HVDC Power Distribution and Protection Architectures for Subsea Electrical Systems

Abstract

Subsea electrification is one of the key building blocks for harnessing deep-water hydrocarbon resources. A subsea electrical system should operate reliably over a long time duration to maximize production and minimize operational cost. State-of-the-art subsea electrical systems utilize high voltage alternating current (HVAC) transmission. Although HVAC is a well-known technology, the large reactive power demand of the transmission cable presents a serious challenge in long-distance transmission. To address these issues, this dissertation proposes a family of novel power distribution architectures based on high voltage direct current (HVDC) technology. A family of novel DC fault protection topologies to be applied in these HVDC architectures has also been proposed. Current HVAC systems supply power to subsea loads through a high voltage submarine cable. With increasing transmission distance, the reactive power drawn by this HV cable increases manifold, resulting in serious cost implications. The line charging reactive power is eliminated in HVDC submarine cables, which offers substantial cost benefits in long-distance transmission. This dissertation proposes three novel HVDC architectures for long tie-back subsea fields. The solid-state transformer (SST) based modular distribution system provides increased redundancy and fault-tolerant operation. HVDC system requires fast protection against short-circuit faults. Fault interruption in DC systems is difficult due to the absence of zero-crossing in the fault current. To address this issue, a family of zero current switching (ZCS) hybrid DC breakers has been proposed. The presented circuit-breakers realize arcless breaking operation for mechanical breakers. Fast fault response by the proposed DC breakers has been verified using experimental prototype units. Subsea production system also uses direct electric heating (DEH) of subsea pipelines to prevent hydrate formation. The existing DEH technology requires significant VAr compensation due to the highly inductive pipeline. An LCCL resonant inverter (LCCL-RI) is presented in this dissertation to alleviate this issue. The LCCL-RI operates as a load-independent constant current source. Tank capacitors provide the required reactive power compensation. The performance of the LCCL-RI is evaluated in a SiC MOSFET based laboratory prototype.