Economic lifetime-aware wind farm control

We present the economic lifetime-aware formulation of wind farm control (WFC), a novel approach characterized by two key innovations with respect to the state of the art. First, the optimization is guided by an economic model of profit. By targeting profit instead of the more widely adopted power yield, the operational optimization considers not only the revenue generated by selling electricity (possibly at a variable price when operating on spot markets) but also the costs due to operation and maintenance (O&M). Second, since fatigue-induced damage is a finite-budget quantity, we explicitly consider that any effect on damage generated by a control action will leave more or less room to other control actions, a coupling that is neglected by current approaches that arbitrarily limit or penalize fatigue-inducing loads. To achieve this goal, the optimization is subjected to explicit constraints on lifetime, which ensure that the turbines in a farm and their components can indeed reach a desired goal duration. As for other optimization-based WFC approaches, the proposed method results in the offline calculation of optimal control set points for each turbine, which are scheduled and dispatched at run time in an open loop as functions of ambient conditions. After introducing the economic lifetime-aware WFC approach, the paper analyzes two case studies. The first represents an idealized scenario characterized by a simplified set of environmental conditions, designed to demonstrate the behavior of the new control strategy and its impact on fatigue loads in conditions of very frequent waking. The second case features a more realistic small wind farm, with wind climate data derived from an existing meteorological mast. The benefits of the proposed methodology are highlighted by comparing it to alternative, previously published control strategies, which either ignore component damage or address fatigue loads in alternative, simplified ways. Results show that the lifetime-aware formulation always ensures the achievement of the desired lifetime targets, whereas methods that do not enforce such a condition may fail to do so. Additionally, the proposed method also results in the best economic performance, i.e., in the highest profit.