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topPower Converter Characteristics

Picture of the converter
Power In 3 ~ 230V/16A
Power Out +/- 600A +/-10V
Converter Type 4 Quadrant
Control type FGC2 / WorldFip
Current Accuracy 10 ppm@ 30 mn
50 ppm@ 24 h
200 ppm@ 1 year
(1 ppm=0.6mA)

topDesign & Operation Responsibles

1st Intervention LPC icon Piquet TE-EPC LHC(161919)
Responsibles: Yves THUREL Yves THUREL
Benoit FAVRE Benoit FAVRE
LPC icon CERN TE-EPC-LPC

topPower 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.
Simplified Schematic

Power Converter simplified Architecture .ppt

 

topPower Part

Voltage Source is based on a variable switching frequency (50kHz..200kHz) half bridge resonnant topology (dual thyristor) followed by a 4 quadrant linear stage to allow the 4 quadrant operation. This topology gives a very low output EMC noise, at a cost of some control complexity given by the different stages.

A 19'' rack provides connectivity from AC network and to the load, housing up to 2 Voltage Source Power Modules.

Power In 3 ~ 230V/16A
Power Out +/- 600A +/-10V
Cooling type Water Cooling (+ forced air ventilation)
Input rack connection: PARKER SH2-62Y AISI 316 Stainless '' BSPP. (female - blue color "cold")
Output rack connection: PARKER SH2-62Y AISI 316 Stainless '' BSPP. (female - red color "warmer")
Nominal Water Condition [2x 600A modules installed]   → 6 l/min @ 3.0 bars of Differential Pressure Drop. *
Nominal Water Condition [1x 600A module installed]   → 5 l/min @ 3.0 bars of Differential Pressure Drop. *
Rack Water Layout, and its typical water pressure drop.
Rack2x Losses@ Full Power Total losses.....4500 Watts [2x(600Ax10V)*(1/0.73-1)]Pwr + 2x65W(FGC+DCCTs)
Water losses....3000 Watts
Air losses........1500 Watts (incl. FGC & DCCTs)
Converter Weight Bare Rack ................ 280 kg (Power Modules and full equipped electronic chassis excluded)
Power Module ........... 72 kg
Electronic Chassis .... 11 kg (Fan Tray + Chassis + 2x FGCs + 2x PSUs + 4 DCCT electronics + AC-DC)
Simplified Schematic

Power Part simplified Architecture / Topology .vsd

 

3 different types exist A, B, C corresponding to.

  • A-Type: Power Module is integrated in rack providing a DC Contactor between Power Module and Rack Crowbar.
  • B-Type: Power Module is integrated in rack without any DC Contactor between Power Module and Rack Crowbar.
  • C-Type: Power Module is integrated in rack providing a DC Contactor between Power Module and Rack Crowbar, and a external Crowbar placed in a Power Module slot being modified is additionnaly connected (Inner Triplet Case).

 

Typical Curves

Curves Meas. Conditions .txt
Output Voltage Ripple 0A 300A 600A
Output Voltage FFT 0A LF/HF 300A LF/HF 600A LF/HF
0V distortion crossing -100A/100A -200A/200A -300A/300A -400A/400A -500A/500A -580A/580A
Rectified Inverter Current [0A 0V] [300A 3V] [600A 6V]
Earth to DC Polarity Volt. Earth-Neg DC/AC AC-Neg/AC-Pos
Earth to DC Neg Pol. FFT 0A LF/HF 300A LF/HF 600A LF/HF
Starting Sequence Vin.DC Vin.DC
Crowbar/Discharge Curves 600A Full-sequence - Zoom @ Conditions .txt
Fast Abort Delay @ 550A Oscillo - Post-Mortem @ Conditions .txt
Voltage Source Efficiency vs Output Power Efficiency Graph, (.xlsx)

topControl Part

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

Detail FGC Regulator Vol.Sour.

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).

 

topMagnet 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 expected to:

  • Always ensure that external protection system can stop the Power Converter.
    Power Converter provide a safe incoming 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 and DC Contactor bobbin, ensuring their opening as required.
  • Stop powering the load always providing a safe path for magnet current.
    Magnet current path is ensured through a dedicated system called crowbar when combined with an output DC contactor (Power Module in case its output stage dies in short would collect all magnet current without the DC Contactor). Crowbar active system is located in the rack and provides a safe resistive discharge path for magnet current, with a capability to dissipate, most of the time, part of magnet energy.
  • Monitor Earth current of the total circuit and take the right action if threshold reached.
    Total circuit = converter + load (magnet and its DC cables).
  • Monitor the voltage across the 2 current leads, and take the right action if threshold reached .

 

  • Crowbar

    The system is based on a 50 mOhms Power Resistance series back-to-back thyristors being fired at a given output voltage (13V), and then providing a safe path for magnet current, providing energy to handle is less than 108 kJ by design. Additional DC-Contactor (Converter type A) ensure that no potential short-circuits at the level of the Power Module can prevent the magnet energy to be actually dissipated in the Crowbar resistance. By the way these additional DC-contators prevent the converter while being in OFF-state to actually deviate some current during magnet discharge (converter output stage is not fully opened in OFF state). One should never forget a Power Module dying with its output stage in short would prevent the crowbar from dissipating magnet energy in the case no DC-Contactor is present.

    No fault    -    converter → OFF    -    Crowbar Fully Active

    A-Type (no REE installed in the circuit). Crowbar System simplified schematic .vsd

    No fault    -    converter → OFF    -    Crowbar Fully Active    -    REE Active (if required)

    B-Type (REE installed in the circuit). Crowbar System simplified schematic .vsd

  • 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. Delay time between a Fast Abort request and actual opening of the 4-quadrant output power stage is less than 1mS, but 20ms, AC Mains Contactor delay time, should be considered as a worst case (internal control malfunction case). A typical sequence could be described as follow:

    1. t=[=0ms] → Fast Abort Request from Machine Interlock
    2. t=[=1ms] → Power Converter Output Stage opens and becomes not conductive
    3. t=[>xms] → Load energy is transfered to the crowbar = a Capacitor up to V.crowbar = 13V.
      Capacitor charge depends on initial load current (I=C.dV/dt). C=C.Crowbar//C.Power-Module
    4. t=[=xms] → Crowbar Thyrsitor is fired, absorbing Crowbar capacitor + Load energy.
      An initial over-current generally happens at initial thyristor start-up.
    5. t=[>end] → Load energy is dissipated in the crowbar (R series Thyristor ON voltage) and in the load resistance.

    This signal being part of the magnet safety scheme, it is acting redundantely at the level of Converter AC Mains Contactor. 2 paths are used and monitored to stop the contactor.
    A possible schematic is described below:

    Simplified Schematic

    Earthing 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.

    Earth fault current is filtered at the level of the Power Module, and a strong earth fault will make the converter trip 20ms after it happens. See this real measurement curves .png.

    Simplified Schematic

    Earthing System simplified schematic .vsd

 

topPower Converter Components .vsd

Components layout

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

Power Converter Rack can accept up to 2 Power Converters. Electronic Chassis, fan tray unit and AC-DC Power Module are shared in such a case.

 

topMagnet Types

Orbital corector QSKxxx

 

topMachine Installation

Air losses Full Rack [2x] @ P.nom (incl. FGCs) 1300Watts
Water losses Full Rack [2x] @ P.nom (incl. FGCs) 3000Watts
P.losses = Module efficiency : 0.75, FGC Chassis : 300Watts.
LHC Use 400 Power Converters (144 A-Type, 248 B-Type, 8 C-Type) .xls
Radiation Safe Locations (280) UA23 (31), UA27 (31), UA43 (24), UA47 (24),
  UA63 (23), UA67 (23), UA83 (31), UA87 (31),
  USC55 (08), UJ33 (46), UL557 (08)
Radiation Exposed Locations (120) RR13 (14), RR17 (14), RR53 (14), RR57 (14),
  RR73 (24), RR77 (24),
  UL14 (08), UL16 (08)

 

topProduction Contract & Contact History

Developped EEI-CIRTEM
2001-2005
Manufactured France-Italy
EEI-CIRTEM
Production 444 Pc
CERN Contact Yves THUREL Yves THUREL

topConverter Circuit Names