Study On Application Of Two Kinds Of Novel Technique--Speed Sensorless Drives And Discrete Space Vector Modulation

Direct Torque Control(DTC) of induction motors, which has been developed in the recent decade, is a powerful control method for motor drives. Following the vector control technique, the quick development of DTC makes itself a new high performance AC driving technique paralleling to the vector control. In this thesis the author made a study of asynchronous motor model, designed a hybrid simulation system of DTC and analyzed detailedly the characteristics of the DTC system and the existing problems.When the DTC strategy of induction motor is implemented by using microprocessor, undesired torque and current ripple, which degrades the precision of speed control, occurs because of the limit number of voltage vector and the time delay due to the digital implementation. In this thesis an improved method, i.e. discrete space vector modulation, is presented . In comparison with other methods, the novel scheme weakens the torque and current ripple without increasing the switching frequency and extra complexity of system. Especially under the low speed, it betters speed-adjusting performance. Numerical simulation has been carried out to validate the new method.The speed estimation without speed sensor is an important trend of modern AC drive. This thesis has probed several primary algorithm of speed estimation and analyzed emphatically the algorithm of speed estimate based on model reference adaptive system. The results of simulation prove its feasibility.