Design And Research Of Speed Sensorless Direct Torque Control

Direct Torque Control (DTC) method puts emphasize on the direct control of motor torque, it overcomes the computational complexity and vulnerable change influence shortcomings of parameters of vector control, and achieves a qualitative leap of AC speed control. Speed sensorless technology is an important direction of DTC, the idea is using detection of physical quantities, such as stator voltage and current which can be easily measured to replace the speed sensor, and adaptive speed observer is the most commonly used speed identification approach.Speed sensorless direct torque control has received widespread concern for its simple control concept, but there still exists some problems, such as accurate estimation of stator flux; the real-time detection of stator resistance value; serious torque pulse at low speed and so on. In this paper, we have made research and simulation to the problems. First, for the gain matrix option of the widely used adaptive speed observer, usual method is to configure the observer pole to the multiple of the electrical pole, calculates G's expression, and then determines value. In this paper, we introduce the linear matrix inequalities, through analysis, it changes the Lyapunov inequalities into linear matrix inequalities, then according to the method of solving linear matrix inequalities to solve specific G matrix values, it replaces the commonly used zero-matrix, makes the role of the feedback gain matrix up to name. Secondly, when using a limited amplitude integrator to estimate stator flux value, the cutoff frequency of integrator is fixed, taking into account that the size of the motor speed is adjusted in a wide range, parameters of the system are changing all the time, here we set the integrator cutoff frequency changing with state on-line and real-time. This plan is verified by simulation, the value of stator flux estimation is more accurate, and motor speed output is more stable.In order to improve the system performance, we use fuzzy PI controller to replace the general speed controller, the PI parameters is changed according to different states, which has more flexibility and can reduce the reference torque ripple. By considering various strategies, we construct a complete set of speed sensorless direct torque control system and use simulation software to verify the operating results under a variety of working conditions, which shows that the control scheme is correct.