General rights
Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright
owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.
Users may download and print one copy of any publication from the public portal for the purpose of private study or research.
You may not further distribute the material or use it for any profit-making activity or commercial gain
You may freely distribute the URL identifying the publication in the public portal
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Downloaded from orbit.dtu.dk on: Aug 10, 2022
Voltage and Frequency Control for Future Power Systems: the ELECTRA IRP Proposal
D’hulst, R.; Merino Fernandez, J.; Rikos, E.; Kolodziej, D.; Heussen, Kai; Greibel, D.; Temiz, A.; Caerts, C.
Published in:
Proceedings of 2015 International Symposium on Smart Electric Distribution Systems and Technologies (EDST)
Link to article, DOI:
10.1109/SEDST.2015.7315215
Publication date:
2015
Document Version
Peer reviewed version
Link back to DTU Orbit
Citation (APA):
D’hulst, R., Merino Fernandez, J., Rikos, E., Kolodziej, D., Heussen, K., Greibel, D., Temiz, A., & Caerts, C.
(2015). Voltage and Frequency Control for Future Power Systems: the ELECTRA IRP Proposal. In Proceedings
of 2015 International Symposium on Smart Electric Distribution Systems and Technologies (EDST) (pp. 245 -
250). IEEE. https://doi.org/10.1109/SEDST.2015.7315215
Voltage and Frequency Control for Future Power
Systems: the ELECTRA IRP Proposal
R. D’hulst
∗
, J. Merino Fern
´
andez
†
, E. Rikos
‡
, D. Kolodziej
§
, K. Heussen
¶
, D. Geibel
k
, A. Temiz
∗∗
, and C. Caerts
∗
∗
VITO, Unit Energy Technology, Boeretang 200, 2400 Mol, Belgium
Email: reinhilde.dhulst@vito.be
†
Tecnalia, Parque Cient
´
ıfico y Tecnol
´
ogico de Bizkaia. C/Geldo, Edif. 700, Derio (Bizkaia), Spain
‡
CRES, 19th km Marathonos Ave, 19009, Pikermi Attiki, Greece
§
IEN, Institute of Power Engineering, Gdansk Division, Mikolaja Reja 27,80-870 Gdansk, Poland
¶
DTU, Center for Electric Power and Energy (CEE), Richard Petersens Plads 322, 2800 Kgs. Lyngby, Denmark
k
Fraunhofer IWES, Division Systems Engineering and Distribution Grids, Koenigstor 59, D-34119 Kassel, Germany
∗∗
TUBITAK, MRC Energy Institute, METU Campus Ankara, Turkey
Abstract—In this paper a high level functional architecture
for frequency and voltage control for the future (2030+) power
system is presented. The proposal suggests a decomposition
of the present organization of power system operation into a
”web of cells”. Each cell in this web is managed by a single
system operator who assumes responsibility for real-time balance
and voltage control of the cell, minimizing the dependency
on inter-cell communication for secure system operation. The
web-of-cells architecture ensures overall system stability by a
combination of decentralized and distributed control patterns for
frequency and voltage control. In each control cell, the operator
maintains an accurate view on the overall cell state, based on
adequate monitoring capabilities, and ensures secure operation
by allocating and dispatching reserves located in the cell. Inter-
cell coordination provides for efficient system-wide management
and economic optimization.
I. INTRODUCTION
An inceasingly renewables-based and distributed energy
system as expected in Europe for the time beyond 2030
requires a revision of the power system operation principles
so that approapriate level of system security and resilience can
be maintained. he ELECTRA Integrated Research Programme
(IRP) [1] has been set-up by the European Energy Research
Alliance (EERA) partners in the joint programme Smart Grids
to research radical new control solutions for voltage and
frequency control in the 2030 power system.
In this paper a high level functional architecture for fre-
quency and voltage control for the future (2030+) power sys-
tem is proposed. Based on a number of scenario assumptions
regarding the 2030+ power system, a new control architec-
ture to better address the fundamental changes of the future
power system is presented. This work focuses on the high-
level functional control architecture related to the real-time
reserves activation currently performed by transmission system
operators (TSOs). Moreover, this work covers the correction
of real-time imbalances -hence frequency deviations-, as well
as the regulation of the grid voltage.
It is expected that due to the expected changes, further
elaborated in Section II, the future frequency and voltage
control can no longer be effectively managed in a TSO-centric
manner exclusively. Instead, a new approach is proposed,
that leverages innovative monitoring systems based on a fully
instrumented network, and dynamic autonomous distributed
control functions especially including distribution networks.
The focus of this work is on the development of new
frequency and voltage control schemes applicable to the func-
tional architecture developed within ELECTRA IRP. Reserves
must be contracted through a market party taking into account
(regulatory) requirements related to amounts, types, character-
istics, location, but this procurement itself is considered out
of scope for this work.
II. KEY TRENDS AND CONSEQUENCES
According to the European Commission Energy Roadmap
2050 for long-term plans [2], by the year 2030, around 25% of
the primary energy will come from RES and the percentage
will increase until up to 60% by 2050. In this context, the
ELECTRA consortium has indentified seven key trends and
assumptions for future power grids:
1) Generation will shift from classical dispatchable units
to intermittent renewables
Based on various reports, it is expected that by 2030,
between 52% to 89% of electricity production will
stem from RES [3], [4]. As a consequence, there is a
paradigm shift needed from generation following load
to load following generation. Also, an increased need
arises for balancing reserves activations to correct in
real-time the residual imbalances caused by forecast
errors and vari ability of intermittent generation and
loads. Even though on a global level these errors
may partially cancel each other out, they may cause
imbalances resulting in insecure power flows that may
eventually cause system instability.
2) Generation will shift from central Transmission System
connected generation to decentralized Distribution
System connected generation
The production share of RES connected to distribution
grids will increase. As a consequence risk of local
voltage problems and congestions have to be handled.
Also, the location of the sources of voltage issues and
balancing problems that require reserves activation,
will shift from central transmission system level to
distribution system level. Additionally, the resources that
can help to address voltage and balancing problems,
i.e. resources that can provide ancillary services
support, will partly move from transmissi on system
level to distribution system level. Therefore a central
system operator requires information from operators of
underlying voltage levels in order to dispatch efficiently.
Finally, the distribution and availability of resources
may vary significantly from location to location.
3) Generation will shift from few large units to many
smaller units
Electricity production units connected to the distribution
grid are typically much smaller than large central
power plants. Moreover, a transition is going on
within electricity production investments from an
”OPEX”-driven model towards a model that is more
”CAPEX”-driven, leading to more investments in
smaller production units as opposed to larger (classic)
production plants [5]. As a consequence, there will be
more places, and chances, where incidents (such as
generation outages) can happen, but each individual
incidents will have a smaller, local impact. Since
the production portfolio within the overall power
system will be subjected to changes throughout the
day (e.g. renewable generators are weather dependent),
the electromechanical time constant of the power
system will depend on the time of the day. Also, the
replacement of large synchronous generation and loads
by converter coupled generation and loads without
counteractive measures will lead to reduced system
inertia. This results potentially in much higher rate of
change of frequency (ROCOF).
4) Electricity Consumption will increase significantly
Due to the GHG emission reduction targets, there is
a drive towards the electrification of transport and
heating/cooling, resulting in an expected increase
of the electricity consumption of around 43% [6].
This i ncrease will be partially compensated by the
electricity consumption reduction resulting from energy
efficiency measures and targets. The consequences
are that the grid load will increase, increasing (the
risk for) congestion and local voltage problems. This
will in particular be the case in the distri bution grid,
where the majority of additional load resulting fr om
the electrification of heating (domestic and tertiary
sector) and transport will be situated, and where
as well the distributed RES generation is located.
Due to increased share heating/cooling consumption,
it becomes much more temperature-dependent and
thus less predictable and volatile. On the other hand,
these loads represent a large potential of flexibility
and storage in the grid. An increase in consumption,
increases the risk for coinciding consumption peaks,
in turn causing large power flows. Power peaks are
expected especially if consumers will be encouraged to
consume electricity following the production pattern of
renewable production.
5) Electrical storage will be a cost-effective solution for
offering ancillary services
According to the recommendations for a European
Energy Storage Technology Development Roadmap,
prices of (electrical) storage are projected to drop,
making distributed storage a competitive solution
compared to traditional resources for reserve
services [2], [7], [8]. Storage is well suited to
deal with continuous small up and down fluctuations
caused by intermittency and forecast errors. Moreover,
it has a larger flexibility range in both directions and
fast reaction time. Additionally, s torage at distribution
level can provide voltage support control thanks to
reactive power compensation and improve voltage
quality.
6) Ubiquitous sensors will vastly increase the power
systems observability
With the proliferation of distributed generation, and the
price of sensors and solutions set to fall dramatically
over the next few years, the inclusion of sensing and
monitoring systems is starting to make more economic
sense [9]. As a consequence there will be many more
measurement points at all voltage levels, such as Phase
Measurement Units, smart metering infrastructure, etc.
providing system operators the possibility to get a
holistic view on their grid.
7) Large amounts of fast reacting distributed resources
(can) offer reserves capacity
Vast amounts of flexible loads will be available at all
voltage levels (especially at the low voltage levels). The
same holds for local storage. Both of these have very
fast r eaction and ramp times. Additionally, both of these
will be connected through public ICT infrastructure
to grid operators and market parties offering there
flex-capabilities as a service.
III. CONCEPTUAL FUNCTIONAL ARCHITECTURE:
WEB-OF-CELLS
Based on the ELECTRA key trends as outlined in the
previous section, the present grid management structure and
organization for frequency and voltage control, with the TSO
being responsible for reserves activation in its Control Area, is
no longer effective [10]. The approach today, with the TSO as
single, central actor responsible has proven effective because
the resources for reserves needed to address frequency (or
balance) issues and voltage problems, are (mainly) located
centrally at the HV level. With the shift to the distribution grid
of the problem causes, as well as the reserves resources that
must be activated to resolve them, a new control architecture
may be more appropriate. Moreover, local imbalances leading
to insecure load-flows may stay unnoticed at system level, thus
a new, decentralized, approach for balance control might prove
to be more adequate.
In ELECTRA IRP, an architecture is proposed that goes for
a decentralized managed future, where the power system is
divided in grid units, called Control Cells, that provide local
balancing and voltage control. In this proposal, the EU power
grid is decomposed into a Web-of-Cells structure, illustrated
in Fig. 1. The Control Cells are defined as:
A group of interconnected loads, distributed energy re-
sources and storage units within well-defined grid bound-
aries corresponding to a physical portion of the grid and
corresponding to a confined geographical area.
Note that being able to operate in island mode is not a
requirement of a control cell. Each control cell has assigned
a Control Cell Operator who takes responsibility for the real-
time reserves activation and dispatching in his own cell ( i.e.
assuming responsibility similar to former TSO responsibility
in its Control Area). In each control cell, the Control Cell
Operator maintains an accurate view on the cell state, and
dispatches reserves located in the cell in a secure manner based
on his knowledge of the cell state. In principle, no global sys-
tem state information is required for this. In this way, a divide
and conquer way of tackling voltage and balancing issues is
implemented. Moreover, local problems are resolved locally,
in the cell (simple and effective control paradigm) in a fast
and secure manner, limiting complexity and communication
overhead (i.e. no bidirectional communication between DSO
and TSO is required for reserve activation). There is no need
to expose local problems at global system level. A control cell
operator is responsible for the balance within his own control
cell. A control cell is considered in balance when it is able to
follow the (day-ahead) consumption/generation schedule. For
maintaining that balance he can procure reserves from within
his cell but also cross cell border reserves from neighbouring
cells. Control Cells have adequate monitoring infrastructure
installed, as well as local reserves capacity enabling them to
resolve voltage and cell balancing problems locally (control
cells are dimensioned accordingly).
While the cell-based ’solve local problems in the cell’
approach is s imple and effective, it has the consequence
that global reserves activation optimization is disregarded.
Examples of such system-wide optimizations are:
• Economic optimization, by replacing (automatically acti-
vated) restoration reserves by more cost-effective restora-
tion reserves
• Imbalance netting, system-wide reduction of opposite
sign activations
Fig. 1. Schematic illustration of proposed ”Web-of-Cells” architecture
Therefore, the proposed control architecture will add an inter-
cell coordination control layer to support system-wide opti-
mized r eserves activation if the control cell state and system
state allows. It must be noted though that by allowing inter-cell
coordination, the local control cell balance will not necessarily
be completely restored by activating balancing reserves in an
adjacent control cell. Still, on a system-wide scale system
balance must be reached.
In the proposed web-of-cell based architecture, control
cell operators are responsible to contribute to containing and
restoring system frequency, as well as containing local voltage
within secure and stable limits. For this purpose, proposals for
frequency and voltage control within a web-of-cells system are
developed, and explained in the following sections. It must be
noted that by moving to a cell-based architecture, different
observables and control aims may be required. Therefore, a
sound cell-based architecture is more than the transpose of
existing practices from the present TSO to a control cell
operator.
IV. BALANCE CONTROL
Frequency deviations result from active power imbalances
between consumption/load/import and generation/export. Fre-
quency stability i s system wide issue. Nowadays frequency
control is designed as cascaded control from fast automatic
primary (containment) and secondary (restoration) control to
slower manual and economically optimized tertiary control.
The proposed cell-based architecture still applies the main
principles of Load-Frequency Control [11], and additionally
introduces a dedicated inertia control for limitation of rate of
change of frequency (ROCOF). These principles are however
applied at control cell level instead of at Control Area level,
an overview of the proposed mechanism is shown in Fig. 2.
As a result, the main control objective within each control
cell is to maintain the balance within the cell, and by this
indirectly restore the system frequency. Moreover, not every
cell-imbalance is visible through the frequency at system level,
Fig. 2. Overview of proposed balance control structure of a control cell
therefore it seemed more suitable to use the term Balance
Control instead of Frequency Control.
A. Inertia Response Power Control
Inertia response power is needed within the overall power
system in order to keep ROCOF due to active power changes,
e.g. caused by disturbances or load changes, within acceptable
limits. In todays power system, the ROCOF is limited by
inertial response power due to changes in the stored kinetic
energy in the synchronous generators, resulting in continuous
power exchanges with the grid that counteract frequency
changes. However, in the f uture power system two challenges
need to be tackled with regard to inertia response power
control: (1) Converter- coupled generation increases while ro-
tating generation decreases and (2), the generation mixes by
means of the ratio between rotating and static generation
will strongly vary during the day. Therefore situations could
occur where direct-coupled inertia response power, i.e. from
rotating machines, has to be replaced by inertia response power
provided by converter-coupled units or loads. This kind of
functionality should replicate the effect of inertia response
power of a synchronous generating unit to a prescribed level of
performance. The control objectives of inertia response power
control are:
1) Limitation of ROCOF to a predefined maximum value
2) Support frequency containment control (FCC) until FCC
is fully activated
The principles of the proposed control scheme are shown
in Fig.3. The inertia response power control functionality
of indirect or synthetic inertia could be activated/deactivated
by the Control Cell Operator. Therefore the Control Cell
Operator has to monitor and observe the inertia response power
capability to initiate appropriate actions depending on the
required inertia response power. The dimensioning of the re-
quired inertia response power should be coordinated with a.o.
the Frequency Containment Control and across Control Cell
boundaries. The functionality of inertia response power itself
depends on local frequency and rate of change of frequency,
therefore each unit/load involved in inertia response power
Fig. 3. Main principles of inertia control.
control automatically changes its active power contribution
or consumption depending on a predefined characteristic. The
basic requirement to be fulfilled is that inertia response power
is proportional to the negative time derivative of frequency.
It is assumed that an emulation of direct-coupled inertia is
not an absolute requirement. Also, alternative characteristics
could be implemented in converter-coupled units/loads which
are more suitable for them if they are not contradicting with
the requirements of power system control.
B. Frequency Containment Control
The goal of frequency containment control (FCC) is to
stabilize frequency deviation to a set safe band. This is
achieved by activating resources providing containment re-
serves automatically based on local fr equency measurements.
In case of a power imbalance the objectives are:
1) To support upstream control of inertia response power
control to keep the maximum dynamic frequency devi-
ation limit through sufficient fast activation of FCC
2) To keep the maximum steady-state frequency deviation
until downstream control actions take over to restore
system fr equency by means of subsequent balancing
mechanisms.
In todays power system FCC is predominantly provided by
conventional power plants. This results from existing market
rules, e.g. in Germany FCC has to be provided for a complete
week and with a minimum capacity of 1 MW power reserve.
This limits the potential contribution of units with a primary
source depending on the weather or with limited storage
capacity. Therefore a transition to a more flexible FCC is
proposed. Especially converter-coupled sources can provide
due to their high dynamics and fast response t imes a valuable
contribution. It has to be taken into account that energy
reservoir of converter-coupled units as e.g. battery units are
limited compared with conventional power plants. Therefore
it is advisable to develop a framework where every unit
(generation and load) is able to bring in its strengths based
on the technology characteristics. This offers the possibility
for an economic optimization through the distribution of the
FCC on different kind of generators or loads. As consequence,
