FPGA Based Digital Controller

Future accelerator projects in India would require magnet power converters in large numbers with stringent output current stability requirements, down to ±10 ppm. For implementation of feedback control scheme in these power converters, digital controllers are preferred over their analog counterparts as the technological advancements in digital hardware have made them more attractive due to their inherent advantages like immunity to component variations, easy implementation of sophisticated control schemes, flexibility and design standardization of digital hardware. Towards this, activities related to the development of FPGA-based prototype digital controller for magnet power converters were taken up which led to the development of a table-top digital controller consisting of Xilinx Spartan-3AN FPGA board, EVAL-AD7634EDZ ADC evaluation board and analog signal conditioning PCB, resulting in output current stability within ±50 ppm with a prototype magnet power converter. Taking this activity further towards consolidation, a 4U size prototype digital control card has been developed which retrofits the existing analog control card in the control rack module of magnet power converter. It mainly consists of an FPGA to implement Proportional-Integral (PI) based close loop control scheme along with high resolution digital pulse width modulation (DPWM), signal conditioning circuit, ADC, oven control circuit and pulse blocking circuit. This card has been programmed with high resolution feedback control scheme, evaluated and tested with a magnet power converter achieving output current stability within ±10 ppm.

Photograph of digital control card