Research On Control Strategies Of Brushless Doubly Fed Machine Applied In Various Variable Speed Constant Frequency Power Generation Situations

Under the current environment of lack of energy,the brushless doubly-fed motor(BDFM)is characterized by its absence of brush and slip rings,high efficiency,and the ability to achieve Variable Speed Constant Frequency(VSCF)with low capacity frequency converter.Therefore,it has a strong competitive advantage in the hydropower generation system and diesel generation system.At first,the antecedents and signification of the paper are discussed.Then the paper analyzes the application advantages of BDFM in hydropower and diesel power generation system,and briefly reviews the development of its control strategy and concludes that vector control is more suitable in variable speed constant frequency generation system.Secondly,the paper gives a brief description of the basic structure and working principle of the BDFM,and analysis its power flow characteristics in different power generation states.Through coordinate transformation theory,BDFM model in arbitrary rotation dq coordinate system is obtained from the model in static three-phase abc coordinate system.Then,the mathematical model of hydraulic turbines and diesel engines are introduced,and detailed description of the maximum power tracking in hydropower and the universal curve of diesel generators.Thirdly,based on voltage vector orientation of the Power Winding(PW)and the power winding synchronous speed as the rotation speed,an active and reactive power decoupling vector control algorithm is derived for grid-connected power generation system.However,due to the different control targets of the independent and the grid-connected power generation system,the mathematical model is based on current vector orientation of the Control Winding(CW)and the control winding synchronous speed as the rotation speed,thus the voltage amplitude frequency decoupling control strategy is obtained for independent power generation system.Fourthly,the premise of vector control is realizing accurate voltage orientation,so a software Phase-Locked Loop(PLL)method is proposed,and the simulation is established in Matlab/Simulink to verify whether PLL can accurately lock the voltage amplitude and phase.The simulation model of the entire grid-connected power generation system was established,and maximum power tracking,VSCF and V-shaped characteristics of the BDFM were simulated.So it can be concluded that the basic characteristics of BDFM were confirmed and the active and reactive power decoupling control strategy meet the requirements of grid-connected power generation.Afterwards,in order to verify the accuracy of the voltage amplitude and frequency decoupling control strategy,simulation analysis was carried out in the corresponding model.BDFM can accurately stable at the set value to achieve VSCF in a short time in the operating state where the constant load speed changes or the constant speed load is abrupt.Besides,BDFM has fast response and stable output characteristics in these two states with voltage amplitude frequency decoupling control strategy.Finally,the hardware design and software design of the power generation system are briefly introduced,and the implementation of control strategies in the whole experiment of grid-connected power generation and independent power generation is combed.The power decoupling control strategy was verified by a number of experiments at the Daliang Hydropower Station and the laboratory.And by carrying out the experiment with resistive load and motor load on the diesel generator power generation experimental platform,the voltage amplitude frequency decoupling control strategy is verified.