<span>The article substantiates the necessity of identifying the dynamics of asynchronous electric drives with frequency control. It is proposed to use nonlinear transfer functions and the formula of a family of frequency responses of an electric drive, depending on the frequency of the stator voltage and slip. Experiments and simulations confirming theoretical conclusions are presented. The frequency responses of the drive of the stand calculated by the proposed method allowed to explain those problems of frequency control that were not explained by traditional methods - analytical, vector diagrams, substitution schemes, etc. This same technique allowed us to formulate a structural correction of the asynchronous electric drives. In contrast to the previously published research materials of asynchronous electric drives, a detailed qualitative analysis of the obtained nonlinear frequency responses and the interrelation of these characteristics with experimental results is shown for the first time in the article.</span>

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<span>The efficiency of analyzing the rotor currents of asynchronous electric drives with frequency control is substantiated in the article. To assess the quality of torque generation in the engine it is suggested to use the spectral analysis of these currents and the fundamental harmonic, as the most accurate "conformity" of slip in an asynchronous motor. The proposed method showed that "sensorless vector" control leads to the appearance of high-frequency harmonics with significant amplitude. Because of these harmonics, a non-sinusoidal electromagnetic moment is created and the performance of the drive is decreased. The most effective method of torque generation is the frequency control with positive stator current feedback. This control is dominated by pronounced harmonic components, which indicates the proximity of this structure to linear and significantly better controllability of the drives, which makes promising their use in high-tech mechanisms, in particular, in industrial robots. Simulation and experiments confirm the proposed theoretical propositions.</span>

The article is a continuation of the authors' work in research, mainly experimental, asynchronous electric drives with frequency regulation (AED FR) of hoisting-and-transport mechanisms, in which for constructive, operational and other reasons it is difficult to install additional sensors, for example encoders. The results of the analysis of the dynamics of AED FR with two types of sensorless control: vector and scalar are presented in this article. The study was conducted by mathematical modeling in the Simulink application of the MatLab software using standard control system models. The processes of sequential acceleration of the engine to fixed speeds with overload and load shedding on each of them were simulated. At the same time, the speed and effective values of the flux linkages of the rotor and stator and the stator current were monitored, by which the dynamics and efficiency of each type of control were evaluated. As in experimental studies, the dynamic and efficiency of a more stable scalar control was significantly improved by the use of dynamic positive feedback on stator current.

The main method for assessment of performance of automatic control systems is assessment of stability of a system as it allows the evaluation of dynamics and accuracy as well as the method for additional adjustment and technological capacity of the whole complex comprising the system. In the suggested paper the known criterion of stability for non-linear systems by Popov is based on non-linear frequency characteristics. It allows the development of conditions of stability and methods of adjustment for such complex systems as servo drives with non-rigid mechanics and alternating-current systems which cannot be analyzed with the help of known methods.