Modeling and Control of Grid Connected Photovoltaic System- A Review

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 3, March 2013)

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Modeling and Control of Grid Connected Photovoltaic System-

A Review Zameer Ahmad

1, S.N. Singh

2

1M.Tech Student,

2Senior Scientific Officer, Alternate Hydro Energy Centre,Indian Institute of Technology Roorkee

Roorkee, Uttrakhand (India) -247667

Abstract This review-paper focuses on the latest development of modelling and control of grid connected

photovoltaic energy conversion system. Modelling of

photovoltaic systems include modelling of SPV array, power

electronics inverter/converter based on

MATLAB/SIMULINK. This present control algorithm of a

three-phase and single phase grid-connected photovoltaic

(PV) system including the PV array and the electronic power

conditioning (PCS) system, based on the MATLAB/Simulink

software. It also discussed advances in MPP tracking

technologies, the synchronization of the inverter and the

connection to the grid.

Keywords-- photovoltaic; converter/inverter, MPPT,

detailed full modelling; MATLAB/simulink; grid connected

PV system.

I. INTRODUCTION

The world constraint of fossil fuels reserves and the ever

rising environmental pollution have impelled strongly

during last decades the development of renewable energy

sources (RES). The need of having available sustainable

energy systems for replacing gradually conventional ones

demands the improvement of structures of energy supply

based mostly on clean and renewable resources. At present,

photovoltaic (PV) generation is assuming increased

importance as a RES application because of distinctive

advantages such as simplicity of allocation, high

dependability, absence of fuel cost, low maintenance and

lack of noise and wear due to the absence of moving parts.

Furthermore, the solar energy characterizes a clean,

pollution free and inexhaustible energy source. In addition

to these factors are the declining cost and prices of solar

modules, an increasing efficiency of solar cells,

manufacturing technology improvements and economies of

scale [1].

The increasing number of renewable energy sources and

distributed generators requires new strategies for the

operation and management of the electricity grid in order to

maintain or even to improve the power-supply reliability

and quality. In addition, liberalization of the grids leads to

new management structures, in which trading of energy and

power is becoming increasingly important.

The power-electronic technology plays an important role

in distributed generation and in integration of renewable

energy sources into the electrical grid, and it is widely used

and rapidly expanding as these applications become more

integrated with the grid-based

Systems. During the last few years, power electronics

has undergone a fast evolution, which is mainly due to two

factors. The first one is the development of fast

semiconductor switches that are capable of switching

quickly and handling high powers. The second factor is the

introduction of real-time computer controllers that can

implement advanced and complex control algorithms [2].

Photovoltaic (PV) power supplied to the utility grid is

gaining more and more visibility, while the worlds power demand is increasing [3]. Not many PV systems have so far

been placed into the grid due to the relatively high cost,

compared with more traditional energy sources such as oil,

gas, coal, nuclear, hydro, and wind. Solid-state inverters

have been shown to be the enabling technology for putting

PV systems into the grid [4].

The photovoltaic (PV) field has given rise to a global

industry capable of producing many gigawatts (GW) of

additional installed capacity per year [5]. In 2010, the

photovoltaic industry production more than doubled and

reached a world-wide production volume of 23.5 GWp of

photovoltaic modules. Yearly growth rates over the last

decade were in average more than 40%, which makes

photovoltaic one of the fastest growing industries at

present. Business analysts predict that investments in PV

technology could double from 35-40 billion in 2010 to over 70 billion in 2015, while prices for consumers are continuously decreasing at the same time [6].

This review paper is organised as follows. In section II,

we described Evolution of grid-connected photovoltaic

system, in section III, we presented Modeling of

photovoltaic module with using of Matlab/simulink, in

section IV, discussed control techniques (power

conditioning system, MPPT) used in grid-connected

photovoltaic (PV) generation plants.



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The continuously decreasing prices for the PV modules

lead to the increasing importance of cost reduction of the

specific PV converters, in section V, we have discussed

inverters circuit which are being used in grid-connected

photovoltaic systems and in section VI, we discussed

discussion and conclusion.

II. EVOLUTION OF GRID-CONNECTED PHOTOVOLTAIC SYSTEM

A. The Past: The past technology of grid connected

photovoltaic system was based on centralized inverters,

which was interfaced to a number of modules. The modules

were normally connected in both series, called a string, and

parallel in order to reach a high voltage and power level.

This results in some limitation; such as the necessity of

high voltage DC cables between the modules and the

inverter, power losses due to a centralized MPP Tracking

(MPPT), mismatch between the modules and at last the

string diodes. If one of the modules in a string becomes

shadowed, then it will operate as a load with lower power

generation as a consequence. On the other hand, if the

modules are connected in parallel, the shadowed module is

still generating power, but the input voltage to the inverter

is inevitable lower due to the parallel connection [13]. A

third scheme is given in [7] [11], where each module is interfaced by a Generation Control Circuit (GCC). Hence,

an individual MPPT is assured for every single module,

which also lower the possibilities of hot spots.

According to [12], full shadowing of one PV-cell (in a

string of 160 cells) causes a temperature raise, inside the

cell, of more than 70 C above the ambient temperature,

whereas the non-shadowed cells only reach 22 C above the

ambient temperature (for an ambient temperature equal to

12 C). This is of great importance, because an overheated

cell rapidly decreases the modules lifetime.

B. The Present: The grid integration of RES applications

based on photovoltaic systems is becoming today the most

important application of PV systems, gaining interest over

traditional stand-alone systems. This trend is being

increased because of the many benefits of using RES in

distributed (aka dispersed, embedded or decentralized)

generation (DG) power systems. These advantages include

the favorable incentives in many countries that impact

straightforwardly on the commercial acceptance of grid-

connected PV systems [14], [15]. This condition imposes

the necessity of having good quality designing tools and a

way to accurately predict the dynamic performance of

three-phase grid-connected PV systems under different

operating conditions in order to make a sound decision on

whether or not to incorporate this technology into the

electric utility grid [16].

The present technology, which is a hot research topic in

Germany, is the string-inverter [17], [18]. String-inverters use a single string of modules, to obtain a high input

voltage to the inverter. However, the high DC voltage

requires an examined electrician to perform the

interconnections between the modules and the inverter.

On the other hand, there are no losses generated by the

string diodes and an individual MPPT can be applied for

each string. Yet, the risk of a hot-spot inside the string still

remains.

The AC-Module, where the inverter is an integrated part

of the PV-module, is also an interesting solution. It

removes the losses due to mismatch between modules and

inverter, as well as it supports optimal adjustment between

the module and the inverter. Moreover, the hot-spot risk is

removed. All this together; a better efficiency may be

achieved. It also includes the possibility of an easy

enlarging of the system, due to the modular structure. The

opportunity to become a plug and play device, which can be used by persons without any education in electrical

installations, is also an inherent feature [13].

III. MODELLINGOF PHOTOVOLTAIC SYSTEM

A. Modelling Of Photovoltaic Module/Array

The photovoltaic module is the result of associating a

group of photovoltaic cells in series and parallel, with their

protection devices, and it represents the conversion unit in

this generation system. The manufacturer supply PV cells

in modules, consisting of NPM parallel branches, each with

NSM solar cells in series shown in Fig. 1.

Fig. 1. Equivalent circuit of a PV array.

Although the mathematical and simulation photovoltaic

modules development began time ago, improvements of

these models are analyzed and presented continually. One

of the objectives of this study is a review of those existing

methods and models.



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M. G. Molina and P. E. Mercado presented the detailed

mathematical model that predicted the power production of

the PV generator becomes an algebraically simply model,

being the currentvoltage relationship as given in equation (1).

(1)

Where: IA: PV array output current

VA: PV array output voltage

IPh: Solar cell photocurrent

IRS: Solar cell reverse saturation current (aka dark current)

q: Electron charge, 1.60217733e19 Cb A: PN junction ideality factor, between 1 and 5 k: Boltzmann's constant, 1.380658e23 J/K TC: Solar cell absolute operating temperature, K

RS: Cell intrinsic series resistance

RP: Cell intrinsic shunt or parallel resistance

The photocurrent IPh for any operating conditions of the

PV array is assumed to be related to the photocurrent at

standard test conditions (STC) as given in equation (2).

(2)

The proposed model used theoretical and empirical

equations together with data provided by the manufacturer,

and meteorological data (solar radiation and cell

temperature among others) in order to accurately predict

the IV curve. The three-phase grid-connected PV system was simulated, under changing solar radiation conditions

while maintaining the cell temperature constant at 25 C in

MATLAB/simulink and validated the obtained result

experimentally [16].

S. Rustemli, F. Dincer, [19] Presented an accurate

photovoltaic module electrical model and demonstrated in

Matlab/Simulink for a typical Lorentz LA30-12S

photovoltaic panel. Such a generalized PV model was easy

to be used for the implementation on Matlab/Simulink

modeling and simulation platform. Especially, in the

context of the Sim Power System tool.

Simulation results showed that a photovoltaic panel

output power reduces as module temperature increases.

This situation was shown with Matlab/Simulink graphics.

There are lots of variety cooling systems for photovoltaic

panels. These systems may increase efficiency of panel

depend on the weather conditions.

F.Bouchafaa et al. [20] presented their work in the

model with two diodes as shown in figure 2.

Fig.2. Model of a photovoltaic cell with two diodes

The current generated by the module is given by

equations (3)

(3)

Where V and I represent the output voltage and current

of the PV; q is the electronic charge; Iph corresponds to the

light-generated current of the solar array. Is1, 2 represent

the current saturation of the two diodes; A1, 2 is ideality

factor of the junction of D1 and D2, K the Boltzmanns constant, T the cell temperature.

Altas, and Sharaf, [21] presented a model as shown in

Fig. 3. The solar cell is modelled as a current source. Iph,

the photovoltaic current is proportional to the ambient

irradiance level and to the temperature of the panel. To

allow for losses, a series (Rs) and parallel resistance (Rp)

are commonly included in the circuit. In this model, the

parallel resistance was neglected in order to simplify the

model.

Fig. 3. Model without parallel resistance

Output voltage is given by equation (4)

(4)

The curve fitting factor, A, was adjusted so that at rated

input values of temperature and irradiance the datasheet

values of output were obtained as model outputs. The same

approach was taken to obtain the temperature and

irradiance correction coefficients. Model had a correct

varying input temperature response, but irradiation

dependences could not be correctly set.



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Huan-Liang Tsai et al. [22] presented a generalized PV

model which was representative of the all PV cell, module,

and array had been developed with Matlab/Simulink and

been verified with a PV cell and a Commercial module

shown in Fig.4.

Fig. 4. Equivalent circuit models of generalized PV.

The proposed model takes sunlight irradiance and cell

temperature as input parameters and outputs the I-V and P-

V characteristics under various conditions. This model had

also been designed in the form of Simulink block libraries.

The masked icon makes the block model more user-

friendly and a dialog box lets the users easily configure the

PV model. Such a generalized PV model is easy to be used

for the implementation on Matlab/Simulink modeling and

simulation platform. Especially, in the context of the

SimPowerSystem tool, there is now a generalized PV

model which can be used for the model and analysis in the

field of solar PV power conversion system. A model of PV

module with moderate complexity which includes the

temperature independence of the photocurrent source, the

saturation current of the diode, and a series resistance was

considered based on the Shockley diode equation.

B. Modeling Of Converter/Inverter

For grid-connected PV applications, two hardware

topologies for MPPT have been mostly studied worldwide,

known as one-stage and two-stage PV systems.

M. G. Molina, and P. E. Mercado, [16] selected to model

the two-stage PV energy conversion system. They

including a dc-dc converter (or chopper) between the PV

array and the inverter connected to the electric grid various

control objectives are possible to pursue concurrently with

the PV system operation at the cost of slightly decreasing

the global efficiency of the combined system because of the

connection of two cascade stages.

The intermediate dc-dc converter is built with an

Insulated Gate Bipolar Transistor (IGBT) as main power

switch Tb in a standard unidirectional boost topology that

employs an energy-storage reactor Lb, a rectifier diode Db

and a voltage smoothing capacitor C. The converter is

linked to the PV system with a filter capacitor CA for

reducing the high frequency ripple generated by the

transistor switching. The dc-dc converter output is

connected to the dc bus of the VSI.For modelling of

voltage source inverter they used IGBT. The VSI structure

is designed to make use of a three-level pole structure, also

called neutral point clamped (NPC), instead of a standard

two-level six-pulse inverter structure This three-level

inverter topology generates a more sinusoidal output

voltage waveform than conventional structures without in-

creasing the switching frequency. The additional flexibility

of a level in the output voltage is used to assist in the output

waveform construction.

F.Bouchafaa et al. [20] the three-level NPC VSI,

presented, was one of the most commonly applied

multilevel topologies.

This type of VSI has several advantages over the

standard two-level VSI, such as a greater number of levels

in the output voltage waveforms, lower dV/dt, less

harmonic distortion and lower switching frequencies. The

main drawback of this type of converter is the voltage

imbalance produced in the capacitors of the DC-link when

one of the phases is connected to the middle point or

Neutral Point (NP).

R. Mechouma et al. [23] focused on different

technologies for connecting photovoltaic (PV) modules to a

three-phase- grid. Some of three-phase topologies are

presented, compared according to the type of control (i.e.

the PWM method; the bang-bang method or the fuzzy logic

method or numerical control); and a comparison with

single-phase inverters was given.

IV. CONTROL OF GRID-CONNECTED PV SYSTEM

The control structure of the grid-connected PV system is

composed of two structures Control:

1. The MPPT Control, which the main property is to extract

the maximum power from the PV generator.

2. The inverter control, which have the main goal:

- Control the active and regulate the reactive power injected

into the grid;

- Control the DC bus voltage;

- Ensure high quality of the injected power.



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A. MPPT Control: The maximum power that can be

delivered by a PV panel depends greatly on the insulation

level and the operating temperature. Therefore, it is

necessary to track the maximum power point all the time.

Many researchers have been focused on various MPP

control algorithm to lead the operating point of the PV

panel to optimum point [24].

F.Bouchafaa et al. [20] propose an intelligent control

method for the maximum power point tracking (MPPT) of

a photovoltaic system under variable temperature and

insulation conditions. This method uses a fuzzy logic

controller. It can be deduced that the fuzzy controller is fast

controller in the transitional state and presents also a much

smoother signal with less fluctuations in steady state. It was

able to find the point of maximum power in a shorter time

runs.

[16] proposed a The proposed multi-level control

scheme for the three phase grid-connected photovoltaic

system consisting of external, middle and internal level, is

based on concepts of instantaneous power on the

synchronous-rotating dq reference frame. They used

perturb and observe, for MPP F. Huang et al. [25] a microcontroller based automatic

sun Tracker was designed and implemented. The automatic

sun tracker is implemented with a dc motor and a dc motor

controller.

The novelty of this unit is that the switching device of

the chopper is not only used for power conversion but also

for Maximum Power Point (MPP) detection. MPP is

determined by simple embedded software with a current

sweep approach.

Amrouche, et al. [26] proposed artificial neural network,

(ANN) based modified P&O method to predict the power

value during the next perturbation cycle so that the value of

perturbation step can be adjusted for next perturbation

cycle.

Zhang. L, et al. [27] built a Genetic Algorithm trained

Radial Basis Function Neural Network (GA-RBFNN)

model to predict the reference DC bus voltage of the

control system to maximize the output power.

Veerachary. M, et al. [28] implemented a feed-forward

MPPT scheme for coupled inductor interleaved boost

converter fed PV system by using fuzzy logic controller,

while ANN is trained offline to estimate the voltage

reference.

Joe-Air Jiang, et al. [29] designed a three-point weight

comparison method to avoid rapidly moving of the

operating points of PV when it is under varying atmosphere

conditions which could overcome the drawback of P&O

method.

References [30, 31] proposed neural fuzzy network for

MPPT control scheme. The neural network used to train

sets of data off-line for inputs of fuzzy logic controller,

while the fuzzy logic controller used to control the duty

cycle effectively and hence the MPP can be tracked

effectively.

B. The Inverter Control: Inverter interfacing PV

module(s) with the grid involves two major tasks. One is to

ensure that the PV module(s) is operated at the maximum

power point (MPP). The other is to inject sinusoidal current

into the grid. In grid-connected PV system, different

inverter topologies and controllers are usually used for

interfacing the PVG and the utility grid [32]-[33]. Two

inverter configurations and three inverter topologies can be

identified in such applications, namely: central inverter,

string inverter and integrated inverter for configuration; and

topologies with or without transformer [34]. These

interfaces use various PWM single-phase inverters

configurations and topologies, governed with different

suitable control strategies to transfer powers and to shape

the utility line current, making it follow a reference

sinusoidal waveform.

M. G. Molina et al. [16] proposed multi-level control

scheme for the three phase grid-connected photovoltaic

system consisting of external, middle and internal level, is

based on concepts of instantaneous power on the

synchronous-rotating dq reference frame as given in Fig. 5.

Fig. 5. Multi-level control scheme for the three-phase grid-connected

PV system.

Ismail et al. [35] presented the development of single

phase sinusoidal pulse width modulation (SPWM)

microcontroller-based inverter. The attractiveness of this

configuration is the use of a microcontroller to generate

sinusoidal pulse width modulation (SPWM) pulses. The

power circuit topology chosen is full bridge inverter. Fig. 6.

Shows the full bridge inverter topology. It consists of DC

voltage source or photovoltaic module, four switching

elements (MOSFETs), LC filter, transformer and load.



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The full bridge topology is chosen with considerations

that it must be capable of delivering high current at low

voltage. This property is important if the inverter is

designed for photovoltaic applications.

Fig. 6. Full bridge inverter topology.

All commercial inverters in this review (Soladin120

[36], OK4 [37], OK5 [37] and Sunmaster 130 [36] (a three

stage inverter)) are based on the resonant principle. In the

case of the OK4 inverter the DC-DC converter are used to

amplify the voltage but also to modulate the rectified

sinusoidal current, which is unfolded in the secondary stage.

The next inverter [38] is based on the series resonant

DCDC converter and a modified full bridge grid-connected

inverter, cf. Fig. 7. The inverter is modified in such a way

that it cannot operate as a rectifier; hence problems with

standby losses are solved. Two additional diodes do this.

The DC-DC converter is, as stated before, based on the

series resonant converter, where the leakage inductance in

the transformer together with the capacitor inserted in the

main path forms a resonant-tank. The resonant tank

together with the output capacitances of the switches makes

the inverter zero-voltage switching.

The DC-DC converter is operated at 100 kHz with a

duty-cycle slightly smaller than 50% in order to avoid

shoot-through.

Fig. 7. The inverter proposed in [36, 42]. The series resonant DC-DC

converter amplifies the voltage from the PV-Module and the grid

connected inverter generates the sinusoidal grid-current.

In terms of topologies, a large interest has been shown

by the scientific community in multilevel inverters [43],

[44], [45], [46], [47], and [48]. At the megawatt range, the

two-level voltage source converter, if compared with

multilevel converters, is not be able to ensure the power

quality required by the standards, the maximum allowed

switching frequency, the higher voltage operation and the

reduction in filter size. The multilevel converters are useful

in achieving an interconnection of the photovoltaic strings

in a better way to reach higher voltages that are closer to

that one at the point of common coupling. The cascaded

half bridge solution is based on the series connection of the

H-bridge, so that a natural voltage increase is obtained and

the adoption of a boost stage or step-up transformer is not

needed.

Resonant harmonic compensators [49] allow performing

selective harmonic compensation in grid-connected

photovoltaic inverters in order to guarantee high

performances in terms of frequency content of the current

injected into the grid. Such a technique is based on the use

of a bank of generalized integrators, namely second-order

band pass filters tuned to resonate at a predefined

frequency.

The control of reactive power has been proposed in

Cagnano et al. [50]: in this paper a decentralized controller

that is able to minimize grid losses by actively managing

the reactive power supplied by PV inverters is proposed. It

allows reducing the burden due to the centralization of the

controller.

In J. Vasquez et al. [51] a converter, controlled by means

of the droop control technique, which is able to provide

active power to local loads and to inject reactive power into

the grid providing voltage support at fundamental

frequency.

Soeren Baekhoej et al. [4] presented a grid-connected

photovoltaic (PV) system with direct coupled power quality

controller (PQC), which uses an inner current control loop

(polarized ramp time (PRT)) and outer feedback control

loops to improve grid power quality and maximum power

point tracking (MPPT) of PV arrays.

To reduce the complexity, cost and number of power

conversions, which results in higher efficiency, a single

stage CCVSI is used. The system operation has been

divided into two modes (sunny and night). In night mode,

the current controlled inverter (CCVSI) operates to

compensate the reactive power demanded by nonlinear or

variation in loads. In sunny mode, the proposed system

performs PQC to reduce harmonic current and improve

power factor as well as MPPT to supply active power from

the PV arrays simultaneously.



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V. THREE-PHASE GRID CONNECTED INVERTER FOR PHOTOVOLTAIC SYSTEMS

The inverters are categorized into some classifications:

the number of power processing stages; the use of

decoupling capacitors and their locations; the use or no of

the transformers; the type of three phase inverter; whether

they are preceded by a DC/DC converter or not .Some of

three-phase topologies are presented. Fig.8. shows typical

circuit diagram of a MOS-equipped VSI with Boost-

Converter for a PV module generation system. This

inverter is a viable alternative to a VSI+BC due to its

voltage step-up characteristic [2], [3]. The CSI directly

connected to the PV module features a single stage power

conversion system for feed-in and MPPT

Fig.8. Typical circuit diagram of a MOS-equipped With Boost-

Converter for a PV module generation System

The inverter shown in Fig. 9. is a viable alternative to a

VSI+BC due to its voltage step-up characteristic [2], [3].

The CSI directly connected to the PV module features a

single stage power conversion system for feed-in and

MPPT.

Fig.9. Circuit diagram of a MOS-equipped CSI for a PV module

generation system.

The topology (depicted in fig.10) is less interesting for a

low-voltage distribution network which is typically a four-

wire system.

Using the three phase three-wire topology, only two

parameters can be controlled, which is disadvantageous in

case active power filtering functions are desired.

Fig.10. Circuit diagram of a 3-phase BJT equipped inverter topology

[53]

The topology shown in fig.11. is a three phase four-wire

BJT-equipped inverter with split DC-link. It was a simple

topology and the advantage is that a three-phase split-link

inverter essentially becomes three single-phase half-bridge

inverters and permits each of the three legs to be controlled

independently, making its current tracking control simpler

than the four-leg inverter.

Fig.11 Topology of the three phase four-wire inverter with split dc-

link [52]

In order to maximize the success of the PV systems a

high reliability, a reasonable cost, and a user-friendly

design must be achieved in the inverter topology. Fig.12

depicts the multi-string topology is commonly used in PV

applications. It permits the integration of PV strings of

different technologies and orientations (north, south, east

and west) [54].

Fig.12 Topology of the three phase four-wire Multi-string inverter

[54]



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Fig.13 depicts a three-phase inverter with stabilizer and

transformer [55]. This topology is very influenced by

variations in the load. When the Load is getting bigger the

variation follows up and the sinusoidal characteristics are

becoming worse off.

Fig.13 Topology of three-phase inverter with stabilizer and

Transformer [55]

VI. DISCUSSION AND CONCLUSION

The accuracy of any of these models is usually

dependant on the location where the PV system is being

installed, thus, it is important to choose a suitable model for

the case under consideration. One of the main activities in

this area is the development of irradiance models suitable

for specific locations. The fluctuations in irradiance due to

passage of clouds also received a lot of attention from

researchers, where most of the work done in this field

relied on the frequency domain analysis. One field that still

requires more attention is the prediction of irradiance,

which is a complicated task as compared to the prediction

of wind speed. This is mainly because of the variety of

factors that affect the accuracy of prediction including the

wind speed and direction and type, height and thickness of

clouds.

Modeling of the PV cells is one of the mature areas in

the field. There are a variety of models available in the

literature and can be divided into two main categories;

detailed and simplified models. Detailed models attempt to

represent the physics of the PV cell and are usually suitable

for studies that require the detailed cell information such as

implementation of maximum power techniques and

analysis of the effect of change in irradiance and

temperature on the performance of the PV cell. On the

other hand, simplified models usually provide a direct

estimate of the maximum power generated from the PV cell

at certain operating conditions.

Thus, simplified models are suitable for system studies

that try to identify the impacts of PV systems on the

electric network.

In the past few years, developing new topologies for

power conditioning units and applying new control

techniques were the focus of many studies, almost

saturating this field of research. Also, the application of

new maximum power point tracking algorithms received a

lot of attention. However, most of these algorithms fail to

operate properly in the case of partial shadings, which is

the case where parts of the PV array are shaded by clouds

or nearby buildings. The conventional MPPT algorithms

are not capable of solving the problems of multiple peaks

that established in the P-V characteristic curves of the PV

systems due to partial shaded conditions. Therefore, further

research should be done to extract maximum power

effectively from the PV systems under non-uniform

insolation.

The use of storage devices with PV systems is currently

receiving a lot of attention. These devices can be used to

bridge fluctuations in the output power of PV systems, shift

the peak generation of the system to match the load peaks,

and provide reactive power support. One of the main

challenges that still face the use of storage devices is the

high cost associated with their installation. Thus, studying

the economical aspect of installing these devices is of great

importance.

Grid-connected PV systems can provide a number of

benefits to electric utilities, such as power loss reduction,

improvement in the voltage profile, and reduction in the

maintenance and operational costs of the electric network.

However, improper choice of the location and size of the

PV systems and unsuitability of the output power profile of

the PV system to the profile of the electric network can

impose operational problems on the network. Moreover,

the fluctuations in the output power of these systems add to

the complexity of the problem. Large, centralized PV

systems, installed in distribution networks, require more

attention at the time being.

Partial shading of PV arrays is considered one of the

main challenges that face MPPT techniques. In this case,

there might exist multiple local maxima, but only one

global maximum power point. The task of the PCU is to

identify and operate at the global MPP. The research in this

field is active.

Multilevel inverters posses the advantage of generating

output voltages with extremely low distortion, generating

smaller common-mode voltage and drawing current with

very low distortion but a complex topology, a large number

of components and a complicated control strategy have to

be overcome.



48

Nevertheless, the multilevel inverter will play an

important role in the future. Advanced inverter, controller,

and interconnection technology development must produce

hardware that allows PV to operate safely with the utility

and act as a grid resource that provides benefits to both the

grid and the owner.

Advanced PV system technologies include inverters,

controllers, related balance-of-system, and energy

management hardware that are necessary to ensure safe and

optimized integrations, beginning with todays unidirectional grid and progressing to the smart grid of the

future.

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Documents

Modeling and Control of Grid Connected Photovoltaic System- A Review