Transformer-Less HVDC Generator Using Modular Rotating Varying Capacitance Machines With Integrated Rectifiers

High-voltage direct current (HVDC) transmission is increasingly being used to improve the efficiency and economic viability of power transmission in applications where AC transmission struggles. However, a barrier to its adoption is the complex network of decoupled transformers and power electronics needed to transform low-voltage AC outputs of electric generators into HVDC. This paper presents an integrated and modular design based on electrostatic machinery and cascaded bridge rectifiers to bypass some of the complexities with contemporary HVDC systems. While the idea of using electrostatic machinery for simplifying HVDC systems dates back to a 1977 concept paper published by General Electric, this work overcomes prior attempts’ bottlenecks by applying modern power electronics architectures and an improved understanding of electrostatic machinery. Moreover, this work demonstrates that HVDC systems can be greatly simplified by utilizing electrostatic generators that naturally facilitate high-voltage operation with integrated modular rectifiers. This conjecture is supported analytically from the perspective of an averaged model along with multilevel bench-scale experiments. A first-order scaling analysis supported by the developed model and FEA shows that for an offshore wind park system, active component mass and volume can be reduced by 5x and 2.5x, respectively, when compared to existing approaches.