High-Speed High-Precision Programmable Magnet Power Supply for a Wide Range of Magnet Time Constants

Rapid current control in highly inductive loads requires a regenerative convertor whose output voltage is a multiple of that determined by the obmic resistance. During the flat top of the pulse the convertor is phased back resulting in a relatively large ripple and a high reactive power. Controlled freewheeling using thyristors between the d.c. terminals and the neutral of the transformer winding improves the output waveform and reduces the power drawn from the mains without reduction of the dynamic performance. Twelve-pulse rectification, a passive smoothing filter with low stored energy and an active filter ensure an extremely low ripple and a fast dynamic performance. Circuits and design principles are illustrated by describing a 220 V/6500 A pulsed power source for testing magnets. Control range 0-6500 A, max. di/dt 20 kA/s, stability 100 mA, p-t-p ripple 30 mA; magnet time constant between 0.05 s and 10 s. The current source is provided with a high-precision digital current programmer; current shaping is achieved with 8 adjustable parameters.