| During the recent 20 years, induction motor Direct Torque Control (DTC) method has been developed rapidly for its concise system scheme, excellent dynamic and static performances. In this scheme, the torque of motor is calculated and controlled in the stator reference frame. By using stator field orientation, the optimum switching mode is achieved to control the inverter.The digital DTC system is implemented easily with TMS320F240, which is a fixed-point digital signal processor (DSP) developed specially for motor and motion control by Texas instruments Inc (TI). The Direct Torque Control scheme is studied and the software of control system without speed sensor is programmed in DSP assembly language. A novel observer method of stator flux in DTC is proposed, which is a modified integrator with amplitude limitation function. Besides the merits of integrator, it can effectively eliminate the error accumulation and DC drift problem of the integrator and also shows better robustness to stator resistance relative to classical observer. On the basis of full order flux observer, another method with higher robustness to the machine parameters is implemented by simulation. Additionally, the traditional PI regulator is improved by change the parameters of PI regulator online.To improve the stability and reduce the price of system, speed observer is implemented by simulation and experiment methods according to the theory of model reference adaptive system. The accuracy of reference model is improved by Modified integrator and the adjustable model is replaced by a novel computing model of rotor flux. Consequently, better accuracy of speed estimator and wider range in which control system without speed sensor adjust speed are achieved. Another adaptive speed observer is also researched based on the full order flux observer by simulation.All the notions and designs above are confirmed in the DSP test-bed for experimentation and development of motor control.
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