fk. bordry ab/po academic training - 27th march 2003 technological challenges for the lhc power...

Fk. Bordry AB/POAcademic Training - 27th March 2003

Technological Challenges for the LHC

Power converters for the LHCFrédérick BORDRY AB-PO

?I (A)

t

11800

20 min

-10 A/sec

+10 A/sec

2 min

several hours

0.1 A/sec350 A

1 min

350 A

pre-injection (1 min - 1 h)

860 A

860 A

500 W

2,2 MW

115 kW


What’s special about Powering Superconducting Magnets ?What’s special about Powering Superconducting Magnets ?

High Current Large Inductance

No Resistance

Need heavy warm cabling Need to be near to feed point

Difficult and expensive power converter output stage

Large Stored Energy, 1/2 LI2

Need to handle carefully!

Large Time Constant, L/R Boost voltages (high voltage only during the ramps) Difficult control loops

Tendency to quench Need to take special precautions (energy)


• The beams are controlled by:• 1232 SC Main Dipole magnets to bend the beams

• 392 SC Main Quadrupole magnets to focus the beams

• 124 SC Quadrupole / Dipole Insertion magnets (in 196 circuits of ~ 6 kA)

• 6340 SC Corrector magnets (in 1460 circuits 60 to 600A)

• 112 Warm magnets (in 38 circuits 600 to 900A)

• SC RF Cavities to accelerate and stabilize the beam

– All ~8000 magnets need to be powered in a very controlled and precise manner

LHC Large Hadron Collider - What needs powering?LHC Large Hadron Collider - What needs powering?


LHC : 1232 SC Main Dipole magnetsLHC : 1232 SC Main Dipole magnets

One circuit or several circuits ?

Magnet inductance : L = 108 mH

Ltotal=1232 * 0.108 = 133 HRamp: LdI/dt = 1330V

Discharge (quench; 120 A/s): 16kV

Nominal current 11.8 kAStored Energy = 9.3 GJ

Ultimate current = 13kAStored Energy = 11.3 GJ

L/R 50 hours !!!!


Natural segmentation into 8 units as no cryostat in straight sections. Warm cable connections costly in copper , power losses (~30MW) and power

converters Total stored electrical energy in LHC main dipoles is ~10.6 GJ. Discharge in

120 seconds means 16 kV! Only 1/8 of the machine needs to be discharged if one magnet quenches

• No risk of total machine avalanche quench, (false quench detection and provocation)

Earthing of the ring in eight galvanically isolated sectors Less risk of build-up of voltages

• Only two sets of switches for dipoles, one for quads, no timing problems

• Smaller resonant circuit Eight sub-units give easier installation, testing, commissioning and fault

finding for many systems Allows sector-to-sector correction of magnet errors due to different cable,

magnet manufacturers, etc..

Need to track from sector to sector

Why an Electrical Segmentation of the machine?Why an Electrical Segmentation of the machine?


Tracking between the 8 main dipole converters

ppm AccuracyB/Bnom = I/Inom = ppm

B = 9 10-6 = 1.8 10-4 TB/Bo = 15 10-6

Orbit excursion :X = Dx . B/Bo = ~ .035 mmX = .7 mm => = 20 ppm

ppm AccuracyB/Bnom = I/Inom = ppm

B = 9 10-6 = 1.8 10-4 TB/Bo = 15 10-6

Orbit excursion :X = Dx . B/Bo = ~ .035 mmX = .7 mm => = 20 ppm

Could be corrected with a pilot runand new cycle => reproducibility10 ppm reproducibility Orbit excursion :X = Dx . B/Bo = ~ 0.35 mm !!!

”It would be better with 5 ppm”Oliver Brüning

Could be corrected with a pilot runand new cycle => reproducibility10 ppm reproducibility Orbit excursion :X = Dx . B/Bo = ~ 0.35 mm !!!

”It would be better with 5 ppm”Oliver Brüning


Power Converter Tolerances for LHCPower Converter Tolerances for LHC

Precision Control

Inner triplet 8000/ 6000

Unipolar ± 70 ± 20 with calibration

± 10 ± 5 1

Dispersion suppressor 6000 Unipolar ± 70 ± 10 ± 5 15

Insertion quadrupoles 6000 Unipolar ± 70 ± 10 ± 5 15

Separators (D1,D2,D3,D4) 6000 Unipolar ± 70 ± 10 ± 5 15

Trim quadrupoles 600 Bipolar ± 200 ± 50 ± 10 30

SSS correctors 600 Bipolar ± 200 ± 50 ± 10 30

Spool pieces 600 Bipolar ± 200 ± 50 ± 10 30

Orbit correctors 120/60 Bipolar ± 1000 ± 100 ± 50 30

Circuit Nominal Current One Year One day 1/2 hour ResolutionType Current Polarity Accuracy Reproducibility Stability

(A) (ppm of Inominal) (ppm of Inominal) (ppm of Inominal) (ppm of Inominal)

Main Bends, Main Quads 13000 Unipolar ± 50 ± 20 with calibration

± 5 ± 3 1


LHC Power Converters

Number of Converters: 1720Total Current :1860 kA

Steady State Input : 63 MWPeak Input : 86 MW

Number of Converters: 1720Total Current :1860 kA

Steady State Input : 63 MWPeak Input : 86 MW

LEP % LHC


LEP versus LHC for Power ConvertersLEP versus LHC for Power Converters

LEP 200 (up to 110 GeV)Number of converters 900Installed Power = 130 MW (80 MW for the magnets and 50 MW for RF cavities)

Total output current = 115 kAMain dipole current = 4500AMain quadrupole current = 420 A

LHC (up to 7.7 TeV)Number of converters 1720Installed Power = 86 MW (40MW for cryogenics)(70 MW for the magnets and 16 MW for RF cavities)Flat top at 7.7 TeV : 50 MW

Total output current = 1’860 kAMain dipole current = 13’000AMain quadrupole current = 13’000 A


Performances : -High current with high precision (accuracy, reproducibility, stability, resolution) and large dynamics-current range (for 1-quadrant converter: from 1% to 100%)- a lot of 4-quadrant converters (energy from magnets)- tracking : Need to track from sector to sector- voltage ripple and perturbation rejection

The Challenges : The Challenges :

Installation (LEP infrastructure) and Operation: - volume (a lot of converter shall be back-to-back)

- weight (difficult access) => modular approach- radiation for [±60A,±8V] converters- losses extraction : high efficiency, water cooling- EMC : very close to the others equipment ; system approach


UA23 (Ex-LEP Klystron gallery)Now used to house the majority of

machine equipment

such as power converters, magnet protection, injection,

extraction, RF generators, etc.

Very Low Radiation DoseNo Access during “Beam-On”

Access with full power on

Very Low Radiation DoseNo Access during “Beam-On”

Access with full power on


Volume, back-to-back, losses , weight,...No Access during “Beam-On”Access restricted without beam

New Enlargement (RR) for Machine Power Converters around ATLAS and CMS

New Enlargement (RR) for Machine Power Converters around ATLAS and CMS

Constraints :


Radiation Dose1 Gy/year under dipoles

No Access during “Beam-On”Access restricted without beam : Low power

Main Arc TunnelMain Arc Tunnel Orbit Corrector PCs4*[60A,8V]

752 converters

Orbit Corrector PCs4*[60A,8V]

752 converters

High reliability :MTBF : 80 ’000 h1 converter breakdown every 4 daysOne campaign every 2 or 3 months


General approachGeneral approach

• Minimise the number of converter types

• Separate out the subsystems that are desirable/acceptable by industry. Place development and production contracts.

• Design and build prototypes of remaining subsystems. Place production contracts.

• Assume system integration responsibility

• Integration and test at CERN before installation


Special DevelopmentSpecial Development• Converter topologies :

– High current (13kA) and high power (2.5 MW) 2-quadrant converters (main dipoles)

– Switch-mode converters (soft-commutation 20 to 100 kHz)• Parallel subconverters

• 4-quadrant converters (energy management)

• High precision current transducer (DCCT)• Current calibration system• High precision ADC (>20 bits ; )• Control loops :

– robust digital loop (RST)

– Inner triplet powering (nested converters => decoupling)


+15o

-15o3 Phase50 Hz

Supply

Good Symmetry

Freewheelcircuit

- Used for booster of Main Bend and large warm magnets

- Heavy and large- Voltage bandwidth < 70Hz- Well proven- Inversion possible

Two Quadrant Phase Controlled Rectifiers for high current SC magnets:

Power Converter Topologies


[13kA,±190 V]Few ppm

Main dipole power converter

11 m

Dev.

I (A)

t

11800

20 min

-10 A/sec

+10 A/sec

2 min

several hours

0.1 A/sec350 A

1 min

350 A

pre-injection (1 min - 1 h)

860 A

860 A

500 W

2,2 MW

115 kW


Power Diode and Thyristor

or SCR (Silicon-Controlled Rectifier )

Link to frequency of the electrical network

50 Hz (60 Hz)

High frequency => high performances (ripple, bandwidth, perturbation rejection,...)small magnetic (volume, weight)

From mercury arc rectifier, grid-controlled vacuum-tube rectifier, inignitron ,….

High frequency power semiconductors :

MosFet, IGBTs , GTOs, MCTs,….


Low speed

High speed

Large Filtering

Light Filtering


Voltage loop: bandwidth few kHz

AC50 Hz

AC20 - 100 kHz

DC DC

Fast power semiconductors (IGBT)

Semiconductor losses :soft commutation

HF transformer and output filter : ferrite

• light weight, reduced volume (HF transformers and filters)

• good power factor (0.95)

• high bandwidth and good response time

• Soft commutation gives low losses and low electrical noise

• small residual current ripple at output

• light weight, reduced volume (HF transformers and filters)

• good power factor (0.95)

• high bandwidth and good response time

• Soft commutation gives low losses and low electrical noise

• small residual current ripple at output

Switch-Mode Power ConvertersSwitch-Mode Power Converters

+

- +

-

Passive high-currentoutput stage

HF soft-commutation inverteron low current input side


OutputModuleInverter ModuleInput Module Reactive network

+

-

HF soft-commutation inverteron low current input side

Passive high-currentoutput stage

Sub-converter

3.25 kA , 18Vor

2kA , 8V

Inverter : 20 - 50 kHz30 - 70 KVA

Since they are natural current sources, and can be easily paralleled to make up very high currents


Current sources in parallel

13 kA, 16V

3.25 kA , 16 V

3.25 kA , 16 V

3.25 kA , 16 V

3.25 kA , 16 V

3.25 kA , 16 V

• n + 1 subconverters : redundancy, reliability• repairability• ease of handling underground• versatility (6.5kA, 9.75kA, 13kA, 21 kA)

• n + 1 subconverters : redundancy, reliability• repairability• ease of handling underground• versatility (6.5kA, 9.75kA, 13kA, 21 kA)


Loop


Line-commutatedthyristor-controlled converter

SCR semiconductor

Switch Mode Converter

IGBTsemiconductor

[14kA,16V] converterVolume : 25 m3

Weight : 8 tonsRipple : ~ 200 mVVoltage bandwidth : 40 Hz

[16kA,16V] converterVolume : 6 m3

Weight : 1.2 tonsRipple : ~ 10 mVVoltage bandwidth : 1000 Hz

Dev.


Imeasured

V

IIref B

+ Reg.

F(s)-

Vref

V

G(s)

Current loopVoltage loop


1- Fast internal current source FCLB ~ 8 kHz

2- Global voltage loop FCLB ~ 700 Hz

3- High precision current loop (DCCT) FCLB ~ 0.1 - 1 Hz

Control loopsControl loops


Digital current loop : RST algorithmDigital current loop : RST algorithm

FrequencyDivider

T 1/Syref(k)

k.Ts

ADC

Power Party(t)

DAC

Antialiasing

filter k

DigitalFilterR

Ts

Over sampling

Digital controller

Tracking and Regulation with independent objectives

Tracking and Regulation with independent objectives

Tracking Regulation


0

20

40

60

80

0 1 2 3 4 5 6 7 8

0

1

2

3

4

Cu

rren

t of

fset

in M

illi

amp

s

Cur

rent

offs

et in

ppm

of 2

0 kA

Time in Seconds

I0 = 1019.9 Amps

Reference

Measured

Cur

rent

in A

mps

500.0

500.1

500.2

0 1 2 3 4 5 6

0

5

10

Cur

rent

offs

et in

ppm

of 2

0 kA

Time in Seconds

1ppm

Reference

Measured


String 2 Powering area


Power cycle, 13A.s-1, ±600A

Reception

270 mm


1200 1400 1600 1800 2000 2200 2400

200

205

210

215

220

225

Start of the ramp (from 200 A to 225 A)

dI/dt = 50 A/s

1950 2000 2050 2100 2150 2200

210

211

212

213

214

215

Iref

ADC

2060 2070 2080 2090 2100 2110

211.5

211.6

211.7

211.8

211.9

212

212.1

212.2

212.3

212.4

212.5

10 ms

No lagging error !


1000 2000 3000 4000 5000 6000 7000 8000 9000

1.2

1.22

1.24

1.26

1.28

1.3

x 104

[13kA,18V] converter 1mH inductance ; 0.8 m resistance( = 1.5 s)dI/dt = 200 A/s

[13kA,18V] converter 1mH inductance ; 0.8 m resistance( = 1.5 s)dI/dt = 200 A/s

8550 8600 8650 8700 8750 8800 8850 8900 8950 9000

1.2999

1.2999

1.2999

1.3

1.3

1.3

x 104

25 ppm

1 A

8700 8750 8800 8850 8900 8950 9000

1.3

1.3

1.3

1.3

1.3

1.3

1.3

x 104

10 ppm

Ramp from 200 A to 13000A


Integration , system with protection, circuitGetting the current into the coldGetting the current into the cold

Current source Power Converter13kA, 10V flat top, ± 180V boostTime Constant = 23000 seconds (6 hours 23 minutes)

2x Energy extraction systems.Maximum rate of discharge = 120A/sec.

Cryo feedboxes, Current leads,…

Cold cryostat : magnets, bus bars, diodes,… 13kA

Karl Hubert Mess


Four Point Feed of LHCFour Point Feed of LHC

Sector

Continuous Cryostat/Cryoline Superconducting bus-bars runthrough cryostat connecting magnets.Current feeds at extreme ends.

Other central insertion elementseg. Low Betas, separator dipoles

COLD (<2K) 2.9km

WARM500m

1

5

Cryogenic feed

DC Power feed

3

Oct

ant

DC Power

Main Arc FODO cellscontaining; main dipoles andquadrupoles, chromaticity sextupoles, octupoles, tuning and skew quadrupoles, spool pieces,orbit correctors

Matching section of insertioncontaining; dispersion suppressors,matching section, and electricalfeedbox.2

4 6

8

7LHC27 km Circumference

Courtesy of P.Proudlock


One Sector (1/8) of the LHC MachineOne Sector (1/8) of the LHC Machine

Cryostat containing 154 Main Dipoles

Nominal Current = 11.8kA (For 7 TeV)Ultimate Current = 13kA (For 9 Tesla)23x3x2=138 magnets in the arc

16 magnets in the two dispersion suppressors154 magnets in total

Ltotal = 0.108 H x 154 16.6 H(LHC sector 1.2GJ at 11.8kA, 1.4 GJ at 13kA!)(HERA ~ 480 MJ)(Tevatron ~ 300 MJ)Charging voltage= 16.6 Hx10A/sec= ±166V (2.2MW)

0 mins

Time Constant = 23000 seconds (6 hours 23 minutes)


LHC power convertersLHC power converters

A- Elementary module [3.25 kA, 18V], [2kA,8V] : (~120) (~700)

Switch Mode Converter (25-40 kHz, soft commutation)Modular approach : 4.0 kA (28) , 6.0 kA (160) , 8.0 kA (8) , 13 kA (24)Redundancy; small volume and weight

B- Unipolar and Bipolar converters 600A [± 600 A,± 10 V] : (~ 328) ; [600 A,10 V] : (~ 70) [± 600 A,± 40 V] : (~ 40)

Energy dissipation SMPC : soft commutation ; 50-100 kHz

C- Bipolar converter [±60 A, ± 8 V] and [±120A,±10V] (~760) (~300)

SMPC : soft commutation SMPC : soft commutation High reliability, radiation resistance (tunnel installation)

D- High voltage power converter [13 kA, ±180 V] (8) High power SCR converter and Topology studies

Ramp (up and down) : [13 kA, ± 180 V] Flat bottom and flat top : [13 kA, 18 V] SCR converter : [13 kA, ± 180 V] with Active filter : ±600A,±12V


DCCT Performance Requirements

Ratings Budget Stability Reproducibility Accuracy LHC 3 5 50 Class 1

Main Dipoles, Main Quadrupoles, inner triplet

13kA 7kA 6kA

DCCT 1 5 20

LHC 5 10 70 Class 2 Other high current converters

6kA 5kA 4kA DCCT 1 7 25

LHC 10 50 200 Class 3 Multipole correctors

600A

DCCT 3 25 110

LHC 50 100 1000 Class 4 Orbit correctors

60A 120A

DCCT 20 70 300


Class1 DCCTs (13kA)Class1 DCCTs (13kA)

- Highest performance - state of the art- Separate Head and electronics chassis 19” rack mounting.- Fitted with Calibration Windings- Temperature-controlled environment in the Accelerator.- Full testing and calibration at CERN on the 20kA Test Bed.

- Highest performance - state of the art- Separate Head and electronics chassis 19” rack mounting.- Fitted with Calibration Windings- Temperature-controlled environment in the Accelerator.- Full testing and calibration at CERN on the 20kA Test Bed.


4kA to 8kA DCCTs

600A DCCTs

120A DCCTs


Main Dipole Current CycleMain Dipole Current Cycle

I

t

11500 A

20 min

-10 A/sec(~20 mins)

+10 A/sec(~25 mins)

3-5 mins

several hours(~24 hrs)

0.1 A/sec350 A

1 min

350 A

pre-injection(0-1 hr)

740 A

740 A

500 W

2.2 MW

115 kW

InjectionPlateau

Acceleration

CoastDumpBeam


One Sector (1/8) of the LHC MachineOne Sector (1/8) of the LHC Machine

Total inductance = 16.6H. Total stored energy = 1.2GJ

Current source Power Converter13kA, 10V flat top, ± 180V boostTime Constant = 23000 seconds (6 hours 23 minutes)

EVENPOINTS

2x Energy extraction systems.Maximum rate of discharge = 120A/sec.

ODDPOINTS

Cryostat containing 154 Main Dipoles 13kA

fk. bordry ab/po academic training - 27th march 2003 technological challenges for the lhc power...

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