Speed ​​sensorless Direct Torque Control System

Direct torque control (DTC) of asynchronous machine, which has been developed after vector control in recent years, is a new technology in domain of variable frequency adjustable speed ac drives. The direct torque control method has many merits, its structure is very simple and the principle is very clear, the response of torque is very rapid and little dependence on the interior parameters of the motor, this method is easy fully digitization. Now more and more people pay their attention on this method.In this thesis, we take the direct torque control method as a center, briefly reviewed the history of the adjustable speed of ac drives. As to the traditional direct torque control method, we make a introduction of its basic principle, make a fully description of the inverter switching states which affect the flux peak-to-peak value of the stator and to the electromagnetism torque. We find out, if we distribute the whole plane into six pie slices, there are only four active voltage vectors that can be used in each area. In order to increase the number of the active voltage vectors in each area, we proposed to distribute the whole plane into twelve pie slices. In this scheme all the active voltage vectors can be selected. But after verified by the simulation, we find by this method, it can only improved the performance of the system in a little extent.In traditional direct torque control method, the strategy of the system is bang-bang control. So it cannot distinguish the real value of the flux linkage and the torque error, also it cannot distinguish the real status of the motor. The strategy in itself cannot select the appropriated switching state and its duration time. So in order to make a further improvement of the performance, we should select the appropriated switching state and it duration time according to the error of the stator flux and the torque. According to the method of how to get the desired voltage vector, we divided it into to two kinds. One way to get the desired voltage vector is by synthesizing using two active voltage vectors and a corresponding null vector. The other use only one active voltage vector and a null...