A current-controlled PWM bipolar power supply for a magnet load

The Advanced Photon Source, at Argonne National Laboratory will produce the world´s brightest X-ray beams when it is complete. A number of correction magnets are used to maintain proper beam position. Basically, two different types of bipolar power supplies are used for all the correction magnets: one requires DC correction only, and the other requires DC and AC correction. Normally linear-mode power amplifiers would be used for the bipolar power supplies. However, linear-mode power amplifiers dissipate a substantial amount of power as heat, resulting in poor efficiency for their large size. In addition, most commercial bipolar power supplies are linear-mode and available for lower power levels. Therefore, for higher power levels it was necessary to design a bipolar power supply that uses switch-mode power conversion. This paper describes a control technique for a pulse-width-modulated bipolar power supply, which can deliver a controlled current, DC plus AC, to a correction magnet. A design example of a 150 A bipolar power supply is presented