Webinar: Control systems for improved yield, reliability and survivability
27 June 2017
11.30am (Brussels, Berlin, Paris)
10.30am (London, Dublin, Lisbon)
Presenters: Ross Henderson, Quoceant
Jochen Bard, Fraunhofer IWES
Control systems for wave and tidal energy converters act to optimise power production and reduce stress and fatigue on components by allowing devices to adapt to changing ocean conditions.
This webinar provided a brief introduction to the theory of control systems, including a look at their use in other sectors, before investigating how such systems can be applied to the ocean energy sector.
Ross Henderson (Senior Consultant Engineer at Quoceant Ltd.) and Jochen Bard (Head of Marine Energy at Fraunhofer IWES) each presented their perspective on control systems in ocean energy before the floor was opened to all attendees for questions, comments and discussion.
- Regarding the recent WES control systems landscaping study: what were the key report findings and lessons learned, and how do they apply to real world actions? The WES strategy is to take a whole system, modular approach to technology development by drawing in outside sector learnings with aim of filling technology ‘gaps’ between State of the Art, and what is actually required. A common understanding is of key importance, with parallel not isolated working groups to understand engineering drivers and resolve successfully a working, fully compatible final product. The communication lesson is key, whilst the landscaping study provided a common technical foundation to avoid repetition, and give common starting point and proper model controls representation in order to find real world solutions.
- With respect to Hardware in Loop testing – how are other systems like generators and pitch system controllers integrated? It is advised to use the real generator/pitch drive hardware and to connect them to controllers, with load machines to introduce real world parameters to excite realistic responses from subsystems. The use of filters are pre-determined in the systems design to limit degrees of freedom, and control interactions. Defining the real world parameters (like absolute speed for example) that exceed system limits are an important prerequisite to HiL testing.
- With regards to dense device arrays: what is the value of defined control systems value, particularly with regards to cost of energy and reliability? From a wave perspective, since it has already considered important on an individual basis, it is even more important for an array. Arrays allow downside mitigation by taking advantage of far-field interactions in wave energy. Power absorption as an array’s sum is greater than the sum if individual devices because phasing. With multiple devices, individual radiation patterns and power adsorption can be phased and focused to maximise energy extraction. This is a good example of useful insight from theoretical work done academically. From a tidal perspective: in a similar way to wind farm energy yields – having devices standing behind each other allows de-rating and a gain in array power. You must also ensure device wakes are considered, so downstream turbines are not operating in wake areas and subject to increased applied structural loads.
- Looking at other wave and tidal energy challenges – relative to other key challenge areas, what is the overall value of continued R&D into control systems? The biggest difference between wave and tidal is that tidal has converged on power stream conversion using single torque/speed control. WECs are still so diverse, so the challenge for wave is far more integrated to R&D compared to other sectors. Controls are considered as very important aspects for wave. Even if tidal does have commercial convergence however, control is still important since it allows system optimisation and cost reductions. So in the commercial world – controls are considered to have the largest impact on reducing LCOE for tidal today. Controls have traditionally been underestimated, since they are considered a marginal expense in relation to early stage CAPEX expenditures. Controls however are able to have a large impact for relatively little investment through continued R&D integration.