map is generated over a certain area around the intended operation range for each individual machine respectively. Depending on specific operational criteria a new optimal current trajectory for sensorless control is developed replacing commonly used maximum torque per ampere (MTPA) strategy, which usually does not take any specific self-sensing capability into account. The paper shows the proposed evaluation process applied to three synchronous machines exemplarily.