Advanced and Fault-tolerant Control of a BLDC Motor

Abstract

This thesis examines the control of a brushless direct current (BLDC) motor used to actuate the park lock and the disengagement clutch in an electric drive unit (EDU) for automotive applications. The primary objective is to enhance the performance of an existing control strategy while developing a complementary open-loop faultdetection method. The motivation for this work stems from opportunities to further improve the existing implementation, where timing inaccuracies during commutation can affect acoustic noise levels and motor smoothness. To address this, the first objective was to improve the existing trapezoidal commutation method by increasing the interrupt frequency from 10 kHz to 15 kHz, thereby enhancing the control system’s temporal resolution. This modification enables more frequent updates to rotor position, commutation states, and pulse-width modulation (PWM) signals, thereby improving control accuracy.

Experimental results show that the enhanced method maintains comparable performance at lower speeds while providing smoother operation and reduced noise at higher speeds. The second objective was to develop a sensorless open-loop control strategy that operates the motor without Hall-effect sensor feedback, enabling fault detection when the closed-loop system becomes inoperative due to sensor failure. In this approach, the rotor is first aligned to known positions and then driven through a full mechanical rotation using predefined commutation timing. Overall, the results demonstrate that relatively simple modifications can significantly improve control performance, while the proposed open-loop method offers potential for increased system robustness, although further work is required for practical implementation and validation.