Hybrid, Multi-Megawatt HVDC Transformer Topology Comparison for Future Offshore Wind Farms

Abstract

With the wind industry moving further offshore, High Voltage Direct Current (HVDC) transmission is becoming increasingly popular. HVDC transformer substations are not optimized for the offshore industry though, increasing costs and reducing redundancy. A suggested medium frequency, modular hybrid HVDC transformer located within each wind turbine nacelle could mitigate these problems, but the overall design must be considered carefully to minimize losses. This paper's contribution is a detailed analysis of the hybrid transformer, using practical design considerations including component library minimization. The configurations investigated include combinations of single phase H-Bridge and Modular Multilevel Converter topologies operating under minimum switching frequency control strategies. These were modelled in the MATLAB/Simulink environment. The impact of the minimum switching control strategy and converter topology on power transfer stability and overall efficiency is then investigated. It was found that the H-Bridge converter generated the lowest overall losses, but there was a trade off with power flow sensitivity due in part to the additional harmonics generated.

Design and Prototyping Medium-Frequency Transformers Featuring a Nanocrystalline Core for DC–DC Converters

“…The parameters associated with power loss must be taken into consideration in the transformer design procedure [8]. The MFTs have a range of applications in DC-DC converters for smart networks [9], electric vehicles [10], wind power generators and plants [11], interfacing of photovoltaic systems [1], and solid state transformers [12,13].…”

Power-from-Shore Optioneering for Integration of Offshore Renewable Energy in Oil and Gas Production

“…They also do not have the added burden of reactive power compensation systems and can rely on a smaller subsea cable footprint. The decision between HVAC and There are also reviews [19] addressing the potential modularization and miniaturization of offshore HVDC systems, which can potentially be incorporated into the design of compact HVDC e-houses for O&G sites. Multiple challenges were found, though, particularly in the control methodologies and inner design of the converters.…”

Coordinated Control for Large-Scale Wind Farms with LCC-HVDC Integration

“…Also, Q w = -u bd i wq + u bq i wd and Q rc = -u bd i rcq + u bq i rcd are the reactive powers from the WECS and they are absorbed by the LCR respectively, and ω 1 is the SEB frequency. Equations (5) and (6) lay the foundations for this study. From the perspective of the filter capacitor parallel branch, the WECS can be seen as a controlled power source (P w and Q w ), while the LCR can be seen as a controlled power load (P rc and Q rc ).…”

“…Consequently, the instantaneous current amplitude will increase, which leads the instantaneous voltage amplitude to increase too. Similarly, if there is a reactive power deviation for Equation (6), e.g., (-Q w + Q rc ) > 0, which indicates that the reactive power generated by the WECS is smaller than that absorbed by the LCR, then the voltage phase-angle (i.e., the instantaneous frequency) will increase, assuming that the voltage amplitude keeps unchanged. As a consequence, the capacitive reactance will decrease due to the frequency increase, and therefore the capacitor will generate more reactive power to try to balance the reactive power.…”

“…It is quite difficult for the system to maintain stable operation when there is no traditional generating set that is available at the sending end of the UHVDC, due to some special factors, e.g., circuit faults, but only islanded WFs and/or photovoltaic power plants. Therefore, it is necessary to study the control scheme of large-scale WFs with LCC-HVDC integration as a technical reserve [4][5][6][7].…”