A Direct Torque Control Of Induction Motor Based On A Three-level Inverter

In high voltage and high power fields, multilevel inverter has significant advantages, such as less distorted output, lower switching frequency, etc. In this thesis, a direct torque control of induction motor based on a three level inverter is to be proposed. Direct Torque Control (DTC) has attracted popular interest because of its high performances. Theoretical analysis, simulations and experiments are made to prove the validity of the proposed algorithm. By the analysis of a three level inverter and direct torque control, the mathematic models of both induction motor and a three-level inverter are built. The problems existing in the system of direct torque control based on a three-level inverter are studied. The voltage model flux estimator is adopted to calculate the stator flux, and a flux compensation method is adopted to compensate the error of flux estimator in low speed region. Some simulations have been made by the MATLAB/SIMULINK software package. The DSP TMS320F240 is used in the experiments. The results of both simulations and experiments have verified the proposed scheme. Based on a full order model of induction motor, a full order flux observer is deduced with stator current and stator flux as state variables to observe stator flux directly and to recognize the stator resistance and estimate the rotor speed. In the observer, only stator resistance is used in the differential equation of flux and no rotor speed appears in the gain matrix, so the flux observation is robust to the motor parameter variation and rotor speed. Simulations are made to validate it.