A NOVEL TOPOLOGY FOR THE BENDING MAGNETS POWER-SUPPLY AT LNLS

The Synchrotron Radiation source under construction at the LNLS in Brazil is composed of 12 bending magnets and 3 quadrupole families. A new topology of high-performance dc current power supply was developed to feed the magnets. The main goal is to get a high performance (mean current stability, tracking, repeatability and ripple better than 100 ppm), highly efficient and reliable system. To achieve these goals, a new power supply topology was developed based on a modular switched-mode power supply associated in series with a 6 pulse SCR bridge. To reduce possible high levels of electromagnetic interference, only a small fraction of the total load voltage is used to feed the SMPS; more than 90% of the power is delivered by the SCR bridge. Furthermore, the load current is shared among the SMPS modules, so that each one switches only a fraction of the total current. Each module is built inside a metallic box, that shields the electric and magnetic fields. The SMPS are controlled by current limit modulation. A 18 kW (300 A/60 V) prototype was built and has been used in the laboratory to characterize magnets. Measurements indicate a mean current stability of +/- 14 ppm (at 300 A), current ripple is +/- 25 ppm and the field ripple is less than +/- 1 ppm inside the vacuum chamber. The tracking error is null. The power factor is 0.95 and the efficiency is better than 90%.