A paper co-authored by Professor Win Rampen, the School’s Chair in Energy Storage, has been recognised with a prestigious international paper award.

The paper, published in the International Journal of Fluid Power, describes the design, build and test of the world’s largest, most efficient and controllable hydraulic transmission system ever deployed in a wind turbine, whose performance was captured by test results for the first time.

It was chosen for 2021 Best Paper Award by the Editor in Chief, Professor Andrea Vacca, after attracting more readers than any other paper in the journal over 2021, following huge interest from the fluid power industry and academics in the field. This was in part due to the commercial secrecy in which the tests were originally conducted, back in 2012.

The paper’s co-authors were Daniil Dumnov, Jamie Taylor, Henry Dodson, John Hutcheson and Niall Caldwell of Artemis Intelligent Power Ltd., a spinout co-founded by Rampen and fellow University of Edinburgh Professor, Stephen Salter in 1994.

Digitally controlled hydraulics

The innovative transmission system being tested was first developed by Artemis using so-called Digital Displacement® technology originated within Professor Salter's Wave Energy Group.

Digital Displacement® is a form of hydraulic machine which uses high-speed digitally controlled valves to regulate and direct fluid in a way that allows large powers to be transmitted efficiently and controllably through extreme, and varying, motion ratios. It has the potential to transform the viability of offshore wind power and low carbon transportation.

The idea of the digital displacement transmission was first proposed in the 1970s by the School’s Professor Salter and Robert Clerk, as they worked on The Edinburgh Duck, a pioneering wave power device. It was conceived as a means to capture the energy from slow-moving, high force and irregular ocean waves and convert this into the constant rotation needed to generate electricity with a synchronous generator.

The Artemis-developed hydraulic transmission system was conceived to replace the mechanical gearbox and power electronics in a typical wind turbine nacelle – the enclosed housing which powers the turbine’s energy-generating components.

Test results

Artemis first tested the transmission in a very large, 1.5 megawatt (MW) wind turbine transmission rig they built in Loanhead, Scotland with funding from Carbon Trust, DECC and Mitsubishi Heavy Industries.

The 1.5MW transmission demonstrated 93.5% shaft-to-shaft efficiency, a control response of less than 30 milliseconds. A world-first in terms of scale, these results demonstrated a huge improvement over previous hydrostatic drives used to power wind turbines, both in terms of efficiency - typically 80 - 85% would be expected - and an order of magnitude faster control.

In 2015 the transmission system went on to be used in a 7MW floating offshore wind turbine developed by Mitsubishi Heavy Industries (MHI) off the coast of Fukushima.

In 2021, MHI, having changed its commercial focus, sold Artemis to Danfoss Scotland. Danfoss is currently constructing a £25 million purpose-built facility in Shawfair, Midlothian to produce Digital Displacement® machines for off-road equipment. These are demonstrating improved fuel economies of 40% on a range of different machines, such as excavators, forklifts and wheel loaders.

The University is hosting a conference on digital hydraulics in September 2022, in collaboration with Danfoss Scotland.

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