Control and modulation of medium-voltage drives

Tutorial T1 - Control and Modulation of Medium-Voltage Drives
Tobias Geyer and Nikolaos Oikonomou, ABB Corporate Research, Switzerland
Abstract:
This tutorial provides an overview of control and modulation methods used for high
power electronic converters in general and medium-voltage (MV) drives in particular.
In these applications, the semiconductor switching losses dominate over the
conduction losses. As a consequence, device switching frequencies between 150 and
650 Hz are typically chosen, leading to high harmonic distortions of the voltage and
current waveforms. Even when using multi-level converters, achieving current
distortions that facilitate motor-friendly operation is a formidable challenge. Similar
challenges exist on the grid side.
The majority of control and modulation methods used today for MV drives have
originally been developed for low-voltage power electronics and two-level converters,
using linear controllers and the technique of averaging to conceal the switching aspect
from the controller. To achieve the highest possible performance for a high-power
converter, however, averaging is to be avoided, and the traditionally used current
control loop and modulator should be replaced by one single controller entity.
The focal point of this tutorial is on control and modulation methods that fully exploit
the performance potential of high-power converters, by ensuring fast control at very
low switching frequencies and low harmonic distortions. To achieve this, the control
and modulation problem is addressed in one computational stage. To this end, the
benefits of deadbeat control methods (such as direct torque control) are combined
with the optimal steady-state performance of optimized pulse patterns, by resolving
the antagonism between the two. As a result, the current harmonic distortions and the
switching losses can be reduced simultaneously, when compared to carrier-based
PWM. Indeed, at low switching frequencies, the resulting steady-state behaviour is
similar to that of optimized pulse patterns. During transients, however, very fast
current and torque response times are achieved, similar to deadbeat control.
Experimental results in the MW range are provided that highlight this.
Outline:
14:00 MV drives (30 min)
• Customer requirements, market trends and challenges
• Existing and emerging topologies, main applications and general purpose vs
special purpose drives
14:30 Classic control and modulation methods (20 min)
• Control problem of industrial MV drives
• Modulation: carrier-based PWM and space vector modulation
• Control: field-oriented control and direct torque control
• Advantages and disadvantages
14:50 Model predictive control based on optimized pulse patterns – Part 1 (40 min)
• Optimized pulse patterns: properties, computational methods and results
•
Fast closed-loop control of optimized pulse patterns
15:30 Coffee break (30 min)
16:00 Model predictive control based on optimized pulse patterns – Part 2 (40 min)
• Insertion of additional pulses during transients
• Implementation aspects
• Experimental results for a five-level MV drive
16:40 Direct model predictive control with long prediction horizons (30 min)
• Control problem formulation
• Solution approach using branch and bound optimization
• Performance evaluation of an NPC inverter drive system with a sine filter
during steady-state operation and transients
• Assessment of the performance benefits when compared to short horizons (the
current THD is reduced by up to a factor of eight for the same switching
frequency)
17:10 Summary and conclusions (20 min)
• Summary of the main results and assessment
• Current status of model predictive control in power electronics and future
trends
• Extensions to modular multi-level converters
• Q&A
17:30 End
Target audience:
This tutorial is intended for researchers in academia and industry that are interested in
an introduction to and a summary of the control and modulation methods available
today for power converters operated at low pulse numbers (i.e. low switching
frequencies per fundamental frequency). Relevant applications include traction
converters for (hybrid) electric vehicles, FACTS and grid-connected MV converters,
to name just a few, albeit MV drives are used as case studies in this tutorial.
Tutorial organizers:
Tobias Geyer received the Dipl.-Ing. and Ph.D. degrees in electrical engineering from ETH
Zurich, Switzerland, in 2000 and 2005, respectively. Subsequently, he
worked at GE's Global Research Centre, Munich, Germany and at the
University of Auckland, New Zealand. In 2012, he joined ABB’s Corporate
Research Centre, Switzerland. His research interests are at the intersection
of power electronics, modern control theory and mathematical optimization.
This includes model predictive control and medium-voltage electrical
drives.
Dr. Geyer has received three best paper awards. He serves as an Associate
Editor for the Transactions on Power Electronics. He has authored and co-authored more than
100 peer-reviewed publications and patent applications. In the field of model predictive
control for power electronics he is one of the most active and highly cited researchers. He
gave a well-received tutorial about model predictive control for industrial drives at ECCE
2013 in Denver.
Nikolaos Oikonomou received his Diploma in Electrical Engineering from
Aristotle University of Thessaloniki, Greece, in 2000 and his Doctorate
degree from the University of Wuppertal, Germany, in 2008. He joined the
ABB Corporate Research Center in Switzerland in 2009. He currently leads
the Power Conversion Systems Group in the Power Electronics Department.
Dr. Oikonomou's research interests include application-oriented design of
power converter configurations, pulse width modulation methods, and timedomain optimal control of grid- and motor-connected converters. He gave a
well-received tutorial about model predictive control for industrial drives at ECCE 2013 in
Denver.