Research Of Speed Sensor-less Direct Torque Control Of Induction Machine

In this dissertation, the design of speed observer, the design of stator flux observer, the improvement of low speed performance and the digital realization of system are studied profoundly and broadly by simulation and experiment methods. The limitation of the classical observer method of stator flux in direct torque control (DTC) is deeply researched, then two novel schemes are proposed, by which the flux can be observed much more accurately. One is the full order flux observer, by which the stator flux can be observed much better than by the classical integrator, and it also shows higher robustness to the machine parameters. The other is a modified integrator with amplitude limitation function, together with the merits of integrator; it can solve the error accumulation and DC drift problem of the integrator effectively and shows higher robustness to stator resistance also. Based on the full order flux observer, two novel adaptive speed observers and a speed estimator are designed. According to the Lyapunov?theory, the first adaptive schemes of speed are designed successfully, which makes it possible to observe the speed, stator resistance and rotor resistance on-line. The second adaptive speed observer is designed by the theory of model reference adaptive system, which is proved hypersiable by Popov抯 theory. At last, a simple speed estimator combined with the flux observer is applied in the direct torque control system. The experiments results show that these methods above-mentioned can improved the accuracy of the observed speed, strengthen the robustness of system, and widen the speed range of drive system. A novel dead-time compensation method is proposed in our system. The dead time effects can be compensated effectively by slight modification of software and without additional hardware. This proposed method is especially suitable for the DTC drive and other controllers, which utilize space vector modulation techniques. The influence of different voltage vector to the torque variation is researched deeply through the theory analysis, and then the classic switching table is replaced with a novel flux and torque two-level switching table. This new switch table is very easy to realize. Simulation and experiment results show that the torque of motor can be improved largely without degrading dynamic performance of system; the torque ripple and electromagnetic noise is weakened greatly. An effective and simple stator weaken technique is adopted in this system. In addition, a novel soft start-up technique is also proposed by which the impact effect in start-up process will be depressed effectively. The test prototype system is implemented on a Digital Signal Processor (DSP? TMS320C32). The real-time controller software is written by C mixed with Assemble language, the research of digital realization and the software design is carried out deeply. Many performances of the prototype have attained the most advanced level in domestic.