|Title:||A large-scale concentrated photovoltaic power generation with an auto solar tracking system|
|Advisors:||Cheng, K. W. Eric (EE)|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Solar power plants
|Department:||Department of Electrical Engineering|
|Pages:||xx, 149 pages : color illustrations|
|Abstract:||Solar energy, as a green energy, has become one of the most important resources for power generation. Photovoltaic plants have become vital parts for renewable power generations nowadays. Many plants focus on enhancing the efficiency of solar power generation systems and most researchers pay their attention to concentrated photovoltaic (CPV) or ultra-concentrated photovoltaic (UCPV) power generation systems which are promising candidates for improving the efficiency of solar power generation systems. In recent years, there are many methods for producing solar cells of CPV's, which is the primary method of improving conversion efficiency for solar energy harvesting. Another method is physically tracking the position of the sun, which can further enhance the production of power generation plants. This will not only capture more solar energy through direct sunlight, but also reduce the cost of the solar cells by using polycrystalline solar panels or mono-crystalline solar modules. Up until now, most CPV solar cells are expensive because of the high cost of the primary materials such as gallium arsenide for the solar cells. By physically tracking the position of the sun using ordinary solar cells, the entire power generation system would become cost-effective and the efficiency of the power generation system is then improved by capturing more sunlight. Therefore, the tracking system for the CPV becomes a salient point for the current solar power harvesting methods of power generating plants.|
This thesis mainly focuses on the tracking system and its conversion for the whole CPV power generation system. Firstly, compared with traditional solar tracking approaches that usually employ two motors and gears to adjust the gesture and position of the solar cells, this study has proposed a new way to track the sun by using a two-degree of freedom motor. The structure of the motor is introduced and its detailed design procedure is given. Meanwhile, after obtaining the magnetic characteristics of the motor, the prototype of the motor is manufactured for the tracking system. Next, besides this kind of two-degree of freedom (2-DOF) motor, a new approach to construct and realize the two-degree of freedom motion is proposed, that eliminates two sets of windings for 2-DOF motors and simplifying the structure of the motors in order to realize two degrees of freedom motion. Secondly, the control method for the motor as well as the CPV power generation system is designed via a basic industrial control algorithm that is proportional-integral-derivative (PID) control. This solar tracking algorithm is integrated into the controller, realizing the CPV tracking system. Finally, a wide-input-wide-output (WIWO) converter is designed and integrated with the whole power generation system to obtain a wide output application. The principles of the circuit topology for the WIWO are elaborated. The theories for the buck, boost and buck-boost mode based converter are introduced and analyzed. To obtain an accuracy efficiency of the converter, the switching loss of the converter is also shown in this section. After manufacturing the converter, the experimental results for the converter with the input and the output are sampled, verifying the improvement of the whole power conversion efficiency. Apart from the experiment, the trials on the tracking system as well as well as the position control for the motor are also carried out. These experimental results including the tracking position, the parameters of the controller and the efficiency of the converter involved show that the proposed CPV power generation is stable. This shows that it is an effective and robust method in renewable energy conversions. According to the study, the tracking system is an effective approach to improve the efficiency of the solar power harvesting and reducing the whole cost for power plants, regardless of CPV power generations or ordinary solar based power generations. It can be expected that the tracking system can substitute the present structure for solar cells to pursue a higher power harvesting efficiency for plants.
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