Research On Direct Torque Control System For Asynchronous Motor Of Two-stage Matrix Converter

Direct torque control is a kind of new AC driving technique followed the vector control technique, with focusing on AC induction motor torque it analyzes and control AC motor torque directly by voltage space vector modulation in the stator static coordinates calculation. In order to obtain optimal control effect of inverter switch state, pulse modulation signal of switch state is produced by two point of discrete directional adjusting and the method of stator magnetic field, so high dynamic performance of torque is get. Compared to vector control technique, it has no vector rotation of coordinate transformation and complex mathematical models processing, which makes the system simple, static and dynamic performance excellent, etc.Two-stage matrix converter is new AC-AC direct electric conversion device with better prospects for development, compared with the traditional AC conversion device, it has salient advantages:the middle parts don’t need big capacity DC energy storage device, changing flow mode is simple and reliable, input/output waveform is good, input power factor can be adjusted freely, etc. Therefore, two-stage matrix converter will make a profound impact in energy, AC variable frequency speed control and electrical transmission field. The main contents of this thesis are as follows:The significance and content of this thesis are expounded, the advantage of direct torque control and two-stage matrix converter in AC variable frequency speed control field is given, then the development background research situation of their related technology are analyzed.The basic principle of induction motor direct torque control is analyzed, the dynamic mathematical model of asynchronous motor are built in three-phase static coordinate system and two phase rotation coordinate, how to choose the inverter switch state, the basic of structure direct torque control and stator flux estimation model as well as basic component are analyzed.Based on the disadvantages of conventional matrix converter circuit topology, two-stage matrix converter topology is introduced. From the point of voltage space vector, space vector modulation strategy is researched about rectifier level and inverter level of two-stage matrix converter, and zero vector modulation strategy is used in the level of the rectifier.The rectifier level and inverter level of two-stage matrix converter are analyzed and converted, each level and their total switch functions are calculated; the analytical model of two-stage matrix converter system is established, the system simulation model is built according to space vector modulation strategy; the input and output characteristic of two-stage matrix converter in state of resistance load are simulated by MATLAB software, for double-stage matrix converter analysis, three-phase input and output waveform of two-stage matrix converter in the simulation results are given, which provide basis theory for the application of two-stage matrix converter in asynchronous motor direct torque control system.Two-stage matrix converter direct torque control system is established, the strategy of rectifier level and inverter level in system are researched respectively, every simulation unit of the system is analyzed as well as simulation of the whole system, the correctness and feasibility of this system get to verify.