Impedance Modeling and Control of Power Electronics in Power Systems
Operation of a circuit is affected by other, electrically connected circuits due to coupling by impedances. The consequence of such coupling can range from performance degradation to loss of stability, which is a common problem for the design of systems consisting of multiple functional blocks or sub-circuits. In analog electronics, the problem is solved by using op-amps – an ideal op-amp would have infinite input impedance and zero output impedance, hence would decouple the circuits connected through it. However, this method cannot be applied in power electronics because it is impractical to implement such “power op-amps”. Instead, power electronics engineers have used impedance-based analysis to characterize and mitigate the problem in space station, telecom, automotive, and other dc power electronic systems. With the increasing use of power electronics in utility power systems for such applications as renewable energy, energy storage, HVDC and FACTS, control interactions and instability due to coupling by impedance also becomes a major problem for the design and integration of grid-connected converters. This talk reviews the impedance-based analysis method originally developed for dc power systems, and extends it to three-phase power systems by means of harmonic linearization and symmetrical component decomposition. Laboratory and field measurement data are presented to highlight practical control instability and harmonic resonance problems of grid-connected converters. As possible solutions, online grid impedance measurement and adaptive control techniques are presented along with application examples in wind and solar inverters as well as HVDC converters. Design validation by real-time and hardware-in-the-loop system simulation is also discussed.
Jian Sun received the B.S. degree from the Nanjing Institute of Aeronautics, Nanjing, China, the M.S. degree from the Beijing University of Aeronautics and Astronautics, Beijing, China, and the Dr.Eng. (Ph.D.) degree from the University of Paderborn, Paderborn, Germany, all in electrical engineering. He was a Postdoctoral Fellow with the School of Electrical and Computer Engineering, Georgia Institute of Technology, from 1996 to 1997. He worked in the Advanced Technology Center of Rockwell Collins, Inc., from 1997 to 2002, where he led research on advanced power conversion for aerospace applications. In August 2002, he joined the Rensselaer Polytechnic Institute, Troy, NY where he is currently a Professor and Director of the New York State Center for Future Energy Systems. His research interests are in the general area of power electronics and energy conversion, with a focus on modeling, control, as well as applications in aerospace and renewable energy systems. He has published more than 160 journal and conference papers on these subjects, and holds nine U.S. patents. Dr. Sun is a Senior Member of the IEEE Power Electronics Society. He currently serves as the Editor-in-Chief of the IEEE POWER ELECTRONICS LETTERS.