Medium Power Converters Section

General SATURN

Power Converter Characteristics

SATURN datasheet

Project Owner

Gilles le Godec

Project Team

Ivan Josifovic – Emilien Coulot – Stephane Reignier – Javier Parrilla Leal – Stefano Rossini – Christophe Mutin

Power Converter Responsibilities

Ivan Josifovic – Emilien Coulot

Power Converter Topology

The main power brick of converter consists of an 18 kV / 50 Hz transformer (for galvanic isolation, voltage adaptation and phase shift), a front-end diode rectifier with DC-link filter (for AC/DC conversion) and an IGBT H-bridge with output filter (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 insufficient energy storage in the DC-Link;
  • Dissipated in a crowbar connected across output in case of fault.

Single SATURN module:

SATURN topology.vsd

Two SATURN modules are assembled in parallel to increase the current capability (SATURN_2p):

SATURN_2p topology.vsd

Two SATURN modules are assembled in series to increase the voltage capability (SATURN_2s):

SATURN_2s topology.vsd

Magnet Protection

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 system is based on axx 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).

Crowbar system simplified schematic.vsd

Earth fault detection ►

The detection system is a passive solution 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 0.5 V hence limiting the fault current to 5 mA (REARTH = 0.1kΩ),
  • R1 is chosen with respect to the requested sensitivity of the system:

VNOM: Nominal value of the voltage,
k: voltage unbalance factor (0.05…0.1).

SATURN Earth System simplified schematic .vsd