Research On Direct Torque Control Of Induction Motor Fed By Three-level Voltage Source Inverter

In recent years, multilevel technology has become an effective and practical solution for high-voltage 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. This paper focuses on the study of direct torque control of induction motor drive based on diode-clamped three-level inverters. In this paper, the model of three-level inverters and that of induction motors had been analyzed firstly. And because there is existing some relationship between the diode-clamped three-level inverters and the load-induction motors that the inverters'neutral-point voltage can be affected by some output currents, building an universal model is necessary. A whole model was constructed in α-βtwo-phase stationary coordination for further research. Secondly, the paper analyzed the principle of direct torque control and introduced the latest improvement of DTC strategy and its nowadays hotspot. Then several DTC strategies based on three-level inverters were introduced. By analyzing a type of DTC method based on synthesized vectors, a improved DTC method fed by three-level inverters was given. Through the simulation in MATLAB, the correctness and feasibility of the given control scheme was verified. Finally, the performance of proposed control strategy of induction motor fed by three-level inverters by experiments on a three-level inverter prototype for induction motors drive, which uses TMS320F240 DSP as the kernel of control system. Using proposed DTC strategy, the neutral-point ripple can be restrained, and the excellent dynamic and static performance of DTC scheme is reserved.