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Performance Improvement of APS Booster Ring Dipole Magnet Power Supplies. Ju Wang ( juw@anl.gov ) The 3 rd Workshop on Power Converters for Particle Accelerators DESY, May 21 – 23, 2012. Outline of the Presentation. The Configuration of Booster Dipole Power Supplies Past performance

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performance improvement of aps booster ring dipole magnet power supplies

Performance Improvement of APS Booster Ring Dipole Magnet Power Supplies

Ju Wang (juw@anl.gov)

The 3rd Workshop on Power Converters for Particle Accelerators

DESY, May 21– 23, 2012

outline of the presentation
Outline of the Presentation
  • The Configuration of Booster Dipole Power Supplies
  • Past performance
  • Improvements
  • Present performance
  • Future upgrade
booster dipole power supply circuit topology
Booster Dipole Power Supply Circuit Topology

Four half bridges connected in parallel and series to produce a 12-pulse circuit

operation specs
Operation Specs
  • Linear Ramping
    • 0 – 1000A in 250 ms, repeats at 2 Hz
  • Original PS Spec
    • -1100 – 1900 V, 0 – 1100 A, peak output power 2000 kW
    • Current Regulation±500ppm(ΔI/IMAX)

(about ±1×10-2ΔI/I at the beam injection point)

    • Current at Beam Injection (325 MeV)
      • 42A, about 11.6ms after the ramp started
  • New Spec at Injection Point (ΔI/IINJ)
    • ±5×10-4, or ±21ppm in full range (1000A)
    • Shot-to-shot reproducibility ±5×10-4 at injection current
past performance
Past Performance
  • Upon delivery the current tracking did not meet the requirement at all
  • We redesigned the voltage regulator, firing circuit, AFG for references, and remote monitoring systems
  • Tried a current loop, but it did not work well. So the voltage loop is in use
  • Developed an external (offline) ramp correction algorithm
    • Measure the current
    • Calculate the tracking error
    • Correct the voltage referencefor the next ramp if necessary
    • Adjust the start time and ramp slope
past performance cont d
Past Performance (cont’d)

After the APS redesign

  • Tracking error reduced to 0.25 – 0.5% at the injection
  • Successfully supported the operations for more than 15 years

Typical Dipole Magnet Current Tracking Error (ΔI/I)

upgrade need
Upgrade Need

Although it works, but

  • Some instability exists in the ramp correction that requires manual intervention from time to time by the operators
  • The magnet currents are sensitive to external changes, such as AC line voltage and harmonic interference from the high powerrfsystem, has been observed
  • In order to meet the increased single-bunch-charge requirement of the APS upgrade, better regulation is required
upgrade plan i external linear regulator
Upgrade Plan I – external linear regulator
  • Linear regulator with parallel and series connected MOSFETs operating in linear mode
  • Tested with a spare sextupole supply on test stand, achieved 0.15% ΔI/I
  • Issues/concerns
    • MOSFET current un-sharing in the linear region
    • Large number (20+) of MOSFETs may be required for dipole supplies
    • High voltage and high power stress, a reliability concern

MOSFET: APTM50UM09F-ALN, 500V/497A, from Advanced Power Technology

upgrade plan ii reduce harmonics and
Upgrade Plan II – reduce harmonics and …
  • Reduce Harmonics
    • Added 360 Hz and 720 Hz notch filters
    • Increased common impedance in the ground loop
  • Reduce transient
    • Added a parabolic section to the current reference at the beginning of the ramp so the voltage starts with a slope instead of a step
  • Redesign electronics
    • Redesigned the voltage regulator with a multilayer board, reduced shot-to-shot variation of ΔI/I at the injection point by nearly a factor of 2
harmonics in output voltage before improvement
Harmonics in Output Voltage (before improvement)

Slave Supply

Master Supply

A lot of 360 Hz component

Very little 360 Hz component

X axis: frequency (Hz), Y axis: voltage (V)

  • Master supply is fed from the same ac line for the RF equipment
  • 360 Hz harmonics is due to ac line distortion caused by RF equipment
  • Not much can be done with the RF systems for various reasons
result of notch filters output voltage
Result of Notch Filters (Output Voltage)

Dipole Slave Supply

Dipole Master Supply

X axis: frequency (Hz), Y axis: voltage (V)

  • Test :
  • Master supply: 360Hz harmonics reduced by 77%, 720Hz harmonics reduced by 53%
  • Slave supply: 360Hz harmonics reduced by 55%, 720Hz harmonics reduced by 58%
result of notch filters output current
Result of Notch Filters (Output Current)

Test Results:

720Hz harmonics reduced by 45%, 360Hz harmonics only reduced by 23%!

comparison of i i almost no difference
Comparison of ΔI/I (almost no difference)

No notch filters

With notch filters

common mode circuit
Common Mode Circuit

100Ω

Common-mode current goes out both terminals of power supplies and returns through capacitive coupling to earth ground and the ground fault detection circuit

Solution – increasing the impedance of the ground fault detection circuit to reduce the common-mode current !

result after increasing impedance gfd
Result After Increasing Impedance GFD

Ground Fault Detection Circuit: 2.5 kΩ Resistor + 5H Inductor

360 Hz component is no longer dominating!

harmonic currents under different circuit conditions
Harmonic Currents Under Different Circuit Conditions

Achievement:

  • 95% reduction in 360Hz harmonics
  • 40% reduction in 720Hz harmonics
reduce voltage transient with parabolic start
Reduce Voltage Transient with Parabolic Start

Final choice is a 16-ms ramp up for the voltage reference.

after the improvement
After the Improvement
  • ΔI/I is close to 0.1% at injection point, but ramp to ramp variation is still bigger (0.13%) than desired.
  • RMS value of ΔI/I is reduced from 0.035 to 0.01

Blue – before

Red – now

benefit of the improvement energy saving mode
Benefit of the Improvement – Energy Saving Mode
  • After the improvement to ramp and ramp-to-ramp stability, an energy saving operation mode is developed
  • The dipole power supplies are put in standby mode for one minute during the two minute interval between the SR top-up shots
  • It saves an average power of 250 kW and about $12.5K annually.
conclusion and future plan
Conclusion and Future Plan
  • Conclusion
    • The regulation of the dipole magnet current is now very close to the desired requirement, but physicists want more
    • Further improvement is more difficult without fundamental changes to the circuit topology
  • Future Plan
    • New switching mode supplies would be ideal, but will have high risks and will be costly.
    • Space can be an issuefor new supplies
    • Incremental improvement is planned for the near future
      • Redesign the firing card to increase the firing angle resolution from 12 bit to 14 bit or more
      • Redesign the remote ADC card to improve the performance and resolve obsolescence issue
      • Close the current regulation loop (a low priority for now)

--- End ---

power supply for electromagnetic variable polarized undulator
Power Supply for Electromagnetic Variable Polarized Undulator
  • High Output: ±2000A
  • Small Load: 2mΩ and 80μH
  • Moderate regulation: <0.1%
  • AC Mode: 10Hz
  • Fast switching: 100% completion of switching between +2000A and -2000A within 5 or 6ms
candidate circuits
Candidate Circuits
  • Resonant circuit plus a DC supply
  • Multiple paralleled H-bridges

Thanks to everyone for responding to my emails!