Research On Dual Three-level Variable-frequency Speed Regulation System For Induction Motor

With the increasing scarcity of energy supply and the deepening of national requirement for building economized society, the traditional high-power transmission equipment needs for technological innovation to achieve energy saving and higher efficiency.Moreover, the traditional mode of inverter supplied by no-control or phase-control rectifier device has made the grid quality worse; the application of variable frequency drive system is restricted by the current tolerance and voltage rating of power electronic devices in high voltage power drive field. In this background, dual three-level converter applied to the large capacity induction motor drive system has become one of the hot research areas in recent years.By making dual three-level converter system for induction motors as the study carrier, according to the diode clamped three-level topology, regarding three-level SVPWM modulation algorithm, three-level PWM rectifier and induction motor vector control system as the research objects, the following research works are carried out in this thesis:Firstly, the three-level converter structure, mathematical model and its three-level SVPWM control algorithm were studied in depth. On this basis, the effect of different space vectors on neutral point balance is analyzed; SVPWM switch sequence is also presented which can reduce the switch losses and limit the dv/dt based on the principle of three-level converter for selecting switch state. Furthermore, with the introduction of 60°coordinate system, the traditional SVPWM modulation algorithm has been improved and the simulation results by Simulink have verified the correctness and feasibility of the algorithm.Secondly, on the analysis of feedforward decoupling double-loop three-level PWM rectifier control system, a software phase-locked loop based on dq coordinate system is designed; the dual-closed-loop direct current control system of three-level rectifier is designed and the specific process and the method for controller designing are presented in accordance with the engineering optimum.In vector control schemes for induction motors, the theoretical basis of rotor indirect flux orientation and control structures are introduced; the current loop and the speed loop of the control system are designed by using the current feedforward decoupling control principle; the specific process and the method for controller designing are presented in accordance with the engineering optimum. Through the Simulink simulation of dual three-level converter system for induction motor, the results show that the control system has good dynamic response and steady state accuracy.Finally, the speed sensorless vector control system based on dual three-level converter system for induction motor is discussed in this thesis. Through the analysis of the mathematical model of the induction motor, full-order state observer has been designed and pole-assigned. Moreover, using Lyapunov stability theory, the identification speed of adaptive rate, stator resistance and rotor time constant of adaptive rate are designd. In connection with the above design and research, simulation and verification are adopted based on three-level full-order observer vector control system through MATLAB/Simulink.