Sensitivity analysis on production tolerances for electric drive systems in automotive application

Production tolerances in electric drive systems with interior permanent magnet synchronus machines (IPMSM) lead to unavoidable deviations in torque and power. This paper presents an investigation of the underlying effects utilizing simulations and measurements as well as methods for detection. In particular, deviations of the sensors and of the machine are studied. For the machine, the permanent magnet flux and the air gap thickness are identified as two main influence factors. Finite Element Analysis (FEA) is used to model deviations and to calculate flux tables in the i
_d
-i
_q
-plane. Also the influence of current and angle measurement errors are analytically analyzed. The simulated results are confirmed at the test bench, performing measurements with custom-built limit sample machines. Torque deviations of more than 10% are detected. Additionally, a method for detecting the individual deviation of an individual machine is introduced. Measurement of short-circuit current and open-circuit voltage are employed since both quantities are measurable with little effort. The combination of the knowledge about the effects in the machine and the detection methods could be used for compensation.