Amit Patel et al.

1

3MW DUAL OUTPUT HIGH VOLTAGE POWER SUPPLY OPERATION:

RESULTS FOR ACCURACY, STABILITY AND PROTECTION

AMIT PATELa, DISHANG UPADHYAY, HITESH DHOLA, NIRANJANPURI GOSWAMI, KUSH MEHTA,

N.P.SINGH, BHAVIN RAVAL, RASESH DAVE, SANDIP GAJJAR, VIKRANT GUPTA, ARUNA

THAKAR, KUMAR RAJNISH , DIPAL SONI , SRIPRAKASH VERMA, RAGHURAJ SINGH , RAJESH

TRIVEDI, APARAJITA MUKHERJEE, UJJWAL BARUAH

ITER-India, Institute for Plasma Research, Gandhinagar, INDIA a Email : ampatel@ipr.res.in

Abstract

In a nuclear fusion, plasma temperature is increased by external heating systems like neutral beam injectors (NBI) and

radio frequency heating. Radio Frequency (RF) heating devices generate frequency ranges from few MHz to tens of GHz viz.

ion cyclotron (IC), electron cyclotron(EC) and lower hybrid(LH) systems where high voltage power supply (HVPS) are

required preliminary. ITER requires 20 MW of ICRF for heating and driving plasma current. Seeing the availability of vacuum

tubes and stringent specifications demanded for plasma heating, a series connection of power amplifiers seems only a feasible

technical solution where RF power amplified at each stage. A required RF Amplifier must be having power capability of

1.5MW supporting matched and mismatched load (VSWR 2) over the wide frequency range of 35MHz- 65MHz. Pulse step

modulation (PSM) based HVPS are in use for similar application since last 2 decades. A unique scheme of feeding two stages

of RF Amplifier by single HVPS is endeavoured. Developed HVPS supports the operation by providing dc voltage to

intermediate stage and end stage of IC RF amplifiers, subsequently 8-13.5 kV, 250 kW and 15-27 kV, 2800 kW. Present papers

describes the consumption of dual output HVPS with IC RF Amplifiers system for different load conditions. A detailed

description of vital wire-burn test towards amplifier side, demonstrating tight synchronization among both stages is discussed

including test set up and fuse wire dimension. HVPS performance parameters of ripple, accuracy and stability over extended

duration are presented for various scenario of RF Amplifier operation taking due care of all interlock protections.

1. INTRODUCTION

For fusion research, various RF heating systems (i.e IC, EC and LH systems) are used for plasma heating using

high power vacuum tubes i.e. Tetrode, Diacrode, Gyrotron and Klystrons. HVPS are used to bias vacuum device

by providing anode/plate voltage which finally appeared as RF Voltage [1]-[2]. The HVPSs are typically with

voltage ranges of 30-100 kV and power level of 3- 8 MW [3]. Such systems demands specialise limits of ripple

voltage, voltage control accuracy and minimal short circuit energy. Besides that, HVPS also supports extreme

dynamics and superior transient response. Pulse Step Modulation (PSM) based HVPS utilizing fast semiconductor

switches (IGBT, MOSFET) being utilized from last two decades [3].

ITER requires 20 MW of ICRF sources where each unit must be having power capability of 1.5MW supporting

operation at matched and mismatched load (VSWR 2) over the wide frequency range of 35MHz- 65MHz. For

such high power, cascaded chain of RF amplifier is possible solution mainly due to available range of vacuum

tubes. The IC RF system at ITER-India test facility comprises of 3 levels RF amplifiers viz. High Power

Amplifier-1 (HPA-1), HPA-2 and HPA-3 where final RF output is 1.5MW as shown in Fig.1 [4]. A required

HVPS voltage range is mentioned in Fig.1 while voltage variation requirement at mismatched load is as shown in

Fig. 2, plotted in reference to phase of reflection coefficients [5] .

FIG. 1: 1.5 MW Cascaded RF Amplifier FIG. 2: Voltage Requirement at VSWR 2

IAEA-FIP/P3-48

2. DUAL OUTPUT HVPS: TOPOLOGY & DEVELOPMENT

A Dual Output HVPS is developed to feed HPA-2 and HPA-3 with novel concept of independent voltage control

in close synchronisation with both output [6]-[7]. The specifications of HVPS are listed in Table 1. Dual output

HVPS appeared as an advantageous over conventional scheme of two individual HVPS for cascaded stages. Single

HVPS feeding two cascaded stages of amplifier proves higher power density as creepage and clearance need to

be taken for one HVPS only. It also holds an economic advantages as it eliminates a necessity of one HVPS. On

the other hand, few challenges also associated viz. voltage control of dual output for both stages by single

controller maintaining a balanced load on both feeding transformers.

Table 1. Specifications of Dual Output HVPS

Rated output voltage

For HPA-2 8 – 13. 5 kV

For HPA-3 15- 27 kV

Rated Current & Power

For HPA-2 15-20 A , 250 kW

For HPA-3 105- 155 A , 2800 kW

Type of duty Continuous/1 Hour ON -3 Hours OFF

Voltage control accuracy ± 1% of the max. value

Output voltage stability ± 1% of the max. value

Ripple of the output voltage ± 270 V

Resolution 100 V

Voltage rise/fall time 100 µs - 1.5 ms (Programmable)

Transient Response from 27 kV to 18 kV 100 µs

Fault energy in the Load ≤ 10 J

Let-through Energy dumped into Load < 250 A2s

Time to be ready for restart after Fault ≈ 20 ms

A configuration of Dual output HVPS is shown in Fig.3 while as built system at ITER-India premises is as shown

in Fig.4 [6].

FIG. 3.Dual Output HVPS Block Diagram FIG. 4 .Developed Dual Output HVPS

SPS Module - 1

Transformer -2

(16 Secondary)

Transformer- 1

(32 Secondary)

22 kV

SPS Module-33

SPS Module - 48

HPA-2

HPA-3

1 mH Choke

2.5 mH Choke

MODULE 1-32 MODULE 32-48

DUAL CONTROLLER

SPS Module-32

CT

CT

V

ΔV

V+ΔV

Amit Patel et al.

3

Likewise the normal PSM based HVPS, it consist of Mutli-secondary transformers [8]-[10], switched power

supply (SPS) modules and controller. A controller is developed with single processor controlling two voltage

control loops with taking care of all protection devices [11]-[12]. A developed HVPS and all subcomponents

conform its traceability to various international standards viz. IEC 60146-1, UL940. Besides same, it also

conforms the requirements imposed by European Conformity (CE) for Electro-Magnetic Compatibility (EMC)

and Safety Directives.

3. TETSING & VALIDATION

Developed HVPS was validated by 3 MW, 9 MJ pulsed resistive load bank units for performance parameters

followed by integration with 1.5 MW IC RH system. As both (HVPS and IC RH) systems are located in single

lab building but on different floor levels, dc power is carried over a ~ 70m HVDC Cable. Besides same, 16 nos.

of fiber optic cables were used for synchronised operation of HVPS with IC RH system. Prior to power tests,

series of interlock tests were carried out to make surety of system investment protection in case of fault in any

system [13].

As used dc cable length is approximately 70 m, cable stored energy accumulates with HVPS stored energy so

short circuit test (wire-burn) was performed at end of cable on both output stages. Test setup is shown in Fig.5

where developed short circuit switch is used [14]. Regarding fuse wire dimensions, vacuum tube manufacturers

owns theirs recommendation viz. (1) 30 AWG, 150 mm copper wire (2) 30 AWG copper wire, length 20 mm /

kV [15]-[16]. As developed HVPS was utilised for two different type of IC RH systems, wire-burn test was

performed with both types of fuse wire lengths. On short circuiting the output of any stage of HVPS, both stage

output switches off in less than 10 µS as shown in Fig (6) qualifying a let through energy limits[6]-[7].

On completion of validation checks, HVPS was operated with IC RF system in integrated mode. RF Output power

was raised in steps from 100 kW to 1.5 MW where maximum power drawn form HVPS was approximately 2.8

MW. Under the condition of mismatched load (VSWR 2) with various degree of reflection coefficients, HVPS

output foresee high voltage – low current mode and low voltage-high current mode. At matched load conditions,

HVPS was operated up to 23 kV, 130 A while 16 kV, 164 A at one of the reflection angle at mismatched load.

[17] - [18]. A high bandwidth acquisition (5 KS/s) of both HVPS output voltage and end stage current is presented

in Fig. 7 for 4000 seconds where voltage build-up with abrupt RF power fluctuation is captured. In spite of

significant power variation, HVPS output proves its stability and accuracy as specified over the said period of

4000 seconds.

FIG. 5. Wire-burn test setup FIG. 6. Short Circuit Test at HPA-3

Ch. 3: HPA-2 Voltage (x 10000)

Ch. 4: HPA-2 voltages.

1 mH

2.5 mH

Driver Stage HVPS

Delta- V HVPS

HVPS Safety Ground

Tri-Axial Cable

Tri-Axial Cable

Motorised Switch

0.5 Ω

0.5 Ω

Fuse Wire

FIG. 7 HVPS extended duration operation

Ch. 1: Current, Ch. 2. : HPA-3 voltages (x 10000) Ch. 3. : HPA-2 voltages (x 1)

IAEA-FIP/P3-48

4. FUTURE PLANS

Increasing a power density should be taken up as future work which include relocation of controller to near vicinity

of power cubicles. An online removal of faulty SPS module without generating any significant voltage glitch is

on second level of future activity.

ACKNOWLEDGEMENTS

Authors are thankful to M/s. Electronic Corporation of India Ltd. for manufacturing and supply of dual output

HVPS. Authors are also thankful to M/s. AMTECH Electronics India Ltd and M/s. Ames Impex Electricals Pvt.

Ltd for manufacturing SPS Module and Cast Resin Transformers. Authors are exceedingly thankful to IC RF team

at ITER-India for integrated campaigns.

REFERENCES

[1] P.J. Patel, N.P. Singh, V. Tripathi, L.N. Gupta, and U.K. Baruah, “A Regulated High Voltage Power Supply for

Accelerator Driven System”, International Topical Meeting on Nuclear Research Applications and Utilization of

Accelerators, May 2009, Vienna.

[2] P.J.Patel et al.,“ Regulated High-Voltage Power Supply (RHVPS) : Integration, Operation, and Test Results With LHCD

System of SST-1” , IEEE transactions on plasma science, Vol. 42, No. 3, March 2014.

[3] Amit Patel et al., “Power Supplies for Plasma Heating: PSM and Involved Challenges”, presented in National Power

Electronics Conference (NPEC-2017).

[4] Aparajita Mukherjee et al., “Status of R&D activity for ITER ICRF power source system”, Fusion Science & Technology,

Vol 65, No.1, Pages 120-128.

[5] Aparajita Mukherjee et al., “Progress in High Power Test of R&D Source for ITER ICRF system”, FEC 2016.

[6] A. Patel et al., “ Development of 3MW Dual output high voltage power supply for ICRF Source”, Presented at IPMHVC-

2016 Conference

[7] A. Patel,” Initial Operation of 3 MW Dual Output High Voltage Power Supply with IC RF System”, Fusion Engineering

and Design, Volume 126, January 2018, Pages 59-66.

[8] A. Patel et al., “Multisecondary Transformer: A Modeling Technique for Simulation”, IEEE Transactions on Plasma

Science 40(7):1-5 · June 2011

[9] A. Patel et al., “Multi-Secondary Transformer: A Modeling Technique for Simulation – II”, Journal of international

Conference on Electrical Machines and Systems. 3. 78-82. 10.11142/jicems.2014.3.1.78

[10] N.P. Singh, U.K. Baruah, P.J. Patel, S.K. Mattoo and NBI Team, “Studies on the behaviour of Multisecondary

transformers used for regulated HV power supplies,” Fusion Engineering and Design, Volume 75-79, November 2005,

Pages 127-133.

[11] H. Dhola et al., “Data transfer methods in Real Time controller of Ion Cyclotron High Voltage Power Supply”, IEEE

Transactions on Nuclear Science, Volume: 65, Issue: 2, Feb. 2018.

[12] H. Dhola, et al., “Integration of EPICS based monitoring for Ion Cyclotron High Voltage Power Supply”, Fusion

Engineering and Design, Volume 123, November 2017, Pages 737-742.

[13] K. Mehta et al., “Fiber Optic Based Field Simulator for HVPS”, at 32nd National Symposium on Plasma Science &

Technology (PSSI 2017) held at EDI, Gandhinagar, 07-11 Nov 2017

[14] N. Goswami et al., “Short Circuit Switch for Joule Energy test of HVPS”, at 32nd National Symposium on Plasma Science

& Technology (PSSI 2017) held at EDI, Gandhinagar, 07-11 Nov 2017.

[15] Application Note titled “Fault Protection AB 17” available on https://www.cpii.com/library.cfm/9.

[16] Thales Electron Device TETRODE TH 558 SC datasheet.

[17] Rajesh Trivedi et al., “Outcome of R&D program for ITER ICRF Power Source System”, to be presented in this

conference.

[18] Kumar Rajnish et al., “RT Amplitude Control Loop: Testing of R&D ICRF Source at High Power” to be presented in this

conference.