Supervisors: Dr. Marcus Mueller, University of Edinburgh and Dr. Dragan Jovcic, University of Aberdeen
PhD Student: Yao Zhou, University of Edinburgh
Status: Closed
The main objective of this project is to investigate topologies for high voltage DC-DC power converters for connecting offshore wind turbines to a multi-terminal HVDC transmission system.
This PhD is focussed on the detailed design of the power converter stages down to the component level and the control of the devices within the power converter. There will be links into the PhD on system modelling so that power converter performance can be assessed under realistic conditions. The two are complementary.
The project will can be divided into the following tasks:
1. Literature survey – critical review of DC-DC converter topologies at all power and voltage levels; assessment of design challenges as applied to DC-DC converters operating in the kilovolt range; review of switching device technology; review of thermal modelling and management techniques; and review of EMC issues.
2. DC-DC Topology Investigation – Develop models of suitable topologies for the Stage 1 and Stage 2 power converters. A model of the impedance characteristics of the active stator generator will be included taking into account the load conditions. It is likely that models will be developed within Portunus, which was originally developed for power electronic converter modelling.
3. Analytical Thermal Modelling – develop thermal models of the devices used. It is likely that Portunus will be used for thermal modelling with FEA used to verify the analytical models. Portunus consists of different layers, so that a power converter topology can be modelled in one layer and the thermal model can be in another layer – the two can then be linked so that the impact of temperature rises can be included in the performance of the converter.
4. Electromagnetic Modelling – transformers and inductors will be used in the power converter, both of which will be subject to losses and saturation. The latter will affect the inductances, which will have an impact on current waveforms. In addition EMC issues will be taken into consideration. It is expected that Portunus can be used to develop analytical models, which can then be linked into the main power converter topology layer.
5. Steady State Simulation Study – The device thermal models will be linked with the topology models. Initially, these models will be tested under steady state operating conditions, so that they can be assessed in terms of switching stresses on the devices, thermal performance, EMC and efficiency. The simulations will be used to investigate control and switching strategies to optimise overall converter performance.
6. Dynamic Simulation Study – within the second set of simulations the PhD will drive the models under operating conditions specified from the PhD in System Modelling, to investigate the same aspects as in task 5.
The simulations have been divided into two in order to gain confidence in the models developed. If anything unusual is observed in Task 5, the models will be refined appropriately. The main outcome from Task 5 & 6 will be an optimum topology for further investigation by the company as the Stage 2 DC-DC converter or as a 2nd generation Stage 1 converter.
7. Experimental Work – using the HWU HV lab a power converter will be built for operation at HV, but not at the MW level expected in an offshore wind farm. Results from this work and the Converteam prototype of the Stage 1 converter will be used to verify the models developed.
8. Thesis write up – The student will write up the outcomes of each task as the project progresses, which will ensure the industrial partners are kept informed, and also lead to journal and conference publications. At each reporting stage input from Converteam will also inform the development of the project.