Performance Improvement of APS Booster Ring Dipole Magnet Power SuppliesJu Wang (juw@anl.gov)

The 3rd Workshop on Power Converters for Particle Accelerators

DESY, May 21 – 23, 2012

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 2

Outline of the Presentation

The Configuration of Booster Dipole Power Supplies Past performance Improvements Present performance Future upgrade

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 3

Half Bridge

Half Bridge

Half Bridge

Half Bridge

CB+

_

Transformer SCR RectifierInterphase

XFMRFilter

3-480V

CB

3-480V

Y1

Y3

Y2

Y4

+

_V1

+

_V3

+V2_

+_V4

Vo

Booster Dipole Power Supply Circuit TopologyFour half bridges connected in parallel and series to produce a 12-pulse circuit

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 4

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 ±1×10-2 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/IINJ)– ±5×10-4, or ±21 ppm in full range (1000A)– Shot-to-shot reproducibility ±5×10-4 at injection current

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 5

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

Booster Ramping

Power Supply

Magnet

Voltage Regulator Card

EPICS Based Control System

Reference Iref

Magnet current IMag

Voltage Reference Vo_ref

Output voltage VoFiring angle

Inner Loop Outer Loop

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 6

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)

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 7

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 8

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

Voltage-Mode Controlled

Booster Ramping Power Supply

Magnets

Magnet current IMag

Output voltage Vo

Voltage Loop PI

Controller

Paralleled MOSFETs

MOSFET drive circuit

Isolation Amplifier

Magnet voltage VMag

+Current Loop PI Controller

_Vmag_ref

Magnet current IMag

+ _ Iref

Linear MOSFET Regulator

Linear MOSFET Regulation System

VMag

VMOSFET

Vo

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 9

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 10

Harmonics in Output Voltage (before improvement)

0 500 1000 1500 2000 2500 30000

10

20

30

40

50

60

0 500 1000 1500 2000 2500 30000

10

20

30

40

50

60

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 11

Harmonics in Output Current (before improvement)

360 Hz harmonics dominates

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 12

Notch Filters for 360Hz and 720Hz Harmonics

Half Bridge

Half Bridge

Half Bridge

Half Bridge

CB+

_

Transformer RectifierInterphase

XFMRFilter

3-480V

CB

3-480V

Y1

Y3

Y2

Y4

+

_V1

+

_V3

+V2_

+_V4

Vo

360Hz Resonant

Filter

720Hz Resonant

Filter

15mH

14uF

1 Ohm

3uF

15mH

1 Ohm

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 13

Schematic of Notch FiltersL1

15mH

12

1 Ohm

R1F1

FUSE

1 2

C12u

C22u

C32u

C42u

C52u

C62u

C72u

Cabinet 1 (360Hz L-R-C Resonant Filter)

Input

Cabinet 2 (720Hz L-R-C Resonant Filter)

R2

_

+

Bleeder Resistor

L2

15mH

12

1 Ohm

R3F2

FUSE

1 2

C80.5u

C90.5u

C102u

InputR4

_

+

T50W2NR * 1

T50W2NR * 7

T50P5NR * 2

MV055F1CAX20E (20A fuse)

MV055F1CAX20E (20A fuse) D225K1R0E

D225K1R0E

C22166

C22166

Bleeder Resistor

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 14

Hardware for 360Hz Notch Filter

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 15

Hardware for 720Hz Notch Filter

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 16

Result of Notch Filters (Output Voltage)

0 500 1000 1500 2000 2500 30000

5

10

15

20

25

0 500 1000 1500 2000 2500 30000

5

10

15

20

25

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 17

Result of Notch Filters (Output Current)

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 18

Comparison of ΔI/I (almost no difference)

No notch filters

With notch filters

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 19

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

100Ω

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 20

Result After Increasing Impedance GFD

Ground Fault Detection Circuit: 2.5 kΩ Resistor + 5H Inductor 360 Hz component is no longer dominating!

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 21

Harmonic Currents Under Different Circuit Conditions

360Hz Harmonics 720Hz Harmonics

Original Circuit 17*10-6 2*10-6

With Notch Filters 13*10-6 1.1*10-6

Filters+2.5K GFD Resistor

2.8*10-6 1.2*10-6

Filters+2.5K R and 5H L in GFD

0.9*10-6 1.2*10-6

Achievement: • 95% reduction in 360Hz harmonics• 40% reduction in 720Hz harmonics

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 22

Reduce Voltage Transient with Parabolic Start

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 23

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 – beforeRed – now

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 24

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.

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 25

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 ---

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 26

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

The 3rd Workshop on Power Converters for Particle Accelerators, DESY, Hamburg, Germany, May 21 – 23, 2012 27

Candidate Circuits

Resonant circuit plus a DC supply Multiple paralleled H-bridges

Thanks to everyone for responding to my emails!