A Holistic Optimization Framework for Optimal Sizing, Cost, and Longer Lifetime of DC-DC Modular Solid-State Transformers in Wind Energy Applications

Abstract

Offshore wind farms have been gaining momentum in recent years. As a result, industrial and research efforts are focusing on improving the performance of power electronics converters for offshore wind turbines. Solid-state transformers (SSTs) are regarded as a prominent alternative to the current energy conversion units in wind turbines. However, application specific performance evaluations for SSTs are missing in the literature. Due to this gap, it is not possible to evaluate the benefits of using SSTs in offshore wind applications. To address this issue, this paper presents the modeling and optimization of the efficiency, cost, and lifetime of a DC-DC SST for an offshore wind application. A direct current system is integrated between the wind turbines; therefore, the wind farm utilizes a DC collection system. The converter is designed with high voltage SiC (Silicon Carbide) MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) (3.3 kV) to achieve high efficiency and medium voltage rating. Dual active bridge topology and its variations are utilized to achieve high power density and isolation. A novel optimization framework is developed and employed to determine the best design parameters to achieve an optimal solution in terms of efficiency, cost, and lifetime. The final results have demonstrated that the efficiency of the optimal design can exceed 98.1%, and its converter material cost is 46.5 ke/MW. Furthermore, the expected lifetime can exceed 45 years. Lastly, a cost sensitivity analysis is conducted to evaluate the future cost of the system. This analysis indicates that the cost of the SiC based SST converter could match that of Si based solutions by the mid-2030s.

Keywords

• Solid-state transformer (SST)
• SiC MOSFET
• lifetime
• reliability
• material cost
• DC-DC converter