Advanced and Fault-tolerant Control of a BLDC Motor

Sammanfattning

This thesis examines the control of a brushless direct current (BLDC) motor used toactuate the park lock and the disengagement clutch in an electric drive unit (EDU)for automotive applications. The primary objective is to enhance the performanceof an existing control strategy while developing a complementary open-loop faultdetectionmethod. The motivation for this work stems from opportunities to furtherimprove the existing implementation, where timing inaccuracies during commutationcan affect acoustic noise levels and motor smoothness. To address this, the firstobjective was to improve the existing trapezoidal commutation method by increasingthe interrupt frequency from 10 kHz to 15 kHz, thereby enhancing the controlsystem’s temporal resolution. This modification enables more frequent updates torotor position, commutation states, and pulse-width modulation (PWM) signals,thereby improving control accuracy.Experimental results show that the enhanced method maintains comparable performanceat lower speeds while providing smoother operation and reduced noise athigher speeds. The second objective was to develop a sensorless open-loop controlstrategy that operates the motor without Hall-effect sensor feedback, enabling faultdetection when the closed-loop system becomes inoperative due to sensor failure. Inthis approach, the rotor is first aligned to known positions and then driven througha full mechanical rotation using predefined commutation timing. Overall, the resultsdemonstrate that relatively simple modifications can significantly improve controlperformance, while the proposed open-loop method offers potential for increasedsystem robustness, although further work is required for practical implementationand validation.