Principles and Practices of Digital Current Regulation for AC Systems
Grahame Holmes
RMIT University, Melbourne, Australia
Professor Holmes graduated from the University of Melbourne in 1974, and has a Masters degree in power systems engineering, and a PhD in PWM theory for power converters. For 26 year he was an academic at Monash University, working in the area of Power Electronics, where he established the Power Electronics Research Group to support graduate students and research engineers working together on a mixture of theoretical and practical R&D projects. In 2010, Professor Holmes moved with his group to take up the position of Innovation Professor – Smart Energy Systems at RMIT University, allowing him to broaden his research activities into a diversity of applications of power electronics, including particularly Smart Grids and Smart Energy technologies.
Professor Holmes has a strong commitment and interest in the control and operation of electrical power converters. His research interests include fundamental modulation theory and its application to the operation of energy conversion systems, current regulators for drive systems and PWM rectifiers, active filter systems for the quality of supply improvement, resonant converters, current-source inverters for drive systems, and multilevel converters. He has made a significant contribution to the understanding of PWM theory through his publications and has developed close ties with the international research community in the area. He is a Fellow of the IEEE, has published over 200 papers at international conferences and in professional journals, and regularly reviews papers for all major IEEE transactions in his area. He has also coauthored a major reference textbook on PWM theory with Prof. Thomas Lipo of the University of Wisconsin-Madison. Prof. Holmes is an active member of the IEEE Industry Applications Society and the IEEE Power Electronics Society.
Abstract
Current regulation plays a key role in modern power electronic AC conversion systems such as variable speed drive systems, reactive power controllers and active filter systems. The essential concept for this type of system is... [ view full abstract ]
Current regulation plays a key role in modern power electronic AC conversion systems such as variable speed drive systems, reactive power controllers and active filter systems. The essential concept for this type of system is to compare a measured load current against a defined reference target, and to minimise the difference (“error”) between these two quantities by adjusting the switching of the associated power electronic converter. However, while simple in principle, achieving this goal for AC current regulators has proved to be a very challenging problem, and has been the subject of ongoing research for several decades.
This tutorial will present the current state-of-the-art for digital current regulation of AC converter systems. The tutorial will begin by showing how PWM transport and digital sampling delays are the primary factors that constrain the performance of a simple stationary frame PI regulator. Strategies to overcome these constraints will then be explored, such as backEMF compensation, PR resonant control and its equivalent synchronous d-q frame implementation. An analytical approach will be presented to determine the maximum possible gains for each of these alternative strategies, verified by both detailed simulations and matching experimental results. Similar concepts will then be explored for the more challenging problems of current regulation with an LCL filter, with semi-bridges linked by coupled inductors, and the influence of common mode EMI filtering on the current regulation process. The tutorial will then move to consider non-linear hysteresis current regulation, investigating how the hysteresis bands can be varied to overcome issues such as variable switching frequency, which is inherent in this type of control, and the implications of digitally implementing what has been traditionally regarded as an analogue type of current regulation system. Finally, the theoretical relationship between variable band hysteresis and predictive current regulation will be presented, to show that that these two strategies are really just “two sides of the same coin” and hence can achieve essentially the same performance when properly implemented.
The emphasis throughout the tutorial will be the application of the latest theoretical developments in digital AC current regulation, to practical structures that can be readily used in real world situations.
Session
Tue-1a » Tutorial, Holmes (09:00 - Tuesday, 24th June, ENG2001)
