Electrical and power supply systems of Helios fusion power plant

This paper presents the preconceptual design of the electrical and power supply systems for ”Helios”, a stellarator fusion power plant developed by Thea Energy, Inc. The design enables a net electrical output of 390 MWe from 1.1 GW of thermal power, with a steady-state auxiliary power consumption of approximately 70 MW. The architecture features a robust 345 kV grid interface and a 34.5 kV medium-voltage backbone for distributing power to all plant subsystems. To ensure grid stability and power quality, the system integrates a Static Synchronous Compensator (“STATCOM”), harmonic filters, and a small Battery Energy Storage System (“BESS”). A primary focus of the design is on the three specialized power supply families required for plasma confinement and heating. These include: (1) high-current (up to 50 kA) bidirectional power supplies for the 12 encircling superconducting coils, utilizing a Constant Voltage/Constant Power charging strategy; (2) AC/DC power supplies with hot-swappable four-quadrant DC/DC converters for the 324 individually controlled shaping coils; and (3) highly efficient and precise modular Pulse-Step Modulation (“PSM”) based high-voltage power supplies for the 10 MW Electron Cyclotron Resonance Heating (“ECRH”) system. The overarching design philosophy emphasizes modularity, redundancy, and hot-swappable components to maximize reliability and maintainability, establishing a comprehensive and resilient electrical infrastructure for continuous, grid-compliant fusion energy generation.