Abstract

Permanent magnet synchronous machines (PMSMs) are widely employed in servo control and automotive applications due to their remarkable characteristics. However, the high-performance three-phase PMSM control strategies rely on accurate current measurements that require at least two phase current sensors. There is an inherent risk of current sensor malfunction which poses a direct threat to the motor drive performance and safety. Observer based single current sensor (SCS) control methods have recently emerged as practical and efficient current sensor fault tolerant control solutions, as they offer a robust and cost-effective alternative when only one current sensor is functioning in the motor drive system. In addition, the SCS control strategy can be used directly for a low cost PMSM drive design as it only requires one current sensor and achieves high performance PMSM control. This thesis delves into different current observer design methodologies aimed at achieving high-performance observer based SCS control PMSM drives with full-speed capability.
The thesis commences with a comprehensive theoretical analysis of observability and stability for observer based SCS control in PMSM drive systems, providing essential insights into feasible operation points. To enhance the system robustness and performance, an augmented linear current observer is proposed, incorporating speed-adaptive gain. Additionally, an innovative position-offset injection method is proposed to address the unobservability issue of observers during zero-speed operation. To further enhance dynamic performance, a novel nonlinear gain function is incorporated into the current observer design, facilitating rapid response and minimal overshoot simultaneously. Lastly, a hybrid discretization approach is presented, achieving a balance between simplicity and accuracy for discrete-time observer design. This approach guarantees the stability of the observer based SCS control system, even under challenging low sampling-to-fundamental frequency ratio conditions. During the thesis investigations, the proposed observer based SCS control approaches are extensively evaluated on a laboratory PMSM drive system under different speeds and load conditions.
In summary, this thesis offers a comprehensive exploration of diverse observer based SCS control strategies for PMSM drives. By scrutinizing existing observer designs, novel observer design approaches are proposed for SCS control in PMSM drives contributing to a cost effective, high performance and reliable PMSM drive solution.