Ocean energy test rig testing get programmable power 05 April 2012
A laboratory scale rig at the Hydraulics and Maritime Research Centre (HMRC), University College Cork, is now capable of emulating the variable power testing required at sea, thanks to control equipment from Emerson Industrial.
Project manager Dara O'Sullivan explains that, with a requirement for flexibility, programmability, safety and robustness, Emerson Control Techniques and Leroy-Somer were the only organisations prepared to provide an appropriate drive, motor, generator combination.
"Emerson Control Techniques was the only company prepared to produce a customised solution to meet our needs," he says. "They were most helpful in advising on how to make an easily reconfigurable electrical control system and were the most competitively-priced too."
O'Sullivan explains that, with the imminent requirement to connect more offshore devices and arrays to the grid, research and development has focused on the control and performance of electrical components in the power train – including generators, power converters and grid interface equipment.
Assessing design performance for these components under the operating conditions experienced in an ocean energy system is an expensive and difficult process, he says – and hence the laboratory scale test rig.
But the university researchers had a demanding list of specifications, including regeneration capability and flexibility – even at the relatively low power of a test rig and for a one-off project. So the supplier had to provide matching motors and drives, custom options (two shafts and a through-hole resolver for instance) and a wound-rotor induction machine – unusual at this power level.
Control Techniques' Drive Centre at Newbridge was able to match these requirements, so Leroy-Somer's motor specialists and Control Techniques' design and software engineers were brought in to support the project.
The experimental test rig now comprises a multi-contactor arrangement that allows for several different generator, power converter and grid emulator configurations, selected via a graphical PC interface program. Multiple time series input formats, prime mover models and control algorithms can be loaded into the PLC, using the same user interface.
As a result, says O'Sullivan, the rig is capable of recreating the dynamic response exhibited by a prime mover onto a motor/generator set, while simultaneously measuring exported power level and quality.
Additionally, the prime mover can simulate – from real or modelled time series data – any varying source such as a wind turbine, a hydraulic motor or a wave energy air turbine.
Three drives have been installed – all Control Techniques Unidrive SP ac drives. One controls the prime mover, whle the others, connected back-to-back, control the generator and, in regenerative mode, convert generator power from the control frequency needed to maintain the generator speed, to 50 Hz for grid synchronisation.
Each of the drives is fitted with a plug-in module for Profibus connectivity for PLC control.
Selection of a Leroy-Somer wound-rotor generator along with a multi-contactor configuration technique gives this system its flexibility in the selection of generator type.
Brian Tinham
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