A DC autotransformer design for medium and high voltage DC transmission systems

This paper studies a dc-dc converter topology dual to the ac autotransformer for medium and high voltage dc-dc conversion. Operation with trapezoidal modulation is analyzed where the dc autotransformer is built of transition-arm bridges. This structure features less power electronics installation and energy storage capacity as compared to counterparts operating in sinusoidal modulation. It also permits the use of low-loss devices such as thyristors or Insulated Gate Commutated Thyristors (IGCTs), promising high efficiency. The paper investigates this topology in steady state as well as DC fault blocking capability.