This article was downloaded by: [Essam Eddin Rashad]On: 31 January 2013, At: 09:54Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Electric Power Components and SystemsPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/uemp20

Performance Improvement of aPhotovoltaic Pumping System Using aSynchronous Reluctance MotorM. Nabil a , S. M. Allam b & E. M. Rashad ba Department of Electrical Engineering, Kafrelshiekh University,Kafrelshiekh, Egyptb Department of Electrical Power and Machines Engineering, TantaUniversity, Tanta, Egypt

To cite this article: M. Nabil , S. M. Allam & E. M. Rashad (2013): Performance Improvement of aPhotovoltaic Pumping System Using a Synchronous Reluctance Motor, Electric Power Components andSystems, 41:4, 447-464

To link to this article: http://dx.doi.org/10.1080/15325008.2012.749554

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representationthat the contents will be complete or accurate or up to date. The accuracy of anyinstructions, formulae, and drug doses should be independently verified with primarysources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.

Electric Power Components and Systems, 41:447–464, 2013

Copyright © Taylor & Francis Group, LLC

ISSN: 1532-5008 print/1532-5016 online

DOI: 10.1080/15325008.2012.749554

Performance Improvement of a Photovoltaic

Pumping System Using a Synchronous

Reluctance Motor

M. NABIL,1 S. M. ALLAM,2 and E. M. RASHAD 2

1Department of Electrical Engineering, Kafrelshiekh University,

Kafrelshiekh, Egypt2Department of Electrical Power and Machines Engineering, Tanta University,

Tanta, Egypt

Abstract This article presents a simple control strategy to improve the performanceof a synchronous reluctance motor drive system fed by a photovoltaic source. The

photovoltaic generator parameters are selected based on maintaining the systemoperating point at the maximum output power of the photovoltaic generator at an

average insolation level of 0.5 kW/m2. The proposed control strategy has three mainfunctions; ensuring successful motor starting, maintaining the motor voltage within

a permissible range, and forcing the photovoltaic array to operate at the maximumpower point possible. Two modes of operation are studied for the proposed system

depending upon the level of insolation compared with a critical value, which is thelevel below which the synchronous reluctance motor cannot work synchronously under

the given pumping load. A sample of simulation results is introduced to confirm theeffectiveness of the suggested strategy. It has been found that, using the proposed

control strategy, the pump flow rate has been increased compared with an uncontrolledsystem.

Keywords photovoltaic pumping system, synchronous reluctance motor, maximumpower point tracking

1. Introduction

Solar energy is free, inexhaustible, and clean; it has a great potential to be a very attractive

supply option for industrial and domestic applications, especially in remote areas, such

as water pumping, heating, and cooling. Solar photovoltaic (PV) systems use the PV

modules in order to convert the sunlight into electrical energy. PV generation is gaining

increased importance as a renewable source due to its advantages, which include few

maintenance requirements, the absence of fuel cost, and lack of noise due to the absence

of moving parts [1].

PV pumping systems are receiving more attention in recent years especially in remote

areas where connection to the grid is technically not possible or costly. In addition, PV

pumps have recently received considerable attention due to major developments in the

Received 27 June 2012; accepted 10 November 2012.Address correspondence to Dr. Mohamed Nabil Fathy, Department of Electrical Engineering,

Kafrelshiekh University, Kafrelshiekh, 33516. Egypt. E-mail: m.nabil_it@yahoo.com

447

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

448 M. Nabil et al.

Nomenclature

Ap proportionality factor of the pump (Nm/rad/sec)

B viscous friction coefficient (Nm/rad/sec)

H total pumping head (m)

Ids , Iqs direct and quadrature axis stator currents, respectively (A)

Ig current drawn from the array (A)

J inertia of the system (Kg.m2)

Lds , Lqs direct and quadrature axis stator inductances of synchronous

reluctance motor, respectively (H)

Lmd , Lmq direct and quadrature axis magnetization inductances, respectively (H)

p differential operator (d=dt)

P number of pole pairs

Pg output power of the array (W)

Pin input power of the motor (W)

Po output power of the motor (W)

Q flow rate (m3/h)

rdr , rqr direct and quadrature axis rotor resistances of synchronous reluctance

motor, respectively (�)

Rs stator resistance of synchronous reluctance motor (�)

Te electromagnetic torque of the motor (Nm)

To constant torque of the pump (Nm)

Vds , Vqs direct and quadrature components of stator voltage, respectively (V)

Vg terminal voltage of the array (V)

Vm, V maximum and effective values of the motor input voltage,

respectively (V)

ı load angle (rad)

!r , !s motor and synchronous speed (rad/sec)

field of solar cell material and technology. They are widely used in domestic and livestock

water supplies and small-scale irrigation systems [2, 3].

DC motor driven PV pumps are used overall the world because they can be directly

connected to the PV generator and an adjustable DC drive is easy to achieve. However,

this system suffers from increased motor cost and maintenance problems due to the

presence of a commutator and brushes [3–5]. Hence, a pumping system based on brushless

motors represents an attractive alternative due to its merits over DC motors. Brushless

permanent magnet DC motors have been proposed [4]; however, this solution is limited

to only low-power PV systems.

Several studies have investigated AC systems using either current source or voltage

source inverters [1]. The PV pumping system based on an induction motor (IM) offers an

alternative motor for more reliable and maintenance-free systems. The main advantages

of IMs are reduced unit cost, ruggedness, brushless rotor construction, and ease of

maintenance [1, 3, 6]. The permanent magnet synchronous motor (PMSM), also called

the brushless DC motor, coupled to a centrifugal pump is found to be suitable for PV

water pumping systems [7, 8].

A synchronous reluctance (SyncRel) motor fed by a PV generator represents a

brushless scheme that should be studied in detail. However, the PV pumping system

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Improvement of a PV Pumping System Using SyncRel Motor 449

based on a SyncRel motor has not garnered any significant attention from researchers

until to date.

The objective of this article is to suggest suitable control strategies to improve

the performance of a SyncRel motor fed by a PV generator. The proposed control

strategy is concerned mainly with ensuring successful starting of the SyncRel motor,

maintaining the motor voltage within a permissible range, and forcing the PV array

to operate as close to the maximum power point (MPP) as possible. The performance

characteristics of the proposed system are studied under different insolation levels with

two modes of operation depending upon the level of insolation compared to the critical

value. The critical insolation level for the system represents the insolation level below

which the SyncRel motor cannot work synchronously under the given pumping load. A

sample of simulation results is introduced to confirm the effectiveness of the suggested

control strategies.

2. System Modeling

Figure 1 shows a block diagram of the proposed system that consists of the following

parts:

� PV generator (denoted by PVG),

� boost converter (DC/DC),

� three-phase pulse-width modulated inverter (DC/AC) (denoted by PWM),

� three-phase SyncRel motor,

� centrifugal pump (denoted by CP) load, and

� control system.

2.1. PV Generator Model

The PV generator converts the solar insolation into electric DC power. It consists of an

array of PV cell modules connected in series-parallel combinations to provide the desired

DC voltage and current. The voltage–current (Vg–Ig) relation of the PV array is given

by [9]

Vg D�

TcNskA

q

�

ln

�

Iph � Ig C NpIs

NpIs

�

��

Np

Ns

�

Igrs; (1)

Figure 1. Block diagram of the proposed system.

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

450 M. Nabil et al.

where

Tc is the cell temperature,

Iph is the photocurrent,

Is is the saturation current,

K is the Boltzmann constant (1:38 � 10�23 J/K),

A is the solar cell ideal factor of the diode,

rs is the series cell resistance, and

q is the electron charge (1:6 � 10�19 C).

The photocurrent which mainly depends upon the solar insolation and cell tempera-

ture is described as [10]

Iph D .Isc C ki .Tc � Tref //G; (2)

where Isc is the cell short-circuit current at 25ıC and the standard value of a solar

insolation (1 kW/m2), ki is the temperature coefficient of the cell short-circuit current

(A/ıC), Tref is the cell reference temperature and G is a solar insolation (kW/m2).

The saturation current varies with the cell temperature as [10]:

Is D Irs

�

Tc

Tref

�3

exp

�

qEG

kA

�

1

Tref

�1

Tc

��

; (3)

where Irs is the cell reverse saturation current at the reference temperature and the solar

radiation, and EG is the band-gap energy of the semiconductor used in the cell.

2.2. Boost Converter Model

The DC-DC boost converter is inserted to adjust the dynamic equivalent impedance

seen by the PV generator. An equivalent pure gain represents the converter model [11].

Therefore, the relation between the PV voltage (Vg) and the boost converter output voltage

(i.e., the inverter input voltage Vbo) can be written as [12]

Vbo D1

1 � dVg ; (4)

where d is the duty ratio of the boost converter. The value . 11�d

) represents the converter

gain.

For a lossless converter, the relation between the boost converter input current

(Ibi ) and boost converter output current (i.e., the inverter input current, Ibo) is given

by [12]

Ibi D1

1 � dIbo: (5)

2.3. Inverter Model

The inverter is used to convert the DC voltage of the PV generator to a three-phase voltage

with variable amplitude and variable frequency. A natural pulse-width modulation (PWM)

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Improvement of a PV Pumping System Using SyncRel Motor 451

switching technique is used to drive the inverter. The three-phase inverter voltages can

be expressed as [13]:

van D1

3.2S1 � S2 � S3/Vbo

vbn D1

3.�S1 C 2S2 � S3/Vbo

vcn D1

3.�S1 � S2 C 2S3/Vbo

9

>

>

>

>

>

>

>

=

>

>

>

>

>

>

>

;

; (6)

where van, vbn, and vcn are the output voltages of the inverter.

Furthermore, the PV current is given by [13]

Ig D Ic C.S1ia C S2ib C S3ic/

1 � d; (7)

where ia, ib , and ic are the SyncRel motor stator currents of the inverter, and Ic is the

capacitor current which is given by the following relation [13]:

Ic D CdVg

dt; (8)

where C is the capacitance of the condenser, which is inserted between the PV generator

and the power converters to smooth the output DC voltage and to reduce the equivalent

impedance seen by the PV generator.

When a switch signal (S1, S2, or S3) equals 1, it means that the corresponding upper

switch is ON while the lower one is OFF and vice versa.

The effective value of the fundamental motor phase voltage is given by [12]

V DMVbo

2p

2; (9)

where the modulation index M is the ratio between the reference sine wave and the

triangular carrier wave. The value ( M

2p

2) represents the inverter gain.

2.4. SyncRel Motor Model

The presented machine is a SyncRel motor with an axially laminated rotor type. The

rotor is equipped with a cage to provide a starting torque. The machine was represented

in the qd -axis reference frame in order to eliminate the time-varying inductances in the

voltage equations. The qd -axis reference frame is fixed in the rotor, which rotates at

!r [14]. The qd -axis voltage equations can be written in matrix form as

2

6

6

6

6

6

4

Vqs

Vds

Vqr

Vdr

3

7

7

7

7

7

5

D

2

6

6

6

6

6

4

Rs C pLqs !r PLds pLmq !r PLmd

�!r PLqs Rs C pLds �!r PLmq pLmd

pLmq 0 rqr C pLqr 0

0 pLmd 0 rdr C pLdr

3

7

7

7

7

7

5

2

6

6

6

6

6

4

iqs

ids

iqr

id r

3

7

7

7

7

7

5

: (10)

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

452 M. Nabil et al.

The electromagnetic developed torque expression can be written as

Te D3

2P.�ds iqs � �qs ids/: (11)

The electromechanical equation is given by

Te D Jp!r C B!r C TL: (12)

The machine power angle ı can be calculated as

ı DZ

.!r � !s/dt: (13)

The qd -axis supply voltage can be expressed as a function of the machine power angle as:

Vqs D Vm cos.ı/; (14)

Vds D �Vm sin.ı/: (15)

2.5. Centrifugal Pump Model

The hydraulic output power of the pump can be characterized by [15]:

Pp D 2:725QH: (16)

The relation between the hydraulic output power (Pp) of the pump and the mechan-

ical input power (Pm) can be defined as the pump efficiency and is given by [16]

�p DPp

Pm

: (17)

On the other hand, the load torque of the centrifugal pump is given by [9]

TL D To C Ap!1:8r ; (18)

where To and Ap are constants.

3. System Control

The purpose of the control strategy is to improve the performance of the SyncRel motor

drive system. The proposed control strategy performs the following functions:

� ensuring successful motor starting,

� maintaining the motor voltage within a permissible range, and

� forcing the PV array to operate at the MPP as possible.

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Improvement of a PV Pumping System Using SyncRel Motor 453

3.1. Ensuring Successful Motor Starting

In general, the motor starting capability depends on the operating motor voltage and

loading conditions. Moreover, the motor voltage depends on PV voltage for given values

of insolation levels. Therefore, there is a critical insolation level for the system below

which the SyncRel motor cannot work synchronously under the given pumping load.

However, due to the presence of a rotor cage, the motor can work asynchronously at

insolation levels below the critical value. Moreover, there is a minimum value of insolation

level below which the motor cannot run.

To overcome the problem of starting, the ratio of the motor voltage to the motor

frequency is kept constant. The motor frequency is controlled according to the variation

of its input voltage as follows [17].

V

fD

MVbo

2p

2fD constant: (19)

3.2. Maintaining the Motor Voltage Within a Permissible Range

With high insolation levels, the motor voltage increases. In the proposed control strategy,

to keep motor voltage at its rated value, the modulation index (M ) is varied.

3.3. Forcing the PV Array to Operate Closely to MPP

Generally, when a PV array is directly coupled to a load, the operating point of the system

depends upon characteristics of both the PV generator and the load. This operating point

is seldom at the MPP of the PV array (i.e., the PV generator is not producing the

maximum power). This mismatching between a PV module and a load requires further

oversizing of the PV array, thus increasing the overall system cost [18].

The peak power can be reached with the help of a DC-DC boost converter that acts

as an interface between the load and the PV array. By changing the duty ratio of the boost

converter, the load impedance as seen by the source is varied and matched at the point

of the peak power with the source so as to transfer the maximum power.

In the literature, several techniques of MPP tracking (MPPT) have been proposed,

analyzed, and implemented. However, the perturb and observe (P and O) and incre-

mental conductance (INC) algorithms are most widely used, especially for low-cost

implementations [16]. Figure 2 shows the flowchart of the P and O MPPT algorithm [19].

4. Results and Discussions

In order to investigate the performance of the system being considered with the proposed

control strategy, a sample of simulation results is introduced. The given samples are

obtained using the measured parameters of a SyncRel motor rated at 470 W, 400 V,

and 4 poles. The PV generator parameters are estimated depending upon determining

the steady-state operating point of the system (Vg , Ig) at an average insolation level

of 0.5 kW/m2. The steady-state operating point (Vg , Ig) is assumed to correspond to

maximum output power of the PV generator, which equals the required motor input

power.

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

454 M. Nabil et al.

Figure 2. Flowchart of P and O MPPT algorithm.

Appropriate parameters of the centrifugal pump parameters are selected. All system

parameters, including the PV cell, SyncRel motor, and centrifugal pump, are given in the

Appendix (Tables A1, A2, and A3, respectively).

The PV generator operating point has been obtained for the following assumptions:

� the motor runs at its rated output power of 470 W,

� the motor efficiency is 0.83 so that input motor power is 565 W,

� the PV generator output power equals the motor input power (assuming lossless

converters),

� the boost converter gain ( 11�d

) equals 1,

� the inverter gain ( M

2p

2) approximately equals 0.3, and

� the motor is loaded by a suitable centrifugal pump that can be used in an irrigation

system or other human needs (the used pump parameters are given in Table A3

in the Appendix).

According to the previous assumptions, it was found that the PV generator operating

point is Vg D 665:5 V and Ig D 0:85 A. The given operating point can be obtained

using 3 parallel strings (Np) of 1730 series cells (Ns) for each. Figure 3 shows the

characteristics of the PV generator at different solar insolation levels.

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Improvement of a PV Pumping System Using SyncRel Motor 455

Figure 3. Characteristics of the PV generator for different insolation levels.

In the absence of a control system, the following values of insolation levels can be

defined, assuming standard level (1 kW/m2) as a base value:

� design insolation level (Gd ) is 50%, at which the MPP of the PV generator

corresponds to motor rated power;

� critical insolation level (Gcr ) is the minimum value to be satisfied in order to start

the motor and operate synchronously; and

� minimum insolation level (Gmin) is the level below which the motor cannot run.

For the proposed system, the critical insolation level (Gcr ) and the minimum inso-

lation level (Gmin) are found to be equal 55% (0.55 kW/m2) and 25% (0.25 kW/m2),

respectively. Accordingly the operation has been studied for two modes; the first mode

for G � Gcr and the second mode for G < Gcr .

For the present system, the results of these modes are given in the following sub-

sections.

4.1. First Mode of Operation (G � Gcr )

When the insolation level is equal or higher than the critical value (Gcr), the motor

can start stably and operates synchronously at the rated conditions without any control

method. However, since G > Gd , the motor voltage is higher than the rated value, which

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

456 M. Nabil et al.

represents the main problem in this mode. The modulation index (M ) of the inverter is

implemented to control the motor input voltage and maintain its level at the rated value.

The modulation index (M ) is controlled using a proportional-integral (PI) controller. A

trial-and-error approach has been used to obtain the controller parameters kp and ki ,

which are given in the Appendix (Table A4). However, in this mode of operation, MPPT

is not required since the PV output power of the array will be greater than the motor

rated power.

In the simulation process, for this mode of operation, the insolation level is first

assumed to equal 55% for to 1.5 sec; then it is increased to 75%. The presented simulation

results are obtained with and without using the proposed control strategy.

Figure 4 shows the run-up response of the SyncRel motor with and without control.

It is obvious that the motor starts and reaches synchronous speed for insolation levels

equal to or higher than the critical value (55%).

Figure 5 shows the response of the PV output voltage and the motor RMS voltage for

two different insolation levels (55% and 75%). It can be noted that without control, the

motor voltage is higher than the rated value for all insolation levels equal to or higher than

the critical value (55%). Furthermore, it can be observed that, aiding with the proposed

control system, the problem is solved and the motor voltage can be maintained at its

rated value.

Figure 4. Run-up response of a SyncRel motor with and without control for different insolation

levels. (color figure available online)

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Improvement of a PV Pumping System Using SyncRel Motor 457

Figure 5. Response of the PV output voltage and the motor RMS voltage with and without control

for different insolation levels. (color figure available online)

At the same conditions, the response of the PV output power is shown in Figure 6.

It is noted that the steady-state PV output power is kept at the rated value so that MPPT

is not required in this mode of operation.

Moreover, the response of the pump flow rate at a total pumping head of 10 m is

shown in Figure 7. It can be noted that the steady-state pump flow rate is constant with

or without control, as there is no control on the PV output power and the motor operates

at the rated conditions.

4.2. Second Mode of Operation (G < Gcr )

When the insolation level is higher than the design value (Gd ) and less than the critical

value (Gcr ) (i.e., 55% > G � 50%), the motor voltage is equal to or slightly higher

than the rated value. As in the first mode of operation, the motor input voltage can

be maintained at its rated value by varying the modulation index (M ). However, when

the insolation level is less than the design value (50%) and in the absence of control

action, the motor voltage is less than the rated value. The motor cannot start and reach

synchronous speed when loaded by the given pump at all insolation levels less than the

critical value. The use of a voltage per hertz (V/f) control method is suggested to deal

with this situation.

On the other hand, at insolation levels less than the design value, the maximum

output power of the PV array is less than the motor rated power. Therefore, the MPPT

technique is required to maximize the PV usage. In order to achieve this target, the

DC-DC boost converter is controlled via varying its duty ratio.

In the simulation process, for this mode of operation, the presented sample of simu-

lation results is obtained at three different insolation levels: 35% (> Gmin), 25% (Gmin),

and 22% (< Gmin), with and without the proposed control strategy.

Figure 8 shows the run-up response of the SyncRel motor with and without control

for the adopted insolation levels. It is obvious that the motor cannot work synchronously

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

458 M. Nabil et al.

Figure 6. Response of the PV output power with and without control for different insolation levels.

(color figure available online)

without control at insolation levels of 35% and 25% because they are less than the critical

value. In this case, the motor operates in asynchronous mode. Furthermore, it can be noted

that at an insolation level of 22%, the motor cannot run without control. However, with

the proposed control strategy, the problem of starting is solved at all insolation levels, as

shown in the figure. In order to ensure the effectiveness of the proposed control strategy

to operate the motor at the synchronous speed, the frequency pattern is also shown in

Figure 8.

The response of both the PV output voltage and the motor RMS voltage are shown

in Figure 9 for the given insolation level variation. It can be noted from Figures 8 and 9

that the voltage per hertz (V/f) is kept constant for controlled system.

Figure 7. Response of the pump flow rate with and without control for different insolation levels

at H D 10 m. (color figure available online)

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Improvement of a PV Pumping System Using SyncRel Motor 459

Figure 8. Run-up response of a SyncRel motor with and without control for different insolation

levels. (color figure available online)

Figure 9. Response of the PV output voltage and the motor RMS voltage with and without control

for different insolation levels. (color figure available online)

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

460 M. Nabil et al.

Figure 10. Response of the PV output power with and without control for different insolation

levels. (color figure available online)

Figure 11. Response of the pump flow rate with and without control for different insolation levels

at H D 10 m. (color figure available online)

Figure 10 shows the response of the PV output power for insolation levels of 35%,

25%, and 22%. At these insolation levels, without control, the PV output power is less

than the maximum available power. However, it is clear from Figure 10 that, using

the MPPT control strategy, the steady-state PV output power is increased to be equal

to the corresponding maximum value shown in Figure 3. As a result of extracting the

maximum power from the PV array, the PV voltage as well as the motor voltage are

increased, as shown in Figure 9.

Figure 11 shows the pump flow rate at a total pumping head of 10 m corresponding

to the adopted insolation changes given. It can be noted that, due to using the MPPT

control strategy, the pump flow rate is increased compared with uncontrolled system.

5. Conclusions

This article has presented a simple control strategy to improve the performance of a

SyncRel motor drive system fed by a PV generator suitable for pumping loads. The

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Ta

ble

1

Fin

alo

bta

ined

resu

lts

of

the

pro

po

sed

con

tro

lst

rate

gy

Inso

lati

on

level

Mai

nfe

atu

res

25

:5

0%

50

:5

5%

55

:1

00

%

Cap

abil

ity

of

star

tin

g

un

der

the

giv

en

pu

mp

ing

load

Wit

ho

ut

con

tro

lN

ot

stab

le(a

syn

chro

no

us

mo

de)

Sta

ble

(sy

nch

ron

ou

sm

od

e)

Wit

hco

ntr

ol

stra

teg

y

Sta

ble

(sy

nch

ron

ou

sm

od

e)

usi

ng

V/f

con

tro

l

No

tre

qu

ired

25

:5

0%

50

:5

5%

55

:1

00

%

Mo

tor

vo

ltag

eW

ith

ou

tco

ntr

ol

Eq

ual

or

less

than

the

rate

dval

ue

Hig

her

than

the

rate

dval

ue

Wit

hco

ntr

ol

stra

teg

y

No

tre

qu

ired

Mai

nta

ined

atit

sra

ted

val

ue

usi

ng

the

inver

ter

mo

du

lati

on

ind

ex(M

)

con

tro

lled

by

aP

Ico

ntr

oll

er

25

:5

0%

50

:5

5%

55

:1

00

%

MP

PT

Wit

ho

ut

con

tro

lA

vai

lab

leN

ot

avai

lab

le

Wit

hco

ntr

ol

stra

teg

y

Avai

lab

lean

d

extr

acte

du

sin

g

Pan

dO

alg

ori

thm

No

tre

qu

ired

461

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

462 M. Nabil et al.

proposed control strategy aims at ensuring a successful motor starting, the motor voltage

to be within a permissible range, and the PV array to operate at the MPP as possible. Two

modes of operation have been studied in detail depending upon the level of insolation

compared to the critical value. It has been found for the proposed system that the

critical and minimum insolation levels equal 55% (0.55 kW/m2) and 25% (0.25 kW/m2),

respectively. The critical insolation level is the insolation below which the SyncRel

motor cannot work synchronously under the given pumping load. On the other hand,

the minimum insolation level represents the insolation below which the motor cannot

run. In the first mode of operation, in which the insolation level is higher than the

critical value, it has been found that the motor voltage is higher than the corresponding

rated value. The modulation index (M ) of the inverter has been used to control the

motor input voltage and maintain its level at the rated value. However in the second

mode of operation, in which the insolation level is less than the critical value, it has

been found that the motor cannot reach synchronous speed when loaded by the given

pump. Employing a voltage per hertz (V/f) control method has been suggested to remedy

this situation. Moreover, MPPT has been applied only at all insolation levels less than

50%. The P and O algorithm has been used for MPPT due to its simplicity and low-cost

implementations. The obtained simulation results prove the effectiveness of the control

strategy on system performance. As a result, it has been observed that, using the MPPT

control strategy, the pump flow rate has been increased compared with an uncontrolled

system. The final obtained results of the proposed control strategy can be concluded as

shown in Table 1.

References

1. Betka, A., Perspectives for the Sake of Photovoltaic Pumping Development in the South,

Doctoral Thesis, University of Banta, Algeria, 2005.

2. Elgendy, M. A., Zahawi, B., and Atkinson, D. J., “Comparison of directly connected and

constant voltage controlled photovoltaic pumping systems,” IEEE Trans. Sustain. Energy,

Vol. 1, No. 3, pp. 184–192, October 2010.

3. Raju, A. B., Ramesh Karnik, S., and Jyoti, R., “Maximum efficiency operation of a single

stage inverter fed induction motor PV water pumping system,” First International Conference

on Emerging Trends in Engineering and Technology, pp. 905–910, Nagur, India, 16–18 July

2008.

4. Chandrasekaran, N., Ganeshprabu, G., and Thyagarajah, K., “Comparative study of photo-

voltaic pumping system using a DC motor and PMDC motor,” International Conference on

Advances in Engineering, Science and Management (ICAESM), pp. 192–132, Nagapattinam,

India, March 2012.

5. Malla, S. G., Bhende, C. N., and Mishra, S., “Photovoltaic based water pumping system,”

International Conference on Energy, Automation, and Signal (ICEAS), pp. 1–4, Bhubaneswar,

India, 30–31 March 2012.

6. Corrêa, T. P., Seleme Jr., S. I., and Silva, S. R., “Efficiency optimization in stand-alone

photovoltaic pumping system,” Renew. Energy, Vol. 41, pp. 220–226, May 2012.

7. Chenni, R., Zarour, L., Bouzid, A., and Kerbach, T., “Comparative study of photovoltaic

pumping systems using a permanent magnet synchronous motor (PMSM) and an asynchronous

motor (ASM),” Rev. Energ. Ren., Vol. 9, pp. 17–28, 2006.

8. Zarour, L., Chenni, R., Borni, A., and Bouzid, A., “Improvement of synchronous and asyn-

chronous motor drive systems supplied by photovoltaic arrays with frequency control,” J. Elect.

Eng., Vol. 59, No. 4, pp. 169–177, 2008.

9. Rashad, E. E. M., and Shokralla, S. S., “PV system fed DC motor controlled by boost

converter,” Eng. Research Bull., Vol. 22, No. 2, pp. 237–252, 1999.

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

Improvement of a PV Pumping System Using SyncRel Motor 463

10. Tsai, H.-L., Tu, C.-S., and Su, Y.-J., “Development of generalized photovoltaic model using

MATLAB/Simulink,” Proceedings of the World Congress on Engineering and Computer Sci-

ence, pp. 846–851, San Francisco, CA, 14–16 March 2012.

11. Benlarbi, K., Mokrani, L., and Nait-Said, M. S., “A fuzzy global efficiency optimization of a

photovoltaic water pumping system,” Solar Energy, Vol. 77, No. 2, pp. 203–216, 2004.

12. Mohan, N., Undeland, T., and Robbins, W., Power Electronics Converters, Applications and

Design, 2nd ed., New York: John Wiley & Sons, pp. 172–178, 1995.

13. Bacha, F., and Gasmi, M., ”Sliding mode control of induction-motor-pump supplied by pho-

tovoltaic generator,” IEEE International Conference on Industrial Technology, pp. 182–187,

Auburn, AL, March 2011.

14. Ferraz, C. A. M. D., and deSouza, C. R., “Reluctance synchronous motor asynchronous

operation,” Canadian Conf. Elect. Comput. Eng., Vol. 1, pp. 195–200, August 2002.

15. Daud, A.-K., and Mahmoud, M. M., “Solar powered induction motor-driven water pump

operating on a desert well,” Renew. Energy, Vol. 30, No. 5, pp. 701–714, April 2005.

16. Arrouf, M., and Ghabrour, S., “Modelling and simulation of a pumping system fed by photo-

voltaic generator within the Matlab/Simulink programming environment,” Desalination, Vol.

209, No. 1–3, pp. 23–30, April 2007.

17. Bose, B. K., Modern Power Electronics and AC Drives, Upper Saddle River, NJ: Prentice Hall

PTR, pp. 440–444, 2002.

18. Oi, A., Design and Simulation of Photovoltaic Water Pumping System, Master Thesis, Poly-

technic State University, San Luis Obispo, CA, September 2005.

19. Jamri, M. S., and Wei, T. C., “Modeling and control of a photovoltaic energy system using

the state-space averaging technique,” Amer. J. Appl. Sci., Vol. 7, No. 5, pp. 682–691, 2010.

Appendix A

Table A1

Parameters of PV cell

Open circuit voltage, Voc 0.54 V

Short circuit current, Isc 0.8 A

Series cell’s resistance, rs 0.05 �

Solar cell’s ideal factor, A 3.0191

Short circuit current temperature coefficient, ki 3e�3 A/ıC

Reverse diode saturation current, Irs 0:5e�3 A

Reference cell’s temperature, Tref 25ıC

Band gap energy, EG 2

Capacitance of the condenser, C 220 �F

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013

464 M. Nabil et al.

Table A2

Parameters of syncrel motor

Rated power, Po 470 W

Rated voltage, V 200 V

Rated current, I 2 A

Stator resistance, Rs 10 �

q-Axis stator inductance, Lqs 0.2228 H

d -Axis stator inductance, Lds 0.6366 H

q-Axis rotor inductance, Lqr 0.0177 H

d -Axis rotor inductance, Ldr 0.0745 H

q-Axis rotor resistance, rqr 19.29 �

d -Axis rotor resistance, rdr 38.9 �

q-Axis magnetization inductance, Lmq 0.2043 H

d -Axis magnetization inductance, Lmd 0.5621 H

Viscous friction, B 0.000005 Nm/rad/sec

Pole pairs, P 2

Moment of inertia, J 0.0015 Kg-m2

Table A3

Parameters of centrifugal pump

To 0.3 Nm

Ap 0.0003

�p 80%

Table A4

Parameters of PI controller

kp 0.45

Ki 7.5

Dow

nloa

ded

by [

Ess

am E

ddin

Ras

had]

at 0

9:54

31

Janu

ary

2013