Modular high voltage DC/DC converters and converter control

Abstract
Efforts in decarbonization lead to electrification, not only for road vehicles but also in the sector of mobile machines. Aside from batteries, those machines are electrified by tethering systems, nowadays featuring an AC low voltage system. Those systems are applied, e.g., to underground load haul dumpers with short tethering lines and low machine power. To expand tethering to further markets as agricultural machinery, this work proposes an HVDC tethering system allowing higher machine power and transmission length due to thinner, lighter tethering lines. The HVDC voltage is converted by distribution over a number of series connected DC/DC converters. Less blocking voltage on the semiconductors allows faster switching technology to reduce the converters’ weight and volume. The concepts modularity allows for flexible adaption on various application scenarios. Since comparable concepts exist for offshore wind farms connectivity, its applicability for this is discussed. A full bridge inverter/rectifier LLC resonance DC/DC converter is presented for the modules. A switched LTI converter model is developed and a Common Quadratic Lyapunov Function (CQLF) is computed for prove of stability. The converter control features soft startup and voltage control over all modules. The concepts are validated by simulation and on a scaled prototype.