Speed-Sensorless Direct Torque Control of the Induction Motor with the Persistent Switch Frequency

A new method of the direct torque control with the persistent switch frequency is presented in this paper. By means of relationship equations of the stator voltage, stator flux and synchronous speed, the stator voltage needed in the next sample period is calculated, and the decoupled control of the induction motor is realized. So the space voltage vector pulse width modulation method is adopted to realize the persistent switch frequency of inverter switch devices. In the low speed region, the proposed method has better performance than the conventional method; and the new method has the same advantages as the conventional method in the high speed region, which is characterized by fast response and performance unaffected by motor parameter changing. The sensorless method is also described and the simulation result illustrates the effectiveness of the proposed method.