A modular, multi-megawatt, hybrid HVDC transformer for offshore wind power collection and distribution

Michael Smailes, Chong Ng, Paul McKeever, Robert Fox, Mark Knos, Jonathan Shek

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

As converters are required on both primary and secondary sides of the magnetic transformer in a HVDC station, higher operational frequencies may be considered. A Medium Frequency Power Transformer (MFPT) operating between 500 and 2000Hz would reduce the transformer size and weight, and also the construction cost. However, higher frequencies correspond to increased losses in both the converters and magnetic transformer. There is limited published work on MFPTs but that presented by S. Meier et al has primarily focused on optimising the magnetic transformer efficiency. The converter design, however, will also have a significant impact on the overall losses of a MFPT. The converter topology, modulation and control strategy not only determine the converter losses but also the output waveform and hence magnetic transformer losses. It is therefore vital that in a MFPT, the converters are designed to minimise the overall losses rather than the converter or magnetic transformer losses alone.
Two converter topologies, the H-Bridge (HB) and Modular Multilevel Converter (MMC) will be investigated in three configurations: HB-HB, HB-MMC and MMC-MMC. These topologies have been selected because the Modular Multilevel Converter (MMC) can produce smooth sinusoidal outputs while the H-Bridge topology introduces simpler designs with fewer components. To minimise losses, a new material, nano-crystalline amorphous, normally used for low power high frequency applications, has been selected for the core. Its Steinmetz parameters have been calculated from experimental results and will be used in the improved General Steinmetz Equation (iGSE) ensuring accurate representation of core losses.
Original languageEnglish
Title of host publicationEWEA Offshore Wind Energy Conference
PublisherEuropean Wind Energy Association
Publication statusPublished - Mar 2015

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