| Distributed generation is regarded as the most effective way to lower the energy depletion, improve power system stability and flexibility, and have been one of developing trend for power industry. The controllability, stability and reliability of connected grid are worse than conventional large electricity grid because of the limited support ability to grid for distributed dc grid system with permanent magnet (synchronous) wind generator. Hereby, the effective control of generator-side with wide operation rang, the study of dc-side voltage stability and system reliability operation are the key techniques for distributed dc grid converter study and implementation.The aim of this dissertation is to focus on the key techniques above, the theoretical analysis and experimental research are carried out such as the variable speed constant voltage control of permanent magnet wind generator with wide operation rang and generator-side converter parameters optimum selected for inductance and capacitance, the dc chopper circuit design and constant voltage based on the structure of auxiliary surport capacitor, the cascade constant voltage control and the system efficiency optimization and so on. The dissertation includes the following aspects:(1) The variable speed constant voltage control with wide operation rang based on permanent magnet wind generator and generator-side converter are studied. The principles of excitation compensation calculation and compensation defined firstly, and the generator voltage level is controlled within the range through change the armature current of permanent magnet wind generator. Secondly, the power factor control of permanent magnet wind generator is analyzed, and the constraint conditions of satisfying power factor adjustable requirements are given. Finally, the deeply study and comparative analysis of parameters optimum selected for inductance and capacitance are designed in detail.(2) A dc chopper topology structure with auxiliary surport capacitor is designed in order to improve the voltage regulation capacity and the tracking performance of dc-side voltage. The composite control schemes is achieved considering forward PWM converter voltage control characters, and accomplish the fast adjustable of dc-side output voltage and stable grid. The calculative process and the influence of system for dc chopper circuit inductance and capacitance are expatiated and analyzed.(3) In view of the topology structure and control characteristic of distributed dc grid coverter, the cascade expression of generator PWM converter and dc chopper is deduced based on the duty cycle expression, and the cascade coordination constant voltage control mode is designed. The influence factors of dc-side voltage stability are analyzed, and considering the efficiency optimization of system, the simple, feasible efficiency optimization scheme is obtained considering dc-side voltage stability and takes the optimal goal for dc-side power.(4) The reason and influence of distributed dc grid voltage sags is analyzed, and multiple states operation mode of permanent magnet wind generator is analyzed based on wide wind speed operation range. The dynamic voltage decoupling compensation control with multiple states operation mode of generator-side is introduced to widen the scope of input and ensure the reliability of the grid connected.(5) The design and implementation process of distributed dc grid converter are given in detail. The study of this coverter is relatively few, so the 100kW converter implemated as a prototype, the simulation analysis and relevant experimental results above control schemes and strategies ate validated base on the perfect hardware design. The performance satisfied the requirements:the generator rotational speed ranges from rating speed 20% and 120%, the power factor can be adjusted from -0.95 to +0.95, dc voltage voltage regulation factor lower rating voltage 3%. |
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