Research On Direct Torque Control For Induction Machine Based On Variable Structure Theory

Direct torque control(DTC)technique debuted in the AC drive field in 1980's.It is a new efficient AC drive control technique,which follows field-oriented control technique and intends to exceed field-oriented control technique.After analysing and comparing with advantages and drawbacks of classical DTC,a new control strategy-SVPWMDTC combining SVPWM and variable-structure control was presented to ensure quick and accurate control of the stator flux and electromagnetic torque of induction machine,in order to improve operating performance and robustness of the whole system.The accuracy of the stator flux observer is critical to steady and transient behavior of the whole DTC system.The paper in detail analies advantages and shortcomings of u_s -i_s model stator flux observer and i_s -n model stator flux observer,and asserted that u_s -n model stator flux observer was employed to obverse the stator flux of the induction machine.Up to date,the speed estimation without speed sensor is another popular trend of AC drive.Through weighing advantages and disadvantages of many kinds scheme of speed estimation,the paper adopts a model reference adaptive control to identify rotor angular speed.Additionally,as a result of the drawbacks of the SPWM voltage type inverter:the low utilization ratio of DC voltage and the harmonic of the voltage outputted,the paper applies SVPWM to control the inverter.Finally,in order to prove that proposed scheme is valid and feasible,the simulating experiments model of the whole speed regulation system was established by using Matlab/Simulink,and the paper carries out simulink verification and analysis.