Optimizations of Structure the Generators in Isolated Microgrids in
Russia
K. V. Suslov
Irkutsk State Technical University, 83, Lermontov str., Irkutsk, Russia
Keywords: Small Isolated Territories, Technical and Economic Features, Microgrid Concept, Development
Optimization Procedures.
Abstract: Many parts of Russia is not connected to centralized electricity supply by virtue of their geographical
position. A large number of distributed consumers which can be supplied with electricity only from the
autonomous energy sources and problems in the existing decentralized electricity supply system require that
the issues of development and optimization of electricity supply be urgently solved. Taking into account a
nonstationary character of electricity generation, presence of electricity storage devices, as well as stricter
requirements of consumers to power quality and reliability of electricity supply, we can say that operating
conditions of such systems and their control represent a difficult problem that needs to be studied. In the
paper the specific features of microgrid operation in different seasons of a year and different time of a day
are analysed, a set of problems related to control of operation are formulated and specific features of their
solving are discussed. The main principles of building the isolated power systems and control of operating
conditions are suggested. A case study is introduced and calculation results are discussed.
1 INTRODUCTION
In Russia there are many small isolated settlements.
They are supplied with electricity from diesel power
plants using expensive fuel delivered at large
distances. However, in many cases it is possible to
supply electricity to consumers on the basis of
renewable energy sources, such as wind turbines,
small hydropower plants, power plants based on
biomass, in particular by converting it into gaseous
or liquid fuel. The studies show that in the majority
of cases the use of renewable energy sources is
economically sound. Besides, for this purpose it is
also advisable to consider energy storage systems.
The power supply system to be formed in such a
way is a microgrid of specific structure. Because of
unsteady character of power generation, availability
of energy storage systems, electricity demand
management and also stricter requirements of
consumers to power quality and power supply
reliability development optimization of such power,
is not an easy problem that calls for further research.
2 ISOLATED POWER SUPPLY
SYSTEMS
About 60% of Russia’s territories, mostly in the
North, are not connected to centralized electricity
supply due to their geographical position
.
Many studies are devoted to technical and
economic assessment of electricity supply to isolated
consumers. The feasibility of connecting them to
centralized power source or using local small power
sources has been shown (Ivanova, 2010). Also the
areas of efficient centralized and decentralized
power supply are presented depending on electricity
tariffs and diesel fuel cost.
This approach makes it possible to identify at the
regional level the zones which require further
detailed estimation of applicability of one power
supply option or another in terms of their
technological feasibility and cost efficiency. Results
of the studies for different regions allow one to make
recommendations concerning prospective directions
of technological progress in the area of small-scale
energy, estimate feasible scales of implementation
and market of equipment for economically attractive
projects.
A large number of scattered consumers which
99
Suslov K..
Optimizations of Structure the Generators in Isolated Microgrids in Russia.
DOI: 10.5220/0004357800990104
In Proceedings of the 2nd International Conference on Smart Grids and Green IT Systems (SMARTGREENS-2013), pages 99-104
ISBN: 978-989-8565-55-6
Copyright
c
2013 SCITEPRESS (Science and Technology Publications, Lda.)
can be supplied with electricity only from
autonomous power sources and the problems in the
existing decentralized power supply system require
urgent development and optimization of power
supply to isolated consumers. An obvious way to
enhance energy efficiency of such areas is maximal
use of alternative and local energy resources.
The problems of power supply to isolated
territories are actively studied in different countries.
The models created for isolated microgrid also
include those intended to optimize the systems for
control of distributed generation, including, in
particular renewable energy sources (Arai, 2009;
Hugo Morais et al., 2010; Darvishi et al., 2010;
Martinez-Cid and O’Neill-Carrillo, 2010;
Hatziargyriou et al., 2009). Models of the kind make
it possible to optimize network operation by
different parameters.
3 PROBLEMS OF ISOLATED
POWER SUPPLY SYSTEMS
The above characteristics of isolated territories in
Russia make the systems of power supply to these
territories specific in terms of load flows and their
control in different seasons of the year and different
time of the day. Because of variable renewable
generation, presence of energy storage devices,
control of electricity consumption and ever growing
role of consumers in this process as well as higher
requirements of consumers to power quality and
reliability of power supply operation of such power
supply systems and their control represent a problem
that requires research.
Trends towards change in power supply - from
both sources and consumers are presented in Table.
1. These changes impose new requirements on
power quality, reliability and, hence, on problem
formalization.
Analysis of data presented in Table 1 allows the
conclusion that it is necessary to thoroughly consider
load and generation curves, and parameters of power
flows in the electricity supply system.
Analysis and control of isolated power supply
systems should solve the following problems:
study of the nonstationary character of power
supply system operation which is determined by
varying operating conditions of wind turbines
and small hydropower plants in different seasons
of the year and different time of the day;
optimization of long-term and short-term
operation of power plants with variable operating
conditions;
monitoring and control of voltage levels in
distribution network;
joint optimization of power supply system and
load-controlled consumers’ operation;
study of the emergency control problems to
provide system stability and survivability;
study and provision of reliability of power
supply to isolated territories.
Table 1: New factors in power supply in Russia.
Sources Consumers
New generation
technologies (wind
turbines, photovoltaic
panels, etc.)
New domestic appliances
with higher requirements to
power quality and reliability
of power supply
Energy storage devices
Specific requirements
imposed by industrial
consumers
Currently the studies on many of the foregoing
problems are under way (N.I.Voropai and co-authors
2010, 2012), etc.
4 MICROGRID EXPANSION
PLANNING AND CONTROL
The main objectives to be accomplished when
expanding the isolated electricity supply systems
are:
choice of the type and structure of generation
sources;
choice of configuration and parameters of
electrical network;
estimation of electricity supply reliability;
analysis of operating conditions.
Conditionally the problem of isolated microgrid
expansion planning and optimization can be
represented by the following structure (Tabl.2).
The main generating capacities to be included in
the structure of isolated electricity supply system
are: diesel generators, mini-CHP, energy storage
devices, wind turbines, solar panels ect.
The generation mix is chosen on the basis of
specific requirements of industrial and domestic
consumers, availability of energy resources.
Stochastic character of generation when using
renewable energy sources also has a great impact on
the choice of generation sources.
Table 3 presents the problems of operation
SMARTGREENS2013-2ndInternationalConferenceonSmartGridsandGreenITSystems
100
control in isolated electricity supply systems.
Table 2: Isolated supply system expansion planning.
Problems Requirements
Choice of type
and mix of
generation
sources
• Requirements imposed by
consumers
• Availability of fuel
• Capabilities of continuous fuel
supply
• Climatic conditions
Choice of
network
configuration
and
parameters
• Economic feasibility
• Geographical features of the
territory
• Choice of place for installation of
generation
Estimation of
electricity
supply
reliability
• SAIFI: System Average
Interruption Frequency Index
• SAIDI: System Average
Interruption Duration Index
• ASAI: Average Service
Availability Index
Since the isolated electricity supply system
includes active consumers, energy storage devices, it
operates like a virtual power plant. In this case the
virtual power plant has first of all technical purpose.
Table 3: Problems of operation planning and control.
Operation Problems
Long-term
planning
of
operating
conditions
• Adjustment of protection and
automatic systems
• Maintenance planning
• Consideration of seasonal consumption
and generation of electricity
• Reliability analysis
Daily
control of
operating
conditions
• Optimization of daily operating
conditions
• Reliability analysis
On-line
control of
operating
conditions
• State estimation
• Calculation of operating conditions
• Reliability analysis
Automatic
control of
operating
conditions
• Automatic control of system frequency,
voltage levels and loading of tie lines
5 PROBLEMS OF GENERATION
MIX OPTIMIZATION
According to the characteristic of isolated electricity
supply systems in Russia optimization of their
expansion requires consideration of generation units
that use fuel resources for electricity and heat
production and renewable energy sources (Voropai
and Styczynski, 2010). Due to variability of
consumer load curves and uneven electricity
generation from renewable energy resources account
is taken of energy storage devices of different types.
The representation of an isolated electricity
supply system relies on balances between generation
and load that are specified with certain discretization
of the week. Taking into account a relatively small
number of some types of generation units, their mix
is considered to be discrete.
Thus, the optimization problem of the isolated
electricity supply system expansion is represented as
the following mixed-integer linear programming
problem for each time instant of the day, taking into
account the level of discretization of power
generation and consumption curves:
n
i
giii
PuC
1
min
(1)
subject to constraints
n
i
egi
PP
1
;
(2)
maxmin
giigigii
PuPPu ;
(3)
ni ,1
(4)
where u - binary variable that takes a value of 0 or 1
to take into account the presence (1) or absence (0) of
power generation from the unit of a certain type i;
n - the number of time instants during the period
at discretization of power generation and
consumption curves;
K – the number of intervals in which the cost
characteristic of power generation by the units of
power plants is linearized;
e
P - total load of a system;
gi
P - power generated by the unit of type i.
By solving the formulated problem we:
1. Minimize the costs of electricity
production during the considered day by following
procedure:
for a given daily or weekly load curve,
for the given wind and radiation conditions,
calculate the wind and PV load using generic
models of wind and PV generators,
substrates the energy generated by renewable
from the daily (or weekly) load profile,
use the traditional generation to fully balance
OptimizationsofStructuretheGeneratorsinIsolatedMicrogridsinRussia
101
the needed power (energy).
2. If the generation form renewable energy
will be higher for some period of time then a given
daily (weekly) load profiles an electric energy
storage can be used for save the produced green
energy. This saved energy can be in-feed into the
system replacing the traditional generation and in
this case save the fuel resources.
6 CASE STUDY
The test system consists of:
Load - by 25 MW given by a load curve (in
this calculation for one week).
Wind generation - 10 MW
PV generation – 2,5 MW.
CHP generation - 25 MW.
The calculation will be done in 4 scenarios:
A. Basic mix of generation given below.
B. High PV generation – PV – 5 MW.
C. High wind generation – 25 MW.
D. High RES – PV-5MW, Wind -25 MW
Using wind and radiation profiles the wind and
PV generation can be computing in to account the
generic models of wind and PV systems.
The necessary generation mix for each hour is
finding by using of mentioned mixed-integer linear
programming solved. The priority of renewable
injection has been set.
For optimization parameters are investigated:
fuel cost, emission CO
2
, emission NO
x
.
The emission is calculated taking in to account
the equivalent emission for different technologies
(Ackermann et al., 2001).
The results of investigation for 4 scenarios are
given in the table 4. All data are presented in relative
units. For the basic scenario A the computations
show the maximum value of each of the indicators.
Table 4: Different variants of mix generations.
Scenario
Fuel
cost*
Emission Energy per week
CO
2
NO
x
CHP,
MWh
RES,
MWh
A 1 1 1 1526 794
B 0,78 0,95 0,95 1460 860
C 0,61 0,76 0,76 1143 1177
D 0,59 0,73 0,73 1085 1235
*fuel cost taking in to account transport cost
Figures 1-4 shows the share of the participation
of different generation in the covering of the load
profile for one selected week.
In general the investigation results strongly depend
on the local wind and radiation conditions. This
dependency also changes seasonally, and therefore it
is recommended to conduct a one year simulation.
Figure 1: Unit commitment for one week (Scenario A).
Figure 2: Unit commitment for one week (Scenario B).
Figure 3: Unit commitment for one week (Scenario C).
SMARTGREENS2013-2ndInternationalConferenceonSmartGridsandGreenITSystems
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Figure 4: Unit commitment for one week (Scenario D).
The input date for this simulation should come
either from local measurements or from global
weather data, e.g. RENO- Database, so that it
reflects the local conditions well. Also, the load
curve should correspond as closely as possible with
the local conditions.
The Figure 5 graphically presents the results for
the test cases A, B, C and D.
We can see that the best option in this case is a
scenario D, i.e, high increases of RES generation.
Anyway two observations can be done:
The emission factor does not change very much
with the increasing of RES generation;
doubling the RES decreases the emissions by
only about 25%
The SO
2
and NO
x
emissions are quite the same,
so it is enough to use one of this indexes
Figure 5: Diagram for different scenarios.
It is clear that a further increase in PV-generation
will not reduce the fuel cost of this test system, as
evident (Fig. 1-4) that the contribution - is small.
And it will not bring significant increase in results.
This is due to the climatic conditions and the length
of daylight. For the final decision the limiting factor
is the cost and the climatic conditions.
7 CONCLUSIONS
The systems of electricity supply to isolated areas
and populated settlements in Russia are rather
specific which affects the structure of microgrids.
The renewable can provide a crucial amount of
energy locally without very high cost of fuel. Also
the emission can be limited using renewable
generation. The problems of stabile and control of
operation of such isolated electricity supply systems
should be solved taking into account their specific
features. This will be done more specific in other
studies also taking into account the use of electric
energy storage.
ACKNOWLEDGEMENTS
The author gratefully acknowledge the contributions
of Z. Styczynski, P. Lombardi and Mrs Ge form
Otto-von-Guericke-University (Magdeburg,
Germany) for providing some technical calculations
which results are used in this paper.
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