Transcript Simulations_serial_magnets

TE EPC
Simulation results for powering
serial connected magnets
OUTLINE : Serial configuration of full rated converters against the
use of active trimmers, principle of neighbourhood assistance in
case of failure. Several investigated scenarios in the reconfiguration
of the converters.
Daniel Siemaszko, Serge Pittet
02.03.2010
Serial converters solution
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Serial connection of converters approach, IDEAL voltage sources with regulated
output currents. (Converters ratings : 100A, 20-40V) (Static conditions).
Advantage : Serious reduction in number of cables. Possibility of using smaller cable
section if the difference current between two consecutive magnets is small.
Questions : Validity of neighbourhood assistance of converters in case of failure?
Simulation of the failure of fourth converter. Previous converter takes the lead, several
scenarios are investigated. (Inductors ratings : 20mH, 150mW)
02/03/2010
Daniel Siemaszko, Serge Pittet - EDMS 1060161
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No action (short circuit)
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When converter 4 fails, no action is taken, the converters is in short-circuit.
Neighbourhood assistance is impossible since half of the current flows in the cables.
Only half of the nominal current is reachable (depending on cable resistances!).
In case of the need for bypassing a magnet (zero current), a negative voltage must be
applied and the full nominal current will flow through the intermediate cables.
t=~0.6s
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Removal of the cable
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When converter 4 fails, the connection to cable 4 is removed. Converter 3 takes the
lead and feeds two consecutive magnets with same mean current. In this case,
converter 5 could also give the needed assistance.
Peak current reached in cables is around 1 A, thanks to regulators action. In order to
achieve such dynamics, the converters must be twice rated in case of assistance.
Question of mean current in two consecutive magnets.
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Adding a passive trimmer
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When converter fails, a tuneable resistive load (around 200W) is connected in series
to the cable 4.
With accurate tuning the needed current can be achieved with the assistance of
converter 3.
Still, if converter 1 fails this solution is not able to produce the needed assistance.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Using permanent resistances
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All cables have an added permanent resistance, unbalance in voltage ratings.
When converter 4 fails (short-circuit), current trimming in magnet 4 inadequate.
Value of resistance limited by voltage drop. Instabilities reached when it exceeds the
magnet voltage drop. Slow current recovery and bad voltage sharing.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Power limitation in converters
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Serial connected converters solution needs the use of double rated converters in case
of assistance.
When the converter reaches its limitation in power, the assistance is not anymore
possible and magnet current cannot reach its nominal value (ex. with 2.5kW limit).
Same behaviour with and without adding a passive shunt.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Bypassing a magnet sequence
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When a sequence of converters is
shorted, the corresponding magnets
are bypassed. Non zero current
because of cable impedance.
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In order to achieve zero current in a
sequence of magnets, the converter
corresponding to the first bypassed
magnet must compensate with
negative voltage.
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In order to achieve zero current in
one isolated magnet, the full
negative voltage must be applied.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Parallel active trimmers
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One big converter with parallel connection of active trimmers approach (Converters
ratings : 100A/300V, trimmers ratings 0.1A/15-275V, assuming 16 magnets).
Advantage : Serious reduction in number of converters. Common ground (higher
precision in current measurement), same current ratings for the trimmers.
Questions : Control, behaviour of the magnet currents in case of failure?
Simulation of the failure of Converter 4. Open circuit scenario is investigated.
(Inductors ratings : 20mH, 150mW)
02/03/2010
Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Removal of the cable
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When converter 4 fails, the connection to cable 4 is removed. As in the neighbour
assistance approach, the fourth magnet takes the same current as the previous one.
Possible mean value to be reached.
Oscillating effect due the disconnection of the inductive cable. Can be dumped
through a capacitor.
Again question of mean current in two consecutive magnets.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Serial active trimmers
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One big converter with serial connection of active trimmers approach (Converter
ratings : 100A/300V, trimmers ratings 0.1-1.6A/15-25V, assuming 16 magnets).
Advantage : Same rated voltage in almost all trimmers.
Questions : Control, stability, behaviour of the magnet currents in case of failure?
Simulation of the failure of Converter 4. Several scenarios are investigated.
(Inductors ratings : 20mH, 150mW)
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Serial trimmer, short case
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When converter 4 fails, no action is taken, the converters is in short-circuit.
Same as before, the cables see half of the nominal current.
Need for a high impedance in case of short-circuiting the converter.
t=~0.6s
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Serial trimmer, open case
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When converter 4 fails it is brought to an open circuit. The magnet sees the nominal
main converter nominal current.
Peak current reached in cables depends on the position and might reach 1A.
Question of acceptable current in magnet in case of failure.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Serial trimmer with diodes
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Trimming cables are implemented with serial diodes.
Current profile in the magnet sequence can only present a negative slope.
When converter fails in short-circuit, the diodes do not allow the current magnet to
fall lower than the following one. Open circuit case affects all previous magnets.
Few seconds are needed for stabilising the currents in the remaining magnets.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Comment on main converters
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Reliability of solutions using trimmers highly depends
on the reliability of the main converter
(N+1) redundancy is achieved with serial connected
voltage controlled converters or parallel connected
current controlled converters.
When one module fails, the remaining converters can
go on operating.
Number of module depends on current need for the
magnets (drive beam case 100-10A).
Failed converter must be bypassed in serial approach.
Failed converter must be opened in parallel approach.
02/03/2010
Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Comment on precision
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In serial connected converters, precision of current in magnets depends only on each
converter precision. Precision of possible active/passive trimmer influences only the
magnet corresponding to the faulty magnet.
In serial connected active trimmers, precision of current in magnets depends on the
big converter precision plus its corresponding trimmer. Use of 1% trimmers possible.
In parallel connected active trimmers, precision of current in magnets depends on
the big converter precision and the number of magnets in the sequence, since each
trimmer takes a proportion of the main current.
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Solution for powering 16 magnets
main converter
trimmer
Serial connected converters
100ppm (10mA)
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Parallel connected active trimmers
90ppm (9mA)
500ppm (1/16 mA)
Serial connected active trimmers
90ppm (9mA)
1% (1 mA)
Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Comment on MTBF
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Assuming very reliable converters with MTBF of 3·105, the high number of
converters in the main Linac (~45’000), there will be statistically one individual
failure every 7 hours.
With a very optimistic repair time of 4 hours, the whole complex will be down
most of the time.
With the principle of redundancy for main converters in powering groups, it is
possible to consider hot swap of failed modules during operation or to stop the
whole complex at some specified maintenance days once a month. With one
failure every 5 years in one group of 6 modules, the down time of the complex
would be theoretically zero.
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Daniel Siemaszko, Serge Pittet - EDMS 1060161
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Conclusions
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Efficiency of the presented solutions still depends on beam physics requirements.
Reliability of additional passive/active shunts must be taken into account in overall
MTBF considerations.
No serious dynamic issues have been observed assuming static conditions.
The use of active trimmers instead of full rated converters is preferred for price and
volume aspects.
Price of the converters significantly depends on operation type, namely one/two
directions of voltage/current and required dynamics (di/dt in magnets operation).
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Solution for powering 16 magnets
main converter
trimmer
Serial connected converters
16 x (100A/40V)
Passive/active?
Parallel connected active trimmers
1 x (100A/300V)
15 x (0.1A/15-300V)
Serial connected active trimmers
1 x (100A/300V)
15 x (0.1-1.6A/20V)
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