An investigation of new type robust servo control system by using sqirrel-cage induction motor

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The purpose of this investigation is to develop a voltage source inverterfed squirrel-cage induction motor servo system in which the transfer function between the torque and its command is simplified like a DC motor by the vector control. In this system, an improvement of robustness for the change of load and system parameters is studied. The results obtained by the analysis and experiment are as follows:1. System design and analysis: A model following controller is adapted to a PWM inverter-fed induction motor servo system. The gains of controller is designed by using the optimal regulator theory to minimize the specified performance index. In order to study the influence of machine parameter change, a linear model of the system is derived by using a small displacement theory. The trajectories of poles and zeros and the transient responses are studied.2. Experimental equipment: The microprocessor V40 is used for the implementation of the model following control and the vector control. The software is described by the assembly language to reduce the computation time. For the data transmission, the debugging of control program and the display of state variables, a controller monitor is developed.3. Analytical and experimental results: The model following control is superior to the conventional PI ( proportional plus integral ) control with regard to following points: (1) The optimal gains of the model following controller are easily determined for the specified weighting constant. (2) The overshoot for the change of command values is decreased. (3) By selecting a large value of the weighting constant, the system is robust for the change of load torque and plant parameters.