Economic implications of microgrid operation dispatching using

Cuckoo Search Algorithm

ANDREEA GHINET

Research, Development and Implementation software Department

22nd Electronicii, 2nd District, Bucharest

ROMANIA

Abstract: As a method for analyzing fractals taking the source-network-load-storage into consideration, this

slide will show the improved cuckoo search algorithm, inspired by some cuckoo species by laying their eggs in

birds' nests host from other species. This improved algorithm can be applied for various optimization problems,

but in this paper it was applied only for coordinated energy management based on demand in distribution

networks. For short, the algorithm starts by initializing the data and the surplus sale conditions, each hour with

sale is a nest and all the PV powers are a population. Each egg is a load-storage-production-surplus profile.

This profile is randomly analyzed according to the optimal cost between sale or purchase or storage. The result

is an ordering of the intervals of the day at a optimum microgrid operating cost. This advance algorithm has

been integrated in Siemens PLC and a logic diagram is developed in this paper.

Key-Words: Cuckoo Search Algorithm, operation cost, microgrid, financial analysis

Received: September 23, 2022. Revised: August 17, 2023. Accepted: September 14, 2023. Published: October 6, 2023.

1 Introduction

One of the European Union's strategic goals is the

development of a new energy system that

incorporates climate change policy. The European

Commission's for Energy Development for 2050

[1], which was announced more than ten years ago,

set goals for promoting the transition to a more

reliable, durable, and carbon-free energy system. In

order to transition to future intelligent grids (future

Smart Grids) [2]-[5], remodeling will focus on

integrating massive amounts of renewable energy

sources, storage devices, and, in terms of workload,

a larger proportion of active and controllable tasks.

It will also integrate all necessary intelligent

management functions.

Modern society relies on a highly reliable electricity

supply system [6]-[9]. The current problems

regarding the availability of primary energy, the

aging of the transmission and distribution

infrastructure of electricity networks, the need to

install new sources of production (such as

renewable sources) and the sale of electricity

through wholesale markets constitute a challenge for

system operators in terms of security, safety and

quality [10]-[15]. That is why important investments

are needed for the development and modernization

of the electrical infrastructure, and the most

effective way to respond to social demands will be

the incorporation of innovative solutions,

technologies and network architectures.

Implementing three key goals for energy

generation—transition to intermittent renewable

sources, distribution network connectivity, and

adoption of advanced ICT solutions [16]-[19]for

decentralized energy management—has resulted in

evolution in the design of intelligent energy

transmission systems.

It is important to emphasize that all of these goals

can be connected to the idea of a multi-microgrid.

In addition to the classic infrastructure of a power

grid, which includes lines, transformers, protection

and automation systems, a microgrid includes smart

consumers, distributed generators, advanced fault

detection systems, intelligent switching equipment,

an advanced measurement infrastructure, backup

power supply, as well as a monitoring and control

system that includes IT products and with the help

of which the following objectives can be achieved:

 Isolation of the microgrid in the event of a

blackout in the SEN;

 Optimizing the cost of electricity, compared

to the one obtained on the electricity

market, using own resources, both electric

generators and storage sources, as well as

active consumers;

 Improving the reliability and quality of

electricity through the possibility of

reconfiguring the electricity network;

WSEAS TRANSACTIONS on COMPUTER RESEARCH

DOI: 10.37394/232018.2023.11.37

Andreea Ghinet

E-ISSN: 2415-1521

408

Volume 11, 2023

 Increasing efficiency and reducing

emissions of polluting substances by

integrating renewable energy sources, such

as photovoltaic panels, micro-hydro plants,

wind turbines;

2 Related work

A microgrid [22]-[25] can be developed within an

electric distribution network (RED), medium

voltage or low voltage.mOperators of microgrids

will run more microgrids because of the smaller

size.

The multi-microgrid concept is an emerging

architecture for a medium-voltage (MV) power

generation system made up of more active low-

voltage (LV) active wires, also known as micro-

reels, distributed generation units with controllable

tasks, and storage devices.

Distribution networks begin to transform from

passive networks to active networks in the sense that

decision-making and control are distributed, and

power flows bidirectionally [25]-[29]. This type of

networks with the participation of distributed

generation, renewable energy sources and storage

devices, offers solutions for new types of equipment

and services, each of which is required to comply

with common standards and protocols.

The classification of consumers and their control

within a microgrid can also contribute to flattening

the load curve either in isolated mode or in grid-

connected mode.

A commercial or industrial microgrid can become

isolated when the quality of electricity from the

main grid does not meet the requirements and can

even affect the quality of the electricity provided by

the microgrid [30]-[33]. The independent operation

from the main grid of the commercial/industrial

microgrid can be planned, e.g., at peak load when

the price of electricity absorbed from the main grid

is high.

A microgrid can also supply a small residential

consumer, i.e. a group of city houses. The

residential microgrid ensures a convenient and

efficient electricity supply system that is customized

according to the demands of consumers and the

distributed generators used. The generation of solar

panels and microturbines in cogeneration constitute

attractive distributed sources for residential

applications and commercial buildings.

3 Advanced load control

Depending on the geographical characteristics of a

remote area and the availability of resources of

various types such as: microturbines, windmills,

photovoltaic cells and gas turbines with low

emissions, can be used. A major difference in the

remote microgrid model [34]-[38] is that the

production must be sized to serve the entire load

with an adequate level of reserve capacity. In

addition, the dispersion of the load and the big

differences between the minimum and maximum

load of the microgrid make the selection technology,

the size of the DER a competitive thing. The

following methods are suggested to realize the

short-term or long-term energy balance of

withdrawn microgrids designed to overcome power

fluctuations introduced by intermittent generation

and variable load:

 Advanced power sharing and engagement of

units through a set of multiple generation

sources to select the right combination of

DER as a function of load variation.

 Using the optimal size of energy units

 Advanced load control

The management and control of a multi-microgrid is

provided by the hierarchical control architecture.

Each microgrid, managed by the micro-grid central

controller (MGCC), communicates with the

distribution management system (DMS) designed to

monitor and control the distribution network. The

implementation of a multi-microgrid concept

therefore implies the technical and commercial

integration of several micro-grids with upstream

distribution management systems and with the

operation of decentralized energy markets and

ancillary services.

One of the best-known microgrid pilot centers is the

internal network at the Illinois Institute of

Technology (IIT), Chicago-USA. For this project

IIT benefited from a grant worth $7 million in 2005

from the DoE; another $5 million was secured from

own funds and from private companies.

The project was based on 3 components:

 reliability (high degree of continuity in the

supply of electricity to consumers)

 own production (use of own sources from

IIT

 integration of new renewable sources) and

reduction of electricity consumption.

Interconnection methods and technologies:

WSEAS TRANSACTIONS on COMPUTER RESEARCH

DOI: 10.37394/232018.2023.11.37

Andreea Ghinet

E-ISSN: 2415-1521

409

Volume 11, 2023

 directly by means of an interconnection

switch

 by means of static switches

 using a power electronics based interface

a) Interconnection switch.

This solution is simple and cheap. The actuation

mode is slow, requiring between 3 and 6 periods to

achieve complete disconnection. The electrical

characteristics present on both sides of the switch

must match, making the operation of the microgrid

closely related to the operation characteristics of the

main grid. Thus, the use of the interconnection

switch requires the microsystem to have at least one

AC distribution system installed. to respect the

characteristics of the electrical network. The flow of

power through the common connection point cannot

be controlled.

b) Static switches.

In general, the construction of these types of

switches is based on the use of semiconductor

rectifiers in an anti-parallel configuration in order to

allow bidirectional power flow. Silicon Controlled

Rectifiers (SCR - "Silicon Controlled Rectifier") are

semiconductor devices that work like an electrically

controlled switch. These devices are more expensive

and much more complex in terms of operation than

classic switches. Conventional circuit breakers are

still commonly used with the aim of achieving

complete galvanic isolation. A Bypass switch is

introduced in the circuit with maintenance-related

functions. Semiconductor interrupt devices are

reliable and can be used for a high number of on/off

operations. They act much faster than conventional

switches (1/2 - 1 cycle less). Sometimes insulated

gate bipolar transistor (IGBT) systems can be used

as an alternative, as they tend to be faster than SCR

systems. Power transfer cannot be controlled in this

situation either. Conduction losses may occur in this

equipment.

c) Power electronics

This approach is the most expensive but also the

most flexible of all. First, it allows electrical

systems located on both sides of the connection to

operate with completely different characteristics.

Active and reactive power circulation can be

controlled. The connection and disconnection

response times are similar to those provided by

static switches, although in this case the response

speed also depends on other parameters, such as

dynamic performance (provided by the control

system, network topology and storage system

characteristics). However, in many cases it is

necessary to install a circuit breaker on the network

side in order to effectively physically separate the

microgrid from the main network. Also, the

presence of technology based on power electronics

leads to the appearance of energy losses at the time

of operation.

4 Cuckoo Algorithm

As a method for analyzing fractals taking the

source-network-load-storage into consideration, this

paper will analyze improved cuckoo search

algorithm.

However, in the conditions where the market would

be regulated for each fractal, such a concept would

be based on a standard price of the cluster and

meeting local consumption of new energy. This cost

is equal regardless of the time at which power

dispatching is done, because a first condition is that

a microgrid cannot buy from another microgrid and

sell in the network at the same time.

The result of the algorithm searches in multi-

microgrids demands or storage to respond to the

market cost and thus the demand with the offer in

the market was optimized.

Figure 2. Cuckoo Flow Chart

A microgrid, through its control system, must

ensure all or a subset of functions (for example:

energy supply, participation in the energy market,

black-start, provisions for auxiliary services, etc.)

[39], [40].

The dynamic of proposed architecture can respond

to the cost requirements of the market and was

analyzed [41].

WSEAS TRANSACTIONS on COMPUTER RESEARCH

DOI: 10.37394/232018.2023.11.37

Andreea Ghinet

E-ISSN: 2415-1521

410

Volume 11, 2023

5 Develop CS in microgrid PLC

A decentralized system can be applied with

difficulty because coordination problems can arise

between local systems, due to the large distances

between them. A minimum level of coordination

between the different control systems is required

[42], and this cannot be ensured using only locally

measured variables.

TIA Portal (Totally Integrated Automation Portal) is

a software developed by Siemens for the

programming of Siemens Step series PLC’s (S7-

1200, S7-1500, S7-300, and S7-400 families), which

integrates multiple development tools for

automation, such as: Simatic Step 7, Simatic

WinCC, and Sinamics Starter. There is also an

integrated simulator (PLCSIM), with which the user

can test their code by randomly giving values to

tags, values which can be modified by the user via

Force tables to resemble a certain scenario more

closely.

However, in order to simulate an actual PLC, a

more complex simulator can be used along TIA

Portal, called PLCSIM Advanced. This Simulator

uses an instance of a PLC in order to run and gives a

more realistic simulation.

After creating the project, the user can select from

multiple programming languages: FBD (Function

Block Diagram), SCL (Structured Control

Language), LAD(Ladder), and the following

communication protocols: Profibus, PROFINET,

and AS-I (Actuator Sensor Interface). Additionally,

communication modules are available for protocols

like CANOpen and Modbus.

In the case of a FBD project, the program is

comprised of predefined logic blocks are used in

networks, blocks that usually act as logic gates:

AND, OR, NOR etc. or timers (TON), counters

(CTU), limits (IN RANGE), formulas

(CALCULATE blocks) selectors (SEL) and many

others. Languages like SCL and more closely

resemble traditional programming languages,

relying on conditional structures (if, if else

statements) and loops (for, while).

Figure 3. PLC Network

Organization blocks are split into function, or FCs,

function blocks, called FB and DBs: data blocks.

The Organization Block1, called “main” plays an

essential role in the programming of the PLC: it

initializes all the other blocks and scans for their call

to run, with the exception of Cyclic Interrupt blocks,

which execute automatically on a preset time. The

main block is used cyclically: at the end of the

execution, it resumes the execution of the code in a

process that runs indefinitely as long as the PLC is

powered.

Figure 4. Program blocks

Real time monitoring of tags and variables is

possible by selecting “Online” and entering either

the “All tags” menu or the related networks,

provided the PLC is connected and active, or if there

is a running simulation

Figure 5. Initialization CS

Loading the program is also easier in TIA Portal:

the user can select “Advanced download to device”

and then load the program into the PLC after

selecting the IP addresses and devices.

WSEAS TRANSACTIONS on COMPUTER RESEARCH

DOI: 10.37394/232018.2023.11.37

Andreea Ghinet

E-ISSN: 2415-1521

411

Volume 11, 2023

Figure 6. Random Cukoo Search Logic Diagram

6 Conclusion

The dynamic of proposed architecture can respond

to the cost requirements of the market and was

analyzed in terms of power systems operation based

on a multi-microgrid optimization algorithm, which

allows the exchange of the load for an efficient and

safe operation.

As was mentioned, the optimization of energy

production was done under the conditions of respect

for robustness and adaptability.

In the future studies, there will be a more elaborate

analysis on cost and microgrid on real data from a

real microgrid source-network-load-storage and the

optimization based on improved CS will be

simulated and evaluated in the relevant

environment, thus being an update to the work.

Acknowledgement:

This work was funded by a grant through the

Norwegian Financial Mechanism 2014-2021, in the

frame of the Energy Programme in Romania, Focus

area in Calls 5 R&D, project ID: 2021/332805.

References:

[1]Marnay, C. (coord.) – “Microgrids 1

engineering, economics, & experience”, WG

CIGRE, USA, 2015

[2]Shahidehpour, M., McDonald, J.D., Asmus, P.,

Ravlndra, K., Burr, M.T., Roach, M. – “The

Maturation of Microgrids”, IEEE

Electrification Magazine, 2014

[3]Hu, X., Strbac, G., Usera, I., Zhang, Y., Chen,

H., Moreno, R., Farrokhabadi, M. - “Opening

the Door to Energy Storage”, IEEE

power&energy, vol. 15, no. 5, 2017

[4]Hirsch, A., Parag, Y., Guerrero, J.,“Microgrids:

A review of technologies, key drivers, and

outstanding issues”,ScienceDirect ELSEVIER,

2018

[5]Cañizares, C.A. (coord)“Microgrid Stability

Definitions, Analysis, and Modeling”, IEE-

PES, 2018

[6]Salomonsson, D., Soder, L., Sannino, A. - “An

adaptive control system for a DC microgrid for

data centers, ” - IEEE Trans. Ind. Appl., vol.

44, no. 6, pp. 1910–1917, Nov./Dec. 2008.

[7]Byeon, G., Yoon, T., Oh, S., Jang G. - “Energy

management strategy of the DC distribution

system in buildings using the EV service

model”, IEEE Trans. Power Electron., vol. 28,

no. 4, pp. 1544–1554, Apr. 2013.

[8]Dragicevic, T., Guerrero, J.M., Vasquez, J.C.,

Skrlec, D. - “Supervisory control of an

adaptive-droop regulated DC microgrid with

battery management capability”, IEEE Trans.

Power Electron., vol. 29, no. 2, pp. 695–706,

Feb. 2014

[9]Che, L., Shahidehpour, M. - “DC microgrids:

Economic operation and enhancement of

resilience by hierarchical control”, IEEE Trans.

Smart Grid, vol. 5, no. 5, pp. 2517–2526, Sep.

2014.

[10]Jin, C., Wang, P., Xiao, J., Tang, Y., Choo,

F.H. - “Implementation of hierarchical control

in DC microgrids”, IEEE Trans. Ind. Electron.,

vol. 61, no. 8, pp. 4032–4042, Aug. 2014.

[11]Lu X., Guerrero, J.M., Sun, K., Vasquez, J.C.,

Teodorescu, R., Huang, L. - “Hierarchical

control of parallel AC-DC converter interfaces

for hybrid microgrids”, IEEE Trans. Smart

Grid, vol. 5, no. 2, pp. 683– 692, Mar. 2014.

[12]Wang, B., Sechilariu, M., Locment, F. -

“Intelligent DC microgrid with smart grid

communications: Control strategy

consideration and design”, IEEE Trans. Smart

Grid, vol. 3, no. 4, pp. 2148–2156, Dec. 2012.

[13]Shaﬁee, Q., Dragicevic, Vasquez, T., J. C.,

Guerrero, J. M. - “Hierarchical control for

multiple DC-microgrids clusters”,IEEE

Trans.Energy Convers., vol. 29, no. 4, pp. 922–

933, Dec. 2014.

[14]Nasirian, V., Moayedi, S., Davoudi, A.,

Lewis, F. - “Distributed cooperative control of

DC Microgrids”, IEEE Trans. Power Electron.,

vol. 30, no. 4, pp. 2288–2303, Apr. 2015.

[15]Meng, L., Dragicevic, T., Guerrero, J.M.,

Vasquez, J.C., “Dynamic consensus algorithm

based distributed global efﬁciency optimization

of a droop controlled DC microgrid”, in Proc.

IEEE Int. Energy Conf., 2014, pp. 1276–1283.

WSEAS TRANSACTIONS on COMPUTER RESEARCH

DOI: 10.37394/232018.2023.11.37

Andreea Ghinet

E-ISSN: 2415-1521

412

Volume 11, 2023

[16]Lewis, F.L., Qu, Z., Davoudi, A., Bidram, A. -

“Secondary control of microgrids based on

distributed cooperative control of multi-agent

systems”, IET Gener. Transmiss. Distrib., vol.

7, no. 8, pp. 822–831, 2013.

[17]Lu, X., Guerrero, J.M., Sun, K., Vasquez, J.C.

- “An improved droop control method for DC

microgrids based on low bandwidth

communication with DC bus voltage

restoration and enhanced current sharing

accuracy”, IEEE Trans. Power Electron., vol.

29, no. 4, pp. 1800–1812, Apr. 2014.

[18]Behjati, H., Davoudi, A., Lewis, F. - “Modular

DC-DC converters on graphs: Cooperative

control”, IEEE Trans. Power Electron., vol. 29,

no. 12, pp. 6725–6741, Dec. 2014.

[19]Abhinav, S., Binetti, G., Davoudi, A., Lewis,

F.L. - “Toward consensus based balancing of

smart batteries”, Proc. IEEE 29th Annu. Appl.

Power Electron. Conf. Expo., 2014, pp. 2867–

2873.

[20Salomonsson, D. - „Modeling, Control and

Protection of Low-Voltage DC Microgrids”,

KTH Electrical Engineering, Stockholm, 2008

[21]Meng, L., Shafiee, Q., Ferrari-Trecate, G.,

Karimi, H., Fulwani, D., Lu, X., & Guerrero, J.

M. - „Review on Control of DC Microgrids and

Multiple Microgrid Clusters”, Denmark, 2017

[22]Unamuno, E., Barrena, J.A., „Equivalence of

Primary Control Strategies for AC and DC

Microgrids”, energies, 2017

[23]Dragicevic, T., Lu, X., Vasquez, J.C.,

Guerrero, J.M. - „DC Microgrids—Part I: A

Review of Control Strategies and Stabilization

Techniques”, IEEE Trans. On Power Elec., vol.

31, no.7, 2016

[24]Lopes, J.A.P., Moreira, C.L., Madureira, A.G.

- „Defining Control Strategies for Analysing

MicroGrids Islanded Operation”, EU Project

MicroGrids, 2002

[25]www.smartgrids.eu

[26]www.galvinelectricity.org

[27]Comisia Europeană – Vision and Strategy for

Europe’s Electricity Networks of the Future,

Platforma Tehnologică Europeană SmartGrids,

2006.

[28]Comisia Europeană – Strategic Deployment

Document for Europe’s Electricity Networks of

the Future, Platforma Tehnologică Europeană

SmartGrids, 2008.

[29]EPRI – The Integrated Energy and

Communication Systems Architecture, Vol. IV,

Technical Analysis, Electric Power Research

Institute, 2004.

[30] Hannan, M. A., Tan, S. Y., Al-Shetwi, A. Q.,

Jern, K. P., & Begum, R. A., Optimized

controller for renewable energy sources

integration into microgrid: Functions,

constraints and suggestions. Journal of Cleaner

Production, 256, 2020

[31] Cecilia, A., Carroquino, J., Roda, V., Costa-

Castelló, R., & Barreras, F., Optimal Energy

Management in a Standalone Microgrid, with

Photovoltaic Generation, Short-Term Storage,

and Hydrogen Production. Energies, 13(6),

1454, 2020

[32] . N. Liu, L. He, X. Yu, L. Ma, Multiparty

Energy Management for Grid-Connected

Microgrids With Heat- and Electricity-Coupled

Demand Response, IEEE Transactions on

Industrial Informatics, vol. 14, no. 5, pp. 1887-

1897, 2018

[33] Zhang, J., Cho, H., Mago, P., Energy

conversion systems and Energy storage

systems, book: Energy Services Fundamentals

and Financing, pp. 155-179, 2021

[34] Zhang, L. et al, Optimal Energy Management

for Microgrids with Combined Heat and Power

(CHP) Generation, Energy Storages, and

Renewable Energy Sources, Energies,

10(9):1288, 2017

[35] Kermani, M., et al, A Nearly Zero-Energy

Microgrid Testbed Laboratory: Centralized

Control Strategy Based on SCADA System,

Energies, 13:2106, 2020

[36] Ali, A., Liu, N., Li, H., Multi-Party Energy

Management and Economics of Integrated

Energy Microgrid with PV/T and CHP system,

Renewable Power Generation, IET 13(3), 2019

[37] Muqeet, H. A., Sustainable Solutions for

Advanced Energy Management System of

Campus Microgrids: Model Opportunities and

Future Challenges, Sensors, 22:2345, 2022

[38] Y. Achour, A. Ouammi and D. Zejli, Model

Predictive Control Based Demand Response

Scheme for Peak Demand Reduction in a Smart

Campus Integrated Microgrid, in IEEE Access,

vol. 9, pp. 162765-162778, 2021

[39] Redko, A., Redko, O., DiPippo, R.,

Geothermal energy in combined heat and

power systems, in book: Low-Temperature

Energy Systems with Applications of

Renewable Energy, pp. 225–259, 2020

[40] Fontenot, H., Dong, Bi., Modeling and

control of building-integrated microgrids for

optimal energy management – A review,

Applied Energy, Elsevier, vol. 254(C), 2019

[41] Mahmoud, M.S., Alyazidi, N.M., Abouheaf,

M.I., Adaptive intelligent techniques for

WSEAS TRANSACTIONS on COMPUTER RESEARCH

DOI: 10.37394/232018.2023.11.37

Andreea Ghinet

E-ISSN: 2415-1521

413

Volume 11, 2023

microgrid control systems: A survey,

International Journal of Electrical Power &

Energy Systems, 90, pp.292-305, 2017

[42] Korkas, C. Et al, Occupancy-based demand

response and thermal comfort optimization in

microgrids with renewable energy sources and

energy storage, Applied Energy, 2016

[43] Kermani, M., et al, Intelligent energy

management based on SCADA system in a real

Microgrid for smart building applications,

Renewable Energy, 171, pp.1115-1127

Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

Msc. Ec. Andreea Ghinet dealt with the analysis of

the hourly cost on peak and empty intervals. In

accordance with the electrical market, an oprim bill

was chosen and a financial analysis was identified

for the dispatching and sales conditions.

PhDs. Eng. Teodora Mindra developed the

Cuckoo Search Algorithm Flow Chart and

integrated the scientific algorithm with optimal

microgrid cost operation conditions, to increase

resilience, efficiency and intercommunication with

higher levels of control.

PhD. Eng. Luiza Ocheana took part in the

development of the control logic of the microgrid

solution: A controller developed by SIS SA using a

redundant Siemens hardware platform will allow

monitoring and control of system elements.

Communication configuration of microgrid between

the controller and the SCADA application is carried

out through the IP protocol ISO S7 (ISO-on-TCP),

that it uses the Ethernet infrastructure.

MsC. Eng. Emil Spiroiu developed a new diagram

that will be integrated into the logic already

developed, validated and running for 2 years,

automatically. The diagrams were implemented in

TIA Portal and based on them the forecast is made

for the training of a real microgrid, developed in an

office building: integrates solar panels with a totally

installed power of 120 kW, two storage units of

different capacities one with 40 kWh and other with

56 kWh.

Prof.PhD.Eng. Radu Dobrescu integrated the parts

of research, specialized literature, concept of interest

from R&D projects, future solutions, and a vision of

creative development, multiplication of this

microgrid control solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

This work was funded by a grant through the

Norwegian Financial Mechanism 2014-2021, in the

frame of the Energy Programme in Romania, Focus

area in Calls 5 R&D, project ID: 2021/332805.

Conflict of Interest

The authors have no conflicts of interest to declare

that are relevant to the content of this article.

WSEAS TRANSACTIONS on COMPUTER RESEARCH

DOI: 10.37394/232018.2023.11.37

Andreea Ghinet

E-ISSN: 2415-1521

414

Volume 11, 2023

Creative Commons Attribution License 4.0

(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

Creative Commons Attribution License 4.0

https://creativecommons.org/licenses/by/4.0/deed.en

_US