| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 96 === This thesis presents the design and implementation of power converters for wind generators. In this system, ac-dc-ac power converters are proposed to convert three-phase electrical power generated by wind with varying-voltage and varying-frequency to single-phase electrical power with constant-voltage and constant-frequency. The perturb-and-observe algorithm is applied for maximum power point tracking to enhance conversion efficiency for the energy management of wind generator. The output power of the overall system is adjusted by detecting the speed and phase current of the generator. The system can be operated in both stand-alone and grid-connected fashions.
In ac-dc power converter, the mathematical model of three-phase rectifier built under rotating-frame and input power range of generator is introduced to reduce the current harmonics and increase the power factor on the input side, so that the efficiency of the generator can be increased. Besides, voltage feedback from an auxiliary generator is used to estimate rotor position and speed to facilitate speed and torque controls. This requires no rotor position detector and thus increases the reliability of the system.
A single-phase dc-ac power converter using unipolar switching method with low switching loss is designed to reduce the output voltage harmonics and increase conversion efficiency. As mentioned above, the realized system can be operated either in a stand-alone fashion or connected with power grid by voltage and current control modes, respectively.
A high-performance and low-cost digital signal processor (DSP, TMS320F2812) is used to control the system for reducing the circuit complexity. A prototype of 240 W hybrid power conversion system is developed under 8m/s wind speed. The system can feed proper power to the grid in grid-connected operation, while for stand-alone operation, the rated output voltage is 110 V and the frequency is 60 Hz. The efficiency of the whole system in grid-connected operation reaches 80%. Experimental results are given to verify the proposed system.
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