A Modular Magnetic Linked Converter Station for Offshore Power Transfer Through HVDC Link

Abstract

This paper proposes a modular magnetic linked converter station (CS) for offshore power transfer through a high voltage dc (HVDC) link. The proposed converter station can collect medium voltage ac and dc power simultaneously and transform the power to HVDC suitable for offshore power transmission. The proposed CS adopts multiple half-bridge (HB) converters to form a front-end interface that can collect both medium voltage ac and dc power. Moreover, several high-frequency magnetic linked multiport converters (MLMCs) are employed in the CS to isolate and step up the voltage. The MLMC is operated at a unity step-up voltage ratio which matches the turn ratio in multiple windings shared by a common magnetic link. This condition facilitates minimum current stress on the switches and inherent soft-switching operation. In the proposed CS, the hard switching operation of the front-end HB converters does not affect the switching condition of the MLMCs. Furthermore, the application of the switched capacitor-based HVDC converter enables discretized dc-link capacitor arrangement to limit high inrush current under dc fault. A controller structure is also proposed for the CS to balance the electrical parameters. The results from a simulation study of the proposed CS, both in steady-state and dynamic conditions, show that the proposed CS performs satisfactorily with the proposed controller, which is validated by the laboratory scale experiment.