IMPROVED DYNAMIC FILTERS FOR THE MAIN RING MAGNET
POWER SUPPLY OF THE KEK 12 GeV PS
H. Baba, H. Sato, S. Matsumoto, T. Kubo
K. Kitagawa, K. Asaji and A. Kabe
National Laboratory for High Energy Physics
Abstract
The dynamic filters of the KEK 12 GeV PS were improved in the voltage
ripple detector, in the control system and in the power-up of the PWM and Bclass amplifiers. As the results, the output of the low frequency voltage
ripple ( < 300 Hz) could be reduced to less than - 25 db to the inputs in theB, QF and-QD m~~net power supply. These suggest for the current ripples to beto flat top current 2,850 A during extraction.
a factor of 10Introduction
Dynamic filters have been operated in the MRMPS (main ring magnet powersupplies) for the 12 GeV PS to reduce the current ripples. These ripples generate undesirable fluctuations in the circulating beam. During slow beam
extraction, the ejected beam spill is modulated remarkably by the current
ripples. These ripples have to be suppressed less than 10- 5 •The ripples come from the desired pulse voltage fed by phase control of16 SCR rectifiers with 3 ¢ bridge connection as the MRMPS. Two 6 pulsed
rectifiers make a 12 pulsed rectifier connected in cascade with 3 ¢ transformers of Y - ~ and 6 - ~ winding.
One group of the rectifiers working at flat top in B~MPS (magnet powersupply) has the fundamental characteristic ripple of 300 Hz because of different phase control patterns between these 6 pulesed rectifiers, and the othersof B and both QF and QD have the ripple of 600 Hz with the same pattern between
the pair of 6 pulsed. As the uncharactristic ripples of 50 Hz, 100 Hz andharmonics are generated from jittering of ignition angle on the SCR and 3 ¢unbalance in available ac line, passive filters were set up to reduce theseripples. The low pass filters have the cut-off frequency 55 Hz and the gradient - 12 db/oct with under-damping characteristics and the resonance filters
have tuned frequency 100 Hz. The previous dynamic filters were designed forthe residual ripples to be suppressed to the desired level in the entire pulse
operation. But the filter could not compensate the low frequency ripples ( <300 Hz).
Some improvements were carried out in the ripple detector, in the control
system and in power~up of the PWM (pulse wide modulation) and B-class amplifiers connected in cascade through each reactor transformers.
Developed voltage ripple detector
Fig.l shows a schematic diagram of the MRMPS included dynamic filter
The voltage pattern has frequency components less than 25 Hz and the ripple
has higher than 50 Hz. In the previous, to separate the voltage patterncomponent and the ripple signal, the ripples were regarded as the difference
between the pulsed voltage from a high impedance resistive voltage divider
and a equalizer output. The equalizers had an approximate transfer characteristics of the MPS and the inputs were the voltage patterns from the control
computer of the MPS.
But the first of error signals came from multi-grounding currents throughthe center of the dividers connected to the ground, the second from the mismatch
between the MPS and the equalizer, the third from the phase difference between
input and output signals of the voltage divider.
The developed voltage ripple detector given in Fig.2 consists of a low
impedance resistive voltage divider, an equalizer and a high pass filter toimprove these errors. The reactor transformer and the divider could reject theerror signals, but the low frequency components of the voltage pattern still-189--------

remained in the output. These components could be excluded by the simple CR
equalizer and the high pass filter.
Amplifier system
The detected signals have been possible to control the dynamic filters bynegative feed back loop. But the output power of the amplifiers had to increase
up to reduce these ripples.
The powers are fed through the output reactor transformers by the PWM andB-class amplifier systems with appropriate phase compensations.
The PWM system with the carrier frequency of 40 KHz covers the ripple
frequency range from 50 Hz to 1 KHz and has the same 22 water-cooled power
amplifier modules with 4 high power switching transistors (selected from 2SC1471)
per module. Two groups with the 9 modules serve to the B-MPS and two with the2 modules to the Q - and Q - MPS through the same numbers of reactor transformer. The outpu{ power o~ the PWM increased up to about ten times larger
than the previous by changing the power source from 110 V to 300 V.
The B-class amplifier covers the ripples from 50 Hz to 2 KHz and has thesame 20 water-cooled power amplifier modules with 8 transistors (2SD465)
connected in parallel.
Two groups with the 6 power amplifier modules serve to the B-MPS and eachwith the 4 modules to the QF and QD - MPS through the reactor transformers.
The power-up of B-class amplifier was carried out at 4.5 times larger than theprevious by changing the power source from 30 V to 48 V.
·Experimental results
After these improvements, the current. ripples have been estimated at afactor of 10- 6 to flat top current 2,850 A. For example, Fig.3 (photo.) shows
the output of the voltage ripple detector at input (top) and output (bottom)
to the dynamic filter for the B-MPS on the fl<i.t top. Fig.4 gives a spectrum
analysis of the same signals. The similar results have been obtaind in the QF
and QD - MPS. The more detailed results will be described in some places
before long.
REACTOR
TRANSFORMER

FIG.2
FIG.lSCHEMATIC DIAGRAM OF
THE DYNAMIC FILTERSVOLTAGE RIPPLE DETECTOR15010050 100600300Hz900Vrms

50 V/div
2 ms/div

FIG.3

VOLTAGE RIPPLES OF
THE INPUT AND OUTPUT-190-FIG.4

SPECTRUM ANALYSIS OF
THE VOLTAGE RIPPLES~-~~---