Block diagram of asynchronous motor with short-circuit rotor for a variable frequency drive with scalar and vector control

Modern control systems for variable-frequency asynchronous electric drives (ED) are based on three-phase asynchronous motor (AM) represented by two-phase general electric machine. This simplifies mathematical description of AM and practical implementation of control systems of frequency-controlled asynchronous EDs, while the mathematical description of AM can be carried out in various coordinate systems. In practice, when studying processes in AM, mathematical description and their structural schemes are most often used in fixed coordinate system ,  rigidly connected to the stator and axis d synchronously rotating with the stator magnetic field coordinate system d, g, oriented on rotor interlinkage vector  , which greatly simplifies the study of their mathematical models. The obtained structural layouts contain internal back couplings, including nonlinear ones, resulting from the equations of the stator voltage projections. To compensate for the internal EMF of the motor induced in its stator, back couplings are used at the input of the converters, allowing to simplify the block diagrams of motors and, accordingly, the analysis of control systems. The resulting mathematical models and block diagrams of AM in a fixed coordinate system α, β and axis d synchronously rotating d, g, oriented on rotor interlinkage vector ψ , it is feasible to use in systems of frequency-controlled asynchronous EDs, respectively, with scalar and vector control . The introduction of back couplings voltages at the inlet of the converter into the system of the mentioned ED, compensating the EMF of the AM rotation, by analogy with DC motors, ensures independent control of their magnetic flux and electromagnetic moment .  The obtained mathematical models and AM block diagrams can be used for development of sensorless systems of frequency-controlled asynchronous EDs, where the motor parameters such as interlinkage, angular velocity, electromagnetic moment, etc .  are calculated from the measured values of phase current and stator voltage of electric motor .

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