Research On Brushless Doubly Fed Induction Machine For Wind Power Generation

In recent years,wind power as a main renewable energy power generation technology has been widely concerned and has achieved great development in many countries.Wind turbine is an important part of wind energy conversion system.In different types of wind turbines,doubly-fed indutction generator(DFIG)is one of the main models used in wind farms due to its characteristics such as low cost of converter,operation of variable speed constant frequency,active power and reactive power.However,it is difficult to maintain the brush and slip ring structure of the doubly-fed generator and it needs to be replaced frequently,which has caused some difficulties in the application of wind power generation,especially offshore wind power.The Brushless doubly-fed Machine(BDFM)out the brush and slip ring structure,maintenance more convenient,more reliable,more adapt to bad environment of offshore wind farm,and retain the converter of the doubly-fed generator characteristics such as low cost,adjustable power factor,can make up for the shortage of the Brushless doubly fed generator,has a broad application prospect in the field of offshore wind.Therefore,in view of the brushless doubly-fed machine in the study of the application of the wind power generation,it is very meaningful.The research object of this paper is the Brushless double-fed Induction Machine with special cage rotor structure(BDFIM).The main research work and innovation points are as follows:1.Through the in-depth analysis and research of the generalized vector model of brushless doubly-fed induction machine,a series of electromagnetic torque equations are derived,and the torque equations of these electromagnetic torque equations are similar in the form,which proves that the torque generation mechanism of the brushless doubly-fed induction machine is the same as that of the double fed induction machine,while the more concise torque equation can be more convenient to analyze the control strategy of brushless doubly-fed induction machine,and the mature control strategy can be transferred to the control of brushless doubly-fed induction machine.2.In this paper,the vector model of power winding flux orientation of brushless doubly-fed induction machine is deeply analyzed and studied.The results show that the cross-coupling between the speed control loop and the reactive power control loop can be calculated by the power winding flux value and the speed value,which can simplify the cross-coupling calculation in the control strategy.3.Under the power winding flux orientation vector model,analysis shows that electromagnetic torque is proportional to the q axis of control winding current,and reactive power can be calculated by d axis of control winding current,thus put forward the brushless doubly-fed machine current hysteresis control strategy,by controlling the d axis and q axis of control winding current to control the speed and reactive power respectively which can avoid controlling the d axis and q axis control winding voltage to control the speed and reactive power.4.Based on the study of the power winding voltage orientatied generalized vector model,the control strategy of brushless doubly-fed wind generator that does not depend on the machine parameters is put forward.In the control strategy,the cross coupling compensation item is calculated through the current value and the voltage amplitude of the power winding.No machine parameters are required which can improve the robustness,and then the maximum wind energy capture control strategy of the wind power generation system is simulated.5.For the brushless doubly-fed induction prototype,a wind power experimental platform was built to conduct experimental research.6.Finally,the three vector control strategies are tested and verified,and the feasibility and effectiveness of the control strategy are proved,which shows the good application prospect of brushless doubly-fed motor in wind power field.