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

Raul HERRERO	CERN Project Leader
Yves THUREL	CERN Project Referent

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 medium current switch mode power converter, designed for powering of superconducting loads requiring positive or negative current and positive or negative voltage control (4 quadrants). Constructed from a modular architecture composed of 2x [+/-400A +10V] power modules (active redundancy up to 400 A current level).

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.

Power part is identified as a 4 quadrant voltage source, even if an internal current source control is required to adequately share output current between all the power sub-modules.

[+/-400A +/-10V] Power Module simplified Architecture / Topology Power Part .vsd

Power Module is actually a high frequency fully bidirectionnal (+/-400A +/-10V) current source (7-8kHz) controlled by a 1kHz bandwidth voltage loop. It should be noted that Power Module 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. 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).

[+/-600A +/-10V] redundant Voltage Source simplified Architecture / Topology .vsd

Redundance operation relies mainly on [+/-400A +/-10V] 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.

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 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, combined with an output DC contactor which prevents a Power Module dying in fault mode with its output stage to deviate the magnet current. Crowbar active system is located in the rack and provides a safe resistive discharge path for magnet current, with a capability to dissipate the total magnet energy, but requiring reasonnable time to do it.- voltage level to be validated
• 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.- to be validated.

• Crowbar

  The system is based on a xx 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 xxx kJ by design. Additional DC-Contactor ensure that no potential short-circuits at the level of the several Power Modules can prevent the magnet energy to be actually dissipated in the Crowbar resistance.It should be noted that 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 No fault    -    converter → OFF converter → OFF    -    Crowbar Fully Active Crowbar Fully Active    -    REE Active (if required) REE Active (if required)

  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:

  

  Fast Abort Interface 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 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

Machine Installation

Production Contract & Contact History

Developped	Designed/CERN
	2017-2020
Manufactured	Contry(s)
	Manufacture
Production	xxx Pc
Responsibles:	Raul HERRERO

Converter Circuit Names

 RPxxx