I bob. Tadqiqotning nazariy asoslari Quyosh nergiyasidan foydalanish yo’llari

Kirish

I bob. Tadqiqotning nazariy asoslari

1. 
   Quyosh nergiyasidan foydalanish yo’llari
   
2. 
   O’zbekistonda quyosh energiyasidan foydalanish imkoniyatlari va muommolari
   
3. 
   Quyosh fotoelektr stansiyalari va ularning taxlili
   

II bob.

2.1 Avtonom quyosh fotoelektr stansiyalari

2.2 Quyosh fotoelektr stansiyalarining istemolchilari va ularning yuklamalari

2.3 Fotoelektr tiziniming energiya samarorligi oshirish yo’llari

2.4 Avtonom quyosh fotoelektr stansiyalarida moslashuvchan boshqaruv tizimi

https://uchitel.pro/%D0%BF%D0%BE%D1%81%D1%82%D0%BE%D1%8F%D0%BD%D0%BD%D1%8B%D0%B9-%D1%82%D0%BE%D0%BA/

http://www.matic.ru/clients/articles/harmonics-voltage-and-current-in-electrical-networks/

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Modelling and Power quality analysis

of a Grid-connected Solar PV System

S.V. Swarna Kumary*, V.Arangarajan Aman Maung Than Oo, GM Shafiullah, Alex Stojcevski

School of engineering, Faculty of science

Engineering and Built Environment

Deakin University, Waurn Ponds

e-mail: [e-mail]

Abstract— Increased concern about global warming coupled

with the escalating demand of energy has driven the

conventional power system to be more reliable one by

integrating Renewable Energies (RE) in to grid. Over the

recent years, integration of solar PV forming a grid- connected

PV is considered as one of the most promising technologies to

the developed countries like Australia to meet

the growing

demand of energy. This rapid increase in grid connected

photovoltaic (PV) systems has made the supply utilities

concerned about the drastic effects that have to be

considered

on the distribution network in particular voltage

fluctuations,

harmonic distortions and the Power factor for

sustainable

power generation. However, irrespective of the

fact that the

utility grid can accommodate the variability of load or

irregular solar irradiance, it is essential to study the impact

of grid connected PV systems during higher

penetration

levels as the intermittent nature of solar PV adversely effects

the grid characteristics in meeting the load

demand. Hence,

keeping this in track, this paper examines the grid-connected

PV system considering a residential

network of Geelong region

(38^◦.09' S and 144^◦.21^’ E) and explores the level of impacts

considering summer load profile

with a change in the level of

integrations. Initially, a PV power system network model is

developed in MATLAB/Simulink environment and the

simulations are carried out to explore

the impacts of solar PV

penetration at low voltage

distribution network considering

power quality (PQ) issues such as voltage fluctuations,

harmonics distortion at different load conditions.

Keywords—Renewable energies, Grid connected PV, level of

integration, MATLAB/Simulink

I.

INTRODUCTION

Most of the world’s energy is derived from fossil fuels

especially by burning coal as it has the substantial reserves

of conventional resources. Now a days, generation of

electricity via traditional methods is a challenging issue as it

contributes to greenhouse gas (GHG) emissions and in

fact the continuous usage of these fuels will outstrip the

ability to produce them [1- 3].In addition to these facts,

in developed countries like Australia the government has

abandoned plans to shut down some of most dirtiest coal-

fired power as part of the Contracts for Closure program

(CFC) to cut down their GHG emissions which amount to

about 1.5 % of GHG emissions, placing it among the top

20 polluting countries in the world. Hence, it is essential to

use alternate energy sources for power generation to meet the

growing demand and as well to conserve nature. In

response to climatic change Australia is developing a suite

of options aimed at delivering more efficient and sustainable

low emission generations. Interest in and production of

renewable energy in Australia has undergone substantial

growth since 2006[4] and among the RE sources, solar PV

has an unpredicted growth in power generation due to its

reliability in power conversion and cost effectiveness [5].

This unpredicted growth in PV market mostly has been

driven by the residential Grid connected PV systems-‘A

source of emission free power generation’[6].Grid-connected

photovoltaic (PV) power systems are energized by PV

panels which are connected to the utility grid via an inverter

can upload the excess energy to the grid during average or

low peak demands. Grid connected PV systems reduces the

line losses as the consumer power is generated close to the

load demand. In addition, grid connected system benefits the

utilities economically in delaying the line upgrades by

means of peak load reduction [7]. However, integration of

solar PV into grid has several impacts contributing to

operational problems due to its intermittent nature. Integrating

solar PV effects the functional operation of the power

system network like load/frequency control, load following,

unbalancing of voltage and current levels in the network

and PQ issues including voltage disturbance, poor power

factor, reactive power compensation flicker and harmonic

distortions. Though integration issues/effects are not the

major focus of this paper it is essential to study some of the

effects of the Grid connected PV system that has to be

analyzed for efficient power generation and distribution for

sustainable energy flow [6, 8-10]. Keeping this in view,

section II explains the effects of Grid connected PV systems

on the distribution network.

The main aim of this paper is to assess the effect

of penetration levels of a grid connected PV system

considering a residential low voltage distribution network in

Geelong. This basic study will explore the impacts of PV

integration on PQ at different solar irradiance levels and daily

load demand based on the summer profile with a change in

the level of PV integrations. Initially, a PV model is

developed using MATLAB and simulations are analyzed

considering different cases with reference to voltage and

harmonic analysis.

II.

EFFECTS OF GRID CONNECTED PV SYSTEMS ON

DISTRIBUTION NETWOK

As per AS4777 standard, the nominal AC voltage of

230V at the point of supply in single phase line to neutral

and 400 V in three phase line to line with a tolerance of

10% -6% and a frequency of 50Hz has to be

maintained at low voltage distribution network side [11].

Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014

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Grid connected PV system causes several operational

problems due to the intermittent nature of the solar PV

and the bidirectional power flow in accommodating the

excess power produced by the Solar PV during low load

demands. Hence, it is essential to study the impacts to

estimate the level of impact to maintain the As4777

standards. Following are some of the issues that have to

be considered in analyzing the performance of any grid

connected PV systems.

A.

Over Voltage/Reverse Flow

Excess power generated by the solar PV should be

properly accommodated by the grid for consistent power

flow to avoid the worst case scenarios like power outage.

For instance, the excess power generated by the solar PV

during lower demands should export the active power to the

grid which could result in over voltage or reverse power

flow affecting the utility grid and household appliances

leading to other safety and protection challenges.

B.

Voltage Fluctuations

The intermitted nature of the solar PV is one of

the reasons for voltage fluctuations in grid connected PV

systems Irregular solar irradiance caused by the passing

clouds, PV installation area, and the selected angle of

incidences/reflections also plays a major role in driving

the system to instability by means of voltage fluctuations.

This irregular fluctuations causes voltage flicker /flicker

noise, overloading problems, line losses and network losses

in the distribution network.

C.

Power factor

Grid operated PV systems usually operate at unity

power factor and the power produced by the PV units is

active/real power. In addition to this active /real power

supplied by the solar PV, the grid still has to still

supply the reactive power. During this process the

regular power flow of the system may have the adverse

effect due to the insufficient reactive power and may

decrease the power implying insufficient transmission.

D.

Harmonics

Harmonic distortion is one of the major effect that has

to be considered during the operation of grid connected

PV systems. Inverters used for conversion of DC current

to AC current, inject voltage harmonics and current

harmonics to the system and will result in power

harmonics. As the number of inverters increases the

system becomes more unstable and unreliable due to

the overheating in capacitor banks and transformers.

III.

GRID CONNECTED PV POWER SYSTEM NETWORK MODEL



Fig 1 shows the solar PV power system model developed

in MATLAB to analyze the voltage variations and the

Harmonics for the considered location in Geelong. To

investigate the various impacts of the proposed grid

connected PV system model a rigorous study has to

be done on the model considering level of solar

irradiance and load demand. This section describes the

proposed distribution network model developed in

MATLAB, the typical load profile, solar profile used

in analyzing the model. .





Fig.1 Solar PV Power system model.

.

Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014

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A.

Grid source

A three phase source block available in MATLAB is used

as a grid source in this network model. The power source

block specifications used in this analysis are base voltage

22kV, frequency 50 Hz, three phase short circuit level 100

MVA.

B.

Low voltage distribution transformer

A low voltage distribution transformer (DT) with star-

delta configuration is considered in this network model. The

DT specifications with respective to winding voltage ratio,

impedance ratio, and transformer rated capacity are

considered as 22 kV/400 V, 4.5%, and 100 KVA

respectively.

C.

2kv feeder

G. Load Profile

The Fig.2 depicts the typical residential daily load

profile of particular area in Geelong. As per load profile,

the daily peak load of each house is considered around

0.865 kW and similarly, minimum average load during

sun shine hours is considered around 0.488 kW.

Therefore considering 30 houses in each load group, the

total peak load, and minimum average load for each load

group is considered around 25.95 kW, and

14.64 kW respectively.

A 22KV feeder is used between the utility source and

the high voltage end of the transformer .The assumed

length of the line per phase is 1000m and with respect to

the positive sequence values of resistance, inductance, and

capacitance of the line are considered to be 0.1153 Ω/km,

1.05 mH/km and 11.3 nF respectively.

D. Solar PV power system

H. Solar profile

Fig. 2. Load profile.

A PV system with a combination of three different

groups of solar PV is used as a unique solar PV power

system in analyzing the proposed model. The rated capacity

of each group of solar PV system at Standard Test

Condition (STC) is 31.9 kW. Each PV system consists of

around 110 numbers of solar PV modules with

configuration of 5 solar PV modules connected in series per

string and 22 strings connected in parallel. The maximum

voltage (Vmp), and maximum current (Imp) of each solar

PV module is considered as 54.7 V and 5.58 A

respectively. In each group of solar PV system, a Voltage

Source Inverter (VSI) of rated capacity 50 KVA is

considered with the implementation of current control

scheme [12].

E.

Low voltage (400 V) distribution feeder

The above mentioned three solar PV groups are

connected in low voltage distribution feeder with a length

of 600 meters in distance. From the figure 1 it can be

noticed that group 1 (solar PV 1) is connected very close to

the transformer, group 2 (solar PV 2) is connected around

300 meters apart from first solar PV group, and similarly

group 3 (solar PV 3) is connected around 300 meters

apart from second PV group. The distribution feeder

specification parameters are like; resistance 0.646 Ω/km,

inductance 0.24 mH/km, and capacitance C=0.07 nF/km.

F.

Load group

Three load groups are considered in this model and

the maximum capacity of load in each group is assumed

to be around 25.95 kW which is equivalent to residential

load of 30 houses.

As per daily solar irradiance level during summer days,

for the selected location in Geelong, the daily maximum solar

irradiance level is considered around 871.5 w/m² at peak

sun shine condition and similarly, a minimum average solar

irradiance of 319.8w/m² is considered for this study.

IV.RESULTS AND DISCUSSION

A study of voltage and harmonics analysis has been

carried out for the developed PV power system network

model considering different solar irradiance and different

load conditions. Three different cases are used in analyzing

the voltage scenario with respective to the PV integration in

to the grid and two cases are considered in analyzing the

Total Harmonic Distortion (THD).

Case A: Voltage analysis with only Grid (without PV

integration)

The voltage analysis has been carried out in LV network

at minimum average load condition (14.64 kW) for each load

group. Initially, the simulation has been done by

considering only grid connected system (without PV

integration).Fig.3 clearly shows the behavior of voltage

level at three different bus nodes A1, A2, and A3. From the

simulation results it was observed that the voltage level at bus

node A1, which is close to the distribution transformer is

around 240V whereas the voltage at bus node A2, and A3 is

observed as 232 V and 220 V respectively. From this voltage

level graph it can be clearly stated that the voltage is in

decreasing order from bus node A1 to A3. The reason

behind the voltage drop is due to the increase in the

impedance values with respective to the line distance length of

line.

.

Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014

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Fig. 3

.

Bus voltage levels without PV int

e

Case B: Voltage analysis at maximum PV

g

minimum average load

The voltage analysis has been carried ou

t

Fig. 4

.

Vo

Case C: Voltage analysis at minimum PV

g

with peak load

The voltage analysis has been

minimum solar irradiance (319.8 W/m2)

(25.95 kW) conditions. As per voltage

Fig.5, it can be seen th at the vol

t

decreasing mode, from bus node

A

minimum solar irradiance, the power

g

each group of solar PV is around 9.7

5

only around 37% penetration with re

fe

load level. The voltage level at bus no

d

216 V whereas at bus node A2 and A1

i

and 236 V respectively which is same

results in without PV integration conditio

n

Fig. 5. Bus voltage levels with minimum PV integr

a

e

gratio

n

g

eneration with

t

at maximum

Solar irradiance (871.5W/m

2

)

(14.64 kW) conditions. The

indicates the voltage level i

n

results, the voltage level at

bu

246 V as compared to bus no

at A2 around 236 V respec

t

graph shown in Fig.4 that the

v

trend from bus node A1

t

irradiance, the power generati

o

PV is around 27.8 kW whi

c

considering for minimum av

e

kW. Due to this excessive g

e

flow causing voltage rise at

b

significant as compared to other

ltage analysis at maximum PV generation and minimum average loa

d

g

eneration

carried out at

and peak load

level graph in

t

age level is in

A

1 to A3. At

g

eneratio

n

from

5

kW which is

fe

rence to peak

d

e A3 is around

i

s around 220 V

as the case of

n

.

a

tio

n

and peak load.

Case D: Harmonics analysis

with peak load

The THD analysis is ca

r

irradiance (871.5 W/m

2

)

a

conditions. The level of v

o

distortions have been analy

z

at far end of feeder and sim

i

near to LV distribution tr

a

shows the harmonic analy

s

A1.From the results it can

voltage and current harm

o

around 3.19% and 3.84%

voltage and current harm

o

3.13% respectively. At ma

x

the PV generation of arou

n

of solar PV contributes h

i

node A3 as compared to

bu

of current harmonics are

compared to voltage har

m

and minimum average load

result analysis in Fig 4.

n

each bus node. As per the

u

s node A3 is high around

de at A1 around 232 V and

t

ively. As per voltage level

v

oltage level is in increasing

t

o A3. At maximum solar

on

from each group of solar

c

h is in excess level when

e

rage load of around 14.64

e

neration, the reverse power

b

us node A3 which is more

bus nodes.

d

.

at maximum solar irradiance

r

ried out at maximum solar

a

nd peak load (25.95 kW)

o

ltage and current harmonics

z

ed at bus node A3 which is

i

larly, at bus node A1 which is

a

nsformer. Fig 6 and Fig 7

s

is results at nodes A3 and

be seen that THD values of

o

nics at bus node A3 are

whereas at bus node A1 the

o

nics are around 2.37% and

x

imu

m

solar irradiance level,

n

d 27.8 kW from each group

i

ghe

r

harmonics level at bus

u

s node A1. The THD level

high in both cases as

m

onics level

Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014

4

. .

Fig. 6. THD analysis at bus node A3.

Fig. 7. THD analysis at bus node A1.

Case E: Harmonic analysis at minimum solar

irradiance with peak load

The THD analysis is also carried out at minimum

solar irradiance (319.8 W/m²) and peak load (25.95

kW) conditions. Fig 8.and Fig 9. shows the harmonic

analysis results and from the results it can be seen

that the THD values of voltage and current harmonics

at bus node A3 is around 2.26% and 2.91% whereas

at bus node

A1 it is around 1.18% and 1.35% respectively. The

results clearly indicate that the THD values are higher

at far end of the feeder (bus node A3) as compared to

transformer near bus node A1.From the above two cases

it can be clearly stated that THD values of current and

voltage distortions at minimum solar irradiation

condition is less compared to maximum PV generation

condition with peak load.

Fig. 8 .THD analysis at bus node A3.

Fig. 9 .THD analysis at bus node A1.

Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014

5

IV CONCLUSIONS

This study is developed a simulation model to analyze the

power quality attributed such as voltage fluctuations and

harmonic injection in the low voltage distribution network

with the integration of solar PV systems. From the voltage

analysis results the following conclusions are drawn.

Considering case‘A’ it can be seen that the voltage level

at far end of the feeder (bus node A3) is less as compared

to bus node which is near to the distribution transformer.

The level of drop in the voltage level at far end of the

feeder depends on the distribution network length or

distance and impedance level. From the case ‘B’ results it

can be stated that there is significant voltage rise at far end

bus node feeder as compared to other bus nodes due to

reverse power flow with excessive PV generation from

solar PV group at minimum load condition. Case ‘C’

results concludes that the voltage level at far end feeder of

bus node is less as compared to other bus nodes, which is

mimicking case ‘A’ results.

From the THD analysis results the following

conclusions are drawn. At maximum PV generation as well

as at minimum PV generation considering peak load

condition it can be observed that the level of harmonics of

voltage and current harmonics are high at far end feeder

of bus node as compared to bus node near distribution

transformer. The only difference is that the THD values of

current and voltage harmonics are in reduced level at

minimum solar PV generation as compared with the

maximum solar PV generation condition. This is due to

cumulative contribution of harmonics from more number of

PV inverters used during maximum solar PV generation

conditions. However irrespective of the case selected, the

maximum voltage deviation and the harmonics are within the

tolerance level as per the AS777 standard. This research

study will be helpful for utilities and customers in future to

estimate the level of impacts of PQ factors in distribution

network while integrating large scale PV in to the network.

In this context, future work will extended this analysis to

investigate the model with storage under higher

penetrations and lower load demands to optimize the

provision of power from PV system and support the

network for sustainable energy generation and distribution.

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https://www.researchgate.net/publication/286651421_Modelling_and_power_quality_analysis_of_a_grid-connected_solar_PV_system