Unprecedented accuracy/performance ratio for
system-wide phenomena on Pan European scale
Tests proved that the algorithm is able to achieve
an unprecedented ratio accuracy/performance for
large systems, on local events simulation, but more
importantly on full-scale scenarios involving large
parts of the system:
Network splitting with cascade tripping of
overloaded lines;
Inter area oscillations;
Whole areas losing synchronism.
Each of these tests was performed in less than
10 minutes. For example:
A voltage collapse scenario activating more
than 10 LTC and 2 generator field current limiter:
4.4 minutes;
A simple generator set point change: 0.3 minute;
Changing the AC grid impedance in parallel with an
embedded VSC HVDC: 1.4 minute;
Extreme case of voltage collapse with system
splitting: 9.8 minutes.
Making on-line DSA possible
at the Pan European scale
Tests proved the algorithm (simplified numerical
scheme) able to achieve unprecedented
performances for dynamic simulation on such a large
system and in the range of targeted phenomena (slow
dynamics), making online dynamic security analysis
at the Pan European level possible.
The following figures were extracted from tests
performed on the “UCTE+TEIAS” system:
Trip a line below 400 kV: 26 seconds;
Tripping of two parallel 400 kV lines: 44 seconds.
Both contingencies lead to significant voltage
deviation over a large zone with the triggering of
many automata.
A whole online dynamic security assessment at the
Pan European scale would require the consideration
of 2000 N-1 contingencies in less than 5 minutes.
With an average of 26 seconds by N-1 contingency,
this target can be reached through the simultaneous
use of 192 cores. This could be performed using less
than the computation power available in a single
modern blade enclosure.
Achievement 3: Paving the Way
for future research
and for industrialization
The computation engines developed can now
be considered as perfectly suitable for Security
Assessment at the ETN level. Even if the Waveform
Relaxation has shown promising results for a
decentralized computation, the best results are
obtained with a centralized approach were all the
data are, during the computation, centralized on the
same computer.
Before proceeding to the industrialization, additional
elements still need to be considered:
Filtering: depending on the number of simulations,
which have to be performed and the time constraint
on the DSA, additional contingency filtering could be
needed.
HPC aspects: All the IT aspects surrounding the
computation engines needs to be taken into account:
How are the data stored and handled? How to
minimize the power consumption of many parallel
simulations? How to set-up automatic backup
system?
Framework for TSOs collaboration in the field
of Security Analysis: TSOs need a framework to
collaborate. A single model of the whole ETN is
needed to perform Security Analysis. This model
must be automatically updated on the basis of the
available national models.
Definition of a Common Information Model (CIM)
for system dynamics: CIM is mature for definition
of static characteristics of transmission systems.
Similar approach for system dynamics, already
initiated by two members of the PEGASE consortium,
would help for model aggregation and consistency.
publications
A The following non-exhaustive list of publications
illustrates the numerous scientific advances
performed during the PEGASE project:
D. Fabozzi, T. Van Cutsem, “On Angle References
in Long-Term Time-Domain Simulations”,
Power Systems, IEEE Transactions on, vol.26, no.1,
pp.483-484, Feb. 2011.
D. Fabozzi, T. van Cutsem, “Assessing the Proximity
of Time Evolutions through Dynamic Time Warping”
Proc. IET Generation, Transmission & Distribution
(2011), 5(12), pp. 1268-1276.
D. Fabozzi, T. Van Cutsem , “Localization and
latency concepts applied to time simulation of large
power systems”, Proc. IREP Symposium on Bulk
Power System Dynamics and Control - VIII, Buzios
(Brazil), 1-6 Aug. 2010.
V. Savcenco, B. Haut, E. Jan W. ter Maten,
R. M.M. Mattheij, “Time domain simulation of power
systems with different time scales”, Proceedings
of Scientific Computing in Electrical Engineering
(SCEE) Conference, Toulouse, France, September
19-24, 2010.
V. Savcenco, B. Haut, “Multirate Integration of
a European Power System Network Model”,
Proceedings of 8th International Conference of
Numerical Analysis and Applied Mathematics,
Volume 1281, pp. 2037-2040, 2010.
B. Haut, V. Savcenco, P. Panciatici, “A multirate
approach for time domain simulation of very large
power systems”, HICSS 45 Proceedings,
pp 2125-2132, 2012.
fp7-pegase.eu
F. Pruvost, P. Laurent-Gengoux, F. Magoulès,
F.X-Bouchez, “Speed-up the Computing efficiency
of waveform relaxation for Power system Transient
Stability”, SC’11, Seattle, WA, USA, November 13,
2011.
F. Pruvost, T. Cadeau, P. Laurent, F. Magoulès,
F.-X. Bouchez, B. Haut, “Numerical Accelerations
for Power Systems Transient Stability Simulations”,
Proceedings of the 17th PSCC conference,
Stockholm, Sweden, 22-26 August 2011.
D. Fabozzi, A.S. Chieh, P. Panciatici, T. Van Cutsem,
“On simplified handling of state events in timedomain simulation”, Proceedings of the 17th
Power System Computation Conference (PSCC),
Stockholm, Sweden, Aug. 2011.
F.-X. Bouchez, B. Haut, L. Platbrood, K. Karoui,
“HPC for power systems in the framework of the
PEGASE project”, Proceedings of IEEE PES General
Meeting 2012, San Diego, CA, USA, 22-26 July 2012.
website
he following deliverables present the project
T
results for time domain simulation and may be
downloaded on the PEGASE website:
D4.1: Algorithm for simulation of large network
extreme scenarios.
D4.2: Prototypes and report on their simulation
performances.
D5.1: Modelling requirements for the ETN.
time domain simulation
Design: www.gayacom.fr. © Fotolia. Imprim’Vert printer.
…
time domain simulation
time domain simulation
Achievement 1: New generation
of ground-breaking algorithms
A power system is a complex dynamic process
displaying a series of possibly unstable phenomena.
Those phenomena are:
The loss on synchronism of generators
Unstable growing oscillations (of power, voltage, etc.)
Voltage instability
Frequency stability
Cascade trippings
All those phenomena can be intermingled and can propagate to the entire
interconnected system, leading to complex scenarios ending possibly to a
blackout.
To simulate the dynamic behaviour of the power system, an extended
electromechanical model (EEM) must be used. The EEM includes a
detailed representation of the generating units and their controllers.
The EEM has very tough mathematical properties. It is large (typically
5 times the static model, non-linear, stiff (mixing fast and slow variables),
oscillating, poorly damped and full of discontinuities.
The EEM requires a very robust integration algorithm: implicit,
simultaneous, A-stable and using a variable step size.
The Dynamic Security Assessment (DSA) of a power system consists in
simulation the system facing a series of incidents like short-circuit, line
switching or generating unit tripping.
DSA is today most of the time run off-line. It is used to understand
the dynamic behaviour of the system, to tune the parameters of the
controllers, to check the protection settings or to assess the stability of an
operating point, for the day ahead.
In case of well-known typical behaviour of the studied network, some
simplifications of the EEM can apply, for instance to measure the
distance to instability resulting from a known phenomenon (such as
voltage collapse). The resulting speed-up of the computation has allowed
implementing on-line phenomenon-oriented DSA.
In all other case, the accuracy of the EEM model must be as high as
possible and the entire ETN should be represented to track all kind of
possible unstable phenomenon.
Due to the change of paradigm of the European Transmission Network
(ETN) operation, the classical approach of the on-line security assessment
must be reconsidered. Today, the so-called (N-1) rule consists in checking
the existence of an acceptable steady state point after the tripping of each
line, one by one, without consideration for dynamics. This could be no
more sufficient as, when operating the system close to its stability limits,
the trajectory to the new steady state equilibrium point could be unstable.
For this kind of application, the computation speed is paramount.
The PEGASE target for time
domain simulation is very
ambitious
Simulating the whole ETN (the
size of the EEM is around 125.000
state variables).
Less than 15 minutes for an
off-line simulation where no
compromise is done on the
accuracy and much faster for an
on-line simulation where a tradeoff between accuracy and efficiency
applies.
Simplified simulation is usually
performed by replacing a detailed
model by a simplified one. The
drawback of this approach is
that two sets of models must
be maintained. The innovative
approach taken in PEGASE was
to use only one model for both
simulations and to introduce the
simplification in the numerical
scheme.
To achieve the required
performances, new algorithms
were needed. Different approaches
were considered:
Fine grain parallelization
approach for the function and
Jacobean evaluation. It allows
exploiting the new computer
architecture presenting a constant
increase of shared memory cores.
Advanced direct and iterative
linear algebra algorithms
dedicated to power system.
Achievement 2: Prototypes demonstrated on Pan-European systems
Improvement of time domain simulators
STATE-OF-THE-ART
New algorithms
IT aspect
OPENMP
PARALLELIZATION
MEMORY
OPTIMIZATION
SCHWARZ
METHOD
MULTIRATE
DECOMPOSITION
LOCALIZATION
SEQUENTIAL
OPTIMIZATION
LINEAR
ALGEBRA
UPDATE
HH4
Accuracy control
NUMERICAL
FILTERING
WAVEFORM
RELAXATION
LATENCY
EXPLOITATION
PARAMETER
TUNING
HYBRID
NORM
SELECTION & MERGING
Full accuracy prototype
Simplified prototype
DTS engine prototype
Domain decomposition methods allowing exploiting the new
parallel computers characterized by a reduction of their clock
frequency counter-balanced by a significant increase of the number
of cores:
> Schwarz method coupled with advanced preconditioning
techniques to exploit shared memory architectures;
> Waveform Relaxation algorithm to exploit distributed
computation architectures.
Multirate algorithm dedicated to power system to exploit the
strong localization of some events.
Localization techniques, which allows to automatically replace
components with negligible impact by linear equivalents.
A new step size control strategy dedicated to very large system,
which prevents missing some local instability.
All these algorithms have been developed and evaluated. For the
two targets considered (Full Dynamic simulation and Simplified
Dynamic simulation), the best mixes have been identified. These
mixes have allowed achieving very important speed-up:
The time needed for a detailed dynamic simulation has been
reduced by a factor 10 with respect to industrial simulators
available before the start of the PEGASE project.
It is now possible to replace N-1 static security analysis by
simplified dynamic simulations while respecting the on-line time
constraint.
A
Based on the research results of the
PEGASE project two time-domain
simulation prototypes have been
developed
The first one is the Full accuracy
prototype, which includes a new fine
grain parallelization, the best up-to-date
direct linear algebra and the new stepsize control.
The second one is the Simplified
simulation prototype which includes
the best up-to-date direct linear algebra
and the new localization technique. This
prototype being dedicated to security
assessment, the parallelization is
introduced at the contingency level and
not in the core of the computation engine.
These two prototypes use the same
model, which can be described by the
user through block diagrams. It allows
to include easily all the new models
developed in the framework of PEGASE
like wind turbines, wind farms and HVDC.
Generic models for wind turbines,
wind farms, and VSC HVDC have been
developed. The models can be adapted
to some FACTS devices as well. The
models are simplified to the extent that
they are capable of reproducing only the
phenomena affecting the power system
stability. They do not necessarily represent
specific control architectures or rely on
parameters of a particular wind turbine.
As a result the same model is capable
of simulating wind turbines of different
manufacturers or even different turbine
concepts or whole wind farms consisting
of any realistic number of wind turbines.
Most relevant testers: Transmission
System Operators (TSO)
To evaluate these 2 prototypes in terms
of performance and quality of results,
they were put in the hands of actual
users of that kind of tools. Number
of Transmission System Operators
participated in an intensive testing
framework: SO-UPS (Russia), TEIAS
(Turkey), HEP (Croatia), Transelectrica
(Romania), RTE (France), LITGRID (Lithuania).
Also participated ENERGOSETPROJECT
(Consultancy company in Russia) and Riga
Technical University.
Realistic test models of the European,
Russian and Turkish systems
In order to demonstrate the capability
of the prototypes to run large, real systems,
2 test models have been built.
The first one is an actual snapshot of the
IPS-UPS system, provided by the Russian
TSO (SO-UPS).
The second one is built upon a merging of
the load flow data of 2 systems: an actual
snapshot of the Turkish system and an
anonymous, noised but realistic model of the
grid of continental Europe. The energy mix of
each country is respected and typical dynamic
models are used for each kind of generator
(nuclear, hydro...), including standard speed
governors, AVR and PSS.
The network structure includes step-up and
load transformers to represent accurately
a broader range of phenomena (voltage
collapse...). Complex controls have also been
introduced: secondary voltage regulations,
4-loop PSS and complex devices models have
been included: HVDC LCCs and VSCs, SVCs,
wind farms.
This results in a huge system: 16000 nodes,
13000 lines, 9000 transformers,
3000 synchronous generators, 700 wind
farms,... The size of the mathematical problem
is 140000 variables.
It reproduces some characteristics similar to
the real European system, like weak damping,
slow inter-area oscillation modes between
West and East, around 0.3 Hz.
European grid-like model has been made
public for benchmarking purposes: it is fully
described in a paper submitted at ISGT 2012
Berlin, and downloadable from the PEGASE
website.
…
Thermal cascade leading to system splitting simulated
in full accuracy prototype
Frequency (Hz)
50.2
50.1
50.0
49.9
node F0201611
node E0268611
49.8
49.7
CPU time: 12 min 35 s
49.6
49.5
49.4
Time(s)
0
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100
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400
450
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A 400 kV line is tripped at the time t =1s. As consequences nearby lines
are overloaded and tripped by thermal protection.
System splits at FR-ES border at time t=6.18s.
Frequency in ES and PT part dips and when it reaches 49.5 Hz load shedding is
activated at time t = 48 s. At the same time 3x600 MW generating units are shut
down in FR area to restore power balance.
After frequency restoration interconnection branches between ES and FR
are closed causing successful resynchronisation at time t = 150s.
Voltage Collapse simulated
in Simplified Simulation Prototype
Detailed simulation simulation
Simplified simulation
V bus 1041 (pu)
0.98
0.96
0.94
0.92
0.90
0.88
0.86
0.84
Time(s)
0
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