The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

MAGNET POWER SUPPLY WITH SMES IN THE DC LINKFOR LARGE SCALE ACCELERATORS
Toshifumi Ise, Osaka University, Suita, Osaka, JAPAN
Hikaru Sato, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan
Abstract
The power supply for large scale accelerator magnets
draws large amount of power from utility network. For
example, the JHF 50-GeV main ring will require 104MWof total active power and 28.8MW of dissipation powerby estimation. Moreover, the charging and discharging
cycle is repeated with 3.64s of the cycle time at the initial
operation, and the repeating frequency will be raised up
by twice in future. In this paper, the power supply using
SMES is proposed. The power supply can absorb thefluctuation of active and reactive power caused bycharging and discharging the synchrotron magnet. The
system is composed of current source ac/dc converter,
chopper circuits and superconducting magnets. The
chopper circuits for superconducting magnets andsynchrotron magnets can be connected to the same dc busof the power supply and this feature can reduce the power
rating of ac/dc converters.

INTRODUCTION
The Japan Hadron Facility (JHF) Project is underprogress as the joint project by the Japan Atomic Energy
Research Institute (JAERI) and the High Energy
Accelerator Research Organization (KEK). The system
has the 50-GeV synchrotron main ring consists of 96
bending magnets, 216 quadrupole magnets, 72 sextupolemagnets and 189 steering magnets. The power supply
system for the magnets of the 50-GeV synchrotron ismade up of a large number of power supplies, one is forthe bending magnets, 11 ones for the families of thequadrupole magnets, 3 ones for the families of thesextupole magnets and 189 ones for the steering magnets.
The total amounts of active power of these power supplies
become about +104MW~ -69.0MW in peak without cable
loss and other losses for 50-GeV operation[1].
As well known, conventional thyristor rectifiers with ahigh power and trapezoidal dc side output current usually
generates a very large cyclic variation of reactive powerand raises unallowable line voltage fluctuation. In order toovercome this problem, power converters using IGBT orIEGT are investigated for the power supply of the JHF
project. By using power semiconductor devices of thistype, it is possible to construct power supplies with thecharacteristics of unity power factor operation. The line
voltage fluctuation estimated is about +2.5%~-2.5% for
50GeV operation, if the reactive power is compensatedperfectly. This fluctuation is not acceptable for power line.
As a result, some active power compensation device isnecessary for 50GeV operation. Already, adjustable speed
flywheel generation system to flatten the very large powerswing has been studied as a candidate[1]. This paper
shows the study on application of superconducting
magnetic energy storage (SMES) for the purpose. In thecase of SMES, it is possible to connect the SMES magnet
at the dc side of the synchrotron power supply andexchange energy between the accelerator magnet and theSMES magnet. The circuit configuration, control system,and some simulation results using PSCAD/EMTDC
software are presented in this paper.

THE MAIN CIRCUIT OF POWER SUPPLY
Requirement for the Power Supply
The largest power supply for the synchrotron is for thebending magnets. Other power supplies for quadrupole
magnets, sextupole magnets and steering magnets are
small and do not affect line voltage fluctuation.
Requirements for the power supply of the bending magnet
is shown in Table 1. Charging and discharging current
pattern of the bending magnet is shown in Fig.1.
The power supply with SMES proposed in this paper isfor the bending magnets.

Circuit Configuration
Fig.2 shows various configuration of the power supply.
Fig.2(a) shows the system using line commutated ac/dc
converter. In this case, SMES should compensate bothactive and reactive power variation. As a result, the power
rating of the SMES becomes the largest. The
configuration shown in Fig.2(b) shows the system using
forced commutated ac/dc power converter using IGBTand IEGT. In this case, the magnet power supply canoperate at unity power factor. As a result, SMES
compensates only active power variation. But there ispower exchange through two ac/dc power converters,
resulting with high power supply cost and losses. The
configuration shown in Fig.2(c) uses forced commutatedac/dc power converter and dc type SMES. In this case,power rating of the ac/dc converter for magnet power
supply can be reduced, resulting with the reduced cost of
the total system. The system shown in Fig.2(c) is theproposed system and studied hereinafter.
Table 1:Requirements For Power Supply Of Bending Magnet
Excitation dc current
Peak dc voltage
Active power (peak)
Coil inductance
Coil resistance
Number of coils

202A ~ 3015A+24.7kV, -32.6kV
71.1MW, -55.3MW
104mH/coil
45mΩ/coil96

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

CurrentInjection

Acceleratoin

Extraction

Deceleration

0.17s

1.9s

0.7s

0.87s

AC LineLineCommutatedac/dcPowerConverter

Bending Magnet

SMES (Active andReactive PowerCompensation)(a) Configuration using line commutated ac/dc converter

TimeTerm 3.64s

AC Line(a) Current pattern

(kV)
20

ForcedCommutatedac/dcPowerConverter

Bending Magnet

SMES (Only ActivePower Compensation)0(b) Configuration using forced commutated ac/dc converter-2 0
AC Line0123(s )ForcedCommutatedac/dcPowerConverter

Bending Magnet(b) Voltage patternFig.1: Typical excitation pattern of the bending magnet for
50-GeV operation.
The power supply of the bending magnets is divided into six
separated power units, because the electric power rate for thebending magnet is too large to construct a power supply as one
unit. By this method, the power rating for one power unit isreduced to the possible level about 5 kV and 10MW. Fig.3
shows connection scheme between the power units and thebending magnets. As seen in the figure, the 96 bending magnets
are divided into three groups and both upper and lower coil ofthe magnet are connected separately by series in each group, andconnected with the power units in turn so as to make one
excitation loop. The configuration of one power unit, which is
1/6 of the bending magnet power supply, is shown in Fig.4.
Each of the power unit is composed of a current source ac/dc
converter and SMES. The 40GeV operation can be carried out
by the configuration without SMES, because of the acceptable
voltage fluctuation in the case.

DC type SMES (Only
Active Power
Compensation)(c) Configuration using forced commutated ac/dc converter anddc type SMES

Fig.2: Various configuration of magnet power supply withSMES.

SMESSMES

Fig.3: Connection of power supply of the bending magnets
with SMES.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

(kA)

Ibm

Ibm2

3.5
2.8
2.1
1.4
0.7
0
18

18.5

19

19.5

20

20.5

21

21.5

22(s)

Current of bending magnet(Reference and output are almost same)(A)

Itrack5
2.5
0-2.5-5

Fig.4: Connection of one unit power supply.

1818.5

19.5

20

20.5

21

21.5

22 (s)(b) Tracking error of bending magnet current

SIMULATION RESULTS
Fig.5 shows
thesimulation results using
PSCAD/EMTDC software. The current of the bending
magnet was controlled with the low tracking error. The
reactive power was controlled at almost constant value,
which is due to the capacitor of the ac side filter. Thepower variation of the ac/dc converter during theoperation cycle was about 11 MW. As the Fig.5 is thesimulation of the 1/6 of the total system, the total
variation of active power will be 66MW, which is almost
half of the power variation of 50-GeV operation, which iscalculated to be 126.4MW (71.1 - (-55.3) MW) from Table
1. The average current of the SMES coil is controlled tobe constant except the initial transient. The charging anddischarging energy of the SMES was about 5MJ.
Although the voltage and current waveforms are notshown in this paper, the phase difference between thevoltage and the phase current was almost 0 or 180 degree
during the simulation, which shows low reactive power.
The current waveform was almost sinusoidal, whichshows low harmonic current.
Fig.6 shows the impedance map of the system, wherethe JHF synchrotron will be installed. The voltage
fluctuation of ac line considering the total system wasalso calculated using PSCAD/EMTDC software. The
calculated results are shown in Fig.7. The calculated
voltage fluctuation is acceptable for the system.

19(MW,MVar)

P

Q

128.5

P5
Q
1.5
-2
18

18.5

19

19.5

20

20.5

21

21.5

22 (s)(c) Active (P) and reactive (Q) power of the ac/dc converter(kA)

Is mes

5.6
5.3
5
4.7
4.4
4.1
3.8
0

2.5

5

7.5

10

12.5

15

17.5

20

22.5

25(s)

(d) Current of SMES coilFig.5: Simulation results of the proposed system.

%Z=3.178%

Quadrupole
Magnet%Z=12.5%

Bending Magnetand SMES
Power Supply
154kV/66kV
100MVA

154kV

Other Loads

Fig.6: Impedance map of the ac side of the system.

CONCLUSIONSThe power supply system using SMES for the JHF 50GeV main ring was proposed and the fundamental
characteristics have been calculated. The proposed system
has advantages over the flywheel system, because of thedc side coupling between the energy storage device andthe accelerator coil, resulting with the reduced ac/dc
converter power rating. The proposed system can beapplicable for magnet power supplies of large scaleaccelerators.

REFERENCES[1] Accelerator Technical Design Report for HighIntensity Proton Accelerator Facility Project(http://hadron.kek.jp/member/onishi/tdr/index.html.

(%)
0.5
0.25
0-0.25
-0.5
00 .5

1

1. 5

22.5

3

3. 54 (s)3

3. 54 (s)(a) 154kV line(%)
210-1-200 .5

1

1.5

2

2.5(b) 66kV line

Fig.7: Calculated line voltage fluctuation.