| With the rapid development of modern industry,there have been a larger consumption and reliability for energy.Fossil fuels like coal,oil and gas are still the most widely used at present.There are only limited amount of non-renewable fossil fuels,which means they are about to exhaust one day.Besides that,Extensive combustion of fossil fuels produces toxic gases and greenhouse gases,which not only bring air pollution,but also cause a series of climate problems such as global warming.Only through rational development and utilization of renewable energy can we achieve the goal of sustainable development.This has already become a strategic consensus of the whole world.As one of the most important renewable energy sources,wind power can not only save conventional energy,but reduce environmental pollution as well.It has drawn huge attention internationally and experienced rapid improvement these days.Wind power has become the most widely used renewable energy currently.More and more novel and high-efficiency wind turbines have been designed with increasingly improved performance.More intelligent algorithms are also applied to control strategies.The research object of this essay is a novel brushless doubly-fed generator(BDFG)based on magnetic field modulation technology.Similar to the structure of magnetic gears,the magnetic ring modulates the permanent magnetic field into two different magnetic fields with different number of pole pairs.The permanent magnet is able to improve power density and power factor.What's more,the brush and slip ring for traditional doubly-fed induction generators are not needed in this highly reliable BDFG system,which makes the system less expensive for maintenance.This paper firstly analyzes the structure and characteristics of BDFG and its grid-connected system.After introducing the field modulation mechanism,working principle,power flows and operating modes of the generation system,a complete mathematical model of the system is built,including namely the mathematical models of wind turbines,BDFG,wind speed,and PWM converters.Based on the mathematical model of the BDFG generation system,control strategies are developed analogy with the permanent magnet synchronous generator(PMSG).Then the basic principle of vector control is briefly described.The control strategies for grid-side converter and machine-side converter are determined respectively.The grid-side converter uses grid-oriented vector control,and the machine-side converter adopts rotor flux-oriented vector control with i_d=0to achieve the target of the maximum power tracking and variable-speed constant-frequency operation.Separate simulation models of grid-connected and off-grid systems were built in MATLAB/Simulink and the results proved the feasibility of the control strategies.In addition,virtual synchronous generator(VSG)technology for wind turbines to realize grid frequency regulation is studied.The research overview is summarized first.A conventional VSG control strategy is analyzed,and on this basis,a new VSG algorithm with adaptive parameters is put forward.Through MATLAB/Simulink simulation,it verifies that VSG technology can help grid frequency modulation,and VSG with adaptive parameters has a better effect than conventional one.In the end,hardware circuits and software algorithms for the BDFG control system are designed.dSPACE1104 is chosen as the main controller.An experimental platform is set up.After debugging the hardware circuits separately,some preliminary experimental tests are performed on the whole system.Finally,an outlook for the unfinished research is proposed at the end of the paper. |
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