Development of a Mathematical Model to Study the Energy Indicators of Electric Drives Using the DFC-IM System

The paper is devoted to the peculiarities of constructing a mathematical model of a frequency-controlled electric drive, and with regard to powerful units justifies the need to power the windings of an induction motor with a short-circuited rotor from the output of a direct frequency converter (DFC) assembled according to a symmetrical scheme using six-pulse or three-pulse thyristor converters. The justifications are given using the example of electric drives of ditching machines and hydraulic presses. These machines perform operations that are fundamentally different from each other, but have the same structure of the electric drive control system. At the same time, these differences do not affect the choice of the basic structure for creating a mathematical model of a frequency-controlled electric drive. The givenblock diagram, which is common for both machines and is made taking into account the power of the convertible electric energy, makes it possible to justify the issue of powering the stator windings of the induction motor from the output of the direct frequency converter, if the converter operates in the current source mode. The chosen processing units involved in various technical processes give the basis for the possibility of applying the results of the study to any units where the AC electric drives are used according to the DFC-IM system. The developed mathematical model will allow studying the energy characteristics of the consumed electric energy during the operation of the electric drive in a steady mode. Equations describing the power part of the DFC-IMsystem are compiled using the state variable method. At the same time, such elements of the power circuit as the transformer and the induction motor are represented by their replacement schemes with reduced parameters; thyristors of the frequency converter are replaced – in a closed state by their dynamic resistances RT, in a closed state – by zero current sources. The obtained mathematical model of the electric drive according to the DFC-IMsystem allows studying the energy processes occurring during energy conversion and formulating practical recommendations for choosing the rational design schemes of power circuits.