Research Of Speed Sensor-less Direct Torque Control System

Since the application of new types of power electronic devices and the rapid development of the microprocessor,AC variable frequency speed control technology has achieved an unprecedented development,the direct torque control technology has advantage of simplifying the control method,excellent static and dynamic performance,so it is widely used in controlling many kinds of motor.The speed feedback loop which is often used in high-performance AC speed control system is essential.Actually,in most cases photoelectric encoder is used for speed feedback,but the installation of high-precision photoelectric encoder brings potential insecurity.The application of speed sensor-less not only can effectively improve the efficiency of the system,but also simplify system hardware circuits design.In this paper,we focus on the working principle and control method of the speed sensor-less direct torque control system.Conventional stator flux observer uses the voltage model mostly formed by the integrator.The model which structure is very simple only depends on the parameter of stator resistance,and has good observation precision at high speed.When the system is running at low speed,the integrator will generate the DC offset error and the initial value of the integral error,which will affect the observation accuracy of the stator flux,even will lead to the increase of the system torque ripple and worse performance of the motor at low speed.In view of the above problems,a low-pass filter with amplitude compensation as a stator flux observer is utilized.The model reference adaptive method is the key to realize the speed sensor-less technology.The traditional model reference adaptive system is composed of the rotor side variables,which completely eliminates the advantages of the direct torque control technology.In this paper,a new model reference adaptive system based on the stator side variable is adopted.Based on the Popov stability theory,the velocity adaptive rate is deduced,and the improved stator flux observer is connected with the direct torque control system.The accuracy of speed estimation and robustness of the new MRAS system based on the modified stator flux observer are verified by MATLAB/SIMULINK.Finally,this paper uses TMS320F28335 as the core controller for the system software and hardware design.After the individual hardware circuits were debugged separately,the whole system is tested.The experimental results show that the system has a rapid dynamic response capability.