Study On Key Technologies Of Sensorless Direct Torque Control For Induction Motors

Taking the project "Study on Sensorless Direct Torque Control Method" cooperating with Liaoning Saves Energy Technology Co., LTD as engineering background, this dissertation researches on key technologies of sensorless direct torque control for induction motors. In order to reduce torque ripple of conventional DTC, speed adaptive stator flux linkage observer and nonsingular terminal sliding mode control for stator flux linkage and electromagnetic torque are studied extensively and intensively in this dissertation. The traditional SVPWM algorithm is improved to reduce the common-mode interference of PWM motor drive system. The main work is described in detail as follows:A speed adaptive stator flux linkage observer based on pole assignment is presented firstly in this dissertation. Then, advantages and existing problems of the observer are analysed. In order to improve the robustness of the state observer and restrain bad effect of parameter perturbation, the stator and rotor resistance uncertainties are considered simultaneously in the proposed speed adaptive stator flux observer. The observer uses stator current and stator flux linkage as state variable, the observation of flux linkage and estimation of speed were proceeding at the meantime. The observed flux linkage could be applied to direct torque control system and the observed speed could be used as speed feedback for the sensorless system. The speed adaptive scheme of speed estimation was obtained utilizing Lyapunov's stability theory. Quadratic stability theory is used to transfer gain matrix design problem into standard H∞design problem. The gain matrix is obtained based on H∞state feedback theory. System simulation is given to verify the effectiveness of the observer.For its inherent drawbacks of classic DTC, such as torque, flux linkage, and current ripples, a novel DTC scheme is presented, in which a terminal sliding mode variable structure control (TSMVSC) method is applied to electromagnetic torque and stator flux linkage control. In order to improve convergence performance of the conventional sliding mode variable structure control, the nonsingular terminal sliding mode surfaces of torque controller and flux linkage controller are independently designed in this dissertation. The torque controller and flux linkage controller are composed of equivalent control item and nonlinear switch item. The chattering of symbolic function sign(S) is reduced by integral action. Then, lower chattering torque controller and flux linkage controller are obtained. System simulation is given to verify the effectiveness of the controllers.In order to reduce the common mode interference of PWM motor drive system, the causes of SVPWM algorithm generating the common mode interference and suppression mechanism of improved SVPWM algorithm are researched in depth. Considering the reduction of the common mode voltage and common mode currents and DC bus voltage utilization, an improved SVPWM algorithm employing three effective voltage vectors without using zero voltage vectors to suppress common mode interference is improved in this dissertation. Its working principle based on that two opposite direction voltage vector function the same time to/2 equivalent to zero voltage vector function to. DSP implementation process of the improved SVPWM is described in detail. System simulation is given to verify the effectiveness of the improved SVPWM algorithm.Sensorless direct torque control system for induction motor is built based on digital signal processor TMS320F2812, the hardware and software design described in detail. The effectiveness of the above methods is verified by experiment results. System performances meet static torque ripple less than 4%, torque rise time less than 10ms, static speed ripple less than 0.5% and common-mode voltage of the system not more than one-fifth of the dc bus voltage.