The Design And Realization Of Direct Torque Control System For Asynchronous Motor

Direct Torque Control(DTC) of asynchronous motors,which has been developed in the recent decades, is a powerful control method for motor drives after vector control. Following the vector control technique,the quick development of DTC makes itself a new high-powered Alternating Current(AC) driving technique paralleling to the vector control. The DTC is good at its robust characteristics, simple realization and excellent dynamic response.In this paper, DTC discards the control method of fussy current decoupling in vector control, removes PWM and current feedback part, cuts down complex vector transform and simplifies the process of motor's mathematic model. Moreover, through detecting generatrix's voltage and stator's current, DTC can compute motor's flux and torque directly and implement the decoupling control to stator's flux and torque by two lag comparers. It makes the system's structure more simple, the control method more direct and the concept of signal process clearer. However, DTC has some shortcomings about torque pulse when in low speed. Furthermore, the features and problems of DTC method are analyzed in this paper, and through researching asynchronous motor's mathematic model and according to features of DTC system and requires of timing performance of motor, the adjusting method to stator's flux is changed and the flux track of stator becomes a ring, moreover, the scheme of torque tracking control is advanced in order to improve the dynamic response of system torque.In order to simplify the structure of alternating current speed adjusting of system, reduce the cost, and improve the system performance, the speed estimation without speed sensor is an important trend of modern AC drive. This thesis has discussed several primary algorithm of speed estimation and emphasized on the algorithm of speed estimate based on model reference adaptive system(MRAS).Finally, the direct torque system without speed senor is designed and implemented in C language with TMS320LF2407 as its core and EXB841 as its hardware driving circuit based on theory analyse, which proves the validity of system scheme.