**3. Experiments and simulation results of the Energy Management System: operation scenarios**

The Energy Management System implies independent automatic decisions from a potential user's decisions. The developed microgrid is operational even without an Energy Management System, but it is not provided with automatic decisions which aim the control of the energy flows or connection/disconnection actions of the component elements. Consequently, it results in the energy management for the optimization of both the microgrid operation and beneficiary's income/benefit. Moreover, in order to demonstrate the functionality of this system, the following operating scenarios, available for the "Enable management—ON" state, are suggested.

*Operating scenario number I.* The distributed energy generation sources (wind energy conversion system, photovoltaic system), the battery storage systems as well as the connection to the low-voltage distribution grid are available. This operating scenario involves the variation of the meteorological parameters during the microgrid functioning. Also, a calculation step Δ*t* = 40 s is used, during which all the parameter values are maintained constant.

The first operating scenario, represented in **Figure 12**, considers two time moments when the meteorological parameters vary, respectively, *t* 1 —the moment when the solar irradiation drops and *t*<sup>2</sup> —the moment when the solar irradiation increases. These two time moments are established randomly by the user of the LabVIEW application.

**Figure 9** contains the block diagram of the Energy Management System concept designed for the islanded or interconnected operation of the microgrid with the national power system while **Figure 10** shows the graphical interface of the developed application related to the

**Figure 10.** The graphical interface of the developed application for the modeling and simulation of a small-scale

In addition to the LabVIEW environment, MATLAB was used as well by introducing a MATLAB script within the developed VI related to the Energy Management System. **Figure 11** shows a section of the main loop management, presenting a MATLAB residue code which was

microgrid design and simulation.

56 Smart Microgrids

microgrid and the related Energy Management System.

then implemented in the general LabVIEW diagram.

**Figure 11.** Section of the MATLAB script related to the LabVIEW Energy Management System.

**Figure 12.** The graphical interface of the developed application for the modeling and simulation of a small-scale microgrid and the related EMS. Operating scenario number I.

It is to be noted that at the first moment *t* 1 , the photovoltaic power plant lowers the power output from 26.28 to 20.36 kW due to a decrease of the solar radiation from 1000 to 800 W/m2 . Until then, there is no need to transfer any energy from the public electric grid. From this moment on, the generated power within the microgrid decreases, and a necessary input from the National Power System is needed (*Pgrid* = 911.5 W). At the second considered moment *t* 2 , the solar irradiance increases from 800 to 900 W/m2 . Therefore, the generated solar power increases from 20.36 to 23.28 kW, and the power input from the National Power System is no longer needed. Contrary to the situation before, after the moment *t* 2 , the excess energy production will be injected into the public grid.

As suggested by **Figure 12**, it is possible to fully ensure the load supply (20 kW) from the production of energy from renewable energy sources during the intervals (0; t<sup>1</sup> ) and (t2 , end of the simulation), while maintaining the batteries fully charged. Following the supply of the battery storage systems and of the end users, the excess available energy will be injected into the public grid (*Pgrid* = 1.6003 kW; *energy* = 1.8354 kWh). The power losses are also considered (related to lines and conductors and to the electronic power devices, respectively). It is noted that the Energy Management System decides to use the National Power System as an energy dump load while the excess energy production is injected into the public grid.

*Operating scenario number II.* The distributed energy generation sources (wind energy conversion system, photovoltaic system), the battery storage systems as well as the connection to the low-voltage distribution grid are available. In this case, the end users necessary energy is higher than the one considered in the first scenario (*Pload* + *Pload p* = 50 kW) and higher than the energy produced from renewable sources. This operating scenario involves the variation of the meteorological parameters during the microgrid functioning. Also, a calculation step Δ*t* = 20 s is used, during which all the parameter values are maintained constant.

*Operating scenario number III.* The distributed energy generation sources (wind energy conversion system, photovoltaic system), the battery storage systems as well as the connection to the low-voltage distribution grid are available. This operating scenario does not involve the variation of meteorological parameters during the microgrid functioning. A calculation step Δ*t* = 30 s is used, during which all the parameter values are maintained

**Figure 13.** The graphical interface of the developed application for the modeling and simulation of a small-scale

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1

of 15%, established by the Energy Management System. Until the moment *t*

microgrid and the related Energy Management System. Operating scenario number II.

system takes place in order to supply the end users. The battery discharges up to a safety limit

power from the public electric grid for the end users supply was equal to *Pgrid* = 27.11 kW. From this moment on, when the battery discharges, the power input from the National Power System decreases to *Pgrid* = 16.557 kW due to the energy transfer from the storage systems

The Energy Management System detects the unwanted discharge of the battery storage system

shows a new charging cycle of the considered storage systems and the complete load supply from renewable energy sources as well as from the electric public grid (*Pgrid* = 27.657 kW,

2

, the unwanted discharge of the battery storage

, when the 15% limit is reached. Thus, **Figure 15**

are established randomly by the user of the LabVIEW

1

, the necessary

constant.

(*Pbat* = 10.71 kW).

application.

As shown in **Figure 14**, at the first moment *t*

and stops its discharging at the moment *t*

**1** and *t* 2

*Ppv* = 26.284 kW, *Pwind* = 160 W). These two time moments *t*

The second operating scenario, represented in **Figure 13**, considers two time moments when the meteorological parameters vary, respectively: *t* 1 —the moment when the solar irradiation drops and *t*<sup>2</sup> —the moment when the location wind velocity increases. These two time moments are established randomly by the user of the LabVIEW application.

It is to be noted that at the first moment *t* 1 , the photovoltaic power plant lowers the power output from 26.28 to 20.36 kW due to a decrease of the solar radiation from 1000 to 800 W/ m<sup>2</sup> . Until then, the necessary power from the public electric grid for the end users supply was equal to *Pgrid* = 26.82 kW. From this moment on, the generated power within the microgrid decreases, and a larger necessary input from the National Power System is needed (*Pgrid* = 31.87 kW). At the second considered moment *t* 2 , the location wind velocity increases from 8 to 12 m/s. Therefore, the generated wind power increases from 450 W to 1.08 kW. The microgrid-generated power increases as well and consequently the power input from the National Power System decreases (*Pgrid* = 31.242 kW).

As suggested in **Figure 13**, it is possible to fully ensure the load supply (50 kW) from the production of energy from renewable sources and the electric public grid. The power losses are also considered (related to lines and conductors and to the electronic power devices, respectively). It is noted that the Energy Management System decides to use the National Power System as an energy generation source, while the microgrid energy production is completed by the public grid.

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It is to be noted that at the first moment *t*

58 Smart Microgrids

duction will be injected into the public grid.

the solar irradiance increases from 800 to 900 W/m2

the meteorological parameters vary, respectively: *t*

(*Pgrid* = 31.87 kW). At the second considered moment *t*

National Power System decreases (*Pgrid* = 31.242 kW).

It is to be noted that at the first moment *t*

tion drops and *t*<sup>2</sup>

m<sup>2</sup>

longer needed. Contrary to the situation before, after the moment *t*

1

output from 26.28 to 20.36 kW due to a decrease of the solar radiation from 1000 to 800 W/m2

Until then, there is no need to transfer any energy from the public electric grid. From this moment on, the generated power within the microgrid decreases, and a necessary input from the National Power System is needed (*Pgrid* = 911.5 W). At the second considered moment *t*

increases from 20.36 to 23.28 kW, and the power input from the National Power System is no

As suggested by **Figure 12**, it is possible to fully ensure the load supply (20 kW) from the

of the simulation), while maintaining the batteries fully charged. Following the supply of the battery storage systems and of the end users, the excess available energy will be injected into the public grid (*Pgrid* = 1.6003 kW; *energy* = 1.8354 kWh). The power losses are also considered (related to lines and conductors and to the electronic power devices, respectively). It is noted that the Energy Management System decides to use the National Power System as an energy

*Operating scenario number II.* The distributed energy generation sources (wind energy conversion system, photovoltaic system), the battery storage systems as well as the connection to the low-voltage distribution grid are available. In this case, the end users necessary energy is higher than the one considered in the first scenario (*Pload* + *Pload p* = 50 kW) and higher than the energy produced from renewable sources. This operating scenario involves the variation of the meteorological parameters during the microgrid functioning. Also, a calculation step

The second operating scenario, represented in **Figure 13**, considers two time moments when

output from 26.28 to 20.36 kW due to a decrease of the solar radiation from 1000 to 800 W/

from 8 to 12 m/s. Therefore, the generated wind power increases from 450 W to 1.08 kW. The microgrid-generated power increases as well and consequently the power input from the

As suggested in **Figure 13**, it is possible to fully ensure the load supply (50 kW) from the production of energy from renewable sources and the electric public grid. The power losses are also considered (related to lines and conductors and to the electronic power devices, respectively). It is noted that the Energy Management System decides to use the National Power System as an energy generation source, while the microgrid energy production is completed by the public grid.

. Until then, the necessary power from the public electric grid for the end users supply was equal to *Pgrid* = 26.82 kW. From this moment on, the generated power within the microgrid decreases, and a larger necessary input from the National Power System is needed

1

—the moment when the location wind velocity increases. These two time

2

production of energy from renewable energy sources during the intervals (0; t<sup>1</sup>

dump load while the excess energy production is injected into the public grid.

Δ*t* = 20 s is used, during which all the parameter values are maintained constant.

moments are established randomly by the user of the LabVIEW application.

1

, the photovoltaic power plant lowers the power

2

. Therefore, the generated solar power

—the moment when the solar irradia-

, the location wind velocity increases

, the photovoltaic power plant lowers the power

, the excess energy pro-

) and (t2

.

2 ,

, end

**Figure 13.** The graphical interface of the developed application for the modeling and simulation of a small-scale microgrid and the related Energy Management System. Operating scenario number II.

*Operating scenario number III.* The distributed energy generation sources (wind energy conversion system, photovoltaic system), the battery storage systems as well as the connection to the low-voltage distribution grid are available. This operating scenario does not involve the variation of meteorological parameters during the microgrid functioning. A calculation step Δ*t* = 30 s is used, during which all the parameter values are maintained constant.

As shown in **Figure 14**, at the first moment *t* 1 , the unwanted discharge of the battery storage system takes place in order to supply the end users. The battery discharges up to a safety limit of 15%, established by the Energy Management System. Until the moment *t* 1 , the necessary power from the public electric grid for the end users supply was equal to *Pgrid* = 27.11 kW. From this moment on, when the battery discharges, the power input from the National Power System decreases to *Pgrid* = 16.557 kW due to the energy transfer from the storage systems (*Pbat* = 10.71 kW).

The Energy Management System detects the unwanted discharge of the battery storage system and stops its discharging at the moment *t* 2 , when the 15% limit is reached. Thus, **Figure 15** shows a new charging cycle of the considered storage systems and the complete load supply from renewable energy sources as well as from the electric public grid (*Pgrid* = 27.657 kW, *Ppv* = 26.284 kW, *Pwind* = 160 W).

These two time moments *t* **1** and *t* 2 are established randomly by the user of the LabVIEW application.

**Figure 14.** The graphical interface of the developed application for the modeling and simulation of a small-scale microgrid and the related Energy Management System. Operating scenario number III—Section 1.

**Figure 16.** The graphical interface of the developed application for the modeling and simulation of a small-scale

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**Figure 17.** The graphical interface of the developed application for the modeling and simulation of a small-scale

microgrid and the related Energy Management System. Operating scenario number IV—Section 2.

microgrid and the related Energy Management System. Operating scenario number IV—Section 1.

**Figure 15.** The graphical interface of the developed application for the modeling and simulation of a small-scale microgrid and the related Energy Management System. Operating scenario number III—Section 2.

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**Figure 16.** The graphical interface of the developed application for the modeling and simulation of a small-scale microgrid and the related Energy Management System. Operating scenario number IV—Section 1.

**Figure 17.** The graphical interface of the developed application for the modeling and simulation of a small-scale microgrid and the related Energy Management System. Operating scenario number IV—Section 2.

**Figure 15.** The graphical interface of the developed application for the modeling and simulation of a small-scale

**Figure 14.** The graphical interface of the developed application for the modeling and simulation of a small-scale

microgrid and the related Energy Management System. Operating scenario number III—Section 1.

60 Smart Microgrids

microgrid and the related Energy Management System. Operating scenario number III—Section 2.

*Operating scenario number IV.* The distributed energy generation sources (wind energy conversion system, photovoltaic system) as well as the battery storage systems are available. This operating scenario does not involve the variation of meteorological parameters during the microgrid functioning. A calculation step Δ*t* = 20 s is used, during which all the parameter values are maintained constant. **Figure 16** shows the absence of the connection to the low-voltage distribution grid.

CIA\_CLIM - Smart buildings adaptable to the climate change effects, and project number PN-III-P1-1.2-PCCDI-2017-0254/ SMARTIRRIG - Innovative technologies for irrigation of agricultural crops in arid, semiarid and subhumid-dry climate, within PNCDIIII. The work was also financially supported by ANCSI, Romania, under the scientific Programme

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Moreover, I would like to thank Professor Nicolae Golovanov for his expert advice and also my colleague from the National Institute for Research and Development in Electrical Engineering ICPE-CA, Bucharest, Romania, Dr. Adrian Nedelcu, who provided the simula-

The author declares that there is no conflict of interest. Thus, there are no conflicts of interest

NUCLEU 2009-2015, Contract PN 09350201.

**Conflict of interest**

**Appendices and nomenclature**

Pcon power consumption

RES renewable energy sources

Address all correspondence to: andreea.elleathey@icpe-ca.ro

National Institute for Research and Development in Electrical Engineering ICPE-CA,

Pgen generated power

Pp power losses

Pstorage (Pst) stored power PV photovoltaic

SOC state of charge

**Author details**

Bucharest, Romania

Lucia-Andreea El-Leathey

EMS Energy Management System

MPPT maximum power point tracking

to disclose.

tion insight and expertise that greatly assisted the research.

The Energy Management System evaluates initially the necessary of the end users' power supply (*Pload* + *Pload p* = 50 kW), establishes that there is not enough energy for the complete supply and then connects only the priority or critical load (*Load P*) and not the standard one (*Load*). As seen from **Figure 16**, EMS attempts the reconnection, but it fails and supplies only the priority load.

At the moment *t* 1 , when the connection to the low-voltage distribution grid becomes available, EMS decides to use the National Power System as an energy generation source, while the microgrid energy production is completed by the public grid (*Pgrid* = 32.155 kW). Thus, the other consumers are also reconnected (*Pload p* = 40 kW) as indicated in **Figure 17**.

The time moment t1 is established randomly by the user of the LabVIEW application.
