METHOD OF AND APPARATUS FOR CONTROLLING THE BRAKING RESISTOR OF A FREQUENCY CONVERTER

摘要

A method of and apparatus for controlling a braking resistor, provided in a d.c. circuit of a frequency converter, by rectifying a mains voltage, by means of a first rectifier bridge connected to a threephase mains supply, to form an actual value voltage; comparing said actual value voltage and a reference voltage; and operating a switch in series with the braking resistor to cause the latter to conduct when the comparison indicates that the actual value voltage is greater than the reference voltage. The reference voltage is formed from a rectified voltage obtained from the three-phase mains supply and rectified by a second rectifier bridge.