Development of the luenberger observer for the automated electric drive of hermetic compressor

The basic requirements for control systems of automated electric drives of hermetic compressors of small refrigeration units are determined. The analysis of the existing sensorless control systems of three-phase AC drives is carried out. The topology of the adaptive Luenberger observer is proposed, which allows real-time evaluation of the current value of the rotational speed and torque on the shaft of the hermetic compressor motor. Based on the linearized model of a three-phase asynchronous motor, the Luenberger observer is synthesized by the modal method with the distribution of the roots of the characteristic polynomial in the standard linear Bessel form. Expressions are obtained for calculating the coefficients of the Luenberger matrix and the geometric mean root of the characteristic polynomial of the observer. To ensure the necessary accuracy of identifying the coordinates of the state of an automated electric drive of a hermetic compressor, an observer structure is proposed based on a complete mathematical model of a three-phase asynchronous motor made in a fixed coordinate system. Using simulation tools, the work of the designed Luenberger observer is studied on the example of a modernized three-phase asynchronous motor of a hermetic compressor of a domestic refrigerator. For this example, the coefficients of the Luenberger matrix and the geometric mean root of the characteristic polynomial of the observer are calculated. The effectiveness of the proposed method for identifying the rotational speed and moment of resistance of a compressor electric motor by an adaptive observer based on the calculation of the electromagnetic torque of the motor from measured sensors of phase voltages and currents is confirmed. The error of the observer under investigation does not exceed 0.5 % in rotation frequency and 10 % in respect to the moment of resistance. The resulting structure of the adaptive Luenberger observer allows to build closed-loop control systems for automated electric drives of the hermetic compressor of a small refrigeration unit.