| The direct torque control (DTC) of induction motors is one of the high performance control strategies, which was proposed after the vector control scheme. It directly controls the electromagnetic torque and stator flux, using the analyzing method of space vector and stator flux orientation. It has a good prospect in the industrial variable speed field because of it's novel control method, simple structure, direct control means, and high stable/transient performance.In this paper, this scheme is investigated thoroughly. On the basis of the mathematical model of induction machine, simplified mathematical model is deduced, at the same time the theory of DTC is introduced with the concept of space vector. For the flux trajectory PWM control is the basis of direct self-control, it is also a common controlling means used by modern transducer. We deduce a method to choose the proper voltage space vector. To understand the theory of DTC deeply, the paper analyzes the difference between DTC and FOC(field oriented control) in the field of theory and application. Because estimation of stator flux is an important part of DTC, it is investigated carefully. At first several common methods are studied deeply such as U-I observer I-n observer U-n observer and low pass filter(LPF) observer and the advantage, short-coming are analyzed. On the base a compensator to LPF is brought forward and the simulation approves its effect.On the base of pointing DSP character, the hardware and software of DTC are designed based on TMS320F2407. In part of hardware design , voltage and current sampling circuit, IGBT driving circuit communication and man-machine interface circuit are designed. In part of software design, the basic flow-chart is designed ,at the same time a solution of SVPWM(space vector pulse width modulation) is analyzed and achieved. With a simple and practical prediction solution, the problem of torque and flux which leads to the lag of the torque and flux in a period is solved.
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