Speed Sensorless Direct Torque Control Of Induction Motor

In recent years,multilevel technology has become an effective and practical solution for high-voltage and high-power application field. As described in many literatures,by using multilevel technology,the voltage stress on switches will be reduced,the shape of output waveform will be improved and the rate of voltage and power can be increased too. Diode-clamped three-level inverter is the most widely used and investigated topology at present. Direct Torque Control(DTC)is an advanced AC drives control principle where inverter switching directly controls the motor variables:flux and torque. DTC technology has been widely researched for the characteristics of briefness,robust,excellent dynamic response. The speed sensor increases the expensive of control system,and makes it more complex and uncertainty. Speed sensorless of asynchronous motors is a power control method for motor drives. So this paper focuses on the study of direct torque control of induction motor drive without speed sensor based on diode-clamped three-level inverters.By studing a type of DTC method based on synthesized vectors,a improved dummy synthesized vectors was given. This method is good at restraining the neutral-point ripple. Through the simulation in MATLAB and trial,the correctness and feasibility of the given control scheme was verified.For the dependence on the motor parameter in the control system of induction motor, a stator flux estimator based MRAS is designed. This estimator not only can observe parameter ,but also can observe speed and the stator flux. According to this model, a speed sensorless control system is constructed. Results of simulation show that this method is correct.In this paper,the key circuit of three-level inverters is showed,besides hardware of control system based on DSP. A three-level inverter prototype for induction motors drive is designed,and based on which the experiment was made. Using proposed DTC strategy,the neutral-point ripple can be restrained,and the excellent dynamic and static performance of DTC scheme is reserved.