Study On The Intelligent Observer And Intelligent Control Theory When The AC Motor Works At Low Speed

The technology of frequency conversion is used widely in the field of Ac timing.The Direct Torque Control (DTC) method of asynchronous machines control was developed rapidly in 1980's, and it has been one new high performance control technology after vector control method. It has some advantages, for instance, novel control strategy, simple control, not easy to be affected by machine parameters, and having better dynamic and static state performance. DTC control has good development future in the field of AC machines control.Because the electromotor is typical nonlinear, coupling system, so the classical control methods cann't get ideal effect when control it. It is a feasible method to use intelligent control theory, and in this paper, the primary work is introduce intelligent control method to the Ac motor timing.According to the mathematical model of asynchronous machines, this paper presents the principle and basic structure of direct torque control, and analyses the reason of worse performance at low speed. By analyzing, we come to a conclusion that since the stator resistance varies with the temperature, and the integrated role of the resistance error can't be neglected, if calculating the flux linkage with the fixed resistance value, it must lead to the ripples of torque and flux linkage.A new type of neural network resistance observer is developed, on basis of BP neural network, to measure the real time stator resistance of induction motor. The data groups obtained through the industrial experiments were used for the learning of networks as well as the comparison with the results observed respectively. The stator voltage is compensated by the observed resistance in order to improve the low speed stability of the induction motor. With the results of simulation, it has been proved that the neural network resistance observer enjoys a high accuracy.In this paper, another improved method using fuzzy and adaptive principle is presented to reduce the torque and flux linkage ripples. By regulating the duty ratio of the voltage space vector, the controller can track the change of torque. It is possible to apply any small voltage value to the motor. Simulation illustrates this method can reduce the torque and flux linkage ripples, and improves dynamic and static performance of DTC system.