icalepcs 2005 advanced uses of the worldfip fieldbus for diverse communications applications within...

ICALEPCS 2005 Advanced uses of the WorldFIP fieldbus for diverse communications applications within the LHC power converter* control system

Quentin KingConverter Controls

Power GroupCERN

* A CERN “power converter” = everyone else’s “power supply”

ICALEPCS 2005 Q. King 2

Context

CERN is building the Large Hadron Collider (LHC) LHC will include 1712 magnet circuits,

each driven by a power converter Each power converter will be

controlled by an embedded computer → Power Group will use a total of 280 man

years and 86 MSF to power the LHC Converter Controls section will use ~50

man years and 7 MSF to provide the controls 1400 out of 2000 controllers have been

produced 100 have been installed


Control the 1700 power converters in the LHC Spread around a 27km machine Tolerate radiation (<10 Gray/year) Send commands and receive responses Maintain synchronisation to better than 1ms Support real-time control for feedback of beam parameters Support transmission of start/stop events Support status publication Support remote diagnostics Support remote software updates

We have been able to meet these challenges with the WorldFIP fieldbus

The Networking Challenge


In the 1970s…

Communications used enormous connectors and parallel data buses Very expensive Unreliable


In the 1970s…

Communications used enormous connectors and parallel data buses Very expensive Unreliable Lots of wire wrap More than 350

converters are still controlled this way today!


Then in the 1980s…

LEP was built 800 power converters One control computer per converter Huge step forward in networking: MIL1553 fieldbus Separate timing network


And in the 1990s…

LHC was started in 1996 1700 power converters One control computer per power

converter: TheFunction Generator/Controller (FGC)

In 1997 a survey of fieldbuses was conducted: WorldFIP was identified as

particularly interesting


Why WorldFIP? What is WorldFIP?

Industrial network similar to Profibus Uses 150 Ω twisted pair cable Long distances:

500 m at 2.5 Mbps 800 m at 1 Mbps 1900 m at 31.25 kbps

Excellent noise immunity Transformer coupled for galvanic isolation Inexpensive components

So nothing special so far!


WorldFIP components

150Ω

FieldDrive

FullFip

150Ω

Z=150Ω

FieldDrive

μFip

Gateway FGC


WorldFIP Synchronisation

FieldDrive

FullFip

CPU

TimingReceiver

TimingNetwork

Ethernet

Synch

Gateway

150Ω 150Ω

Z=150Ω


No need for a timing network!

All traffic is controlled by the FullFip device in the gateway

Each transmission cycle is triggered by the synchronisation signal

The first transmission is a broadcast so all FGCs receive a synchronised interrupt request from their uFip chips

All FGCs can synchronise their local real-time clocks – so no timing network is required!


Time distribution

FullFipTiming

Gateway

FGC

μFipTiming

Receiver

50 Hz Synch

ms Period

50 Hz IRQ

1 kHz

Gateway: Time broadcast

Synch μFip IRQ

450 μs ± 3 μs

PLL

Clock

PLL + local clock required so that FGC can run autonomously in case FIP traffic stops for a while

Drift < 1ms after 1000s (1 ppm error)


WorldFIP cabling for FGCs

30 out of 200 FGCs in our reception and test lab The green cables are

WorldFIP fieldbuses One gateway can support

up to 30 FGCs


WorldFIP cabling for FGCs


FGC Gateway


50 Hz Synch

Time distribution

FullFipTiming

Gateway

FGC

μFipTiming

Receiver

PLL

Clock

ms Period

50 Hz IRQ

1 kHz


Synch μFip IRQ

450 μs ± 3 μs


FGC Gateway connections

50 Hz Synch

FullFipTiming

Gateway

TimingReceiver


Time distribution

FGC

μFip

PLL

Clock

ms Period

50 Hz IRQ

1 kHz



Synch μFip IRQ

450 μs ± 3 μs

PLL

Clock

ms Period

50 Hz IRQ

1 kHz


How does the PLL work?

If the CPU includes the necessary timer functions (input capture and output compare for Motorola devices), the whole thing can be done in software

In the paper I explain how the PLL can be implemented in three lines of C

The PLL disciplines the period of the local real-time clock, which can be implemented in ten lines of assembler

The same functionality can also be implemented in a small piece of VHDL


But does it work?


PLL Error data

Error = PHASE_REF - (IC - OC)


Proportional-Integral PLL data

Clock Period = Integrator + GAIN x Error

Integrator += Error


And the frequency?

So the PLL captures nicely, but what is the frequency error? Is the drift < 1ms after 1000s?


And the frequency?

So the PLL captures nicely, but what is the frequency error?

Error = 0.8 μs in 40 s


And the frequency?

So the PLL captures nicely, but what is the frequency error?

Drift = 0.8 μs in 40 s

0.02 ppmor

2 in 108


Comments

This is a tribute to the amazing stability of cheap quartz oscillators

It is also an excellent result from a tiny amount of software combined with a bit of control theory

This is not an lucky result, repeating the test has similar results everytime

However, low drift over a minute does not prove that the drift will be less than 1 ms after 1000 s because the oscillator has a temperature coefficient of >1 ppm per degree


Conclusions

WorldFIP is an excellent networking choice for the LHC power converter control system

The real-time behaviour has saved us the need for separate timing and real-time control networks

With more than 1700 systems, this is huge saving in connectors and cabling Big financial savings Improved reliability

Protocol supports all our diverse communications needs with one twisted pair cable


Thanks to:

My colleagues in AB-PO-CC Stephen Page, Philippe Fraboulet, Philippe

Semanaz, Alex Frassier, Denis Hundzinger, Gilles Ramseier, Daniel Calcoen

The excellent collaboration from my colleagues in AB-PO and AB-CO

To you for listening!

icalepcs 2005 advanced uses of the worldfip fieldbus for diverse communications applications within...

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