Fault Tolerant Operations of Induction Motor-Drive Systems
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FAULT TOLERANT OPERATIONS OF INDUCTION MOTOR-DRIVE SYSTEMS by Chia-Chou Yeh, B.S., M.S. A Dissertation submitted to the Faculty of the Graduate School, Marquette University, in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Milwaukee, Wisconsin May, 2008 ii Preface FAULT TOLERANT OPERATIONS OF INDUCTION MOTOR-DRIVE SYSTEMS Chia-Chou Yeh Under the Supervision of Professor Nabeel A. O. Demerdash at Marquette University This dissertation presents fault-tolerant / “limp-home” strategies of ac motor soft starters and adjustable-speed drives (ASDs) when experiencing a power switch open-circuit or short-circuit fault. The present low-cost fault mitigation solutions can be retrofitted into the existing off-the- shelf soft starters and ASDs to enhance their reliability and fault tolerant capability, with only minimum hardware modifications. The conceived fault-tolerant soft starters are capable of operating in a two-phase mode in the event of a thyristor/SCR open-circuit or short-circuit switch-fault in any one of the phases using a novel resilient closed-loop control scheme. The performance resulting from using the conceived soft starter fault-tolerant control has demonstrated reduced starting motor torque pulsations and reduced inrush current magnitudes. Small-signal model representation of the motor-soft starter controller system is also developed here in order to design the closed-loop regulators of the control system at a desired bandwidth to render a good dynamic and fast transient response. In addition, the transient motor performance under these types of faults is investigated using analytical closed-form solutions, the results of which are in good agreement with both the detailed simulation and experimental test results of the actual hardware. As for ASDs, a low-cost fault mitigation strategy, based on a quasi-cycloconverter-based topology and control, for low-speed applications such as “self-healing/limp-home” needs for vehicles and propulsion systems is developed. The present approach offers the potential of mitigating both transistor open-circuit and short-circuit switch faults, as well as other drive- related faults such as faults occurring in the rectifier bridge or dc-link capacitor. Furthermore, iii some of the drawbacks associated with previously known fault mitigation techniques such as the need for accessibility to a motor neutral, the need for larger size dc-link capacitors, or higher dc- bus voltage, are overcome here using the present approach. Due to its unique control algorithm, torque pulsations are introduced as a result of the non-sinusoidal current waveforms. Meanwhile, application considerations and opportunities for practical use of the conceived design are also investigated here in this work. The results of this research suggest that the conceived approach is best suited for partial motor-loading operating condition, which is normally the case for many practical industrial applications where the motors are usually oversized. The reason for choosing to operate under such conditions is the resulting reduced torque pulsations that the motor will experience when supplied by the conceived topology at light-load conditions. In addition, the negative impact of inverter switch fault on motor performance is also analyzed in this work using the averaged switching function modeling concept. Simulation and experimental work have been performed to demonstrate the efficacy and validity of the conceived fault-tolerant solutions for induction motor fault mitigation applications. iv Acknowledgement First of all, I wish to express my sincere and deepest gratitude to my advisor, Professor Nabeel A. O. Demerdash, for his encouragement, time, and expert technical guidance throughout the completion of this work. Without his open-mindedness and patient guidance, this dissertation would not come to exist. His endless hours of advice and help in my research work are very much appreciated and will always be remembered. Our discussions involve not only technical matters, but also life in general. In fact, he serves as a father figure to me. It is my extreme privilege to have him as my advisor as well as my dear friend. His famous quote: “No question is a stupid question” will always be buried in my mind. I would also like to extend my deepest gratitude to my other dissertation committee members, namely Prof. Ronald H. Brown and Prof. Edwin E. Yaz of Marquette Univesity, Dr. Thomas W. Nehl of Delphi Automotive Research, and Dr. Russel J. Kerkman of Allen Bradley- Rockwell Automation, for their precious time, support, and useful suggestions/insights. I am also very grateful to my internship employer, Eaton Corporation, when I was with them for the majority part of my Ph.D. studies, for the technical experience, skills and knowledge that I gained which enabled the completion of this work. Furthermore, I wish to thank my co-workers, Madhav D. Manjrekar, Ian T. Wallace, Vijay Bhavaraju, Jun Kikuchi, and Edward F. Buck for all the helpful discussions in various projects. In addition, I wish to acknowledge the financial support from the US National Science Foundation under Grant ECS-0322974 and the Rev. John P. Raynor Fellowship. I also wish to thank the Marquette University EECE department, professors, and support staff, especially Jean M. Weiss, for providing the environment that made this research work possible. v The support of the Eaton Corporation, Allen Bradley-Rockwell Automation, and A. O. Smith Corporation, in providing the test motors, drives, and other electronic equipment, is gratefully acknowledged. The experimental portion of this research work would not be possible without their support and generosity. I also wish to extend special thanks to my dearest friends, Ahmed Sayed-Ahmed, Behrooz Mirafzal, Gennadi Y. Sizov, and Anushree Kadaba for their support, useful insights, and fruitful discussions throughout my graduate studies at Marquette University. The time when we all spent together in the lab is something I will never forget. I will definitely miss the moment and fun in our weekly “Tuesday Pizza”. Most importantly, I would like to thank a special person, my lovely wife Huili, for her infinite patience, kindness, and endless love throughout this period. Her continued support and belief in me in things I wish to accomplish in my life will always be remembered. Her strong character has kept me motivated in the completion of this work. She definitely plays a major role in my life. Finally, I owe my deepest appreciation and special thanks to my family for their love, support, and encouragement throughout my life and education. This dissertation would not be possible without them. There are many other people who have helped me in some ways in my research work. Although I cannot mention each one of their names, I never forget their kindness. Once again, I would like to express my greatest gratitude to all these people. Thank you all, it is good knowing you. Chia-Chou Yeh May 2008 vi Contents List of Figures .........................................................................................................x List of Tables.......................................................................................................xvii 1 Introduction.....................................................................................................1 1.1 Motivation behind This Work ......................................................................................1 1.2 Literature Search Surveying Preceding Work..............................................................6 1.3 Objectives and Contributions .....................................................................................16 1.4 Dissertation Organizations .........................................................................................18 1.5 Summary ....................................................................................................................19 2 Transient Analysis of Induction Motor-Soft Starter .................................20 2.1 Introduction ................................................................................................................20 2.2 Soft Starters................................................................................................................21 2.2.1 Topology .......................................................................................................21 2.2.2 Principles of Operations................................................................................22 2.3 Closed-Form Derivation.............................................................................................25 2.3.1 Closed-Form Expressions of Motor Phase Voltages.....................................25 2.3.2 Closed-Form Expressions of Motor Phase Currents .....................................34 2.4 Analysis of Failure Modes and Effects ......................................................................38 2.4.1 Short-Circuit SCR Fault ................................................................................39 2.4.2 Open-Circuit SCR Fault ................................................................................44 2.5 Summary ....................................................................................................................46 3 Fault Tolerant Soft Starter...........................................................................48 3.1 Introduction ................................................................................................................48