Efficient Control of Induction Motor Current in a Frequency-Controlled Electric Drive
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cient Control of Induction Motor Current in a Frequency-Controlled Electric Drive A. N. Ladygina, *, D. D. Bogachenkoa, and V. V. Kholina aNational
Research University Moscow Power Engineering Institute, Moscow, 111250 Russia *e-mail: [email protected] Received July 26, 2019; revised July 26, 2019; accepted August 20, 2019
Abstract—An analysis of methods for controlling the current of an asynchronous electric motor in a frequency-controlled electric drive is performed. The disadvantages of a control system with relay current controllers that provide system operation in the “current corridor” mode are shown. Such disadvantages as increased thermal losses in the transistors of the frequency converter are caused by the unstable switching frequency of the motor current. The relevance of the principles of current control using the predictive model to form control actions in the frequency converter circuit with relay controllers is noted. A method of current control in an asynchronous electric drive is considered that makes it possible to stabilize the switching period of the inverter power switches when controlling the current in the motor. To obtain this result, it is proposed to influence the width of the hysteresis loop of the relay current controllers and form it depending on the parameters of the load circuit. The required accuracy of the current control is maintained. The structure of the control system is proposed, in which the considered method is implemented. A key element of the system is a computing unit that generates signals that set the required width of the hysteresis loop of the relay controllers. The method of predicting changes in the controlled current after the next switching of transistors in the inverter of the frequency converter of the electric drive is the analytical basis of the calculations. Analytical expressions providing the calculations necessary for the computing unit operation are presented. The effect of applying the relay current controllers with variable hysteresis in the control system of a frequency-controlled electric drive is shown. Keywords: frequency converter, current control, current switching frequency, switching losses DOI: 10.3103/S106837122006005X
When considering the synthesis of electric drive systems, the quality of the drive current control, as it is a key coordinate determining the result of controlling the basic mechanical coordinates (moment and rotation rate), is of primary importance. The current control efficiency is totally determined by the circuit design solutions and control algorithms for frequency converters (FCs); therefore, since FCs are steadily improving, the search for increasingly efficient ways to control current in a frequency converter–asynchronous electric motor (AEM) systems is still important. The configuration using an FC with a self-excited voltage inverter and a pulse width modulation (PWM) as a power supply for an AEM stator is the most widely used frequency-controlled electric drive structure. It is known that, in this contro
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