A soft-startup device for an induction motor with supply-network voltage control

Abstract

The use of a thyristor voltage converter to limit voltage dips during the induction motor startup is considered. It is shown that the traditional solution—the current-cutoff startup mode—does not solve the problem of maintaining the residual voltage at supply-network bars during the motor startup at a level, at which the uninterrupted operation of other equipment connected to this supply network is provided. To limit the voltage dips during the startup, it is necessary to control the supply voltage during the startup. A control-system structure of the thyristor soft starter, which implements a closed loop of supporting the supply-network voltage during the startup, and the synthesis procedure of a controller in this structure are proposed. It is shown that the controller, which is created based on a simplified object model, gives acceptable results in practical use. Results of modeling and experimental data that show the operability of the proposed approach are presented. The desired supply-network voltage is directly set to the input in the system with the voltage control, and the possibility of maintaining this voltage during the induction-motor startup with the structural and parametric variations in the supply network and load is provided with high accuracy and adequate quality of transient processes.