Performance and reliability comparison of grid connected small wind turbine systems

Arifujjaman, Md (2010) Performance and reliability comparison of grid connected small wind turbine systems. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (35MB)

Abstract

Small wind energy conversion systems are electromechanical devices that generate electricity from wind power for use in commercial as well as residential applications. System level comparison pertaining to such conversion systems is an important and challenging problem and in-depth analysis is essential for high penetration of wind power. A set of unique problems associated with this technology requires that the maximum power point tracking control be achieved through a simple, efficient, and most importantly, highly reliable manner. This research identifies these challenges and subsequently presents a comparison in terms of the performance and reliability of a furling control grid connected Permanent Magnet Generator (PMG) and Wound Rotor Induction Generator (WRIG)-based small wind turbine system. The power conditioning system for grid connection of the PMG-based system requires a rectifier, boost converter and a grid-tie inverter, while the WRIG-based system employs a rectifier, a switch and an external resistance in the rotor side with the stator directly connected to the grid. The proposed research develops the system level mathematical model for the power conditioning system losses that fluctuates with the wind speed. It is found by the simulation that compared to the PMG-based system, the WRIG-based system can provide low power losses at low wind speeds, thus resolving the typical obstacle of variable speed operation. The comparison is further enhanced by investigating the annual energy capture, annual energy loss and efficiency for the wind speed information of eight test sites in Newfoundland and Labrador, Canada: Battle Harbour (BH); Cartwright (CW); Little Bay Island (LB); Mary's Harbour (MH); Nain (NA), Ramea (RA); St. Brendan's (SB); and St. John's (SJ). It is demonstrated that the WRIG-based system yields lower energy loss which results in a system of higher efficiency for a wind speed of 2 m/s (cut-in) to 17 m/s (cut-out). Furthermore, experimental test benches are developed for both systems based on a wind turbine emulator that incorporates furling control and associated dynamics, as well as power conditioning systems required for variable speed operation. The maximum power extraction to the grid for both systems is ensured by tracking the optimum tip speed ratio. The experimental energy production is calculated for the regions considered during simulation. It is found that the WRIG-based system provides 2% more efficiency than the PMG-based system and corresponds well with the simulated conclusion. -- Additionally, the reliability of the power conditioning system for the systems is analyzed at a predetermined wind speed. The analysis reveals that the Mean Time Between Failures (MTBF) of the power conditioning system of the WRIG-based system is much longer than the MTBF of the power conditioning system of the PMG-based system. The investigation is extended to identify the least reliable component within the power conditioning system for both systems. It is shown that the inverter has the dominant effect on the system reliability for the PMG-based system, while the rectifier is the least reliable component for the WRIG-based system. This research finally concludes that the WRIG-based small wind turbine system with a simple power conditioning system is a much better option for a small wind energy conversion system.

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