Advances in High Voltage Converter Modulator and Performance · 2017-06-26 · 8 SNS AAC 2013 –Advances in High Voltage Converter Modulator and Performance ... FlexRIO systems consists

Advances in High

Voltage Converter

Modulator and

Performance

Presented at the

Accelerator Advisory Committee Review

David E. Anderson, HV, PP & MS Manager, Research Accelerator Division

May 2013

2 SNS AAC 2013 – Advances in High Voltage Converter Modulator and Performance

IGBT SWITCH PLATE ASS'Y. (3X)

SAFETY ENCLOSURE

B PHASE SHOWN

CRes

CRes

CRes

A

B

C

5th Harmonic Trap 7th Harmonic Trap

13.8 kV : 2100 Vdelta wye

50 mH

OUTSIDE FILTERS AND TRANSFORMER

1.5 MVA

FUSEDDISCONNECT

BUILDINGINTERFACE

Fuse / Contactor

4 mH450 A

4 mH450 A

SCR CONTROLLER

+/-1300 V, 450 A

DC+

DC-

DC+

DC-

0.112 F

0.112 F

40X RG-8

40X RG-8

RdeQ

2X 0.03 uF500 pF

HV divider

CT

OIL-FILLED MODULATOR TANK

CONTROLRACK &

CONTROLLER

CAP RACK

Modulators provide pulsed power to high power RF klystrons

using 20 kHz switching with IGBTs

• Provides up to 135 kV, 1.35 ms pulses at 60 Hz to amplify RF to 5 MW

• 3 phases employed to increase output ripple frequency

– Minimizes output filter requirements

– Minimizes fault energy available to klystron

• Powers multiple klystrons up to 11 MW peak power

• Currently there is up to a 5% pulse droop operating in open-loop


15 Modulators in 3 different configurations power 92 klystrons

to support operation of the Linac

• 15 modulators: 3 - DTL, 4 - CCL, 8 – SCL (1 added 2008)

• Multiple HVCM/Klystron Configurations

• 690,000 combined operational hours on all modulators

115 kV 125 kV ≤135 kV 71 kV 75 kV

DTL (8.5-10.6 MW peak)

CCL (8.4-9.1 MW peak)

SCL (8.0-8.8 MW peak)


2 additional Modulators in both configurations are available to

support modulator development and testing activities

RFTF HVCM

• NCL variant of HVCM

• Primary mission is to support RF- and

cryomodule-related testing

• Secondary mission is HVCM work

• Extended run testing and MTBF

characterization

• NCL HVCM-specific issues

HEBT HVCM

• SCL variant of HVCM STS-rated beam

stick load

• Dedicated mission is to support HVCM

testing

• Most development work is initiated here


Single Phase Test Stand available to support modulator

development and pre-qualifying HVCM assemblies

• Useful to test IGBT assemblies, assuring timing properly matched on all 4 IGBTs

• Eliminates need for adjusting after installation reducing MTTR

• Assures transformer flux doesn’t saturate due to different V-s for each switching cycle

• Perform pulsed hipot of transformers prior to installation

• Tool for development of alternate concepts that doesn’t require lengthy reconfiguration of HVCM


Switch plate cap installation

completed here 2012 increase due to:•In-tank component failures recurring

•IGBT shoot-thru (first in 3 years)

•Series of SCR problems (SCRs,

drivers, etc.)

Transitioning from a prototype modulator directly to production

units created challenges for a high availability operational

facility

180

59

4049

23

84 82

0

20

40

60

80

100

120

140

160

180

200

2009-2 2010-1 2010-2 2011-1 2011-2 2012-1 2012-2

Do

wn

tim

e h

ou

rs


Analysis of failures by major component & subsystem is

critical to improving overall system availability

Downtime

HoursFeb.-July

2010

Sept.-Dec.

2010

Feb.-July

2011

Sept.-Dec.

2011

Jan.-June

2012

Aug.-Dec.

2012 Σ Hours

Scheduled

Beam Hours 3131 2985 3099 3353 3040 2846 18,454

Fault Type

2/4kV Caps 8 - - - - - 8

IGBT/driver - 6* 4* 5* 5 24 44

SCR 10 16 9 - 32 3 70

DFDC Trip - - - 6 1 - 7

Mod. Tank - 5 - - 37 4 46

Cable Arcing - - 20 - - - 20

Rectifier 23 - - - - - 23

Water Panel - 1 2 - 2 - 5

Timing Faults - - 2 - - - 2

Oil Pump - - 5 3 2 6 16

Fiber - - - - 2 16 18

Misc./? 18 12 6 15 3 29 83

Σ 59 40 48 29 84 82 337

*IGBT driver only


SNS Major System Downtime Hours by Run Period

The HVCM systems are no longer the major contributor to

accelerator downtime

0

20

40

60

80

100

120

140

160

CY10-1 CY10-2 CY11-1 CY11-2 CY12-1 CY12-2

E-HVCM

Ion Source

RF

Elect-chopper

E-MagPS

Target

Vacuum

Cooling

Controls

Elect-other

Cryo

AccelPhys

Prot. Sys.

Fac./Mech. Sys.

BeamInstr

Ops

Misc./Mag/RS/ESH

CryoMod/SRF

Neut. Inst.

×10


Summary of major HVCM upgrades to-date

• SCR Controller

– Forced air cooling

• In-tank components (component de-rating)

– Capacitors

– De-Qing resistors

– Transformers

• IGBT Switch Plates

– Optimize pulse length (discussed later)

– Replace bypass capacitors w/ metallizedfilm units

– Gate drivers (partially installed)

– Thorough pre-installation testing

• Reduced SCL klystron loading with additional modulator

• Better preventative maintenance plans in place


A discovery of transformer failures creates some

concern regarding the long-term reliability

• A combination of materials selection, winding placement, corona ring placement & possibly temperature cause the problem

• Significant field enhancement under corona ring

• Mitigation plans• Move inner winding layer away from

surface of coil form• Increase corona ring dimension• Eliminate potential trapped air sites• Select winding layer material with a better

dielectric constant match to oil


A key vulnerability to continuing reliable operation are

the boost capacitors

• Presence of air bubbles inside results in corona inception which leads to catastrophic failure

• The capacitor is now mounted at a 2-3º angle to force any air that may be trapped away from center and terminal no longer near the side of unit

• Newest capacitors incorporate air-free filling technique and integrated shims

• Alternate vendor capacitor tested and appears promising


Necessary steps to advance to 1.4 MW operation and ultimately

to support 2nd

Target Station are under development

• Currently, klystrons are at saturation at the end of the pulse with no remaining control margin due to cap bank droop in open-loop

• Increasing klystron voltage with no additional changes will significantly degrade HVCM reliability

• Upgrades of cooling system underway• Provide higher component reliability• Reduce MTTR of key subsystems• Improve water chemistry

• Transitioning to even higher power presents other unique challenges• The current circuit topology creates stresses on components which

may be insurmountable with existing technology• Switching losses in the IGBTs will significantly degrade their

reliability

• N+1 redundancy can be achieved in conjunction with topology changes

• Two options exist to permit longer pulse operation• Modifying the IGBT circuit to permit higher voltage

operation (likely reducing klystron lifetime)• Pulse flattening which presents challenges for the

HVCM IGBTs (closed-loop operation)


0

200

400

600

800

1000

1200

1400

0 2 4 6 8 10 12 14 16 18 20

VC

E O

verv

olt

age

, V

Duration of last diagonal pair "runt" pulse, ms

End Of Pulse IGBT Over Voltage at +/- 1100 V bus Operation, worst measurable case (to date)

unsnubbed overvoltage at +/- 1100 V bus

snubbed RCD (0.66 uF, IXYS FRED diodes)overvoltage at +/- 1100 V bus

snubbed RCD (1.32 uF, Cree diodes) overvoltage at+/- 1100 V bus

snubbed RCD (1.32 uF, Cree diode +0.01 uF CE)overvoltage at +/- 1110 V bus

IGBT rating limit (3300 V rating – 2200 V bus)

Adding IGBT snubbers permits higher voltage operation with

comparable reliability & eliminates fault over-voltage problem


DC bus ripple creates problems for the snubber resistor

which tries to track bus fluctuations

• Snubber capacitor tracks bus fluctuations through the bleed resistor – energy exceeds ratings of the water-cooled resistor

• Air-cooled resistor will not tolerate the average power dissipation requirements for the snubber application

• Attempting to resolve by

– Testing to understand bus ringing to minimize or eliminate it

– Identifying resistor or resistors that handle both the energy and power dissipation – EBG helpful

Large cap bank ringing (green)

vs. switch plate bus ringing (others)

-50

-40

-30

-20

-10

0

10

20

30

40

50

0.0E+00 2.0E-04 4.0E-04 6.0E-04 8.0E-04 1.0E-03 1.2E-03 1.4E-03

C phase snubber R current

B phase snubber R current

A phase snubber R current


Additional ripple introduced with pulse flattening can be

mitigated by improving bus structure

• Current multiple cables and switch plate bypass capacitors create oscillations on DC bus

• Bypass capacitors cannot be removed without significantly reducing inductance between energy storage capacitors and switch plates in the current design

• Working with Mersen Corp., we are developing a retrofit laminated ring bus structure to address these issues, a standard in traction motor applications

• Thermal and electrical optimization using simulation tools under way

To +/- energy storage capacitors

To A/B/C phase switch plates


Output Voltage= 61.8 kV

Bus Voltage= +/- 1004 V

FM = 20 kHz to 22 kHz

PSM = 95% to 100%

∆𝑉𝑑𝑟𝑜𝑜𝑝 = 304 V/ms (0.5%

vs. 3-5% currently

∆𝑉𝑟𝑖𝑝𝑝𝑙𝑒 = 664 V

-5 0 5 10 15 20

x 10-4

-7

-6.8

-6.6

-6.4

-6.2

-6

-5.8

-5.6

-5.4

-5.2x 10

4

X: 0.000945

Y: -6.644e+004

time (SECS)

Out

put

Vol

tage

(V

OLT

S)

X: 0.0009595

Y: -6.716e+004

Phase Shift and Frequency Modulation achieves pulse

flattening and has been demonstrated at 60 Hz full power

59

60

61

62

63

90 92 94 96 98 100V

out(k

V)

PM (%)

Vout(kV) vs PM(%) @ fixed DC bus @ 1000 V bus

59

60

61

62

63

17 18 19 20 21 22 23

Vou

t(k

V)

fsw (kHz)

Vout(kV) vs fsw(kHz) @ 1000 V busImproved adjustable output filter components on order to reduce ripple and “tune” rise time.


The existing controller does not support the proposed

modulation scheme but the new controller does and can

provide additional functionality…


The new controller enables all types of modulation and

provides real-time waveforms for immediate assessment of

timing changes…


The new controller mimics current user interfaces and

enhances them…


All these features available in a COTS package utilizing

LabView for programming flexibility and ORNL ownership

FlexRIO systems consists of:

•An embedded controller for communication

and processing

•Reconfigurable chassis housing the user-

programmable FPGA

•Hot-swappable I/O modules

•Graphical LabVIEW software for rapid real-

time, Windows, and FPGA programming

Future versions of the new controller will provide:

• EPICS interface

• Flexible smoke detector logic

• Control of series switches for IGBT fault isolation

• 3 & 4 phase operation with semi automatic IGBT fault recovery

• IGBT shoot-through monitoring & warnings

• IGBT turn on & turn off monitoring, compensation & warnings


Enhanced reliability and reduced MTTR can be achieved by

replacing existing oil cooling system

• Prototype HVCM cooling skids is being built to determine the appropriate flow and oil distribution within the tank – start mid-May

• In parallel with this a Computer Flow/Heat Model is being built to simulate the cooling effects on the individual components within the tank

• The cooling system design will provide enhanced flow and heat removal capacity, remove the heat exchanger and filters from within the tank, and allow for quick and easy maintenance of the filter and pump

• Plan to upgrade the Accelerator HVCM cooling systems in FY-2014 & -2015

Prototype Pump Skid

Pump Duplex

Filter

HX


Simulations of temperature profiles and flow rates with

current system reveal system shortcomings

42.7

52.4*

44.2

51.2

53.3*

47.6

36.3

39.9

39

40.684.7

44.8

43.546.6

• Actual measured temperatures at rated power shown in °C in white boxes• Model based on calculated power losses and estimated flow rate only• Temperatures acceptable but oil stagnation indicates heat not being removed efficiently

*diode heat sink temperatures

capxfmr xfmr

diode

diode


An alternate topology is under investigation for the 2nd

Target

Station with applications to other long pulse facilities

• Single phase waveforms shown• Reduced stress on capacitors• Single phase tested, parts for full

system under procurement• Less sensitive to load variations• Improved soft switching using

magnetizing inductance of transformer• Better efficiency


Opportunities for redundancy with the alternate topology

have been explored and are promising

• 4 phase → ±750 V DC

• 3 phase → ±990 V DC

• Controller reconfigures system for

3 phase operation

• Series switch built and tested for ½

HVCM, incl. severe fault testing

• Would be used in conjunction with

alternate topology

1 vout 2 vout#a 4 ipri

100u 300u 500u 700u 900u

time in seconds

-4.00k

-2.00k

0

2.00k

4.00k

ipri in

am

pere

s

-80.0k

-60.0k

-40.0k

-20.0k

0

vout, v

out#

a in

volts

Plo

t1

2

1

4

Vout w/ 1 bridge non-operationalVout w/ all 4 phases operational

I primary from H-bridge IGBTs

IGBT and cold plate

IGBT driverSegmented DC bus


20KHz @ Start of Pulse & 21.2KHz

@ End

• Pad poured at ORNL and awaiting delivery

• Discovery June 2012 that induced eddy current

losses in secondary shields and field-grading

structures high at full average power operation

• Subsequent discovery that secondary conductor

losses too high led to replacement with Litz wire

• 2013 discovery that excessive losses in primary

led to design of cooling plenums for primary

• Factory acceptance testing scheduled for mid-

May through June, delivery early August

• Specified to meet STS requirement to drive 12×

700 kW CPI klystrons (85 kV, 160 A)

An alternate STS solution, the hybrid inverter – Marx

modulator from JEMA, is awaiting testing at ORNL


20KHz @ Start of Pulse & 21.2KHz

@ End

• HVCM availability improved substantially

• Synergistic solutions in development or installed to address remaining

problems with HVCM to further improve reliability, increase available

power and flatten pulse

• Capacitor problems continue but multiple options being evaluated

• Implementation of proposed alternate topology allows for future expansion

& major subsystem redundancy

• Supports needs of 2nd Target Station

• Permits more flexibility with respect to load configuration

• The SNS modulator team and the demonstrated HVCM high availability

makes this topology attractive to the ESS, KAERI and others

Summary

Documents

Advances in High Voltage Converter Modulator and Performance · 2017-06-26 · 8 SNS AAC 2013 –Advances in High Voltage Converter Modulator and Performance ... FlexRIO systems consists