Modeling of flux linkage identifier, velocity and parameters of an induction motor based on a system of difference equations

The article uses structural computer modeling to study the digital method for constructing an identifier of the state and parameters of the equivalent circuit of an induction motor. The method is based on the use of difference equations of electric equilibrium of the motor instead of differential equations. In the identification process, the state of the motor is understood as an assessment in dynamics of the rotor flux linkage components and the shaft rotation speed. The use of a flux linkage identifier is caused by the difficulties of direct measurement of the magnetic field components. In practice, signals of electrical variables and speed are used for this purpose, and the difficulties of constructing an identifier consist only in the formation of the initial conditions of flux linkage. If the speed sensor must be excluded from the design scheme of the electric drive, a completely sensorless version is implemented. In this case, the speed estimate is affected by changes in the parameters of the equivalent circuit of the machine due to heating of the windings and the effect of current displacement. The use of simulation modeling tools in MatLab made it possible to analyze the details of the flux linkage identifier implementation in three variants of combinations of input signals available for assessment. The errors arising in the identification process are analyzed. The necessity of using a low-pass filter with a small time constant at the identifier output for compensation of high-frequency components of the modulated voltage feeding the induction motor from the inverter is revealed. The speed identifier variant is simulated on difference equations taking into account the drift of the equivalent circuit parameters. The results are compared with the identification method based on the application of differential equations and sliding modes. The considered approaches to the construction of a system for estimating the parameters and state of the motor can be used in information systems when designing identifiers in a sensorless induction electric drive.