OBSERVER OF SPEED AND FLUX LINKAGE IN THE SYSTEM OF VECTOR CONTROL OF ASYNCHRONOUS ELECTRIC DRIVE

Abstract

The use of physical sensors in electric drive control systems requires taking into account their additional dynamics in the model of the control object, which can cause problems with the synthesis of regulators due to an excessive increase in the order of the control object model. The use of observers makes it possible to recover state variables that are not available for direct measurement and to exclude additional sensors, which contributes to the improvement of operational and cost indicators of control systems. The structure of the observer in asynchronous electric drives must contain such an adaptation function that ensures the asymptotic convergence of the observer to the reference model, which is a real object of control.             The article presents a synthesis of the speed observer and flux linkage of the rotor of an asynchronous machine in a sensorless field-oriented control system. Equations of electromagnetic processes in an asynchronous machine, formulas of coordinate converters and equations of a PI controller are used as the initial mathematical model. By transforming the differential equations of the asynchronous machine, the structure of the adaptation function is determined, which adjusts the observer model in such a way that the deviations of the stator currents from their calculated values ​​go to zero. In this way, the adaptation function, which uses the vector product of the rotor flux linkage vectors and the stator current, ensures the stability of the movement of the speed identifier.             In the proposed observer of the speed of an asynchronous machine, which uses stator currents to ensure the asymptotic stability of the observer, in the process of research on mathematical models, self-oscillations of the speed estimate were not found, in contrast to the well-known observer, which uses deviations of the flux links. It is possible to avoid self-oscillations not only by selecting the gain factors of the PI controller, but also due to the fact that there are no integrators not covered by negative feedback in the structure of the observer's electromagnetic circuits.