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:	Vincent BARBET
	Ludovic CHARNAY
	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

A high current high frequency (25 kHz) switch mode power converter, designed for powering of superconducting loads requiring only positive current and positive voltage control (1 quadrant). Constructed from a modular architecture composed of 2kA power modules, the system can be easily adapted to suit specific powering requirements. Used extensively in the LHC particle accelerator. The converter is water cooled, and is thus ideally suited to situations where air losses must be carefully managed. Designed for underground operation, extensive remote diagnostics have been foreseen to allow efficient monitoring and fault diagnostics without requiring being present locally.

Additionnal free wheeling diodes located in the Power Rack always provide a current path, independent of the converter status.

Power Converter is normally assembled using a n+1 Power Bricks [+2kA +08V] to provide active redundancy in case of one subconverter is lost. For example, a [+8kA +08V] is composed of 5x [+2kA +08V] Power Brick, working as current source being controlled by a Voltage Source main control.

/ Topology

[2kA 08V] Sub-Converter simplified Architecture / Topology .vsd

Power Brick is actually a high frequency current source (7-8kHz) controlled by a 1kHz bandwidth voltage loop. One can notice that Power Brick is actually a current cource in its structure, even if voltage source capacitors are located in this block for mechanical reasons. Representation below gives a symbolic structure of the power converter, clarifying the cascade loops. ( Is1 & Is2 are actually assumed to be representative and equal to the current of each power transformer secondaries). The multiplication of rectifier stages in each output module gives the following advantages: easier design of magnetic parts, lower rating fuse (lower losses) to protect whole Power Converter being short-circuited by a faulty secondary (fuse would immediately blow in case one of the schottky dies, giving the possibility to the whole power converter to reconfigure the current level in other current sources to maintain required voltage level).

[4-6-8kA 08V] Voltage Source simplified Architecture / Topology .vsd

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. Dedicated systems QPS (Quench Protection System) + PIC (Power 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. This redundant signal uses 2 paths to interlock and stop the converter and its redundancy is checked each time it acts. It directly acts on AC Contactor bobbin, ensuring its opening as required.
• Stop powering the load in safe way (handling the magnet energy even when stopping, through dedicated system called Free Wheeling Diode Safe Paths). This passive system based on different paths using several free-wheeling diodes in the rack provide a safe 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.

• Free Wheeling Diode Safe Paths

  The system is based on 3 different paths provided by Free-Wheeling Diodes providing a safe path for magnet current. The number of Free-Wheeling diodes (x40..x80, 20x per cards) to be considered depends on the converter type (see chapter Machine Installation below). Only one unique Additionnal Free-Wheeling Diode is always present as a last chance 3rd path.

  

  Crowbar System simplified schematic .vsd

• Earth System

  The circuit injects a 100 mA DC current on a grounded resistive branch, resulting in a common mode voltage at the output circuit easing the earthing fault detection. Output circuit Common mode voltage is, without any earth fault, around 10V (=100 mA x 100 Ohms), and is not relying on load operation, making possible to detect an earth fault even with converter being OFF. (OFF, not condamned).

  If an earth fault occurs on the output circuit, a faulty current will be deviated from the initial path back to earth by using the shunt 10 Ohms resistor path (monitored for detecting this fault).

  Overcurrent protection is achieved through a 1A-100V fast fuse in series in the path provided for the earthing fault current.

  

  Earthing System simplified schematic .vsd

Power Converter Components .vsd

A power converter is actually a sum of different equipments under several different sections in the SY-EPC group. The modularity is a key factor for easier maintenance with regards to LHC tunnel access conditions.

Power Converter Rack

• Power Converter Rack
  • Voltage Source Unit
    • n+1 Sub-Converters
      • 1x Input Power Module
      • 2x Output Power Modules
    • Common Control Elec. (CCE) _{4x-sub, 5x-sub}
    • Aux Power Module
    • Free-Wheeling Diode Circuit
    • Eq. Stop & Earthing Protection Circuit
  • FGC2 Fan tray unit
  • 2x Current sensors: DCCTs Heads
    • DCCT Head
  • 2x Current sensors: DCCTs Electronics
    • DCCT Electronic
  • Electronic Chassis (Ref: HCRFEFA - Type 5) .edms
    • Digital Controller: FGC2
    • AC/DC Power Module
    • PSU FGC Tri-volt
• Calibration Rack (Inner Triplet Only)
  • 2x Current sensors: DCCTs Electronics
    • DCCT Electronic
  • Sigma Delta 22 bits ADC
    • Sigma Delta 22bit Modulator
    • Sigma Delta 22bit Module
    • Sigma Delta 22bit Power Supply

Magnet Types

Machine Installation .xls

Overview of the different converter types in LHC machine .xls

Production Contract & Contact History

Developped	KEMPOWER
	2001-2003
Manufactured	Lahti, Finland
	KEMPOWER
Production	203 Pc
CERN Contact	David NISBET
	Vincent BARBET

Converter Circuit Names