Research On Vector-controlled Induction Motors Based On The Sliding Mode Variable Structure Control

The vector control system of three phase asynchronous motors without Using Speed Sensor is a hot issue in AC drive control theory and application research. The main research contents of this paper are:(1) improved SVPWM algorithm to control the neutral point voltage balance of the three level NPC inverter;(2) Mathematical formula derivation and modeling based on rotor field oriented vector control of three phase induction motor;(3) Several methods of speed estimation were analyzed and compared. The model reference adaptive(MRAS) method and the sliding mode observer method were discussed.Firstly, this paper introduced the working principle of three level NPC inverter, mainly talked about the neutral point voltage offset of the SVPWM, and on the basis of this, the virtual SVPWM algorithm was adopted. The problem of the middle point voltage deviation was solved from the root. So it was helpful to supply higher quality three-phase power for three phase induction motor.Secondly, the paper was based on the mathematical model of rotor flux oriented vector induction motor control. By modeling the flux regulator, torque regulator and speed regulator, there built up the whole asynchronous motor vector control system model. In order to get rid of the speed sensor, rotor speed was estimated by sampling stator voltage and current data which was based on the vector control system of induction motor. Two mathematical model of simple speed calculation method was introduced in this paper, there were slip calculation method and the direct synthesis method for the equation of state. The problem of the parameter dependence on the pure integral saturation would seriously affect the stability of the system. To solve this problem, this paper focused on the model reference adaptive method, and then used the Popov super stability theory to prove the feasibility of the model reference adaptive algorithm. The transfer function of the adaptive algorithm was derived in detail. The adaptive algorithm PI regulator was designed based on the transfer function. Finally, according to the motor parameter variation that was caused by the instability of the system such as interference problem, this paper adopted sliding mode observer instead of adaptive algorithm PI controller.Finally, On Matlab/Simulink the software platform, the simulation of speed sensorless vector control system of induction motor was realized. The simulation results show that: aiming at the problem of inaccurate model and other disturbances which was caused by the changing motor parameters, comparison of simulation results by model reference adaptive method and sliding mode observer method, the method of mode observer can obtain a better speed tracking effect with strong stability and anti-disturbance.