Digital Control System of High Precision Magnet Power Supply for SPring-8-II

Abstract

For the SPring-8 upgrade plan, SPring-8-II, a variety of magnet power supplies (PS) from 10 W to larger than 100 kW with a high current stability of about 10 ppm (pk-pk, typ.) are required. In order to develop the PSs within a given time and budget, we plan to use a common control system based on a digital control technology that can be adopted for the variety and the high precision PSs. The system consists of a high-precision analog-digital converter (ADC) circuit and a field programmable gate array (FPGA). Since the precision of the ADC circuit determines the current stability of the PS, we first developed the ADC circuit of high accuracy of less than 10 ppm (pk-pk). A proportional-integral (PI) control logic and a digital pulse width modulation (PWM) function was implemented in the FPGA firmware. These functions can be easily modified for each power supply by a desktop computer. We prototyped a DC power supply equipped with the newly developed digital feedback control system and confirmed that the current fluctuation was suppressed to less than 10 ppm (pk-pk). In the presentation, we will report the current status and future perspective of our power supply development including the evaluation results of the new circuits and the power supply we have developed.