Innovative wave energy conversion: Optimization of the energy harvesting cycle and converter design for a wave energy converter with Electro Active Polymers

Innovative wave energy conversion: Optimization of the energy harvesting cycle and converter design for a wave energy converter with Electro Active Polymers

Van Kessel, C.L.

Bauer, P. (mentor)
Czech, B. (mentor)

Electrical Engineering, Mathematics and Computer Science

Electrical Sustainable Energy

Electrical Power Processing

2010-10-20

Studies performed in the last decade have shown that wave energy could contribute as much as 10% in the current world electricity demand, making the ocean one of the most underrated and unexploited renewable sources so far. Wave energy offers distinctive advantages compared to other renewable technologies, providing a constant and predictable source of energy with minimal environmental impact. Although research on this topic has just been reinitiated, the devices that have been developed in these programmes typically suffer from the operation conditions in the marine environment. A new approach in this field is to use deformable materials, which should result in mechanical structures with improved reliability and survivability. An innovative new concept is to use smart materials in these deformable structures, which eliminate the need for additional generators and the typically related moving parts. This research addresses the application of Dielectric Electro Active Polymers (DEAP) in wave energy applications, and focusses on the electrical aspects involved in the energy conversion. Electrically, the EAP structure is represented by a variable capacitor, which capacitance is a function of the mechanical deformation. It is found that the energy conversion of an ideal EAP film is maximized when charging and discharging is performed infinitely fast at the maximum and minimum capacitance, respectively. An intermediate constant electric field stage results in the electromechanical conversion process. An optimized current waveform is investigated that results in the optimal energy cycle, maximizing the electrical energy output of the DEAP structure. For this purpose, the current amplitudes and the amount of charge left on the film are optimized in accordance with the material and excitation properties. It is found that even with poor material properties, reasonable energy output can be obtained by applying an optimized energy harvesting cycle. The energy cycle optimization has shown that energy harvesting in applications with low deformation ratios requires an highly efficient Power Take Off system (PTO). The specifications of this PTO converter have been derived using the parameters of a given test setup and the corresponding optimal energy cycle. In accordance with the purpose of the converter, a basic Buck and Boost topology has been selected, using a Zero Voltage Switching-Clamped Voltage (ZVS-CV) switching strategy. A single high-voltage switch configuration has been chosen for complexity and reliability reasons. Based on the PTO design procedure, it can be concluded that the high voltage and typically low current application challenge the design of the converter. To investigate the converter efficiency and characterize the losses, an accurate IGBT model has been deployed in the Saber circuit simulator. However, it has been found that the current tail effect is not modeled appropriately for the ZVS-CV conditions. Especially for high-voltage switches, the observed current tail is significantly increased under soft-switching conditions. Therefore, the design has resulted in poor efficiencies. Based on these findings, it can be concluded that topologies with a single high-voltage IGBT switch are not able to operate efficiently under the given conditions. Therefore, it is recommended to extend the research to multi-level topologies or series connected switch stacks using low voltage switches.

wave energy
dielectric elastomer
electro active polymer
energy harvesting cycle
Power Take Off system (PTO)
Zero Voltage Switching Clamped Voltage (ZVS-CV)
EAP emulator

http://resolver.tudelft.nl/uuid:de7c989d-f8ff-47b7-a36e-8cc95065d45f

2011-01-01

Student theses

master thesis

(c) 2010 Van Kessel, C.L.