Novel 4-quadrant thyristor controller

Various forms of a.c./d.c. 4-quadrant thyristor controllers, based on the circulating-current principle, are described. The relative advantages and disadvantages of circulating-current schemes and logic-interlocked schemes are discussed and a new current or voltage controller with a linear transfer characteristic is described. It is shown how such a scheme can be operated on the circulating-current principle with the circulating current effectively zero.