Balarama V. Murty

Robust control of low-cost actuator for automotive active front steering application

Active Front Steering (AFS) system used in automobiles is a position controlled system and requires a high performance electric actuator. In this paper, the control methodology developed to make a low-cost Brushless permanent magnet motor drive (BLDC) suitable for the AFS application will be reported. Detailed simulation models were developed for the actuator to understand the performance under various dynamic conditions. A robust control methodology was developed to achieve smooth operation of the AFS actuator under all vehicle driving conditions and to prevent unwanted vibration at the steering wheel due to motor phase commutation. To achieve position control with high precision, conventional PID controller was used when the angle error was large and two additional control modes were introduced when the angle error was small to improve the robustness of the system. Suitable control logic was used to make the transitions between the operating modes smooth and transparent to the driver. The proposed control methodology was successfully implemented in the AFS system of an experimental vehicle and acceptable level of performance was achieved. The measured results were used for validating the simulation results. The impact of variations in the motor parameter and the torsional stiffness of the various elements of the steering system due to manufacturing tolerances on the precision of the AFS system response were studied through simulations. It was found that robust performance of the actuator can be achieved by proper choice of the PID gains used in the controller. The proposed control methodology enables the use of low-cost BLDC motor drive suitable for the high performance AFS system application.