Research On Direct Feedback Control System Of BDFM's Anlysis And Design Method

Methods are found to solve problems of traditional energy's shortage. On the one hand, wind power generation, hydroelectric power generation, and solar power are exploited to replace the traditonal thermal power generation with oil, coal and natural gas. On the other hand, new energy vehicles are developed and energy saving and emission reduction are adopted to reduce the traditional energy consumption. Wound rotor doubly-fed machina is commonly used in variable speed constant frequency power system, of which the operation and maintenance cost is high because of its slip rings and brushes. The application of brushless doubly-fed machine in new energy vehicles can realize power flows among combustion motor, battery and the vehicle. System efficiency is improved, energy is saved and the driving performance is enhanced. So the high performance control system of brushless doubly-fed machine needs to be researched. With this background, the control system of brushless doubly-fed machine is researched in this paper, the details of which are as follows:Firstly, kinds of mathematical model of brushless doubly-fed machine are introduced briefly. Then the scalar control, direct torque control and the vector control of brushless doubly-fed machine are studied, of which both advantages and disadvantages are constrasted.Secondly, the operating of cascaded brushless doubly-fed machine is analyzed and the mathematic model of CBDFM in rotor coordinate is deduced. Then the power flow of CBDFM in different states is researched.Combining direct torque control and vector control's advantages, a new algorithm called Direct Feedback Control(DFC) for cascaded brushless doubly-fed machine is proposed. DFC controls flux and motor torque precisely in control machine field synchronous coordinate, which applies the basic principle of feedback control, reduces the dependence on machine parameters, and simplifies the control procedure. The differences between DFC and direct torque as well as vector control are discussed in detail. Because of the complex structure of CBDFM and cross coupling in various parts, a fuzzy PI controller is introduced for CBDFM'DFC. Furthermore, in order to reduce the dependence on the machine parameters and observe the flux by current algebraic model, a new type of brushless double-fed motor is designed, using magnetic balanced theory to measure the rotor current both brushless and contactless.DFC for CBDFM is simulated in MATLAB, and the control results are compared between fuzzy PI and normal PI controllers. Finally, an experimental platform based on dSPACE is built.