Comprehensive Modulation and Classification of Faults and Analysis Their Effect in DC Side of Photovoltaic System

doi:10.4236/epe.2013.54B045

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Energy and Power E ngineering, 2013, 5, 230-236

doi:10.4236/epe.2013.54B045 Published Online July 2013 (http://www.scirp .o rg/journal/epe)

Comprehensive Modulation and Classification of Faults

and Analysis Their Effect in DC Side of

Photovoltaic System

Mehrdad Davarifar, Abdelhamid Rabhi, Ahmed El Hajjaji

Universi ty of Picardie “Jules Verne”, Laboratory MIS (Modeling, Information & Systems),

33Rue Saint Leu, Amiens, 80039, France

Email: Davar [email protected]

Received April, 2013

ABSTRACT

The first step in automatic supervision, condition monitoring and fault detection of photovoltaic system is recognition,

exploratio n and classification of all possible faults that maybe happen in the system. This pap er aims to perceive, classi-

fied, simulate a nd discus all electrical faul ts in DC side of photovoltaic s ystem, regarding electrical voltage a nd current

inspections. For that, simplified hybrid model of photovoltaic panel in MATLAB environment is used. Investigation

and classification of each type of faults is down and the effects of the faults are illustrated in this paper. Flash test are

applied to improved electrical model. Current-Voltage curves signature are interpreted and investigated in simulation

environment.

Keywords: Photovoltaic Systems; Modeling; Electrical Fault; Fault Detection

1. Introduction

Nowadays photovoltaic (PV) panels are used in several

sector of industry. They could be found, on building

roofs, illuminated highway signs [1], etc. where rural

electrification is embryonic [2], even in infrastructure

industries such as oil industry [3], huge power plant in

desert and different aspects of life. PV markets are

growing fast because of their advantages such as: pollu-

tion free, safety, noiseless, easy installation, and short

construction period. Also tariff of the solar electricity is

enormous compared to the traditional power especially in

peak load time [4]. Enquiries for lower cost and high-

efficiency-devices motivate the researchers to increase

the reliabilit y o f P V systems.

On the other hand, this wide diffusion has of the dis-

tributed generation (DG) such as photovoltaic panels

have not been supported by monitoring, fault detection

and diagnosis equipment.

In fact, monitoring systems represent an additional

cost and it weighs appreciably on Residential Photovol-

taic System (RPS). For this reason, small PV plants are

not regularly checked and partial system faults can occur,

leading to energy losses that are dificult to be observed

and causing ﬁnancial losses [5-7]. Without proper fault

detection, non-cleared faults in PV arrays not only cause

po wer losses, but also might lead to safety issues and fire

hazards [8].

Photovoltaic system are subjected to different sort of

failures, thus befo re st arti n g sup erviso r y syst em a nd fa ult

diagnosis methods, it is necessary to identify what kind

of failures can be found in the real system. The first step

in this challenge is to cognition and classification all

possible faults, in the first.

On the other hand, the fault detection methods for the

PV array are varied and are classified in the Table 1.

Amon g these metho ds suc h as: vi sual, the rmal, a nd elec-

trical, the visual and the thermal methods need to look

down the PV array and observe the color changes of the

modules or observe the thermal properties such as hot

spots. These methods need thermal cameras or other

equipment in front of the array, while the electrical me-

thod s need o nly t he outp ut ter minal of the array to meas-

ure the volt age, c urre nt, and signa l da ta such as te mpera-

ture and irrad ia tion.

This characteristic of electrical methods is important

for the fault diagnosis technologies to install them into

the power conditioners or into the system inspection

equipment. Then, electrical methods are promising for

PV system fault diagnosis [10, 11]. This paper aims to

perceive, simulate and discuss about electrical fault in

DC side of photovoltaic system and has been focused on

electrical voltage and current inspections. For that sim-

plified hybrid model of PV panel in MATLAB environ-

ment is proposed in third part [12-15].

M. DAVARIF AR ET AL.

231

Flas h test is sp anni ng of the I-V curve range s fro m the

short circuit current (Isc) at zero volts, to zero current at

the open circuit voltage (Voc). The measured and pre-

dicted curve shapes may disagree to some extent even

when the PV string (or module) under test is performing

perfectly. This could be cause d by errors in irradiance or

temperature measurement, or effect of the fault that has

been classified in section two.

2. Classification of Faults in DC Side of PV

System Based on Location and Structures

Generally speaking, faults in PV system could be oc-

curred into t wo side o f the s ystem: DC sid e and AC side,

the interface between this to part is DC/AC inverter that

connected to grid. Internal maximums point power

tracker algorithm with some method must be applied for

rising efficiency of the system.

In AC side of PV system, typically two types of faults

could be happened: total black out which considered as

exter ior faul t for s yste m, l ight ing a nd u nbal anced volt age

or grid outage for AC part defect such as switch frailer,

over current or over voltage and etc. This sort of defect is

not investigated in this work. Besides, it is considered

that the PV array is the only source of fault, since most

PV inverters contain transformers that could provide

good galvanic isolation between PV arrays and utility

grids and perfect electrical protections.

2.1. Typical Faults in PV Array

Typical faults in PV arrays consist of two main groups,

PV panel fault and cabling. In large scale system, some

method of cabal testing could be applied such as earth

capacitance measurement (ECM) and the time-domain

reflect (TDR) [16], but for small PV and domestic appli-

cation these equipment test are so costly. In addition,

number of PV and length of transfer power line in resi-

dential photovoltaic system is finite, and then in this

study has been just focused on integrated panel.

Four of the most co mmon types of fault in PV system

(Earth Fault, Bridge Fault, Open Circuit Fault and Mis-

match Fault) are described and simulated.

2.1.1. PV panel/Module Faults

1) Earth Fault

Earth fault is the most co mmon fault in PV and occurs

when the circuit develops an unintentional path to ground.

According to NEC Article 690.5, two types of grounding

shall be provided for PV system. The first one is system

grounding: (the negative conductor usually is grounded

via the Earth fault protection device (GFPD) in the PV

inverter (Figure 1). The other one is the equipment

grounding: the exposed non-current-carrying metal parts

of PV module frames, electrical equipment, and conduc-

tor enclosures should be grounded.

Two types of Earth faults with zero impedance at dif-

ferent locations have been studied a nd their fault currents

are predicted in simulation

a) Lower Earth fault: the potential fault point is upper

than half o f the maximum voltage po wer point .

b) Upper Earth fault: This fault will cause large backed

current and very high Earth-fault current. This case of

faults is easily detectable by a change of the sign of the

monitored pr imary current o f the solar inverter. An add i-

tional sensor is not necessary. If the primary current be-

comes negative, some modern solar inverters initiate a

controlled internal short circuit [17].

2) Bridging One or More Panels:

A fault bridging in PV system is happened when low-

resistance connection established between two points of

different potential in string of module or cabling. Bridg-

ing faults in PV arra ys may be caused by insulation fail-

ure of cables such as an animal chewing through cable

insulation, mechanical damage, water ingress or corro-

sion.

3) Open Circuit Fa ult:

When one of the current-carrying paths in series with

the load is unintentionally broken or opened, an open

circuit fault can be created. Some examples of this are

poor connections between cells, plugging and unplugging

connectors at junction boxes, or breaks in wires. In gen-

eral, a series arc fault has less energy than a parallel

bridging fault, but it has a much higher probability of

occurring due to the large number of connections in PV

systems.

4) Mismatch Fault:

Mismatches in PV modules occur when the electrical

parameters of one or group of cell are significantly

changed from other. In addition, mismatch faults are

caused by interconnection of solar cells or modules,

which experience different environmental conditions (i.e.

irradiance or temperature) from one another. Mismatch

faults are the most common type of fault compared with

Upper

Ground

Fault

Open ci rcuit Fault

Lower Earth Fault

Bridge Fault

Hot sp ot

Negative

Earth Fault

Shadow

Bypass

diod e fa i l

Delamination

Fault

Hot sp ot

Industrial

MPPT

Figure 1. F ault schematic in DC side of PV system.

M. DAVARIF AR ET AL.

232

Earth fault and bridging faults, among PV arrays. Mis-

match faults may lead to irreversible damage on PV

modules and large power loss. However, they are diffi-

cult to detect using conventional protection devices,

since the y generall y do not l ead to la rge fault currents .

These faults can be categorized into two groups, per-

manent and temporary. Their causes are listed below:

a) Temporary Mismatches: are divided in two groups:

• Partial shading:

Shading effect occurs when a part of the panels array

are shaded which can be caused by a number of different

reasons, like shade from the building itself, light posts,

chimneys, trees, clouds, dirt, snow and other light-

blocking obstacles [18].

Non- uniform temperature: Snow covering,

b) Permanent Mismatches:

• Hotspot:

Hot spot heating occurs when a module’s operating

current exceeds the reduced short circuit current of a

shadowed or faulty cell or group of cells within the mod-

ule [19]. To create a Hot spot fault, a variable resistor in

series with the Rsn of each defective cell could be added

in Simulink. Value of this resistor is considered approx-

imately one unt i l five ohm.

• Soldering: this defective appears in resistive solder

bond between cell and contacted ribbons.

• between cells and contact ribbons, Degradation:

o Discoloration;

o Delaminatio n;

o Transparent layer crack.

Typical Chart of fault in (Figure 2) is illustrated:

2.1.2. Cabling Fault

Such as PV panel three principal type of fault is occur in

power line carrier and cabling system.

1) Bridging Fault:

A very typical location of a possible bridging fault

could be an aged connection box at the back side of a

solar panel or in the corner and bend aria of cable [20].

2) Open-Circuit fault;

3) Earth Fault:

a) Upper Earth Fault

b) Lower Earth Fault

These common faults occur between panels and

ground. Earth fault res ults in lo wered output voltage and

power, and can be fatal if the leakage currents are run-

ning thr o ug h a pe r so n. T he se fa u lts have almost t he same

effect on PV array and PV panel.

Faults

DC side

PV Panel fau lt

Photovoltaic

array

Earth

fau lts

Upper Ground

fau lts

Lower Earth faults

Bridging

faults

Open Circuit

fau lts

Mismatch

faults

Temporary

Mismatches

Partial Shading

Shading

Bird Droppings or

Tress Leav es

Snow

covering

Non-uniform

temperature

Snow covering

Permanent

Mismatches

Soldering

Hot Spot

Degradation

fau lts

Discoloration

Delamination

Crack

Cabling

Bridging

faults

Open Circuit

fau lts

Earth fault s

Upper Earth

fau lts

Lower Earth

fau lts

MPPT

AC si de

(grid)

Grid

outage

Lighting

Inv erter

Total black

out

Not interested in this work

Interested in this work

Figure 2. Classification of Faults i n DC Si de o f PV system bas ed on locat ion and structures.

M. DAVARIF AR ET AL.

233

3. Simulation and Experimental Results

3.1. MATLA B/ Psp ice Cir cuit Ba sed Mode l of PV

Panels for Fault Diagnosis Application

Photovoltaic system are subject to different sort of fail-

ures. Therefore, before stating health monitoring and

fault diagnosis in PV system, finding general and real

time model of PV, with good and fast performance is

inevitable. This general and universal model must have

following specification:

• Applicable for almost all co mmercial PV panel;

• Capable to work in real-time for fault diagnostic

delibera tion and monitoring system;

• Capable to simulate partial shading conditions

(PSC) effect and degradation to investigate pa-

nels fault;

• Possible to connect easily and interfaced to the

electronic devices and power converters model in

MATLAB Simulink for maximum power point

tracking and fau lt diagnosis st ud ie s.

Hybrid model is used and adopted according to the PV

datasheet value for better I-V curve estimation. In fact,

equivalent circuit of a practical PV device includes the

cells connected in series and parallel.

With this modification it is possible to change input

data (irradiating and temperature) for each cell and si-

mulate it individually. Of complying with superposition

rules the simulation result of each cell combine together

to form I-V characteristic of PV module as the output.

In our model (Figure 3):

• Dependent current source to irradiation and te mper-

ature for each cell are considered separately, in or-

der to convert solar energy to electrical form;

• Adopted diode has been superseded instead of nor-

mal silicon dio de;

• Variable resistor is used to appearance effect of

solar irradiation (especially for Amorphous tech-

nology);

• Adopted diode connected in series form to demon-

strate number of P-N junction and became justifica-

tion for high-level ideality factors a.

Using Spice diode block, it is possible to consider en-

vironment temperature effect in the simulation. In fact,

the diode satura tion current Isat and b and -gap energy Eg is

corrected regarding datasheet value, and then parameters

are manipulated in diode block. This procedure could be

extended for PV arrays, output of each PV panel/module

connected together according array configuration to for m

total I-V curve.

3.2. Simulation of Fault in Real Time

The model presented in this work is implemented and

tested on the a-Si:H triple layer amorphous. The panels

are installed in MIS laboratory energy renewable plat-

form in university of Picardie Jules Verne (Fiugre 4).

Solar irradiation data is captured by pyrometer CS300.

This pyrometer connects directly to our data loggers.

PV temperature is sensed with a type K thermocouple

(Silicone rubber patch with self-adhesive aluminum foil

backing) that mounted on panels, also RMS value of

voltage and current are captured by national instrument

data acquisition device (NI DAQ 6212 USB).

IL/n

IL/np

Voc

Voc/ns

Voc

Voc/ns

Rshnp/nsl

Rsnp/nsl

Rshnp/nsl

Rsnp/nsl

Rshnp/nsl

Rsnp/nsl

Rshnp/nsl

Rsnp/nsl

Rsh

Eg, an, Isatn

Amorphou

Cell model

Adopted diode

( )

ITa

scTmax n

a .k.T .T

IT n max

max

satn n

E= -Ln.

gVq.T- T

n max

ocTmax

exp- 1

a.VTm































I+K . T

scn i

sat V+K. T

ocn v

exp- 1

a.Vtn

∆







Figure 3. MATLAB/Pspice circuit based model of PV pa-

nels for fault diagnosis application.

Figure 4. Evaluated Simulink model in MIS laboratory

Energy ren ewable platform.

05 10 15 20 25

-5

Time (h)

Po wer ( w)

-- Power of model

-The real power

Figure 5. Comparison between the actual and the power

provided by the model.

M. DAVARIF AR ET AL.

234

Temperature and irradiation captured as input data.

The voltage and current predicted by simulation in real

time. According to this figure, it appeared that there was

a good agreement between the real data given by mea-

surement sensors and the results obtained by simulation.

This Comparison is fundamental task to Feasibility of

error by considering power lowering.

4. Flash Test Result of Faults in DC Side of

PV System (I-V Characteristic)

Flash test is a fundamental method for measuring the

performance I-V characteristics o f photovolta ic panels b y

spanning the PV voltage from zero to open circuit in

short time. The output of measuring is a set of data,

which are determined by output peak power, open circuit

voltage, short circuit current, operating voltage, current,

or power and efficienc y [21].

Flash test has been applied to PV models for different

type of fault scenario. Results of fore principal of fault,

Open circuit (Figure 6), Mismatched fault (Figure 7),

Bridging Fau lt (Figure 8) and Erath Fault (Figure 9) are

illustrated.

00.5 11.5 22.5 33.5

Voltage

Power & Curr ent

I-V Normal

P-V Normal

I- V Open circ iut

P-V Open c ircuit

Figure 6. Open circuit fault affect ed on ISC.

00.5 11.5 22.533.5

Voltage

Power & Curr ent

I-V M ismat ched

P -V M i sm ached

I-V Normal

P -V Norm a l

P -V Hot Spot

I-V Hot S pot

Figure 1. I-V curve ha s notc hes or s teps in M is matc hed an d

Hot spot fault.

00.5 11.5 22.5 33. 5

Voltage

P ower & Current

I-V Normal

I- V Bridging Fault

P-V Bridging Fault

Figure 2. Bridging Fault Loses power and is effe cted on Voc.

00.51 1.52 2.53 3.5

V oltage

P ower & Current

I-V Normal

P-V Normal

I-V Lower Earth Fault

P- V Lower Eart h F ault

I- V Upper Earth Fault

P- V Upper Earth Fault

Figure 3. Earth Fault affected Voc, Upper Earth fault is

more effective in out-put characteristic.

For simulation initialize three strings in parallel and

each string is included five cells or panel. (It is men-

tioned before that it is possible to consider PV module

instead of cell, because the result is consequence of su-

perposition rules).

Inference and investigated I-V and P-V Curve are in-

terprete d at the end part o f this study:

• The I-V curve shows higher or lower current than

predicted, which is caused by following faults:

- PV array is soiled (especially uniformly).

- PV modules are degraded.

• The slope of the I-V curve near Isc does not match

the prediction, if:

- Shunt paths exist in PV cells (H ot Spot)

- Shunt paths exist in the PV cell interc onnects

- Module Isc mismatch

• The slope of the I-V curve near Voc does not match

the prediction, in cases below:

- PV wiring has excess resistance or is insufficiently

sized

- Electrical interconnections in the arra y are resistive

- Series resistance of PV modules has increased

• The I-V curve has notc hes or steps, if:

M. DAVARIF AR ET AL.

235

- Array is partially shaded

- PV cells are damaged

- Bypass diode is short-circuited

• The I-V curve has a higher or lower Voc value than

predicte d in the following cases:

- PV cell temperature is different than the modeled

temperature

- One or more cells or modules are completely

shaded

- One or more bypass diodes is conducting or s horte d

- One or more PV modules were not included in the

circuit as-built

5. Conclusions

A comprehensive classification of faults in DC Side of

PV system based on location and structures is proposed

for the first time. Flash test applied to validated model

and deferent type of faults are simulated. Inference and

investigated I-V and P-V curves are interpreted.

The future research plans to address some intelligent

algorithm, which is used for fault detection and localiza-

tion i n P V sys tem r egar din g the inference of I-V and P -V

curves characteristics.

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