JAERI-Conf 95-021

PA32
Simulation of Power Supply for Rapid Cycling Accelerator
FQ.Zhang
Department of Accelerator Science
The Graduate University for Advanced Studies
Oho 1-1,Tsukuba-shi,lbaraki-ken, Japan.-------

Abstract=50Hz.
LM + Lch!, = (J) a = _1_
2n 2n LM . Lch . cM
aThis paper presents a simulation of power supplyfor rapid cycling accelerator. Both the normal
and fault condition operations are described.

1. Introduction
rapid cycling accelerator, magnet circuit isIn
designed into a resonant network because of two
important considerations: the need to avoid
drawing a large reactive power from the magnet
a.c excitation source, and a uniform field
intensity in each magnet< 1). These requirements
are satisfied by the method of connection which
is based on the distributed resonance system
proposed by M.G.White. The well-known White
circuit (Fig.l) were consequently employed on
Princeton Pennsylvania Accelerator, Electron
Synchrotron NINA, KEK Proton Synchrotron
Booster etc.. As for a.c excitation source, pulse
method is generally chosen chiefly because of its
operational flexibility and reliable performance.
An energy storage choke is used to seperate a.c
and d.c source and the resonant circuit also
provides a path for circulating d.c current (butthe path for d.c connection is omitted in Fig.l for
simplicity). Here we take the NINA resonant
magnet network and power supply as example tocarry out the simulation.

The total resonant magnet network a.c power loss
is Pa.c=950kW at maximum excitation.
(2). Operation and simulation results
The cyclic operation of the system can be divided
into two periods: charging period and pulse
period.
The normal operation is according to thefollowing basic equations provided by J.A.Fox<l).
During the charging period

(2nn.

lF

=

12n2n~ LFCF

cos(wFt-1t(WF1Wa))

LFWFsin~Vp ~ v,[l + sin(Wp ~~(;pI Wa))]

t;

P

27r

12n~LPCF

(l.b)
(l.o)

note:Vs=V'ch(-~-7~)

During the pulse period

ip =Vs
LFW F

2wP

2wP

[cot~(l+sinwpt)+ wpF coswpt](J)iF == 12.5Hz

VpVs
LFW F

[cot~- Fp cosw Pt]
(J)
(J)

(2.b)

~v{(l-sinwpt)+ : : cot~coswpt]

and the pulse circuit resonate at frequency offp.
(1)= ___t:_ =<I. a)

ip=O------(2.a)(1). Parameters ·The parameter of each element is shown in Fig.l.
The filter circuit has a resonant frequency fF.
(1)

,Vs

2. Normal Operation

JF = _L =n )2w p -7 wa - 2w p------(2.c)=150Hz.

whereAssume the resonant frequency of the magnet
network is fa , we have~=1t ( 2(J) F - (J) F2Wa

(J) pJ

With simulation software PSpice53, eachwaveform of steady-state behavior of the system
is obtained as shown in Fig.2.

- 115-JAERI-Conf 95-021

From the results, we can see that in pulse period
the energy-storage-choke primary voltage V'c hreaches the peak value VM/n, and the energy
storage-capacitor voltage Vp is opposed by V'ch,the capacitor Cp is charged twice the V'ch voltage
peak. The peak capacitor voltage of 2V'ch isobtained by cyclic charging through filter choke
Lp. The choice of V s= V' ch makes it possible todischarge the capacitor voltage VF to zero andutilize the capacity CF economically.
behavior of the pulse
Thus, the steady-state
power supply can be described as follows. The
rectifier set supplying the d.c voltage of V s= V' ch,charges the Cp through filter choke Lp to 2V s.
The pulse thyristor is then triggered to discharge
C F through the pulse choke Lp and the energy
storage choke,. consequently the resulting halfcycle current ip occurs symmetrically around thepositive peak of the choke primary voltage V'ch·self extinction of the pulse thyristorFollowing
at ip=O, Cp is charged once more and the process
is repeated.

3. Fault operations
Under fault condition, such as para·meter
V s variation, andconsiderable
mismatch,maloperation of pulse thyristor, the system
operation will deviate from the normal operation,and result in large voltage or current swing. In
serious case, the system operation will not berecovered.
(1). Parameter mismatch
According to the circuit behavior, the pulse
power supply has to provide the pulse of energy,
equal to the cyclic ac power loss of the theresonant magnet network. Fig.3 shows theresonant network (lmesh) and it's equivalent
the average
The balance betweencircuit.
providedpower
andPa.closs
network a.c powerby the pulse power supply can then be expressed(3.a)
as: Pa.c = Vs X iF(av)-2(3.b)where Pa.c == Vc~rms X 10eand the average value of iF is provided by,.
lF(av) =Vs( 1 Wa

LpW F

2 Wp

r:l1 Wa

1 W aW F )1t W F1t--cotl-'+--------- (4)2Wp

iF(av)=187 A and Pa.c=950kW.
Q,
Accordingly, Re=2.164k
W a ReCM= 108.
and the Q value is,
Now a circuit simulation at

Re :;t:2.164kQ (Fig.4)

shows that VF, iF and ip have no change if
compared with the normal operation in steadystate. But we noted that the related phase changed
and desired magnet current will not be reached.
(2). Vs variationa. Start-up fault operation
Owing to the high Q value of the magnet resonant
network, a number of cycles elapse before themagnet current reaches the steady statecorresponding to the initial Vs.
Fig.S shows a large negative voltage swing on CF
due to sudden starting by the initial value of Vs·b. Vs step reduction
Similar to the starting transient described above,the effect of an unrestrained reduction of V s is ofgreat severity. The case of a step reduction of V s
to half its original steady-state value isexamined. Fig.6 shows the results.
(3). Maloperation caused by pulse thyristor
a. Failure of pulse valve to fire
VF is limited to a peak value of VF=2V s according
to eq(l) at normal operation. However, should thethyristor fail to fire during any one of thesubsequent pulses, V s will rise to a maximum
positive value of 2.64V S• and the pulse thyristor
will be applied an overvoltage of 3.64Vs. This
process is simulated as shown in Fig.7.
b. Firing impulse 180° out of phase
This occurs when firing impulse triggered thethyristor halfway through the charging cycle. As
the simulation (by Micro-cap4) shows(Fig.8), . anoverswing occurs on YF, and ip reaches a value ofalmost twice the normal amplitude.
The knowledge on either the normal operation or
the fault condition behavior of the system will bevaluable for us in designing control andprotection system for this kind of power supply.
Acknoledgement : The author would like toexpress thanks to Prof.K.Endo, Dr.H.Someya andProf.Y.Irie for their great helps in this work.
Reference. (1) Resonant magnet network and power supply forthe 4GeV Electron Synchrotron NINA, J.A.Fox. Proc.I.E.E.Vol
112,No.6,June 1965.

According to circuit parameters, we get- 116-

JAERI-Conf 95-021

CH2.....

:~ illlllllllllillli i I··· ..~ ~··rw&A~~.:i

Lm10

CH<n>

I I ••-u•,.._IlL••·:. f'IUI+Cm10•CH•160 • 3UF
SH
Cm1=Cm2=Cm3•... =Cm<n>• ... Lm10=LH=0.09
4_=Lm<n>=. • •.
Lm1=Lm2•Lm3-.;~0.1896H, N1,N2•1'4Loh(seoondarw
ant ma<>net•,.._,.._...

't'CJ•t

Fig.5 Start-up fault operation (Vs=S.O?kV). ·t for resonoFig.l White cuckuatnd pulse power supply
networ

....
....
Fig.6 Behavior of step-reductionof(V s=50.7V)

vs•••

Fig.2

Steady state normal operationl.lO•
Il.JSIRmV)

Fig.7 Thyristor firing failure (V s=5 Q. 7a ••m•t<LpLm

Fig.3 Equivalent circuit for 1 meshmismatc h at
F.tg. 4 Parameter. Re-4k.

Fig.8 Halfway firing ( 1800 out of phase)Ys-5.07k-117-