Phase-Shifting Device

an electrical device in the control system of a rectifier-type converter, designed to create the required time delay (usually expressed in units of angular phase shift) between the instant of firing of the rectifier and the instant of supplying the rectifier with the driving pulse.

Figure 1. (a) Electrical diagram of a phase-shifting device, (b) diagram of the voltage in the circuit; (U) input voltage, (U_N) output voltage, (Re) saturable reactor, (R) resistor

The simplest phase-shifting device consists of a saturable reactor and a resistor (Figure 1). Until the instant at which the reactor becomes saturated, the supply voltage is applied almost fully to the reactor winding. At the instant of saturation, the voltage drop across the resistor increases sharply; this voltage jump can be used directly as a driving pulse for slow-acting converters. In phase-shifting devices with a pulse transformer, the instant at which the driving pulse is generated in the output winding of the transformer can be altered by changing the polarity and magnitude of current in the control winding, that is, by changing the magnetizing current. Other types of phase-shifting devices use variable resistors and capacitors; some are used to modulate electrical signals.