Resarch On Brushless Doubly-fed Machines And It's Direct Torque Control

The Brushless Double-Fed Machine not only has the simple structure as same as the cage-rotor asynchronous machine has.But also,it possesses some good characteristics of the wound-rotor asynchronous machine and the synchronous machine.It can operate synchronously or asynchronously,also can word as a AC adjustable speed machine or a variable-speed constant-frequency generator aswell. The speed canbe control by power winding iuput frequency power and control winding input variable frequency power, the power of control winding input is only a part of the power supply. So the Brushless Double-Fed Machine can Absorb energy from the energy grid can also be passed energy on to the energy grid.By this way ,the adjustable-speed system can reduce capital cost.Therefore,the Brushless Double-Fed Machine has shown potential for adjustable speed drive applications.In this thesis,a detailed introduction of Brushless Double-Fed Machine with cage-rotor is presented,including the origin Brushless Double-Fed Machine,its development,current situation,research significance as well as its application.Then,other features of Brushless Double-Fed Machine such as the structure of stator and rotor,its operational principle,operatingg mode and power distribution,are also introduced in this thesis.Through the electromagnetic design can get the Motor design then starting from the basic theory of finite element, The Brushless Double-Fed Machine finite element model is established base on the software of Maxwell 2D,after the calculations can get the initial parameters from the finite element model,so we can analyze the special structure of Brushless Double-Fed Machine from "field" perspective. provide a theory for optimal design of this motor.Several mature mathematical model of Brushless Double-Fed Machine at home and abroad are detailed analysis,in this thesis, d-q axis coordinate mathematical model is used to establish the mathematical model base on Simulink environment. the Simulation results of Asynchronous starting, Super-synchronous operation , synchronous operation by DC, Sub-synchronous operation and load operation are analyzed in detail.This can gei a verification to the parameters from element model. The soft-startup Simulation model is established by SPWM voltage source inverter, the Simulation result shows soft-startup is more advantageous than direct-startup.At last, Direct Torque Control priniple is elaborated, The Direct Torque Control simulation model of Brushless Double-Fed Machine is established by using Matlab / Simulink platform. The simulation results are analyzed detaily.so can get a conclusion that Direct Torque Control method is a very good control method. It has simple, fast speed and torque response feature.this control method is better than Vector Control ,because Vector decoupled need more operation. This control algorithm is a good theoretical to study the Brushless Double-Fed Machine in the practical application.