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

2. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20122 Outline of the Presentation The Configuration of Booster Dipole Power Supplies Past performance Improvements Present performance Future upgrade

3. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20123 Booster Dipole Power Supply Circuit Topology Four half bridges connected in parallel and series to produce a 12-pulse circuit

4. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20124 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/I MAX ) (about ±1×10 -2 ΔI/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/I INJ ) –±5×10 -4, or ±21 ppm in full range (1000A) –Shot-to-shot reproducibility ±5×10 -4 at injection current

5. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20125 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 reference for the next ramp if necessary –Adjust the start time and ramp slope

6. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20126 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)

7. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20127 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 power rf system, has been observed  In order to meet the increased single-bunch-charge requirement of the APS upgrade, better regulation is required

8. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20128 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

9. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 20129 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

10. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201210 Harmonics in Output Voltage (before improvement) Master Supply Slave Supply 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 A lot of 360 Hz component Very little 360 Hz component

11. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201211 Harmonics in Output Current (before improvement) 360 Hz harmonics dominates

12. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201212 Notch Filters for 360Hz and 720Hz Harmonics

13. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201213 Schematic of Notch Filters

14. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201214 Hardware for 360Hz Notch Filter

15. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201215 Hardware for 720Hz Notch Filter

16. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201216 Result of Notch Filters (Output Voltage) 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% Dipole Master Supply Dipole Slave Supply

17. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201217 Result of Notch Filters (Output Current) Test Results: 720Hz harmonics reduced by 45%, 360Hz harmonics only reduced by 23%!

18. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201218 Comparison of Δ I/I (almost no difference) No notch filters With notch filters

19. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201219 Common Mode Circuit 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 ! 100Ω

20. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201220 Result After Increasing Impedance GFD Ground Fault Detection Circuit: 2.5 kΩ Resistor + 5H Inductor 360 Hz component is no longer dominating!

21. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201221 Harmonic Currents Under Different Circuit Conditions Achievement: 95% reduction in 360Hz harmonics 40% reduction in 720Hz harmonics

22. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201222 Reduce Voltage Transient with Parabolic Start Final choice is a 16-ms ramp up for the voltage reference.

23. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201223 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

24. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201224 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.

25. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201225 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 issue for 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 ---

26. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201226 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

27. The 3 rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 201227 Candidate Circuits  Resonant circuit plus a DC supply  Multiple paralleled H-bridges Thanks to everyone for responding to my emails!