Optimal design of wind turbine converters using advanced power semiconductor materials
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- Institutt for elkraftteknikk 
Power electronic converters play an important role in interfacing of uncontrolled renewable energy resources such as wind, solar with main power system. However, there are several challenges related to design and performance of power electronic converters. These challenges are related to the electrical and thermal performance, physical size. Many of these challenges can be addressed by the study of power semiconductor devices made by advanced wide band gap semiconductor materials such as silicon carbide and gallium nitride. Silicon carbide power diodes and transistors are among the successful wide band gap power semiconductor devices and are suitable for high power applications such as large wind energy conversion systems.An all DC series connected wind farm configuration has minimum number of conversion stages. Modular multilevel converter has many advantages over other multilevel converter topologies and is a promising topology for medium and high-power applications. As silicon has reached its physical limits, wide band gap semiconductors are emerging as promising alternatives. A combination of all three suggested has not been researched so far for multiple objective optimization. This research is an attempt to realize benefits and challenges of this combination. The scope of optimization is semiconductor power losses, total harmonic distortion and operating junction temperature.The research work is focused on reviewing the state of the art literature regarding modular multilevel converter to understand the operating principles, control methods. A wind generator side converter using modular multilevel converter topology and silicon carbide MOSFET is developed in Simulink/MATLAB environment. Sixty-two number of simulations are carried by varying the number of sub modules per arm and the number of parallel connected semiconductor devices. In each simulation, semiconductor power losses and total harmonic distortion are measured.The simulation results show that the silicon carbide MOSFET with lowest voltage rating is found suitable due to higher number of sub modules and voltage levels, better voltage waveform, reduced filter requirement, lower semiconductor losses, less cost. Furthermore, minimum number of sub modules and maximum number of parallel connected devices result in lower losses.