Plenary Speech 1

Plenary  Speech 1 : Predictive Control - how to use and what to avoid

Prof. Joachim Holtz (IEEE Fellow) received the B.S. degree in 1967 and the Ph.D. degree in 1969 from the Technical University Braunschweig, Braunschweig, Germany. In 1969 he became Associate Professor and, in 1971, Full Professor and Head of the Control Engineering Laboratory, Indian Institute of Technology in Madras, India. He joined the Siemens Research Laboratories in Erlangen, Germany, in 1972. From 1976 to 1998, he was Professor and Head of the Electrical Machines and Drives Laboratory, Wuppertal University, Germany. He is presently Professor Emeritus and a Consultant.

Prof. Holtz is the recipient of the IEEE Industrial Electronics Society Dr. Eugene Mittelmann Achievement Award, the IEEE Industrial Applications Society Outstanding Achievement Award, the IEEE Power Electronics Society William E. Newell Field Award, the IEEE Third Millenium Medal, and the IEEE Lamme Gold Medal. He is a Fellow of the IEEE. Prof. Holtz is Past Editor-in-Chief of the IEEE TIE, Distinguished Lecturer of the IEEE Industrial Applications Society and IEEE Industrial Electronics Society, Senior AdCom Member of the IEEE Industrial Electronics Society, Chair, IEEE Industrial Electronics Society Fellow Committee, and member of the Static Power Converter Committee, IEEE Industrial Applications Society.

Abstract: Switching losses contribute a major portion to the total losses in medium voltage drives. Operation at extremely low switching frequency is therefore mandatory. Nevertheless can low harmonic current distortion be maintained when predictive current control is used. The predictive algorithm directly generates the firing pulses of the inverter, thus eliminating a pulsewidth modulator. A preset maximum magnitude of the current error is permitted, defined as the magnitude difference between the reference and actual current space vector. The inverter gate pulses are generated such as to maximize the time difference between any two switching instants. This minimizes the switching frequency and the switching losses, while harmonic current distortion is held at its predetermined value. Near-optimum operation is achieved at low switching frequency, which makes predictive control only attractive at higher power levels. The switching frequency varies as the inverter fundamental voltage varies. It assumes a maximum value at medium fundamental voltage while reducing at lower and at higher fundamental voltage. This limits the power handling capacity of the inverter. A predictive algorithm can equalize the switching frequency to achieve maximum efficiency. When used as an active front-end converter as part of an regenerative energy system, the inverter harmonics may excite oscillations in the power grid. The respective frequencies are then identified and reduced by a predictive algorithm.