Classical control theory combined with robotics and aerospace double the amount of power a wave energy converter can absorb from waves.
A team from the Sandia National Laboratories in the US are using a combination of modelling and experimental testing to refine how a wave energy converter moves and responds in the ocean to capture wave energy while also considering how to improve the resiliency of the device in a harsh ocean environment.
“We are working to create methodologies and technologies that private companies can harness to create wave energy devices that will enable them to sell power to the US grid at a competitive price,” Sandia engineer Ryan Coe said.
“By getting more energy out of the same device, we can reduce the cost of energy from that device.”
Their wave energy converter is a large one-tonne ocean buoy with motors, sensors, and an onboard computer built at a scaled-down size for a testing environment. Commercial wave energy converters can be large and are generally part of a group of devices, like a wind farm with multiple turbines.
“These devices can be in open ocean and deep water, maybe 50 to 100 miles off the coast,” said Coe.
“An array of wave energy converters, maybe 100 devices, connected to an underwater transmission line would send the wave energy back to shore for consumption on the grid.”
To capture energy from the ocean’s waves, a wave energy converter moves and bobs in the water, absorbing power from waves when they generate forces on the buoy. Sandia’s previous testing focused on studying and modelling how the devices moved in an ocean-like environment to create a numerical model of their device.
Using this model, they wrote and applied multiple control algorithms to see if the converter could capture more energy. The control system uses a feedback loop to respond to the behaviour of the device by taking measurements 1000 times per second to continuously refine the movement of the buoy in response to the variety of waves. The team developed multiple control algorithms for the buoy to follow and then tested which control system yielded the best results.
“Controls is a pretty big field,” said another Sandia engineer, Dave Patterson.
“You can operate anything from planes to cars to walking robots. Different controls will work better for different machines, so a large part of this project is figuring out which control algorithm works and how to design your system to best take advantage of those controls.”
Results from numerical modelling with the control algorithms showed a large potential, so the team took the converter to a US Navy facility in Maryland to test the new control methods in an ocean-like environment. The team ran a baseline test to see how the converter performed with a simple control system directing its movements and actions. Then they ran a series of tests to study how the various control algorithms they had designed affected the ability of the device to absorb energy.