Analysis of bidirectional 15 MW current source DC/DC converter for series-connected superconducting-based 1 GW/100 kV offshore wind farm

A wind farm with series de collection can potentially eliminate the costly offshore platform and its step-up components. Multiple series strings can be connected in parallel to extend the power capacity for a given voltage. In such arrangement, the DC/DC converters for individual generators are rated at only a fraction of the transmission voltage. The maturity of superconducting cable technology will eliminate the difficulty of transmission losses with high current low voltage systems. This paper presents a feasibility study on the DC/DC converter design for a parallel-series-connected wind farm. The isolated front-to-front (F2F) mixed voltage source converter (VSC) and current source converter (CSC) is examined with power back-feeding capability during wind calm periods for a 15 MW generator. A novel configuration using 3-level (3L) VSC and thyristor-based CSC with combinational control of AC voltage magnitude, frequency, and thyristor delay angle is proposed and evaluated for a 1 GW/100 kV parallel/series wind farm based on the superconducting cable. Detailed converter model including power loss estimation in PSCAD is presented to support the converter design recommendations.