Dr Jonathan Shek

The research at the Institute for Energy Systems has a strong emphasis on renewable energy - in particular, wind, wave, and tidal current energies. The work undertaken within the electrical machines and power electronics group aims to develop novel generator technologies and power conversion solutions for wind, wave, and tidal current devices. My work concentrates on different aspects of control of electrical generators using a power electronic interface. Summaries of my core research areas are given below.

Core Research Areas:

Control of linear electrical generators for direct drive wave energy converters [+]
This project aims to develop control strategies for optimising the energy absorbed from a wave energy device, such as heaving buoy, using a directly coupled linear electrical generator. The energy captured by a wave energy device is a function of the frequency of the incoming waves and their amplitude. Maximum energy is captured when the incoming wave frequency matches the resonant frequency of the device, but this condition can never be guaranteed. Waves are random, and hence some form of control is required to optimise the energy captured. Phase control ensures the wave excitation force and the velocity are in phase, which is always the case at resonance. This is achieved at off resonant frequencies by applying an additional spring force by mechanical means. However, in a previous project it has been shown by simulation that a directly coupled linear electrical generator can be used to provide this additional spring force. The aim of this project is to develop control strategies for direct phase and amplitude control using a linear electrical generator. An electromechanical test rig for emulating wave energy devices has been installed in the machines lab at Edinburgh so that the system can be demonstrated.

Power conversion and control for lightweight PM generators for wind turbines [+]
In direct drive wind turbines the electrical generator is directly coupled to the slow moving prime mover, which rotates. It has been convention to use iron-cored machines, that is a machine have iron on both the stationary and moving parts, but the magnetic field between the two results in a large undesirable magnetic attraction force, which requires a significant mechanical structure to maintain the physical airgap between the two. Removal of the iron from one component eliminates the magnetic attraction force completely. Such machines are termed "air-cored". In this project the main objective is to demonstrate a novel form of air-cored permanent magnet machine integrated in a commercially available small-scale wind turbine. A prototype machine will be designed and built to demonstrate the concept: a 15kW, 150rpm rotary machine. The prototype will initially be tested at the University of Edinburgh and subsequently transported to a wind turbine test site for field testing. This project is funded by Scottish Enterprise PRP grant.

Fault tolerant control of power take-off systems for marine energy devices [+]
For offshore marine energy converters, maintenance is regarded as a key issue which directly affects the overall performance of a device or a group of devices. It is well-known that component failure results in significant downtime and poses the risk of damage to other components. Hence minimising failure occurances is crucial for effective maintenance. An initial study suggests that the time-to-failure of certain components within a marine energy conversion system can be extended by controlling the device to operate under different conditions. Previous work has shown that device control is possible through intelligent control of the power conversion stage. This project looks at methodologies for component failure prevention and aims to develop control algorithms that will extend component time-to-failure. The project will also analyse the effect that controlling for failure prevention has on the energy conversion system has a whole in order to optimise the overall performance.

Other Information:

My publications
Previous work [+]
Smart Lighting for Smart Homes [+]
Lighting was identified as an integral part of the research into domestic automation, as the ability to provided effective and controllable lighting for a “smart” environment whilst being energy efficient is a fundamental issue. For this topic, the advancements in technology for both natural and artificial home lighting are investigated. These include solid-state lighting, hybrid solar lighting, and electrochromics. Specific issues relating to each area are also looked into, with their commercial potential assessed. Each of the lighting devices and systems discussed are found to have immense potential, with their widespread use certainly foreseeable. However, each approach requires further research into certain specific areas in order to transform concepts into reality. [more...]

Emulation of Fractional Turns for Switched Mode Power Supplies [+]
The concept of emulating fractional turns in a transformer using an unbalanced secondary has been considered to be beneficial to the design of switched mode power supplies. Previous theoretical work suggests that use of the technique would allow precise output voltages to be achieved in multi-output power converters without the need for fractional turns. The potential for widespread use of the technique is seemingly possible, as it does not possess the drawbacks associated with fractional turns. Through analysis of the emulation of fractional turns using computer simulation and the construction of a hardware circuit prototype, this project report investigated the technique further, with the aim to assess its practical feasibility. From the analysis carried out, the report demonstrates that the application of the technique to the half-bridge converter is certainly feasible, and given research, it is highly possible in other push-pull topologies. [more...]

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