Improvement a Direct Frequency Converter to Start Powerful Synchronous Motor

Abstract

Synchronous motor is usually used in a high-power electric drive, especially for mining and metallurgical enterprises, where the synchronous electric drive capacity is 40%, it consumes of electrical energy and creates production problems at the time of the start-up of powerful synchronous electric drives. There are basic directions for improving the energy efficiency of mining and metallurgical enterprises. However, as a rule, they relate to newly designed or re-equipment of enterprises and then, in the most part, the mining and metallurgical complex. In the long run, modernization of outdated equipment for all indicators, modernization of electric-powered units in order to reduce electric power consumption, modernization of power supply systems and optimization of power consumption processes with the possibility of adaptive management of these processes are the real directions for increasing the efficiency of existing enterprises. The approach and implementation of a new system for starting and driving a synchronous electric drive is proposed, known systems and methods for controlling them are analyzed, and the advantages and disadvantages of these systems are described. During the analysis, it was established that when using a direct frequency converter in the starting system of a synchronous motor, starting currents exceeding the permissible values may occur at the time of starting. A method for separately varying the value of the output voltage and the modulation frequency of a cycloinverter during a transition from a low fixed frequency to a higher one when forming electric power parameters of a synchronous motor is proposed. This method allows a transition to a higher frequency with a smaller current of the converter, which will allow us to obtain the shape of the current and voltage curves at the converter output with a smaller gamut of harmonic components.Ref. 10, fig. 2, tabl. 1.