A nonlinear double-speed electromagnetic vibration energy harvester for ocean wave energy conversion
Creators: name: Liu, Zhenwei
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401703
subject: Energy generation, conversion and storage (excl. chemical and electrical)

description: Nowadays, vibration energy harvesting is becoming one of the most promising technologies. However, the limited applications and techniques of ocean wave energy conversion have been reported. In this thesis, recently published researches for electromagnetic vibration energy harvesting techniques have been studied. The various techniques are classified in terms of micro and macro vibration energy harvesters, broad bandwidth vibration energy harvesters, and large scale ocean wave energy converters. The review of the nonlinear oscillator vibration energy harvester based on magnetic spring is focused. The efficiency of extracting energy from the waves is limited, although various concepts and designs of the power take-off systems and primary interface and circuits have been studied. This thesis will identify the possible power take-off systems from reviewing electromagnetic vibration energy harvesting techniques aiming to increase the power and bandwidth of ocean wave energy converter for maximizing future utilization of the ocean wave energy.<br><br>This thesis invents a cuboid generator with high vibration energy harvesting performance. The cuboid vibration energy harvester consists of a fixed pulley mechanism connecting two magnet array units with a coil unit on the two sides of the pulleys. The two magnet array units are arranged in double Halbach magnet arrays which are used to increase the magnetic field intensity and flux intensity change rate around the coils. The fixed pulley mechanism is used to double the speed of the magnets with respect to the coil unit. As the output voltage of the vibration energy harvester is proportional to the magnetic field intensity and flux intensity change rate around the coils and the speed of the magnets with respect to the coils. The novel design of the prismatic tube vibration energy harvester has a high vibration or wave energy harvesting performance or capacity.<br><br>This thesis investigates the cuboid generator functioning as vibration energy harvester or wave energy converter through linear and nonlinear oscillator dynamic analyses in a low frequency range. Duffing type nonlinear oscillator dynamic differential equation is developed for the nonlinear analysis where the effect of the rotational inertia of the pulleys on the oscillator mass is considered, which is different from the literatures. The nonlinear oscillator dynamic differential equation is solved by using the harmonic balance method and perturbation method in order to widen energy harvesting frequency bandwidth. The formula of the dimensionless harvested power of the nonlinear oscillator mass-spring-damper system is derived and a parameter study is conducted for the design optimisation of the harvester. The parameters that affect the nonlinearity of the oscillator are also studied in this thesis. Finally, the prototype of the novel device is built and tested to validate the analysis.<br><br>The influence of nonlinear oscillator interaction force acting on the moving part on the generator’s potential well is also studied in this thesis. It is found that large displacement excitation amplitude and nonlinear stiffness k3 will increase the nonlinearity, output voltage and harvesting frequency bandwidth.