Supervisor:
Stig Munk-Nielsen

Co-Supervisor:
Asger Bjørn Jørgensen

Assessment Committee:
Tamas Kerekes

Prof. Michael A.E. Andersen DTU Denmark

Prof. Óscar Lucía, University of Zaragoza, Spain

Moderator:
Michael Møller Bech

Abstract:

Industrial heating has played a significant role in moulding the modern human lifestyle.
It is evident from the fact that industrial heating constitutes 20% of the world total energy consumption. Modern industrial dielectric heating plants are based on vacuum tube radio frequency (RF) generator. The vacuum tube RF generator provides an efficiency of 60% or less. This is not optimum, as almost half of the energy is being wasted as heat. Novel semiconductor technology based on wide bandgap (WBG) materials such as silicon carbide (SiC) and gallium nitride (GaN) provides an opportunity to remove the ageing vacuum tube from industrial dielectric heating RF generators.
To develop the next generation of RF generators that can be retrofitted in existing industrial plants as turn-key solution, requires understanding the dielectric heating from the point of view of solid-state technology. In this thesis the literature survey identifies several works based on WBG and silicon devices that have achieved the frequency of operation required by industrial dielectric heating. It is understood that gallium nitride
is a better candidate for operation at 6.78 or 13.56 MHz in ISM band (industrial, scientific, and medical). However the low breakdown voltage of commercially available GaN devices is a challenge as industrial dielectric heating requires high voltage output from the RF generator to deliver high power.
The thesis presents a novel topology called Class-PN that achieves high device utilization in resonant converter topology and delivers high output power. The thesis then expands the Class-PN from standalone to multi-cell approach to achieve the high voltage output as required by industrial RF generators.
The thesis further models and analyses an industrial dielectric plant load structure.
The study begins by considering different load compensation topologies and identifies that series-parallel compensation is best suited for industrial dielectric heating plants.
The load structure analysis is conducted such that it assists in identifying the ratings of RF generator. Finally the developed load structure based on the analysis and three cell configuration of Class-PN is operated at 6.78 MHz generating 1.1 kV peak-peak RF output voltage from 185 V DC input voltage. The Class-PN is based on 650 V GaN HEMT. The overall efficiency achieved from DC input to RF output is approximately 80% for an output power of 856 W.