Abstract
An increase in wave energy converter (WEC) efficiency requires not only consideration of the nonlinear effects in the WEC dynamics and the power take-off (PTO) mechanisms, but also more integrated treatment of the whole system, i.e., the buoy dynamics, the PTO system, and the control strategy. It results in an optimization formulation that has a nonquadratic and nonstandard cost functional. This article presents the application of real-time nonlinear model predictive controller (NMPC) to two degrees of freedom point absorber type WEC with highly nonlinear PTO characteristics. The nonlinear effects, such as the fluid viscous drag, are also included in the plant dynamics. The controller is implemented on a real-time target machine, and the WEC device is emulated in real-time using the WECSIM toolbox. The results for the successful performance of the design are presented for irregular waves under linear and nonlinear hydrodynamic conditions.
Highlights
Renewable energy technologies present a viable and sustainable contribution to the world’s growing energy demands, and the ocean provides potential for an enormous untapped energy resource for the world’s energy portfolio [1,2]
power take-off (PTO) mechanisms, and the lack of application of nonlinear model predictive controller (NMPC) for such class or problems, we have investigated the application of NMPC to nonlinear multiple DoF wave energy converter (WEC) plant with a non-ideal PTO mechanism, and focus on the real-time implementation of the control algorithm on a real-time target machine
The Speedgoat machine is interfaced with a real-time WEC emulator machine through an Ethernet universal data port (UDP) channel
Summary
Renewable energy technologies present a viable and sustainable contribution to the world’s growing energy demands, and the ocean provides potential for an enormous untapped energy resource for the world’s energy portfolio [1,2]. The prospect of ocean wave energy has triggered research in optimal power capture techniques for wave energy converters, including non-ideal operating conditions, such as the non-ideal PTO system constraints [3] and nonlinear sea conditions. Achieving optimal power capture by a WEC in practice is a multifaceted objective It depends on various factors, such as the physical design of the WEC, the design of the PTO system, the ocean conditions, and the control techniques. Model predictive control (MPC) is a promising control approach for wave energy converters’ relatively slow plant dynamics because it maximizes energy capture while respecting the system’s mechanical limits. Nonlinear control algorithms can consider the non-ideal operating conditions and nonlinear effects, including but not limited to non-ideal power take-off mechanism [11], nonlinear viscous drag terms [12,13], and nonlinear mooring dynamics [2]. We have deployed a real-time iterative (RTI) algorithm [20,21]
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