Abstract—Due of absence of grid supply. This solution

Abstract—Due to ever increasing power
demands developing countries like India is facing a major problem of power
deficit. Due to this demand there is tremendous pressure on conventional
sources for power generation. Hence, the demand for unconventional energy
resources has gained rapid pace in the present scenario. Therefore an attempt
has been made in this paper to provide an alternative solution for such real
life problems and to meet the customer’s demand during peak load time. In the
proposed approach of smart power system for home (SPSH) two different loads as
DC and AC load are considered and the results are simulated in MATLAB
environment. A storage battery and solar panel are synchronized to achieve
desired result.  The battery back-up
accounts for the power consumption in case of absence of grid supply. This
solution helps the customer by installing a back up battery system in tandem
with the grid supply and integrating renewable solar energy into a home power
supply system.

 

Keywords—Smart Power System for
Home (SPSH),MATLAB Simulation, Solar power, Power Grid, Battery.

I.  Introduction

 

Excessive usage of
the non renewable sources available in nature like coal, petroleum, natural gas
is causing its resources to being depleted. Therefore, soon there will be a
time when we will face a serious fuel shortage. Hence,it is essential at this
stage for reasonable and effective utilization of resources as an important
path which can deal with the global energy crisis. Integration of sustainable
sources of energy in distribution systems is gaining momentum ever since. In
deregulation and restructuring of power system, the penetration of distributed
resources is usually done at bulk load point but to generate small power likely
for houses it can be done individually provided that the resources are
available easily and at economical prices and on regular basis. For renewable
resources this is possible in case of solar and wind power generation. It is practically
impossible to set up windmills for individual customer for economical reasons
and also wind energy is not always regularly available. Also, wind mills cause
huge noise which is unbearable and hence it needs to be installed at far away
from the residential areas. Therefore, the solar power is found to be most
economical for local generation at a low scale and can be integrated with the
grid system to yield a Smart Home Power Supply to tackle the dependence on
renewable sources and power generation problems. But there are certain challenges to integrate the solar panels with
existing grid system and implementing of the smart grid as the output of distributed
systems keep on changing rapidly. But by installing a battery storage in
parallel this issue can be resolved and thus power usage can be optimized.

While designing solar array a major issue we face is of optimizing
output power to charge the battery completely. Thus we need to design this
system using MPPT (maximum power point tracker). An MPPT is a technique used
for extracting maximum available power from PV panels under certain conditions.
It obtains maximum available power from PV module by directing them to function
at the most efficient voltage (maximum power point). It works the best in cold
weather cloudy/hazy days and also when battery is deeply discharged.

For designing SPSH, MATLAB Simulink approach has been used. Simulink has been developed by Math Works. It is a graphical programming environment for modelling,
simulating and analyzing multi-domain dynamical systems. Its primary interface is a graphical block diagramming tool and a customizable set of block libraries. It offers tight integration with the rest of the MATLAB environment
and can either drive MATLAB or be scripted from it. Simulink is widely used
in automatic control and digital signal processing for multi-domain simulation and Model-Based Design. It supports system-level design, simulation, automatic code
generation, and continuous test and verification of embedded systems.

 

II.   Literature survey

 

It is a
challenging task to design and implement next generation smart grid as
intermittency inherently affects solar energy. This is due to rapid changes in
the output of the distributed system which results in many issues for the
distributor system operator with a large amount of photovoltaic devices
installed. Hence usage of battery storage has increased as it is used to help
in integration of solar power with grid. These systems are capable of absorbing
and delivering both real and reactive power with sub-second response times and
due to these capabilities, battery energy storage systems can mitigate such
issues with solar power generation as ramp rate, frequency, and voltage issues.
It can also focus on system stability and can also integrate energy storage
control systems with energy markets thus making the solar resources more
economical. The reference paper 4 provided an overview of challenges faced
while integrating solar power with electricity distribution system, technical
aspects of battery storage systems and the various modes of battery storage
systems in grid-tied solar applications.

 

The
reference paper 3 has proposed a configuration of a small capacity grid-connected solar power
generation system by a dual output DC-DC power converter and an inverter. To
configure this dual-output DC-DC power converter to convert the output voltage
of a solar cell array into two dependent voltage sources with multiple
relationships voltage doubler based topology can be used. The grid-connected
inverter has been configured by a dual-buck power converter and a full-bridge
power converter where a dual-buck power converter is switched at high-frequency
pulse-width modulation to generate DC voltage and full-bridge power converter
is switched synchronous with the utility voltage, to convert the four-level DC
voltage into AC voltage. The proposed solar power generation system generates a
sinusoidal output current in phase with the utility voltage.

Since past two
decades off-grid solar home systems (SHS) is being used which comprises of
solar panels, batteries, a charge controller and loads. But there are certain
issues with SHS that are cost, reliability, utilization and sustainability. The
reference paper 1 dealt with interconnection of SHS to form a micro grid of
connected prosumers and consumers that may offer a solution by employing smart
management of the power distribution amongst connected households that has
potential to ‘unlock’ latent generation and storage capacity and so improve
reliability and security of supply, reduce the system cost per head, and
ultimately levels the cost of energy supplied. These factors help to improve
the overall sustainability, efficiency and flexibility of SHS technology. This
paper thus represents the functionality of a Smart Power Management (SPM) that
seeks to distribute power across prosumers/consumers connected to a micro-grid
of interconnected SHS. By simulation of the SPM significant improvements in
reliability of supply within the micro-grid can be demonstrated. The power
management methodology utilizes algorithms applied to manage power flows
between customers.

 

III. Methodology

 

Fig. 3.1 shows the block diagram of the
proposed smart power system for home (SPSH), in this paper. Three different power
sources are synchronized in order to meet the load demand at customers end. The
various sources are solar panel, batteries and the grid supply. The solar power
and the battery output are interfaced and the resultant power canal so be fed
to the DC loads. Since the grid power is AC therefore, inverter circuit is used
to convert DC into AC of required voltage level at grid frequency. Static
switches are used to change the input supply to AC load as per the availability.
In day time, the solar power is fed to the load and in night the main power is
switched to the grid supply. However, the battery is always plugged to charge
through battery charger as shown in Fig.(I). Constant charging of the storage
battery allows the utilization of solar power in peak load hours. Interface
allows the connection between solar output and the battery such that power can
flow in one direction only. However, battery charger is a converter circuit
used to converter back ac in to dc for charging at desired level of voltage.2

Figure 3.1

 

 

The electrical
performance of solar system is demonstrated by their current-voltage (1-V) characteristics.
For solar system I-V characteristics represents the
infinite operating points under different operating condition of solar
radiation and the temperature. In mathematical formulations the commonly developed
terminologies are described as under:

a. Open circuit voltage (Voc)

b. Short circuit current (Isc)

c. Maximum power point (P mp)

d. Maximum power voltage (V mp)

e. Maximum power current (Imp)

(i) Open circuit
voltage (Voe): This is the maximum DC voltage developed across the output
terminals when no load is connected in the system. It is independent of the area
of the solar cell and is the indicator of the maximum voltage limit for solar
panel.

(ii) Short circuit
current (Ise): This is the maximum current that can flow through the solar
panel when load terminals are short circuited. In practice, it is directly
proportional to the solar irradiance. But, solar cells are inherently current
limited therefore; care is to be taken if they are shorted for testing purpose
with appropriate shortingdevice.

(iii) Maximum power
point (P mp): Under particular operating conditions of solar radiation and thetemperature,
the maximum value of the product of currentand voltage, in I-V characteristics,
indicate the maximumpossible power that can be drawn from solar system.
Thecorresponding point in I-V curve is known as themaximum power point.

(iv) Maximum power
voltage (V mp): The value of voltagecorresponding to maximum power point is
termed as the maximum power voltage.

(v)
Maximum power current (Imp): The value of currentcorresponding to maximum power
point is termed as themaximum power current. Alternatively, it can becalculated
as the ratio of the maximum power (Pmp) to the maximum power voltage (V mp).In
practice, specific equipment is used to determine thepoint on the I-V curve.
The load on solar cell can bea battery or AC load connected through inverter circuitry.Therefore,
the operating point on I-V curve is found to be loaddependent. Also, the
Maximum Power Point Tracking (MPTT) circuits are integral to the charge
controllers and interactive inverters.

For
mathematical formulations of the above parameters the following assumptions are
made,

ISC1=rated short-circuit
current (in ampere) at irradiance El.

ISC2 = short-circuit current
(in ampere) at new irradiance E2 .

E1 = rated solar irradiance
(W/m2)

E2 = new solar irradiance
(W/m2)

PmPl = rated maximum power
(watts) at irradiance E1.

Pmp2 = new maximum power
(watts) at new irradiance E2 .

ImPl = original maximum power
current (ampere) at irradiance E1

Imp2 = new maximum power
current (ampere) at new irradiance E2

A
solar cells, modules or arrays produce DC power. Thecurrent-voltage (T-V)
characteristic represents the electricalperformance of solar system. At a given
solar irradiance andtemperature an T-V curve represents an infinite number
ofoperating point for current and voltage pairs. . The rated TVparameters are
the basis for sizing and designing thephoto voltaic source and output circuits,
and for comparingwith field measurements on PV arrays.

Fig.
(II) shows the equivalent circuit diagram of the solar cell.

Figure 3.2 Equivalent Circuit of
Solar Cell

 

The
generalized characteristic equation of a solar cell, whichrelates solar cell
parameters to the output current and voltage,can be written as:

 

     (1)

 

 

Here,

I = current following through load
terminals,

IL = photo-generated current,

Io = reverse saturated
current,

V = load terminal voltage,

Rs= series resistance,

Rsh = shunt resistance,

n = diode ideality factor, which is ‘1’
for an ideal diode,

q = elementary charge

k = Boltzmann’s constant

T = absolute temperature

A solar cell
produces voltage and current output that varies with solar irradiance and
temperature. Therefore, the various parameters such as short-circuit current
(Isc), maximum power current (Imp), and maximum power (P mp) can be translated
at another level of irradiance and they are obtained as under,

         (2)

 

       (3)

 

      
(4)

 

Figure 3.3 Circuit Diagram of
Grid Tied Inverter (Part A)

 

 

 

 

Figure 3.4 Circuit Diagram of
Grid Tied Inverter (Part B)

Fig. 3 and 4 shows the equivalent
circuit diagram of the gridtied inverter. For grid-tied inverter the DC input
is the power generated by the solar system or the battery. As long as solar
supply is available it is used at its maximum level and the battery is made
standby. Two stage inverter circuit is used for stepping up the level of
voltage at desired value.

 

IV. Result

 

The design of
the proposed SPSH model will be simulated in MATLAB 2017 environment. Under all
conditions, three sources namely; grid power , solar panel and  battery will be synchronized at load terminal
to yield optimum power generation. The battery of voltage level equal to the
solar panel can be selected so that in every working condition, maximum power
can be derived from the solar panel and any other load requirement can be met
by the batteries. This will keep the voltage demand of load in balance.

 

Component
description

Specification

Solar Energy
System

Temp :35-40o
C
Irradiance
:0.5-1Kwh/m2/day

Battery

NickelMetal
Hydride (NiMH)
Charge
Discharge Efficiency :
60-90%

Grid Supply

250V(peak),50Hz

AC load

DC load
nominal :100V,400W
AC load
nominal voltage :
250V,305W,50Hz

Table 4.1: Component specification

As real time
variables cannot be accounted for in simulation environment softwares we cannot
obtain accurate readings. But ideal condition readings can be observed and
afterhand we can try to account for the variable irradiance and temperature
factors affecting power generation of solar panels.

Hence first we
observe the ideal condition working of PV modules in MATLAB as shown in figure
4.a below.

With battery
assumed to be in fully charged conditions and grid supply is connected after
the DC-AC inverter circuit ,the result of these connections made in Figure 3.3
can be explained by Figure 4.2 which shows current obtained from solar panel in
the synchronization process.

 

Figure 4.1: Solar Panel V-I characteristics

Figure 4.2: Current of solar panel during synchronization

Figure 4.3: DC load current during synchronization

The simulations
of AC and DC loads during synchronization and inverter currents are not yet
performed and these were few of theexpected results.

 

V.    Conclusion

 

The work done
in this paper for Smart Power Systems will be simulated in MATLAB environment.
This will help the consumers to meet their load demand by local power
generation. The SPSH will increase the efficiency of the system when the power
demand becomes more than generation capacity and the synchronization of DC
power from the solar cell and the battery will be achieved, and the grid power
is managed separately. Optimization of the power usage from solar panel,
battery and the grid supply needs to be considered in future works. The
efficiency of solar PV array can be improved for optimum better results.

 

VI. Application and
Future Scope

 

i.Cost reduction

ii.They improve the adeptness of
transmission lines

iii.Intelligent Appliances: Intelligent
appliances have capable of deciding when to consume energy based on customer
pre-set preferences. This can lead to going away along toward reducing peak
loads which have an impact on electricity generation costs. For example, smart
sensors, like temperature sensor which is used in thermal stations to control
the boiler temperature based on predefined temperature levels.

iv.Smart Power Meters: The smart meters provide two-way
communication between power providers and the end user consumers to automate
billing data collections, detect device failures and dispatch repair crews to
the exact location much faster.

v.Smart Substations: Substations are included monitoring and
control non-critical and critical operational data such as power status, power
factor performance, breaker, security, transformer status, etc. substations are
used to transform voltage at several times in many locations, that providing
safe and reliable delivery of energy. Smart substations are also necessary for
splitting the path of electricity flow into many directions. Substations require
large and very expensive equipment to operate, including transformers,
switches, capacitor banks, circuit breakers, a network protected relays and
several others.

vi.Super Conducting Cables: These
are used to provide long distance power transmission, and automated monitoring
and analysis tools capable of detecting faults itself or even predicting cable
and failures based on real-time data weather, and the outage history.

 

VII. References

 

1    
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interconnected solar home systems”,Global Humanitarian
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2    
Pawan Kumar, Iqbal Ali, M.S. Thomas, “Synchronising
Solar Cell, Battery and  grid supply for
development of smart power system for home “, India Conference (INDICON), 2015
Annual IEEE

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Wu, Kuen-Der Wu, Hurng-Liahng .Iou and Sheng-Kai Chang, “Small-capacity
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6     TrishamEsram,
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