Position sensor error analysis for EPS motor drive

Selecting a cost-effective position sensor is an important step in electric power steering (EPS) motor drive system design. Resolvers and high-resolution encoders provide excellent measurement accuracy. However, market competition has forced designers to look into less expensive solutions that have relatively large measurement errors. This paper studies the effect of position sensor measurement errors on torque ripple performance of a permanent magnet synchronous motor (PMSM). The low cost sensor system considered here has a dual Hall sensor IC and a magnet wheel. The effect of relatively poor resolution and magnet wheel tolerance are simulated with Simulink models. With the same motor and controller model, a high performance resolver is also simulated. The simulation results of both types of sensor are compared. The torque ripple performance degradation due to lower cost sensor is identified. The results show an acceptable torque ripple with the lower cost sensor. A DSP based motor controller is built and tested with the dual Hall sensing system. The test results show a torque ripple of about 2 % for the complete motor drive with Hall position sensor. The Hall position sensor meets the smooth steering feel requirement that most EPS manufacturers have specified.