SIRIUS is a modular power converter specifically designed for fast cycling loads such as the electromagnets of Trasfer Lines in Particle Accelerators. It is a regenerative converter with integrated energy recovery of up to 90kJ in its simplest configuration - SIRIUS S(ingle). Its basic building block (the “module” or "brick") is built with the possibility of series or parallel output connection in order to supply a wide range of electromagnet loads.
The power converter is rated for a cycling rated voltage and current of 450V and 450A respectively or for a continuous (DC) output voltage and current of 80V and 200A. The unit can therefore provide a constant RMS power of 16kW to the load whereas the peak cycling power deliverable to the magnet is 202.5kW.
The power converter employs a grid supply unit that consists of a passive rectifier unit with boost converter that acts as grid current regulator (limiter). The grid supply unit limits the power taken from the power grid to just 20kVA with a modest 32A/400V 3-phase line voltage. This unit serves to improve power quality towards the power network by limiting the input power fluctuation.
A capacitive energy storage is employed to recover energy from the magnet during the current ramp down. The built in energy storage to each module is 90kJ with a possible extension by the addition of an extension rack.
Finally, a standard magnet supply unit is used to regulate the output current to high precision as required by the application.
The converter integration is done in two standard 19-inch racks. One rack is the standardised “module” converter and the second rack houses the output filter capacitors, high precision current measurement DCCTs, the Function Generation Controller crate and the cooling distribution equipment.
Power Converter Characteristics
Konstantinos Papastergiou - Christophe Mutin - Javier Parrilla Leal
Power Converter Topology
Single Module SIRIUS
SIRIUS topology .vsd
Two modules SIRIUS are assembled in parallel to increase the current capability (SIRIUS_2p):
SIRIUS_2p topology .vsd
Two modules SIRIUS are assembled in series to increase the voltage capability (SIRIUS_2s):
SIRIUS_2s topology .vsd
Four modules SIRIUS are assembled in parallel to increase the current capability (SIRIUS_4p):
SIRIUS_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
Each SIRIUS module is equipped with its own active crowbar.The system is based on a 2.2 Ω 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).
SIRIUS 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 5 mA (REARTH = 100 Ω)
• 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),
SIRIUS Earth System simplified schematic .vsd