Circuit description of unipolar DC-to-DC converters for APS storage ring quadrupoles and sextupoles

This paper describes the control, interlock, and power circuits for 680 unipolar switch mode DC-to DC converters used to regulate the Advanced Photon Source's (APS's) storage ring quadrupole and sextupole magnet currents. Quadrupole current stability is /spl plusmn/6/spl times/10/sup -5/ and the sextupole current stability is /spl plusmn/3/spl times/10/sup -4/. The stability is obtained with pulse width modulation, operating at a switching frequency of 20 kHz with full current switching. The converters are housed in 200 cabinets located on top of the storage ring tunnel. Raw DC power is distributed from 80 AC-to-DC power supplies, four at each of 20 locations around the storage ring. Voltages, currents, and temperatures are computer monitored and logged for the converters and magnets. All converters and magnets are water cooled with the flow and pressure monitored at the inlet and outlet of groups. Water is interlocked with the raw power supplies and not the individual converters. >