Research of Electromagnetic and Electromechanical Processes in High-Voltage Soft Start Devices with Gate Turn-Off Thyristors

The purpose of the work is to investigate the possibilities of soft-start devices with gate turn-off thyristors in electric drives of bow thrusters with adjustable propeller pitch to increase reliability, reduce mechanical shocks and currents, and improve electromagnetic compatibility with the ship’s electrical power plant. The characteristic features of these drives are operation on fan load and the need for a smooth start in a sufficiently short time to reduce impact torque in the mechanism. As a result of the analysis, a solution with a shunt capacitor is proposed, which provides high accuracy of regulation of the 1st harmonic of the voltage on the motor according to the given law. The minimum value of the capacitor capacity was found, which for the ABB/AMD710L8T motor with a capacity of 2.7 MW is 150-250 μF at switching frequencies from 500 to 1000 Hz. For the first time, the dependences of the GTO switching frequency on the capacitor capacity and the coefficient of harmonic distortion of the current in the stator phase of the selected motor were found. Frequencies are obtained that correspond to the actual physical characteristics of the GTO (500–1000 Hz). At such switching frequencies, the characteristics of the soft start device practically do not differ from the ideal regulator of the phase voltage of an asynchronous motor. This makes it possible to synthesize closed systems with stabilization of the main coordinates of soft starter electric drive, two-circuit systems with the formation of a given tachogram with torque limitation. All this makes it feasible to implement soft start devices based on gate turn-off thyristors.