ELEKTROTEHNIŠKI VESTNIK 79(5): 237-241, 2012 
ENGLISH EDITION 
 
Communication – control concept in the distribution power 
network with dispersed energy resources 
Jure Močnik
1
, Andrej Žemva
2
 
1
RC eNeM in Iskra Sistemi, Ljubljanska cesta 24a, Kranj  
2
Faculty of Electrical Engineering, Tržaška cesta 25, Ljubljana  
E-mail: jure.mocnik@iskra-mis.si 
 
Abstract. This paper describes a communication concept in the distribution power network with dispersed energy 
resources (DER), which regulates and controls the voltage profile in the power network. The communication 
concept is based on fast links between checkpoints on feeders and on DER. The advantage of this concept is 
establishing communication among all DERs, feeders and the area control center, which allows them to 
communicate with each other at any given time without any restrictions. Another advantage is the possibility of 
upgrading to the existing IEC 61850 standard. 
 
Keywords: IEC 61850, information and communication technology (ICT), dispersed energy resources (DER), 
smart grids, substations communication,  
 
1 INTRODUCTION 
The overall economic growth and behavior of the 
consumers has increased the energy consumption by 
some 1.7% per year over the period 1997-2007 which 
has increased electricity consumption by 32.8% [1]. 
This fact forces the world to improve the electric power 
grid and to increase the electricity production. This 
issue can be solved by connecting small wind, solar and 
hydro power plants, the so-called dispersed energy 
resources (DER), into the existing electric power grid 
on the middle (MV) and low voltage (LV) level [2]. 
These DERs unfortunately affect the power network 
reliability and network voltage-profile stability [3] 
which may seriously damage devices owned by the 
distribution utilities as well as users. 
In a power grid network without any DER, the 
problem with the network voltage profile was solved in 
distribution transformer substations where the voltage 
was equally controlled for all the feeders which were 
routed from one substation. This approach to network 
voltage-profile controlling is inappropriate in a power 
network with DER, because of different structures of 
the distribution system. The “old” power grid structure 
is designed in a way that on one side of the network 
there are electricity producers and on the other side 
there are consumers. This type of the network has many 
good qualities. One of them is that the voltage decreases 
quite linearly with the distance from the transformer 
station, enabling the electric power distributor to ensure 
that across the LV feeder voltage value doesn’t exceed 
the legally imposed limits. This process begins by the 
configuring transformers between the high (HV) and 
MV network, which is usually adjustable with on-load 
tap-changers (OLTC [4]) and ends with on MV/LV 
transformer. They are adjustable with off-circuit taps 
which are usually not used for everyday adjustments. 
The problem of the network voltage profile in 
distribution networks without DER is solved in the 
distribution transformer substation where the voltage 
control is the same for all the feeders routed from one 
substation. By adding DER to a LV and MV voltage 
distribution network, this procedure of controlling the 
network voltage profile is insufficient because of the 
uneven distribution of the active power on to one 
transformer feeder. 
In Fig. 1, a simple example of a network with DER is 
shown. In the power network there are three feeders 
which are subsets of a substation, they connect a 
different number of DER on different locations over the 
feeder. Every DER connected on the feeder linearly 
increases the voltage value along the entire feeder and 
represents a local extreme in the network voltage 
profile. 
 
Fig. 1. Voltage profile without any interventions 
 The graph in Fig. 1 shows the network voltage 
profile where it can be seen how the voltage varies with 
the length of the feeder. With the light grey line it is 
shown how the “classic” voltage profile looks. The 
voltage value is reduced from initial 1.1 to final 0.9 per 
 
Received December 4, 2012 
Accepted January 15, 2013 

238 MOČNIK, ŽEMVA 
 
unit (pu) which is acceptable in most countries. On the 
contrary, if DERs are included into the power network 
(feeder 2 and 3), the voltage value may rise from initial 
1.2 pu which is not permitted.  To avoid this scenario, a 
new concept of communication and control mechanisms 
in the LV and MV voltage distribution network is 
presented. 
2 CONCEPT 
The existing power network has a wide variety of 
qualities but unfortunately it also contains one negative 
feature – it does not receive any feedback from the MV 
and LV users. The solution is to establish a network of 
information and communication technologies (ICT) 
which will link together each of the elements, especially 
the elements of production, transmission, distribution 
and end-users of the electric power network.  
Every distribution network contains several levels of 
communication (real time, non-real time and time 
independent). The proposed concept consists of all these 
types and is based on the fast communication system 
between the multiple substations and the control center 
(Fig. 2).  
The structure of the example distribution system is 
shown in Fig. 2, where two types of communication 
lines - emergency and non-emergency (information) are 
applied. The non-emergency lines are required for 
sending measurement and the settings between the 
substations and the Area Control Centre (ACC) where 
the main monitoring takes place. This communication 
permits to supervise the exchange of the information. 
Due to the importance of the emergency lines they send 
crucial information for functioning of the distribution 
network between substations, intelligent electronic 
devices (IED) and advanced metering infrastructure 
(AMI), they get the highest priority in communication.  
This concept solves two key issues. The first is 
establishing the communication in distribution a system 
which improves the overall situation view, the 
optimization of the power network and also 
responsiveness of detection of any serious errors [5].  
The second issue is controlling the voltage profile in 
the entire distribution network. The idea to achieve this 
goal is to install a control box before each main feeder, 
user, and DER, which is for the time being composed of 
two separate components (embedded PC and 
measuring-controlling center), but the development 
proceeds in the direction of integrating both components 
into a single measurement-control device. This 
equipment is marked with a black square in Fig. 2 and 
as PCCI in Fig. 2. 
 One of the benefits of this structure is that it acts on 
the spot, which is convenient for meeting other 
conditions and requirements of distribution systems 
with DER [6]. All control boxes must contain 
specifications that should be: 
o Fast – the system should react as soon as possible to 
prevent damage to the remaining equipment. 
o Reliable – the system should work properly in 
abnormal states or even if the error occurs in this 
system. 
o Sensitive – the system should be able to detect the 
abnormal state, which exceeds the nominal 
permitted value. 
o Selective – the system should switch off only a 
defective part and thereby minimize the 
consequences of error. 
o Automatic – the system should react in combination 
with ACC to adapt network parameters. 
o Easy to install and maintain – the system should 
operate on principles “plug and play”.  
o Integration into the existing control system – the 
system should be compatible with the existing 
control system.  
 
 
Fig. 2. Communications in distribution network with DER 
For better understanding, we will call this IED - Point 
of Common Coupling Interface (PCCI). 
3 METHODOLOGY OF THE CONCEPT 
The proposed concept is demonstrated with the 
network shown in Fig. 2. Within this network, there are 
five different types of PCCI installed which manage 
specific tasks according to their position. Every PCCI 
can send and receive specific measurements and 
commands to/from another PCCI according to its 
requirements.  
The calculation of power and energy is based on 
equations (1) and (2), where the energy (E) is integral of 
power (P) over time (t). 
   
   
  
   
           (1)            
  ∫    
 
 
                        (2) 
To calculate the power, it must be considered that the 
voltage and current inside of alternating circuit are not 
in phase, therefore the root mean square (RMS) value of 
voltage ( 
   
) and current ( 
   
) should be considered, 
multiplied with power factor       ).  
Every network has the specific voltage profile [6] 
which is formed by the presence location of DER. Fig. 4 
shows how the network voltage profile looks like if 
there is a differently sized DER installed on it.  
Depending of the size of the currently delivered 
power, DER can be divided into four groups (inactive, 

COMMUNICATION – CONTROL CONCEPT IN THE DISTRIBUTION POWER NETWORK WITH DISPERSED ENERGY… 239  
 
minor, medium or major DER). Each of these groups 
has its own characteristics and impact on the network 
voltage profile which requires different solutions to 
manage it. 
In all cases, obtaining information is the same. Every 
PCCI makes its own arrays (3) of data, which consist of 
the day of the week, time of the measurement (1 minute 
interval) and measurement of specific parameter 
(power, current, voltage…), which stores the 1 minute 
average value. The information is now averaged to 
obtain the average value for each hour, day, working 
week and weekend by month and season. 
[
 
 
 
 
  
  
 
  
  
]
 
 
 
 
*                        *P = [
           
   
           
] (3) 
There are also data arrays which contain the maximum 
values of parameters in all of the mentioned averages. 
This is done to provide certain guidance in energy 
consumption of the consumer and to predict energy 
reserves calculated according to (4). In this case, P
all 
represents the entire power which is the sum of the 
actual use (P
use
) and power reserve (P
res
), which can be 
calculated with the power average of the last hour 
(P
avgH
) and the maximum value of power (P
maxH
) in the 
last hour of the month multiplied by 1.2. 
P
all 
= P
use
 + P
res 
= ((P
avgH 
+ P
maxH
) / 2) * 1.2           (4) 
When DER is connected to the power network but is 
inactive, or, there is DER connected, the controlling 
network voltage profile using the proposed 
communication concept is relatively simple. All that is 
required is that voltage value at the beginning and at the 
end of the feeder doesn’t fall or rise beyond the legally 
specified value. To ensure this, several PCCIs PLs and 
PCCI USRs are installed across the feeder, which 
provides precise information of the network status. 
Every PCCI sends current measurements to PCCI SUB. 
In this situation, there is no activity and PCCI RV sends 
this information to other PCCI. Unless measurement 
results are inside the prescribed limits, PCCI SUB 
calculates and sends setting to OLTC, which sets the 
appropriate transmission ratio and thereby determines 
the appropriate initial voltage.  
Similar to the previous case is the situation where 
minor DER [7] is connected to the network. The 
difference is that PCCI SUB detects PCCI RV on the 
network and calculates the new network situation 
depending on the measurement results of PCCI RV and 
with a simulation of equivalent circuit (Fig. 3). 
The situation becomes more complicated when the 
medium DER is installed into the network. In the third 
graph (Fig. 4, dotted lines) it can be seen how the 
network voltage profile would look like if there were no 
intervention (more than one third of users on feeder 1 
have an inappropriate voltage value).    
If the system reacted as in the previous case (OLTC 
reduces the initial value of the current), the users who 
are at the end of feeder 2 would have a lower voltage 
value as admissible. Here, we can see the most 
important value of the proposed concept. All the PCCIs 
which are installed across the feeder send the measured 
voltage values to the ACC control device. This device 
detects that the voltage of one PCCI is surpassed or 
unsurpassed and calculates new voltage parameters that 
would arise in the case of switching ratio in OLTC (the 
same as in the previous case). If these parameters were 
unacceptable, the device would find a ratio of OLTC 
which corresponds to the maximum value in the 
network and would calculate where the other feeder 
would drop out of the restricted limits (in our case is 
that PCCI PL). Then, this device finds the nearest PCCI 
(in our case PCCI RV) which has the proper value and 
disconnects feeder 2 from that point on. At the same 
time, PCCI PL sends decision to PCCI RV that it should 
connect the remaining feeder 2 into feeder 1. Now, all 
feeders have a suitable network-voltage profile at the 
expense of the feeder communication which was 
enabled by PCCI. 
 There is another case when the major DER or virtual 
power plant [8] is connected to the power network 
which causes that the network voltage profile exceeds 
tolerance limits. 
 
Fig. 3. Equivalent circuit for calculating a new situation in 
network 
The system acts in the same way as it in the previous 
cases, however the control device cannot set the proper 
ratio on OLTC, so the control device decides to 
disconnect part of feeder 1. This decision of the OLTC 
control device is sent to the PCCI TP on feeder 2 which 
examines the possible solutions and calculates the new 
electrical parameters.  
If DER on feeder 1 has enough power to supply part 
of the feeder, PCCI RV sends this information to PCCI 
TP which confirms this decision. This decision is also 
sent to PCCI SUB, which properly reacts and sends 
setting to OLTC. At the same time, PCCI RV 
disconnects the feeder and operates as a private or 
isolated power distribution network. If the voltage 
values were still outside the restricted limits, the PCCI 
RV would send this observation to the PCCI TP on 
feeder 1, which would disconnect the feeder from the 
primary distribution network and connect it back to the 
distribution network powered by DER. This 
disconnection and connection are realized by using of 
uninterruptible power supply (UPS) and the frequency 
synchronizers which ensure that switching is effected 
without any problem. Advantages of this concept and 
methodology are the improved surveillance over the 
distribution system, which consequently optimizes the 
network, particularly by reducing power reserves. The 

240 MOČNIK, ŽEMVA 
 
proposed concept also provides an updated structure of 
the power network clearing problems with the existing 
mounted DER.  
 
Fig. 4. Possible voltage profile according to the DER size  
4 PCCI STRUCTURE  
The proposed concept is presented with a prototyping 
system – PCCI, which consists of an appropriate 
hardware (Fig. 5) and software (Fig. 6) equipment. 
 
 
Fig. 5. PCCI hardware 
In Fig. 5, the main hardware components of PCCI and 
interfaces between them are shown. The link between 
components is a controller which works on the Ubuntu 
(linux) operation system. This controller has 
programmable digital inputs and outputs used for 
determine operations of bistable relays. These relays can 
handle various tasks depending on the type of PCCI. 
An important link, from the economic prospective, in 
the PCCI structure is the counter of the consumed or 
produced energy. This counter is upgraded in to a 
measurement system which can determine the electricity 
quality according to the SIST EN 50160 standard. All 
the obtained data are transferred via the controller to the 
disk (greater system reliability, data archiving…). Data 
are transferred to ACC and to end users over a 
communication module (Ethernet, GPRS or WiFi), 
which has direct access to the data stored on the disk, 
which can be accessed with an internet application. The 
communication between the VSM and the ACC is based 
on Ethernet, which uses a private network (PN) [9] or 
GPRS [10] based on the IEC 61850. 
 
Fig. 6. PCCI software 
In Fig. 6, the main components of the PCCI and 
interfaces between them are shown. Components are 
divided into two parts using a common shared memory. 
The first part of the software is responsible for 
collecting measurements from MC and sending 
commands to CC. The second part of the software is the 
application which behaves as a traffic light and sorts 
data according to the type of PCCI (ACC, PCCI TS, 
PCCI DER, PCCI USR, and PCCI SUB). When the data 
is properly classified, the application encodes the data 
into the type which is required for the IEC 61850 
standard and then it sends it to the pre-defined 
recipients.  
5 INTEGRATION INTO THE IEC 
61850STANDARD 
To raise the feasibility of the system, it has to be 
integrated with one of the existing standards. IEC 61850 
[11] is the standard for the power industry and is 
becoming the protocol of choice as utilities migrate to 
network solution for substations and beyond [12].  
The IEC 61850-7-420 [13] standard is composed of a 
number of predefined logical nodes which control their 
area. This standard is relatively new and it does not 
cover all the possibilities that a modern power network 
is capable of. One of the missing logical nodes (LN) is 
the logical node used, for controlling the network 
voltage profile. Therefore, in this paper we propose to 
establish a new LN which supports the controlling 
network voltage profile in the power network [14], it is 
called Voltage Profile LN (VP LN).  
In Table 1, presentation of the VP LN class logical 
note is shown. This LN contains all the information that 
is required for controlling the network voltage profile of 
an electric power network. One of the special features of 
this LN is its high activation priority which can be 
turned on or off with an alarm trigger. 
This concept of integration of new LN into IEC 
61850 brings another idea which now will not be 
discussed. There is already a standard which defines 
communication between substations (IEC 61850-90-1) 
and between the control center and substation (IEC 
61850-90-2). Therefor is missing only part which deals 
with the end-user and determines LN and 
communication between them. With the introduction of 
the remaining IEC 61850 standards, the family of 
standards will cover the entire energy sector, which 

COMMUNICATION – CONTROL CONCEPT IN THE DISTRIBUTION POWER NETWORK WITH DISPERSED ENERGY… 241  
 
should lead to simplification of communication in the 
distribution power network. 
Table 1: Proposed logical node (SCP Class) 
 
6 CONCLUSION 
Integration of the distributed energy resources is 
becoming an everyday occurrence, but unfortunately it 
affects the “old” stable and reliable electric power 
network. Despite the closed environment in which it 
operates it should be guaranteed that interferences 
caused by activation of DER will not affect the 
distribution network.  
This situation is solvable by using electrical and 
communication mechanisms which form the framework 
of ICI. With this network several benefits can be 
obtained such as supervision of the distribution network 
and access for all users to internet application where the 
user can monitor power consumption and specifies his 
settings. 
In this paper, a concept of communication 
mechanism to be used for controlling the network 
voltage profile and detecting problems which may 
appear in the distribution network with DER is 
presented. One of the special benefits of a concept is the 
possibility of integration into existing IEC 61850 
standard.  
Our future work will focus on moving the concept 
from the control area to a real power distribution 
network with several DERs and to extending logical 
nodes in the IEC 61850 standard, which will solve 
problems arising with introduction of DER. 
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Jure Močnik is a post-graduate student at the Faculty of 
Electrical Engineering, University of Ljubljana, from which he 
graduated in 2010. Since then he has been employed as a 
researcher with Iskra Sistemi and RC eNeM. His research 
interests include power-quality control, distributed power 
production and new concepts of the smart distribution 
network.  
Andrej Žemva is Professor at the Faculty of Electrical 
Engineering. His current research interests include signal 
processing, standardization, communications, system synthesis 
and optimization.