MAGNET POWER SUPPLY SYSTEM 7000
22
DANFYSIK A/S - DK 4040 JYLLINGE - DENMARK.
4
Theory of operations
4.1
Introduction
The power supply is designed to supply a magnet with direct current stabilised to 100 ppm of
maximum output current.
The main AC input supply is connected through a contactor, which turns on the power in two
steps to minimise the inrush current. Step one with R201 to R204 connected in parallel with the
mains for a certain time. In the second step the resistors will be short circuit. The voltage is
rectified in a 6-pulse rectifier and filtered with a L_C low pass filter.
The output current is controlled by means of a linear Vce controlled four-quadrant power
amplifier.
One power supply is capable of transforming up to 1,5KW of power at a maximum of 20A and
75V. If more current is required up to five power supplies may be arranged in parallel.
A 70 kHz Push-Pull converter supplies the Power Amplifier. The Vce voltage of the Power
Amplifier controls this converter.
Stabilisation is achieved by comparing the voltage across the burden
resistor, connected to an
ultra high precision D.C. current transformer (DCCT), with the ±10V set signal either supplied
from the Analogue interface or the built in precision DAC.
The resultant error signal is feed into a high gain amplifier system. The output from this
amplifier controls the output power amplifier, so that the output current is maintained within
the specified accuracy.
Due to safety reasons it is possible to stop (interlock) the power supply. These interlocks can
either be generated internally (phase_, temperature_, over voltage_, over current_ failures and
others) or externally (two spare_, Magnet over temperature_ or rack fan_failure). These
interlocks are latched on the power amplifier module.
It is possible to control the power supply either from the local control panel located on the front
of the supply, through the remote serial line or through the “PARALLEL UNITS TO
MASTER” and “PARALLEL UNITS TO SLAVE” interface plugs, allowing a parallel control
and analogue current settings. In all modes it is possible to switch the supply ON/OFF, reset
interlocks, read status information as interlocks, internal voltages and output current/voltage.
The slaves must also be connected to the serial line in order to read these individual interlocks.
Efforts have been taken to design the power supply to be fully protected if an error occurs.
However if magnets above 500mH is connected, fast ramping beyond regulation e.g. polarity
change from full positive to full negative set current, might bring the output transistors beyond
SOA. The ensure best protection, it is recommended to adjust the slew rate circuit to the
maximum needed ramp speed and not ramp faster than the loop can regulate.
