Subharmonic Ripple Reduction in SCR-Type Magnet Power Supplies

Subharmonic ripple in a magnet power supply output can cause unwanted low frequency field ripple in a magnet load. Among other things the ripple may be caused by SCR firing circuit imbalance. In critical applications, simply providing equally spaced SCR firing pulses, as is done in some all digital control schemes, may not be sufficient. This paper discusses in general the causes of subharmonic ripple and some approaches to the problem. A negative feedback scheme utilizing bandpass filters is analyzed and applied to a group of twelve phase .5MW power supplies. Results are given which show a substantial improvement in power supply voltage and magnet field ripple content at 60, 120, and 180 Hz. Application of the approach to other types of power supplies and limitations of the approach are discussed.