Download Corrector Magnet Power Supplies for Indus-2

CORRECTOR MAGNET POWER SUPPLIES FOR INDUS-2
SN Singh, TN Singh, HK Khatwani, ML Gandhi and AC Thakurta, RRCAT Indore (India)
THE POWER CIRCUIT
Abstract
First phase of Fast Orbit Feedback System has been
successfully implemented for the correction of fast
disturbances to electron beam in Indus-2 Synchrotron to
provide stable photon flux to beam users. Air cored
combined function fast corrector magnets driven by
bipolar current controlled power supplies have been used
in a fast beam-position controlled feedback loop to
achieve this goal. In order to track the fast varying
references generated by the beam position controller,
higher power supply current loop bandwidth is desired.
The beam position corrector system demands large signal
bandwidth of the power supply to be of the order of 100
Hz.
This paper describes the design of the power and
control circuit of the fast corrector power supplies and the
results obtained. The power supplies are rated for ±15 A,
±150 V and have ±50 ppm stability. The developed twostage power supply has a half-controlled thyristor
converter followed by a four quadrant switching converter
at the output. The load current is sensed using high
stability shunt. The control circuit consists of cascaded
current and voltage loops. Feed-forward of load voltage
has been provided to get better tracking of reference.
These power supplies fulfil the requirement of the desired
large signal current loop bandwidth. The observed small
signal bandwidth is 500 Hz.
The power circuit of the supply is shown in Fig 2. It
consists of a single phase 550VA step-down mains
transformer, followed by single-phase half-controlled
SCR bridge rectifier, LC filter, full-bridge inverter
feeding the load via L-C filter.
The secondary winding of the 550VA step-down
transformer voltage is rectified by single-phase halfcontrolled SCR bridge rectifier and filtered by LC filter
giving constant 155V DC to full-bridge inverter. The filter
capacitor value has been chosen such that its voltage
increases by less than 10 volts even if it absorbs the total
energy stored in the magnet. The inverter uses MOSFETs
switched at 30 kHz employing unipolar switching scheme
as shown in Fig 1. Output of the inverter is filtered by LC
filter and fed to the magnets. The unipolar switching
scheme provides bipolar output voltage with minimum
ripple near zero output voltage. Also, the ripple frequency
in the output is twice the switching frequency.
Provision has also been made to mitigate inrush current
into the transformer and the filter capacitor when the
supply is first powered. For this, a resistor is inserted in
series with the transformer primary. This resistor is
bypassed as soon as the filter capacitor voltage reaches
140V.
INTRODUCTION
RRCAT has taken up implementation of Fast Orbit
Feedback (FOFB) system for Indus-2 for better
stabilization electron beam orbit which is in turn required
to provide specified photon flux stability to the users. It is
to be implemented in three phases. The first phase
towards this activity was to implement local fast orbit
feedback system at beam line 8 which is the most
sensitive to beam position variations. The system was
implemented and achieved the specified performance of
less than 3 micron beam disturbance in both horizontal
and vertical directions.
Indus-2 FOFB system consists of 2 beam position
indicators, 5 combined function air cored fast corrector
magnets, 8 power supplies for driving the fast corrector
magnets and electronics and software for data acquisition
and beam position control.
The power supplies for the fast corrector magnets are
rated ±150V, ±15A and provide current stability of ±50
ppm or better. They are bipolar current controlled power
supplies. The current loop bandwidth of the power supply
is 500 Hz. It provides long term current stability of ±50
ppm or better.
Figure 1: MOSFET Bridge firing Scheme.
The Control Circuit
The supply incorporates slow-start feature suitable for
current reference of any polarity and any magnitude up to
15A. It has protections against over load current and overtemperature
of
heat
sinks
40uH
8 uH
T5
1
2
3
4
8uF
10uFX3/250V
+
.68uF
5E,25W
SHUNT
5408
5408
2500uF/450V
230V/50Hz
120k/2W
RTF 60
IXFK140N30P
25mH
Figure 2: Power Circuit of FOFB Corrector Magnet Power Supply
Figure 3: Schematic Control Circuit for simulating and optimizing the control response
10k/10W
TY6004
TY6004
25mH
current is sensed using high stability Vishay make shunt.
The voltage feedback loop also incorporates filter
capacitor current feedback to stabilise the voltage loop.
15mH LOAD
The feedback control circuit used for simulating and
optimizing the frequency and time response of the
feedback control is shown in fig 3. It consists of cascaded
load-current feedback loop and load-voltage feedback
loop. The control circuit has provision of feed-forwarding
the load voltage to get better tracking of reference. The
power supply receives current reference in digital form
derived from the beam position control loop. The load
40uH
Fig 4 The power supplies inside Power supply cabinet.
Results
Eight
power supplies were assembled, tested and
deployed for the first phase of fast orbit feedback system.
Fig 4 shows the close photograph of the output section of
two power supplies.
The power supplies performed as per the given
specifications and the whole FOFB system achieved the
specified performance of less than 3 micron beam
disturbance in both horizontal and vertical directions. 24
new power supplies are being developed for the second
phase of FOFB planned to be completed by March 2013.
References
[1] Yi-Da Li and Kuo-Bin Liu, “TPS FAST CORRECTOR
MAGNET POWER CONVERTER” ,
THPO019,
Proceedings of IPAC2011, San Sebastián, Spain
[2] K.M Ha, J.Y Huang, S.C Kim, J.H Suh, J.H Kim, S.H
Jeong, H.S Kang, J. Choi and I.S Ko , “PLS FULLY
DIGITAL CONT ROLLED CORRECTOR POWER
SUPPLIES” , 10th ICALEPCS Int. Conf. on Accelerator &
Large Expt. Physics Control Systems. Geneva.
[3] C. Rodrigues, A. R. Silva and L. H. Oliveira, “A NEW
FAMILY OF POWER SUPPLIES FOR THE LNLS
ORBIT CORRECTORS” , MOPAN003 Proceedings of
PAC07, Albuquerque, New Mexico, USA.