Abstract
This paper describes a torque controller design method of brushless AC (BLAC) motor for electric power steering (EPS) system. Especially, this paper is focused on two types of advanced control methods that can be used in reducing torque ripples and in extending the operational region of the BLAC motor. A motor torque ripple compensation algorithm is proposed to improve steering feel of the objective EPS system at regions which require lower speed and higher torque assistance characteristics. The algorithm compensates bad effects of asymmetric back electromotive force (BEMF). The instantaneous electrical angle, compensator gain and delay factor of sinusoidal function are utilized in the algorithm. A flux weakening algorithm is also applied to reduce the catch-up phenomenon that occurred frequently in EPS systems under rapid steering conditions. The applied algorithm uses the differences of dq-axis voltages between the controller outputs and the saturated voltages. So it doesn´t need to establish any complicated flux weakening table which conventional algorithms uses. Finally, we propose a torque controller of the BLAC motor for the EPS system. The controller described in this paper can be easily implemented in software and no additional hardware or sensor is needed. The feasibility of the controller has been verified by simulations and experimental results on laboratory and entry level compact car. The results show satisfactory performance of the torque controller in applying to the EPS system.
Keywords: EPS, MDPS, BLAC, flux weakening, torque ripple