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Master thesis presentations tomorrow Wednesday 3rd of October at 10:00
The presentation is held in the seminar room, Teknikringen 33, 2nd floor.
Four theses will be presented:
1- Sanchit Singh: IGCT Transient Analysis and Clamp Circuit – Design for VSC valves
2- Mattias Rahm: Controller-Inverter for Sensorless Permanent Magnet Synchronous Motors – Application in Onboard Electric Powertrain for Uphill Propulsion in Downhill Mountain Biking
3- Joakim Odnegård: Fault Impact Mitigation in Grid Connected Converters
4- David Jahanbakhsh: Implementation of DC-DC converter with maximum power point tracking control for thermoelectric generator applications
The Abstracts of the four theses are given below:
Abstract Sanchit Singh: IGCT Transient Analysis and Clamp Circuit – Design for VSC valves
IN today’s high power VSCs (Voltage Source Converters), IGBTs (Insulated Gate Bipolar Transistors) are the dominant semiconductors. These converters are in general modular multilevel based and contain several building blocks that are series connected. Each of these building blocks in turn consist of several series connected IGBT valves. One of the advantages of using modular multilevel based VSCs is the ability to switch each building block at a lower frequency compared with the average total switching frequency of the converter. IGBTs have generally lower switching losses than other semiconductors, however, their on-state losses are higher because of a larger on-state voltage. Furthermore, series connection of IGBTs devices imposes voltage sharing complications that are generally difficult to deal with. A solution to this problem is to increase the amount of series connected building blocks and thus avoid series connection of semiconductors. To lower the semiconductor on-state losses, either the IGBTs are replaced by improved IGBT and drives or an alternative semiconductor that is more suited for modular multilevel topologies can be used. In this thesis, an alternative semiconductor called IGCT (Integrated Gate-Commutated Thyristor) is studied; more specifically RC-IGCT (Reverse Conducting IGCT). An analytic analysis is conducted to grasp the switching behavior, furthermore, a simulation model in Pspice is proposed for confirming the analytic analysis. This model is also used for parameter sweeps of clamp circuit components from which a table is created. This table can be used for comprehending the effects of changing values on the switching transient and also for the design of clamp circuit components. However, a numerical and a graphical method together with the Pspice model are proposed for designing the clamp circuit. It is found that the graphical method is far more intuitive and revealing than the numerical. If further accuracy is required, then the graphical method can be used in tandem with the numerical. A fault case analysis of the clamp circuit is conducted in order to reveal how failures in the clamp components affect the semiconductors and other components in a building block. Some of these failures are more destructive than others. The IGCT building block states and current paths are discussed and finally series connection of IGCTs is considered.
Abstract Mattias Rahm: Controller-Inverter for Sensorless Permanent Magnet Synchronous Motors – Application in Onboard Electric Powertrain for Uphill Propulsion in Downhill Mountain Biking
This thesis demonstrates a practical implementation of a sensorless PMSM (Permanent Magnet Synchronous Motor) drive for vehicle propulsion. The main design parameters and overall properties of the motor drive are derived for the case of an on-board electric powertrain as a substitute to the lift shuttle in DH (downhill) mountain biking. The theory behind FOC (Field Oriented Control) for sensorless PMSMs is analyzed in some detail. Controller-inverter hardware and software are designed and prototyped in accordance with the derived design parameters. Initial tuning and testing in a test bench environment is described. The powertrain is finally installed on a test bike and tested on an incline. It is found that the performance of the controller-inverter complies with the target design parameters.
Abstract Joakim Odnegård: Fault Impact Mitigation in Grid Connected Converters
The present thesis deals with fault impact mitigation in grid connected converters used for High Voltage Direct Current transmission. Certain critical fault cases require additional obstructing protection actions to ease the impact on the converter valves. DC sided faults drives high fault currents through the converters. Single phase to ground faults at the converter AC bus results in overvoltages across the converter valve arms. The phenomenon of these faults are described both for symmetric and asymmetric configurations. Different available solutions are explained and evaluated. Simulations in PSCAD/EMTDC show the impact of the protection measures.
A three phase short circuit introduced on the tertiary winding of the transformer is an effective temporary measure against the destructive fault cases. It is shown in this report that a tertiary short circuit will greatly reduce the overvoltages after converter bus faults and redirect a large part of the fault currents after DC faults. With the lower voltage on the tertiary winding, it is a suitable connection point for short circuit devices.
Abstract David Jahanbakhsh: Implementation of DC-DC converter with maximum power point tracking control for thermoelectric generator applications
A heavy duty vehicle looses approximately 40 % of the energy in the fuel as waste heat through the exhaust system. Recovering this waste heat would make the vehicle meet the legislative and market of emissions and fuel consumption easier. Using a thermoelectric generator this recovery is possible by transforming the waste heat to electric power. However, the thermoelectric generator's characteristics makes direct usage of it unprofitable, thus an electric power conditioner is necessary.
First a study of different DC-DC converters is presented, based on that the most suitable converter for thermoelectric application is determined. In order to maximize the harvested power, maximum power point tracking algorithms have been studied and analyzed. After the investigation, the SEPIC was simulated and implemented with a perturb and observe algorithm, and the incremental conductance algorithm. The converter was tested with a 20 W thermoelectric generator, and evaluated. The results show that the incremental conductance is more robust and stable compared to the perturb and observe algorithm. Further on, the incremental conductance also has a higher average efficiency during real implementation.