Predictive Direct Torque Control For Brushless Doubly-fed Machine

Brushless Doubly-fed Machine(BDFM) is a novel AC machine, it is similarity in structure with the asynchronous machine but without slip and brush, may achieve doubly-fed operation mode: It can be used in AC adjustable-speed drive systems as a motor or be used in adjustable speed constant frequency system as a generator. The BDFM system has the characteristics of less capacity inverter, separately adjustable power factor, so it is particularly suitable for variable frequency adjustable speed drives systems in high-capacity and adjustable speed constant frequency generator systems.The method of direct torque control has been successfully applied in induction motor. However, the structure of BDFM is particular and the mathematical model of BDFM is complex, so the use of control methods can not be brought directly. Cage rotor BDFM is the research object and its mathematical model, steady -state characteristics, and direct torque control methods are in-depth studied in this paper. The main works of this thesis are summarized as follows:The method of DTC has been successfully applied in induction motor,this paper analyzed the mathematical model, steady-state characteristics, zero vector, reducing the torque ripple strategy in direct torque control system of BDFM.The two-axis models of cage-rotor brushless doubly-fed machine are different in many literatures. The mathematical model are in-depth theoretical analyzed and deducted, the conclusions re useful for the motor control. Based on the above, the relationship is analyzed between power angleδand epoch angle of control winding voltage, and the d-q mathematical model is used to build the simulation model. The torque–angle characteristics were calculated under different operating of sub-synchronous and super-synchronous.The torque effect of zero vector in BDFM is different from induction machine under different operating conditions in the course of the study. It is proved by the simulation and experiment of conventional direct torque control systems using switch tables in this paper.To reduce the torque ripple of Brushless Doubly-Fed Machine based on conventional direct torque control, this paper proposes two control strategies - torque predict. The simulation shows that torque predict can reduce the torque ripple,improve the current waveform of stator. The second strategy is used for programming, because it is easy to implement and this principle of effectiveness has been proved in induction machine.Base on learning the hardware structure of LF2407A and how to program, the program of predictive torque is designed and debugged to generate the DTC and other modules. It has been completed the software design of variable frequency variable speed system of brushless doubly-fed machine.