Research On Output Voltage Control Strategy Of Brushless Doubly Fed Generator

BDFM(brush doubly fed machine).Different from the traditional asynchronous machine,it can be used not only as a motor,but also as a generator.The utility model has the advantages of simple structure and no electric brush.Performance advantages is adjustable power factor,etc.As a motor,it can operate in different states,such as synchronous state,doubly fed state.In the speed control system,the capacity of the speed control system can be effectively reduced.The control power accounts for a small part of the total power,therefore,it can absorb the energy of the grid,at the same time,send the power back to the grid.Due to the advantages of BDFM structure and performance,it has wide prospects in the field of fan pump and variable speed constant frequency power generation.The research object of this thesis is the BDFG.It is necessary to solve the problem of output voltage stability under the condition of variable speed and load during the operation of isolated grid power generation.By consulting and learning the relevant data,this thesis analyzes the voltage equation and flux equation of BDFG,and establishes the mathematical model of the reluctance BDFG.In this thesis,the output voltage stability of BDFG is taken as the control objective.Based on the slip frequency rotating coordinate system,the expression of the output voltage of power winding is derived.By analyzing the mathematical model of the output voltage of the power winding in the rotating coordinate system,the influencing factors of the amplitude and frequency of the output voltage of BDFG are obtained.The vector decomposition of BDFG is carried out in the rotating coordinate system of slip frequency,and the control method of induction electromotive force orientation of power winding is proposed,the control relationship between the output voltage of the power winding and the current of the control winding is derived in this orientation mode,and the calculation model of the target current of the control winding is established.In order to ensure the actual input current of the control winding can track the target current of the control winding quickly and accurately.In this thesis,hysteresis and SVPWM are used together to establish the control model of control winding current tracking.The output voltage control model of BDFG is simulated under the condition of variable speed and constant load and constant speed.The simulation results show that the control strategy is correct and effective.