Hydrodynamic-Electrical-Control Co-Design of Hydrokinetic Turbines

Abstract The design optimization of a hydrokinetic turbine (HKT) is inherently multidisciplinary, involving hydrodynamic, mechanical, electrical, and control design. In the conventional sequential design process, the system-level problem is divided into sub-problems. These sub-problems are then solved in sequence, leading to sub-optimal solutions because it does not fully exploit cross-disciplinary synergy. This paper explores the optimal design of an HKT system by developing a control co-design (CCD) framework to simultaneously optimize the physical design variables, power transmission variables, and optimal control trajectory for a variable-speed fixed-pitch HKT. The CCD considers a system-level model that captures the couplings between the hydrodynamic and electrical efficiency of the HKT. Case studies are performed by analyzing the final designs and resulting hydrodynamic and electrical efficiencies. Electrical energy generation obtained through the proposed CCD approach is compared with a sequential design-control method. The cases show that the CCD approach, which considers hydrodynamics, electrical system, and control concurrently, leads to a different physical design and improved energy output of 1.76% more than that of the optimized system through a sequential method. The studies demonstrate that CCD benefits HKT design and achieving system-level optimality.