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

Involved Peoples

Nicolas KUCZEROWSKI	CERN Project Leader
Yves THUREL	CERN Project Referent
Edwin ROHRICH	CERN Technician Responsible
Error processing SSI file	CERN Mechanical designer (>2020)
Error processing SSI file	CERN Mechanical designer (2019)

Power Converter Architecture

This Power Converter is used for powering HL-LHC Superconductive Magnets, and for DC applications.

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

• Power Part:
  • Power Rack (AC & DC distribution, interconnections)
  • Ideally Removable Power Modules, including redundancy as much as possible.


• CERN Digital Controller (FGCx?):
  • The high level control from and to the Cern Control Room (using fieldbus to be defined)
  • The high precision digital current loop (when a voltage source is controlled)
  • Collecting and reporting all status, faults, and measurements from all the different parts to the remote services, for diagnostic and operation purposes.


• High Precision Current sensor(s) (DCCTs)
  • Measuring DC current at the required precision.

Power Converter simplified Architecture .ppt

Power Part

A high current switch mode power converter, designed for powering of superconducting loads requiring positive current only, operating in 1 quadrants. Constructed from a modular architecture composed of 07..08 x [+2 kA; +08 V] power modules (active redundancy in a n+1 configuration).

Primary use is in HL-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 [+2 kA; +08 V] to provide active redundancy in case of one subconverter is lost. A [+20 kA; +08 V] is composed of 8x [+2 kA; +08 V] Power Bricks, working as current source being controlled by a Voltage Source main control.

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

Power Brick is actually a high frequency current source (7-8 kHz) controlled by a 1 kHz bandwidth voltage loop, even if voltage source capacitors are located in the current source 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).

[2 kA; +08 V] n+1 redundant Voltage Source simplified Architecture / Topology .vsd

Redundance operation relies mainly on each [2 kA; 08 V] inner current source reactivity, so that load output current is not impacted by the loss of one sub. Of course a sudden short at the level of the output stage of a sub converter will likely lead to a converter global fault stop, despite the presence of output fuse.

No Fault No fault    -    Sub Fault Transition Sub Fault Transition    -    Sub Fault state Sub Fault state

Power converter redundance .vsd

Control Part

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

Control & regulation principles are summarized in a detailled schematic 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 1 or 2 Current sensors (DCCTs: DC current Transducer). Precision is then directly relying on sensor precision: current sensors, 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.

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 DC 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). 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.

• Fast Abort Interface

  Machine Interlock system can request a Fast Abort to the converter, in case a quench is detected. Converter is then assumed to react as soon and as quick as possible, stopping providing energy to the load. This signal being part of the magnet safety scheme, it is acting redundantely at the level of Converter DC Mains Contactor. 2 paths are used and monitored to stop the contactor. The schematic is described below:

  

  Fast Abort Interface .vsd

• Free-wheeling diode

  The converter has been defined in order to run only on resistive load. In order to reduce the converter cost, thre Free-Wheeling Diodes providing a safe path for current is only assured by the rectification diodes inside the modules.

• Earth System

  This converter features the new Earth system made for HL-LHC converters.

  The circuit injects a 50 mA DC current on a grounded resistive branch. This common mode voltage is then applied to the output circuit mid point artificially created by a resistor divider. This system enables to detect leakage current with improved robustness against converter transient voltage. And this 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 100 Ohms resistor path (monitored for detecting this fault). The threshold is set to 5mA

  Overcurrent protection is achieved through a 100mA-1000V fast fuse in series in the path provided for the earthing fault current.

  Tests have been carried out on this converter with prototype unit of this earth leakage current detection. Report is available .

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 is built through two Power Racks. One contains the six Sub-Converter Power Modules, when the second one includes the converter crowbar and DC-contactor systems, the converter power part control electronic, the FGC complete Electronic Chassis, the two DCCTs head and their electronics.

Magnet Types

Production Contract & Contact History

Developped	Designed/CERN
	2020
Manufactured	Internal prototype(s)
	Manufacture
Production	1 Pc
Responsibles:	Nicolas KUCZEROWSKI

Converter Circuit Names

 RPAHN.PHALL.DCCT.20KA