Power Supply Regulation

1
Power Supply Regulation

• WBS 1.1.3 Power Supply System
• Level 3 Manager
• Nancy Grossman
• FNAL
• June 28, 2001

2
Overview of Regulation Needs

• 7 Magnet Strings with regulation requirements
  ranging from 55 ppm to 400 ppm.
• 55 ppm means /- 55 ppm relative to the flattop
  operating current (RMS).
• V105 string requirement is 60 ppm, close to the
  tightest requirement.
• Discussion will center around simulations of the
  V105 string.
• 3 sources of current variation for magnet
  strings
• 720 Hz power supply voltage ripple being applied
  to the magnets.
• Line voltage changes.
• Load changes.
• Simulations of a particular power supply (or
  series of power supplies) can be used to see the
  effects of these changes on the resulting flattop
  current.

3
720 Hz Ripple Effect

• 720 Hz line ripple effect on the PS currents is
  shown in the table below.
• Not acceptable
• Need filters for each string
• Refurbish existing filters
• Have costed 3, have claimed 7 for NuMI.
• Estimated cost to remove, refurbish and install
  10k/string (extra 40K)

4
Line Voltage and Load Changes

• Simulations were run for the NuMI V105 string,
  assuming a constant reference voltage.
• 5 change in line voltage was easily
  corrected for at the level of 25 ppm
• with standard voltage regulation. (most
  variation one would expect)
• 5 load change (resistance) gave a 240 ppm
  current variation.
• Corresponds to about a 100 C change in the copper
  in the magnet or the LCW changing 150C
• Other magnet strings would have similar results
  most likely.
• Not acceptable.
• Need additional regulation.
• HOLEC transductor (5K/string)
• Special FNAL regulation electronics (5K/string)
• Both are designed and installed in the Main
  Injector
• This combination of electronics would give
  another factor of 2 120 ppm

5
Line Voltage and Load Changes

• Three strings are still above the required
  specifications.
• So now what?

6
Additional Factor of 2 - 4

• Bandwidth
• Each string will be tuned for maximum bandwidth.
• 20 Hz is assumed in the previous calculations.
• 40 Hz is frequently achieved (but not
  guaranteed).
• Gives a factor of 2 in current stability.
• Auto-tune
• Load changes are typically slow changes and thus
  Auto-tune can correct for these.
• One could then argue why do you need the extra
  power supply regulation too?
• Auto-tune does not always work.
• Needs beam and working beam position monitors to
  work.
• Assumes next beam pulse like the previous one.
• Experience at FNAL where significant beam control
  is needed says do both.
• Since the power supply regulation is also driven
  some by groundwater concerns, we want something
  that is always working.

7
Other Primary Beam Power Supplies

• Quadropole power supplies (20 KW PEIs)
• Standard regulation is at /- 0.05 of the
  maximum current (100 or 200 amps)
• Corresponds to up to /-0.44 variation in
  operating current.
• Believed to be sufficient.
• Main Injector Trim Magnet power supplies
• Standard regulation is at /- 0.1 of the maximum
  current (15 amps)
• Believed to be sufficient.

8
Summary

• NuMI power supply regulation levels will be
  achieved by
• Filters on all 7 strings.
• HOLEC and FNAL Electronics on all 7 strings.
• Auto-tune.
• Tuning for maximum bandwidth.
• Cost increase to NuMI
• 40k for 4 additional filters (refurbished)
• 70k for 7 sets of HOLEC/regulation electronics
  (one for each string)
• Other slightly less expensive (and perhaps more
  effective) options may be designed by Fermilab
  before NuMI runs, in which case we would
  certainly use them.
• Studies in the Main Injector P1 line will also
  help us to better define the level of regulation
  one obtains with a HOLEC transductor and special
  regulation electronics.