Design And Research Of DTC System Based On DSP

In 1970's, one method of AC induction motor control called Direct Torque Control (DTC) was raised. It was developed rapidly in the middle of 1980's, and it has been successfully applied to many occasions up to now.In this paper, the scheme is investigated thoroughly. On the basis of the mathematical model of induction machine, an optimized voltage vector selection table was deduced based on the theory of the tradition DTC. By utilizing the vector selection table, we need not to transform the flux sections from a - (3 to P coordinate plane to get the flux voltage, but can get it directly from the voltage vector select table after we attained three values, that is, the a fractions of the stator flux and current position of it. According to the torque error signal, we can get the current voltage vector under which the inverter will produce relevant PWM voltage signal to the motor terminals. High dynamic response of torque control of the induction motor is achieved as the stator flux moves along a hexagon approximately, and good real time control is realized owing to the fact that mathematical operation is reduced largely in this method,.In ordinary DTC, Schmitt trigger is usually employed in the regulating of torque and stator flux, which resulted in the unavoidable influence of the tolerance of the regulators on system performance. An idea of replacing Schmitt trigger by fuzzy controller for regulators is described in this paper, considering that tolerance is a kind of fuzzy quantity which is difficult to make out accurately. Results of simulating indicated that better system performance could be derived from introduction of fuzzy controller under the same condition with the traditional method.In addition, a speed model is also deduced in this paper. Compared with the model reference adaptive, this method is simple, and not complex in operation. Depended on this method, a predigested method is developed, from relevant simulating results we can draw a conclusion that the predigested method of speed estimating is doable, and it has quick response.We developed a hardware system based on Digital Signal Processor (DSP) and carried out DTC experiment on it. Results of the experiment indicate that with speed sensor, the algorithm described in this paper can achieve favorable result, and the system has good torque response as well as smooth speed response .