The Effect of the Parameters of an Induction Motor Stator Flux State Observer on the Accuracy in Maintaining the Electromagnetic Moment

Abstract

The influence of the amplification factor in the flux state observer loop made according to the L-shaped equivalent circuit is considered for induction motor equipped with a squirrel-cage rotor. The state observer model is described by equations and by a block diagram. The calculation of the moment made by the state observer is based on estimating the stator flux in a fixed coordinate system. The effective voltage and the stator current were measured to determine the stator flux. The rotor flux and current were determined indirectly using these equations. The effect of the gain in the stator flux estimation loop is evaluated at different frequencies and moments, including the low frequency band and twice as high moment. This is the domain where the main problems of sensor-free control systems develop. The studies were carried out using the MATLAB/Simulink environment with the basic model of an induction motor having a squirrel-cage rotor. The analysis of the process revealed that modern systems of AC electric drives require developing systems having high accuracy in speed control without installing rotor position sensors. It is shown that this problem can be solved by using compensatory state observers, in which errors in estimating parameters of electromechanical converter can be corrected through mathematical operations through comparing the calculated (estimated) and actual alternating current parameters. It is found that the accuracy of the state observer performance gets better with an increase in the scaling compensation coefficient but the upper limit of this coefficient is limited by the noise level in variable measured.