Power Converter Characteristics Design & Operation Responsibles Power Converter Architecture Power Part Control Part

Magnet Protection Power Converter Components Magnet Types Machine Installation Production Contract & Contact History

Power Converter Characteristics

Design & Operation Responsibles

1st Intervention	Piquet SY-EPC LHC
Responsibles:	Laurent CECCONE
	Serge PITTET
	CERN SY-EPC-LPC

Power Converter Architecture

This Power Converter is used in LHC Machine to power superconductive magnets. It is located in the LHC underground installation, close to the loads to limit cable losses in the underground installation.

Different parts were designed and produced separately, Power Converter being finally integrated in a housing rack, with 3 main parts:

• High Precision Current sensors: DCCTs, able to measure DC current at the required precision.
• Power Part: Power Rack and its removable Power Module
• A Digital Controller (FGC) using WorldFip bus in charge of:
  • The high level control from and to the Cern Control Room
  • The high precision digital current loop
  • Collecting and reporting all status, faults, and measurements from all the different parts to the remote services, for diagnostic and operation purposes.

Power Converter simplified Architecture .ppt

Power Part

Voltage Source is based on a phase shifted high frequency DC/DC followed by a 4 quadrant linear stage for the 4 quadrant operation, and crowbar to ensure magnet discharge.

Power Part simplified Architecture / Topology .vsd

Notes:

The crowbar is active on fault and Off-state.
An additional passive protection is present on the DC connector (short circuit) to ensure a discharge of energy from the magnet

Typical Curves

Control Part

Control & regulation principles are summarized in a detailled schematics representating only the part involved in the output current regulation scheme.

Regulation Control simplified schematic .vsd

High precision current control loop is managed by the digital controller called FGC (Function Generator Controller). This unit includes a high precision Sigma Delta Analog to Digital Converter which digitalize the analog current measurement coming from 2 DCCTs (DC current Transducer). Precision is then directly relying on sensor precision: DCCT, the ADCs, and the algorithm being used for the regulation loop. Voltage source is then used as a power amplifier, powering the load through a high bandwidth voltage loop (>500Hz).

Magnet Protection

Power Converter is part of magnet protection scheme, even if not directly fully responsible of the monitoring and diagnostic of the superconductive magnet status.

In LHC complex, LHC60A-08V magnets are considered as safe per design and can handle their own energy without external energy extraction system. Converter then detects a quench when occuring through the magnet impedance growing (resistance) up to a point Power Converter cannot regulate anymore.

LHC60A-08V Power Converter is also responsible of the current leads protection. These current leads are the 2 (minus and plus polarities) electrical conductors located at the transition between cold and warm environment.

Power Converter is then expected to:

• Stop powering the load in safe way (handling the magnet energy even when stopping, through dedicated system called crowbar). This active system located in the rack 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.
• Monitor the voltage across the 2 current leads, and take the right action if threshold reached.

• Crowbar

  The system is based on two back-to-back Power MOSFETs set ON when converter is in OFF-state or in fault, and then providing a safe path for magnet current.

  

  Crowbar System simplified schematic .vsd

• Earth System

  Earthing system is based on a 5V voltage source creating a common mode voltage to easily detect a earth current to ground fault condition.

  

  Earthing System simplified schematic .vsd

• Current Leads Protection

  These current leads are protected monitoring the voltage across them. Per design these current leads must not developp more than 150mV at full current. Such a case would mean their thermal stabilization is not correct.

  Design is simply facing some common mode voltage coming from Earthing system added from the differential voltage, when trying to measure a small voltage of some mV across long distances.

  

  Current Leads Protection System simplified schematic .vsd

Power Converter Components

• Power Converter Rack
  • Power Module
    • 2x Current sensors:120A DCCTs
    • Digital Controller: FGC2

Magnet Types

Machine Installation

LHC60A-08V Location below dipoles .vsd

Electrical & WorldFip Distribution

Electrical & WorldFip are based on same layout described below

LHC60A-08V electrical distribution in LHC machine .vsd

Production Contract & Contact History

Developped	CERN AB-PO-SC
	2000-2003
	Andre DUPAQUIER
	Laurent CECCONE
	Valérie MONTABONNET
	Serge PITTET
Manufactured	France
	CEL
Production	826 Pc

Converter Circuit Names