Power Converter Characteristics
Design & Operation Responsibles
John Baillie - Emilien Coulot - Ivan Josifovic - Stéphane Reignier - Samer Yammine
Power Converter Topology
For the main brick (COMET), a 50 Hz transformer (galvanic isolation – voltage adaptation – phase shift), a diode rectifier, and a DC-Link filter are used for the AC/DC conversion. An IGBT bridge (4 quadrant operation) with an output filter are used for DC/DC conversion.The energy of the magnet is:
• Recovered in a capacitors bank on the DC-Link during cycling mode of operation,
• Dissipated in a brake chopper in case of too small energy storage on the DC-Link,
• Dissipated In a bipolar crowbar in case of fault,
One module COMET:
COMET topology .vsd
Two modules COMET are assembled in parallel to increase the current capability (COMET_2p):
COMET_2p topology .vsd
Two modules COMET are assembled in series to increase the voltage capability (COMET_2s):
COMET_2s topology .vsd
Four modules COMET are assembled in parallel to increase the current capability (COMET_4p):
COMET_4p topology .vsd
Power Converter is part of magnet protection scheme, even if not directly fully responsible of the monitoring and diagnostic of the magnet status. PIC/WIC (Power/Warm Interlock Controller) can interlock Power Converter if magnet safety requires it.
Power Converter is then expected to:
• Always ensure that external protection system can stop the Power Converter through a safe signal called Fast Abort.
• Stop powering the load in safe way (handling the magnet energy even when stopping, through dedicated system called Crowbar). This active system provides a safe resistive discharge path for magnet current (energy).
• Monitor Earth current of the total circuit: converter + load (magnet and its DC cables), and take the right action if threshold reached.
► Active Crowbar
The active crowbar is independant of the configuration of the converter (serial or parallel). The system is based on a 500 mOhms power resistor connected to two thyristors which are triggered when there is a faulty condition on the converter or when the voltage Vmeas goes beyond a predefined threshold (BOD protection).
Crowbar System simplified schematic .vsd
►Earth fault detection
The Detection system is a passive system which is independent of the configuration of the converter (serial or parallel). It's composed of a voltage divider connected between positive polarity, the negative polarity and the earth:
• The voltage threshold VEARTH is set to 0.5V hence limiting the fault current to 1 mA (REARTH = 0.5kΩ),
• R1 is chosen with respect to the requested sensitivity of the system:
R1=(k.VNOM)/IEARTH - 2.REARTH
VNOM: Nominal value of the voltage,
k: voltage unbalance factor(0.05…0.1),
Earth System simplified schematic .vsd