| In recent years, multilevel voltage inverter is widely attracted attention and has becoming one of study hotspots, because of the advantages of less output harmonic, lower switch frequency, lower dv/dt, lower di/dt and so on. The main content of this thesis is three-level inverter asynchronism motor direct torque control (DTC) system PWM arithmetic.On the basis of studying in detail DTC principle of three-level neutral point clamped (NPC) inverter, the mathematic models both induction motor and a three-level inverter are built. Aiming at direct torque control of induction motor and the topology characteristics of a three-level inverter, a new synthesizing vectors PWM method of three-level DTC is presented, through this method, the complexity of vector selection is simplified, at the same time, the neutral-point-voltage is kept balanced and the occurrence of high dv/dt is restrained, flux ripple and torque ripple can be minished. Between the PWM control in a three-level inverter and the induction DTC strategy can be separated by the method, so independent different control target, and it opens up the space to improve the control performance.Simulation researches have been done by the MATLAB/SIMULINK software. The results of simulations have verified validity of the proposed scheme. Finally the experimental sample of three-level inverter has been designed based on TMS320LF2407A DSP core. The control program of PWM arithmetic is written and is verified by experiment, has improved the motor control performance. |
