Research On Speed Sensorless Direct Torque Control Of Asynchronous Machine

In this thesis the author made a profound and broad study on the design of speed observer and stator flux observer, the improvement of low speed performance and the digital realization of system. Speed sensorless asynchronous motor system of direct torque control has been introduced by high performance digital signal processor (DSP) of TMS320LF2407.Because of the limitation of the classical observer method of stator flux, the observing precision of the stator flux observer must be high, a new adaptive stator flux observer is proposed. With this observer, the stator flux , the stator resistance and rotor resistance which vary with motor temperature, are identified simultaneously and the speed can be also observed. The robustness to parameter variations and good performance are fully verified by the simulations. Based on the full order flux observer, according to the Lyapunov' theory and Popov's theory, three kinds of adaptive schemes of speed observer are designed successfully. Comparing the three schemes, at last, the author applied a simple speed estimator combined with the flux observer in the direct torque control system.The defect of the classical DTC is researched deeply, a new tactic of Vector Subdivision Direct Torque Control based on space vector modulation is proposed. Low performance of DTC system is improved. An improvement can be obtained adding a new DTC algorithm based on the application of the discrete space vector modulation(DSVM) to DTC. At each sampling period, the voltage vector is synthesized by three voltage space vectors, each one applied for one third of the sampling. By this means ,a high number of voltage vectors can be generated, and the torque ripple is reduced. At the same time, the classic switching table is replaced with a two-level hysteresis band for the flux, and a five-level hysteresis band for the torque, which widens the speed range of drive system and improves the control performance. Simulation and experiment results show that these methods above-mentioned can hold dynamic performance of the basic DTC, improve the torque at low speed and weaken the torque ripple and electromagnetic noise greatly. Furthermore, the methods are very easy to realize and have improved accuracy ofthe observation.The test prototype system is implemented on a Digital Signal Processor (DSP TMS320LF2407). The real-time controller software is written by C mixed with assemble language, and the research of digital realization and the software design are carried out deeply. Many performances of the Speed sensorless asynchronous motor system of direct torque control have attained the most advanced level in domestic.