Investigation of a novel multiresonant beam energy harvester and a complex conjugate matching circuit

The aim of the work described in this thesis is firstly to improve the collection of vibration energy for piezoelectric cantilever harvesters, by a mechanical technique, so that the devices can harvest energy over a wider bandwidth. Secondly to investigate a new circuit topology for achieving complex conjugate load matching to the piezoelectric harvester. The thesis has been divided into two parts - the mechanical approach and the electrical approach. For the mechanical approach, a novel multiresonant beam, comprising piezoelectric fiber composites on a clamped-clamped beam and side mounted cantilevers, was proposed. The side cantilevers are tuned by tip masses to be resonant at different frequencies. A Rayleigh-Ritz model was developed to predict the vibration response of the proposed model multiresonant beam. This model showed that the bandwidth of the multiresonant beam was increased over that of a single cantilever harvester. A multiresonant beam for energy harvesting was experimentally tested and compared with a single cantilever energy harvester. The transmissibility and voltage responses were investigated, the beam showed a wide frequency response between 14.5Hz and 31Hz, whereas the single cantilever only showed one resonant frequency. Therefore the multiresonant beam system is feasible for wide band energy harvesting. For the electrical approach, the task was to investigate complex conjugate impedance matching for the piezoelectric energy harvesters, so that the output impedance from the piezoelectric harvester can be reduced, and maximum energy extracted from the device with a possibility of frequency tuning. A new amplified inductor circuit was proposed to enable the capacitive output impedance of the piezoelectric device to be cancelled. Experimental and software simulations are provided to verify the theoretical predictions. A prototype amplified inductor circuit was simulated and tested. The results showed that a variable effective inductance was achieved. However the circuit is lossy due to imperfections within the system, and needs further work to eliminate these imperfections.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A Dual-Slot Barrier Sensor for Partial Discharge Detection in Gas-Insulated Equipment

This paper reports on the development and testing of a novel barrier sensor for UHF Partial Discharge (PD) detection in gas-insulated equipment. The sensor features a unique dual-slot planar antenna backed by an air-filled cavity. The dual-slot arrangement allows different parts of the antenna to resonate at different frequency ranges in the UHF spectrum. As a result, the sensor exhibits broader bandwidth and higher sensitivity than other barrier sensors. Finite Element Analysis simulations have been used to optimize the sensor design. Furthermore, testing using a specially made PD test rig, GTEM cell testing and testing on a gas-insulated line section in the high voltage laboratory, have validated the simulation results and the capabilities of the sensor. The Dual-Slot Barrier (DSB) sensor exhibits a bandwidth of 0.3 -2.0 GHz with a mean effective height of 13 mm, and an effective height above 2 mm for 90% of the frequency range. The sensor can be used with both wideband instruments, such as oscilloscopes, and narrow band instruments such as frequency downconverters. Additionally, its optimized dimensions and unique replaceable sealing attachment ensure maximum compatibility for retrofitting on a wide range of equipment

Fast operating moving coil actuator for a vacuum interrupter

Vacuum circuit breakers are the dominant technology in medium voltage distribution networks since they are environmentally friendly and maintenance free. It is a challenge to design an actuator for a vacuum circuit breaker, which achieves a high operating speed whilst maintaining high efficiency. A fast operating moving coil actuator for a vacuum interrupter (VI) has been developed. An analytical model of the actuator was initially developed and then simulated using a three-dimensional finite element (FE) model. The model showed that the opening force was higher than the closing force due to asymmetry in the structure of the actuator, which resulted in a reluctance force component. The complete operating actuator prototype was built to avoid known problems such as contact popping, bounce, rebound and welding. The magnetic field distribution and the static electromagnetic force on the moving coil were measured and provided a good correlation with the FE model simulation predications. The opening operation of the actuator prototype was compared for different capacitor supply voltages. A maximum velocity of 2.3 m/s was achieved when the capacitor was charged to 150 V. The actuator demonstrated successful operation at atmospheric pressure and also in a vacuum chamber. The opening time of the actuator in the vacuum was approximately 5 ms, compared to 5.5 ms at atmospheric pressure. We designed and built this actuator to illustrate that the moving coil actuator is capable to operate the vacuum circuit breaker quickly with high efficiency. Tests showed that further design optimizations for improving the operating speed and efficiency of the moving coil actuator are essential and the options have also been suggested.<br/