Research and development of a regulated high voltage power supply (rhvps) for nuclear fusion facilities

The Ion Cyclotron Resonance Heating (ICRH) system, employed in tokamaks for the heating of fusion plasmas, utilises radio frequency (RF) waves generated by RF generators. These generators can be based on Solid-State technology, which is currently under development, or the well-established Tetrode Grid-Tube technology, which continues to benefit from ongoing advancements. In this study, tetrode technology is selected for the amplification stages of ICRH transmitters. Furthermore, the electrical specifications of power supplies are defined as a function of various parameters, including amplification, efficiency, and load conditions. With reference to the specifications of the DTT ICRH system currently under construction at the ENEA Research Centre in Frascati, this research has identified tetrode technology as the optimal choice for the ICRH transmitter amplification stages. To this end, an exhaustive analysis was conducted to determine the operating points and the most demanding operating conditions, with the aim of determining the specific power supply requirements. This work proposes the development of a high-voltage regulated DC power supply, referred to as HVPS, designed to power the tetrode, which forms the final stage of the RF transmitters. The HVPS requires high performance in terms of accuracy, stability, and response speed. This requirement necessitates the adoption of unconventional solutions, which in turn call for highly customized development. In this study, the optimal architectural configuration for high-voltage power supplies is identified, along with the selection and sizing of the equipment and main components required to power the final stage (FPA) of the RF transmitter. The choice of components was guided by solutions that, in addition to ensuring the achievement of the required performance, meet the needs of sustainability, operator safety, and environmental protection in the system's operating environment. The HVPS system is primarily composed of conversion modules, referred to as Switched Power Supplies (SPS), connected in series. These modules are based on a design featuring a six-pulse rectifier and a buck converter configured with an IGBT and an LC filter. The power section of the HVPS system is made up of multi-secondary transformers, specifically designed and constructed for this application. The transformers utilize a phase-shifting configuration of the windings to achieve compensation of the harmonic components injected by the SPS conversion modules. The developed HVPS system is designed to adequately meet the project requirements through the implementation of a control and regulation system that, despite its complex structure, is highly efficient. In addition, this system employs specific solutions, including the Pulse Step Modulation (PSM) technique, which relies on PWM modulation to drive the IGBTs in the SPS modules. The choice of connections for the secondary windings of the multi-secondary transformers, combined with the phase-shifting technique and the PSM technique, enabled satisfactory results in harmonic compensation. The complete HVPS system was modelled and simulated using MATLAB/Simulink© software, which allowed the representation of the system's behaviour and operational characteristics. This approach demonstrated that the system achieved the desired performance in terms of stability, slew rate and ripple. The modularity and versatility of the developed HVPS system enables its adaptation to a dual-supply configuration, capable of meeting power requirements not only for the FPA stage but also for the second DPA stage or other loads within certain limits. 4 The protection system, which safeguards both the components and the personnel, along with the auxiliary systems, is a fundamental element that completes the design aspects of the HVPS system. Considering the preliminary assessments conducted in this research regarding the choice of Grid-tube tetrode technology versus Solid-state technology, a peer review was carried out, considering the possibility of using an RF Solid-state generator based on LDMOS devices. This research makes a significant contribution to the field of high-voltage electronic power supplies, with specific reference to power supply systems for tetrodes used as RF generators. The results not only advance our understanding of applicable technologies in this field but also provide practical and innovative solutions to improve the efficiency, stability, and versatility of power supplies in high-power contexts.