Investigation of High Temperature Operation Emitter Turn Off Thyristor (ETO) and Electro Thermal Design of Heatpipe Based High Power Voltage Source Converter Using ETO

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Title: Investigation of High Temperature Operation Emitter Turn Off Thyristor (ETO) and Electro Thermal Design of Heatpipe Based High Power Voltage Source Converter Using ETO
Author: Tewari, Karan
Advisors: Mesut Baran, Committee Member
Alex Q Huang, Committee Chair
Subhashish Bhattacharya, Committee Co-Chair
Abstract: The Emitter Turn Off Thyristor (ETO) is an emerging high power device that can be considered as a Mosfet-GTO hybrid. It is very suitable for high power applications due to many of its significant advantages in terms of usability and performance benefits. It combines the advantages of simplified control and improved switching performance. This thesis is focused on firstly investigating the loss characteristics of the ETO with variation in operating junction temperature. The switching loss, leakage loss and conduction loss of the ETO are recorded as a function of junction temperature in order to gain a better understanding of the thermal performance. Switching loss and conduction loss are found to have a linear dependence on temperature, whereas leakage loss is dependent exponentially on junction temperature. An effort is made in order to understand what limits the operation of semiconductor devices beyond a certain temperature limit. All this is then combined to develop a closed loop thermal model which is used to study the thermal stability. Thermal instability at high temperatures is caused primarily by the large leakage current, which rises exponentially with rise in temperature. Thermal stability can be maintained as long as the change rate of losses remains low enough such that the losses can be carried out of the switching junction of the device by means of the thermal conductance. This condition and the loss characteristics were used to predict the high temperature operating limit of the ETO. It is seen that due to the excellent loss characteristics of the device and due to the low thermal resistance from the junction to ambient, that the ETO should be capable of operating at temperatures well above 160 Degrees Celsius. Tests are done on the ETO in order to corroborate this theory and calculations Multilevel converters have become an important technology in high-power applications, especially for Flexible AC transmission system (FACTS) applications. In this thesis, a high power (megawatt range) modular Voltage Source Converter (VSC), using the newly developed Emitter turn-off (ETO) Thyristor, is proposed and a design methodology is developed for the various parameters of such a system. One of the main constraints in the design of such a system is essentially the design of the cooling system to carry the large heat generated by the various components such as switches, diodes and passives. Heat pipe based cooling system is very attractive for very high power applications. The hardware configuration, thermal calculation as well as component selection and design are presented in this thesis. Based on the electrical configuration of the new VSC, loss calculations are done for Statcom operation under different operation modes for components such as ETO and diodes, and the heat removal capability that is required from the heat pipes is determined. 3D Finite Element simulations are done on ANSYS software to understand the working and the selection of heat pipes. Electro-thermal simulations are done using thermal resistances of various components of the VSC including the thermal resistance of heat pipes obtained from tests.
Date: 2006-08-21
Degree: MS
Discipline: Electrical Engineering

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