Tutorials: Monday 4 September 2023 (Full Day)

Multi-phase medium-voltage generators are increasingly employed in offshore wind parks in order to maximize the generated power per wind turbine and thus minimize the cost per MW of installed power. A characteristic example is the Dogger Bank wind farm, an offshore wind farm being developed at the Northeast coast of England. It will become the world’s largest offshore wind farm with an installed capacity of 3.6 GW. Multi-phase medium-voltage generators with a rated power of 13–14 MW will be installed within the frame of the project. Often in such medium-voltage systems, a back-to-back converter configuration is used. One converter system is connected to the multi-phase generator and delivers power to the converter dc-link(s), whereas a second converter system delivers the power to grid via a multi-phase transformer. Control of these systems is more complicated than their conventional low voltage three-phase counterparts due to the low device switching frequencies.

This tutorial is intended to be a brief course on classical as well as on recently developed and deployed advanced control techniques for industrial medium-voltage multi-phase power conversion systems. The tutorial will focus on three closely related core topics, which are of major interest: generator-side control, grid-side control, and system related aspects. Regarding the generator and grid-side control topics, the attendees will get a strong grasp on control design requirements, traditional control techniques, and more recently developed model predictive control and optimization-based solutions in this area. Emphasis will be put on the requirements that need to be fulfilled in real industrial applications and the challenges related to them. In this regard, the shortcomings of state-of-the-art industrial control approaches and the benefits of the advanced ones will be assessed. Moreover, several important system-related aspects will be covered. In particular, the harmonic transfer mechanisms from the generator to the grid side will be analyzed. Characteristic examples of advanced control and modulation concepts for the suppression of the related harmonics are going to be presented. Furthermore, the topic of control stability at resonant grids is going to be briefly covered.