Journal of Engineering and Applied Sciences 15 (6): 1407-1420, 2020ISSN: 1816-949X© Medwell Journals, 2020

Three-Phase Renewable Energy Inverter: Control, Real-Time Simulation andExperimental Results

1, 2Ahmed Emad-Eldeen, 3Adel A. Elbaset, 4Mustafa Abu-Zaher and 2Ramadan Mahmoud Mostafa1Department of Renewable Energy Science and Engineering,

Faculty of Postgraduate Studies for Advanced Science,2Department of Electronics, Faculty of Industrial Education, Beni-Suef University,

Beni Suef, Egypt3Department of Electrical Engineering, Minia University, Minia, Egypt

4Department of Electrical, Faculty of Industrial Education, Sohag University, Sohag, Egypt

Abstract: This research presents a technique of converting the Direct Current (DC) to an Alternating Current(AC) for the Photovoltaic (PV) system through a designed three-phase inverter tied to the grid. As it’s known,the inverter is characterized as an independent and high-quality device in addition to, considered the backboneof the Renewable Energy Sources (RESs). Therefore, this research presents a control strategy of active andreactive power using three-phase inverters which are connected to the grid. The presented control strategy isimplemented by using dSPACE MicroLabBox (1202). Moreover, the laboratory results are recorded usingMATLAB/Simulink Software. During the last decades, the sun has become the best ever source for generatingenergy as it considers a clean, renewable and environmentally friendly source, instead of depending on fossilfuel. Hence, solar energy has become the ideal searching field to sought after by scientists. This study haspresented a fulfill experimental behavior for the proposed controller including curves, simulation results andconclusions according to the obtained outcomes, also all the effort accomplished in this study to achieve thebasic motivation for this study which is designing a three-phase inverter characterized as complete reliabilityto control the active and reactive power easily, also it can Independently inject the active and reactive powerinto grid without exciting for any distortion in the wave forms .The presented control strategy for the activeand reactive power is executed by using indirect power control. Where the function of the Proportional-Integral(PI) controller includes the control of error signal which is the difference between the measured current and thefeeder current in order to reduce the error signal up to zero.

Key words: Three phase inverter, active power, reactive power, filter, photovoltaic, Space Vector Pulse WidthModulation (SVPWM)

INTRODUCTION

At the present time, the solar energy has become theleading source for renewable energyand is considered asthe inspiration source for modern technologies andapplications in most of fields around the world(Kanchev et al., 2011). As expected in the few comingyears, the fossil fuel will be drained, so, the necessity offinding RESs is the most important target for most of theresearchers for facing the world demands of energy andalso solving the pollutions problems. As well known, thesolar energy has been classified as a clean, ongoingenergy source which is able to be invested in severalfields and applications. The most important componentin the PV technology is the three-phase inverterwhich has an effective role as it refines the efficiencyof power transferred to the grid as well as some invertersoperate using the method of active power injection

(Suyata et al., 2015), after a complete study for multi-function inverters specific modes have been classified asfollow:

C The mode of maximum active powerC Reactive power providing mode relies on the voltageC Maximum reactive powerC Reactive power and power factor estimation

The technique of grid connectivity with a three-phaseinverter and improving the performance of includedfactors (Ozbay et al., 2017). In this study, the guidingprinciples for the phase locked loop (pll) scheme and thespace vector are illustrated. The (pll) is the responsiblepart for collecting the data of the variable factors for thegrid like; frequency, voltage amplitude, current amplitudeand phase angle, so that, it can be easy to controlthe whole system (Suyata and Po-Ngam, 2014). It is

Corresponding Author: Ahmed Emad-Eldeen, Department of Electronics, Faculty of Industrial Education, Beni-Suef University,Beni Suef, Egypt

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necessary to transfer the maximum power generated fromthe PV array to the grid. The most common controllersthat have been used in grid-connected three-phaseinverters are (PI, PID controller). This study brieflydiscusses the function of the PI controller, its function isto algorithmically compute the values of error throughmaking the comparison between the registered values ofthe measured current and the source current, thus, itdecreases the error percentage up to zero.

The control strategies of power for the VoltageSource Inverter (VSI) includes two basic types the directand the indirect control (Sarkar and Dalvi, 2017). Theindirect control type depends on the modulation ofvoltage like Space Vector Modulation (SVM) orsinusoidal (PWM) as it calculates the operating andstopping periods for the switches of inverter during theswitching duration and that happens within the estimationfor the voltage source such as the Voltage OrientedControl (VOC) (Susheela and Kumar, 2017). On the otherhand, the type of direct power control depends basicallyon the sliding mode structure and the technique of theDirect Torque Control (DTC) which is implemented bythe electrical devices on the driving regulation. One of thedisadvantages is that the value of switching frequencyis not constant. The main function of the dSPACEMicroLabBox is to perform accurate calculations forpower and also it is responsible for several functions suchas developing and checking the power controllers andreceiving data and dealing with the operations in a simpleand efficient method. The pattern of dSPACE providesperfect schematic arrangement, also it improves thesoftware using the MATLAB emulation and theempiricist controlling equipment. This researchillustrates the evaluation, measurements, structuresdesigns, laboratory results, observations, conclusions andanalysis for the suggested control method.

The experiments and procedures of measurementsand recording results of this study were carried out in themain laboratory of industrial education at SohagUniversity in order to achieve the main motivation forthis study which is represented in designing a three-phaseinverter connected to the grid with a perfect ability ofcontrolling the injection procedure for active and reactivepower into grid without any distortion. After acquaintancewith the previous related contribution for the subject ofthe three phase inverter connected to the grid, a particularsteps have been designed to implement the proposedstrategy for this study to reach the desired results.

In order to secure transferring the energy to the gridthrough the dc connection, the inverter is used to convertthe power from DC to AC form in the final phase(Blaabjerg et al., 2004, 2011; Magdy et al., 2019;Carrasco et al., 2006; Ramonas and Adomavicius, 2013;Meneses et al., 2012). The three types which have theability to control the three-phase inverters are: first one isthe synchronous rotating frame (d-q), the second type is the stationary reference frame (α-β) and the third is

the natural frame (a-b-c), due to the utilization of park transformation the voltages and currents of the threevoltages inverter are being transformed to (d-q) referencewhich turns harmoniously with the grid voltage. For thisreason, the inconstant factors of the three-phase inverterturn out to be DC amounts (Singh et al., 2011). The mostpopular used method for modulation of the three-phaseinverters connected to the grid is a Space Vector PulseWidth Modulation (SVPWM). The function of this method is to control the vector of the output voltage forthe inverter and also supplies the suitable paradigm forswitching by selecting the ideal switching that helps tominimize the frequency of switching and this alsoapplies to the switching losses, the SVPWM got lots ofadvantages. It features a fixed frequency for switching,the DC-link voltage is more accurate than the traditionalsine (PWM) (Yan et al., 2011; Adzic et al., 2009).Nowadays, the PLL considers one of the most important applicated methods used for synchronization.The basic function of the PLL represented in the (d-q)referral frame, the synchronization is being achieved by controlling the (q) element responsible for the voltageof the grid, it is adjusted to equal zero and the error actsas (PI) input, the grid frequency represented in theoutput of the (PI) regulator while the grid angel is theresult of the grid frequency integration which is used togenerate the synchronous source current (Chung, 2000;Guo and Wu, 2013; Moukhtar et al., 2018; Pastor andDudrik, 2013).

In this study, the modulation technique of SVPWMis presented. In case of existing of harmonics, the axis of(q, d) for the currents of the grid related and that wouldaffects the grid performance for current and to avoid thisproblem to occur, the axis of (d, q) for currents whichincluded in the decoupled elements for the currentcontroller of the grid could be replaced with the (d, q)axis of source currents for the grid (Yao et al., 2015).

MATERIALS AND METHODS

Connection model of a three-phase inverter to thegrid: The three-phase inverter connected to the grid andthe electrical circuit are illustrated in Fig. 1, the (dc)voltage source is connected to the inverter whichrepresented as (Vdc), also the whole system structure includes power switches there are six switches (S1:S6) andthere are the inductors of line filter (lg), Fig. 1 explainsthe bond that gather the power source, the producedvoltage for the inverter and the currents of line in thestationary source frame.

The designed structure of the electrical circuit for a three-phase inverter tied to the grid is shown inFig. 1. Whereas the terminal voltages of the three-phaseinverter are Va, Vb and Vc while the terminal voltages ofthe grid are as follow: ea, eb and ec. The generated currentsof the inverter which are being transferred to the grid are:ia, ib and ic.

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Fig. 1: Connection of three-phase inverter to the grid

Implementation of Park and inverse Parktransformations in order to achieve the conversionbetween the two-phases for the stationary frame referenceof the frame and also the synchronization for the twophases with reference frame as follow:

(1)a a a a

b b b b

c c c c

e i id

e = -R i -L idt

e i i

From Eq. 1, the stationary reference frame can betransformed into the d-q rotating reference frame usingparks transformation. By using Clark transformation, wecan obtain as in Eq. 2-5:

(2)a

b

c

1 1 e1 - -e 2 2 2

= ee 3 3 3

0 - e2 2

(3)

aa a

bb b

cc c

di-L -Ri

1 1 dt1 - -e di2 2 2

-L -Rie 3 dt3 3

0 -di2 2 -L -Ridt

(4)

di-L -Rie dt

e di-L -Ri

dt

(5)d d-1

q q

X X X XT , T

X X X X

Where:X : The inconstantT : The conversion to matrix structure

(6)-1cos t sin t cos t-sin tT ,T

-sin t cos t sin t cos t

Fig. 2: Inverter d-axis voltage

(7)d

q

di-L -Rie dt

Te di

-L -Ridt

(8)d

q

diLe Ridt

T -T -Te di Ri

Ldt

(9)d d d d-1

q q q q

e i id= -LT T -R

e i idt

Implementation of the chain rule differentiation:

(10)d d d-1 -1 -1

q q q

i i id d dT T = TT +T T

i i idt dt dt

(11)-1 -11 0 - sin t - cos td

TT = , T =0 1 cos t - sin tdt

(12)-1 0 -dT T =

0dt

(13)d d d q d

q q q qd

e i i id= -L + L -R

e i idt -i

Equation 13 can be communicated in the state spaceform as by Chung (2000). After that the generated voltageof the inverter in d-q reference frame can be obtained by:

(14)d d d q d

q q q qd

e i i id= +L - L +R

e i idt -i

(15)dd d q d

di= e +L - Li +Ri

dt

(16)qq q d q

di= e +L + Li +Ri

dt

Neutralization Eq. 15 and 16 represents the generatedvoltage of the inverter using d-q synchronous referenceframe as seen in Fig. 2 and 3.

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Iq R L LId + -

+ eq

-

+

-

Vq

J. Eng. Applied Sci., 15 (6): 1407-1420, 2020

Fig. 3: Inverter q-axis voltage

Fig. 4: Inverter prototype in the αβ stationary frame

The previous equations and electrical circuitsillustrate the prototype of the three-phase grid connectedinverter and explain the synchronization of d-q referenceframe. The control strategy of the active and reactivepower for the inverter depending on dealing efficiently theVd and Vq. Figure 4 explains the circuit of the inverterprototype in the αβ stationary frame.

Current control: The most widely used type of currentcontroller is (PWM) voltage source inverter and that isowing to its advantages like: fast response, precis control,accurate execution and also the ability of producing an(AC) output in sinusoidal form by securing continuoussupplies of (AC) power (Prodanovic and Green, 2003).The basic function of the current-controlled (PWM)voltage source inverters represented in imposing amandatory path for the vector of current for the used thethree-phase load. The selected strategy for the currentcontroller greatly affects in the whole quality for theconverter scheme (Salem and Atia, 2014).

During the usage of the current control, the procedureof measuring and comparison of the output currents forthe inverter with the reference values of signalsconsidered a basic step in order to generate the voltage ofthe inverter. The current controller considers the errors asan input, one of the PI controller functions is to controlthe constant amounts of dc which can be gainedusing (d-q) transformation. The algorithm features of thePI controller could be easily recompense the currenterrors for the dc amounts, the PI computes the error valueby making comparison between the value of the sourcecurrent and the value of the estimated current and afterthat the PI controller keeps on decreasing the error ratiotill it reach zero. The algorithmic calculations include twofixed gains; (kp) which represents the proportional gainand (ki) which represents the integral gain:

(17)dd d q d

di-e + Li = L +Ri = ud

dt

Fig. 5: Current controller schematic diagram

Therefore, the equation of the d-axis current loop canbe obtained in the s-domain as follows:

(18)(s)

(s )

d

d

I 1=

U R+LS

Referring to Eq. 16:

(19)qq q q q

div -e - Li = L +Ri = uq

dt

Thus, the equation of the s-domain transformation forthe q-axis current loop could be obtained as follows:

(20)(s)

(s)

q

q

I 1=

U R+LS

Obviously, it could be concluded that the system isclassified to be a first order type and that’s clearlyexplained in functions Eq. 18 and 20.

Figure 5 explains the scheme of the current control loop which could detect the value of the referencecurrent in order to control the active and reactive power (Lal and Singh, 2015). The error signal acts as the inputof the PI controller which can be calculated by makingcomparison between the source current and the factualcurrent of the inverter in the(d-q) source frame and thetransfer equation will be (1/(R+LS)) as determined fromfunctions as given in Eq. 18 and 20.

The algorithm controller: From Fig. 6, the voltages ofgrid ae recorded also the PLL is the responsible fordetecting the angle of the grid which has the abilityof achieving the transformation of the currents andvoltages of the grid from the reference frame of thea-b-c to the reference frame of the d-q and that iscould be achieved by using park transformation asshown in Eq. 21:

(21)ga

d

gbq

gc

2 4cos cos - cos -

3 32

3 2 4sin sin - sin -

3 3

1410

+ Id R L LIq -

ed

+

-

Vd

-

+

eαβVαβ

iαβ L R

Inverter Grid

i*dq Error

KP

Udq +

++

-

1

R+LS

KI

S

idq

J. Eng. Applied Sci., 15 (6): 1407-1420, 2020

Fig. 6: Controlling schematic diagram for the inverter

In order to compute the value of error, the referencecurrent and the d-q currents must be measured andthe PI controller receives the errors of the d-q frame asinputs, the reference d-element of the current candetermine the maximal value for the current for the grid. While the q-element of current has dominanceover the flowing of the reactive power. It is adjusted toequal zero just in the case of the injection of activepower, the voltage of feed forward are combinedwith the outputs of the PI and gathering the elements to generate the outputs voltages of the source inverterwhile the PI output is converted to α-β frame asshown in Eq. 22:

(22)d

q

cos sin

sin cos

The voltages of the α-β frame and the d-c link areapplied in the SVPWM, the (Vref) which refers to thevector of the output voltage for the reference as seen inFig. 7. The voltage of the source is the result of adding theα and β elements and the resulted values are applied toadjust the sector for the vector of the source voltagesubsequently, it could be easy to determine the degree ofthe vector angle.

From Fig. 7, the sectors alter every 60°, therefor, theonly way to locate the sector of the reference vector is toestimate the angle degree of the vector. The invertergenerates the voltage depending on two approachingvectors and also zero vectors, the (V1-V6) are representingthe active vectors while the (V0,V7) are the zero vectors,the interval for each vector can be computed for everysector.

The simulation pattern of the system: The currentcontroller is established by the utilization ofMATLAB\Simulink in order to execute the selectedsystem for the connected grid as seen in Fig. 8.

Fig. 7: Swapped sectors for SVPWM

Figure 9 shows the simulation results for the gridvoltage and the wave form of the angel vector. Theimproved (pll) has the ability of generating an anglein conjunction with the voltage of grid, it demandsnearly half a cycle for the (pll) to get the value of thesteady state for the right angle.

As expected for the controlled inverter it can beclassified to first order type and that’s clearly explained infunctions as given in Eq. 18 and 20. Therefore, the PIcontroller is capable for controlling the current of theinverter independently, the current controller (PI) includetwo fixed gains; (kp) which represents the proportionalgain and (ki) which represents the integral gain. The PIcontroller parameters can be selected by the trial and errormethod as (ki = 300 and kp = 50). The response of thecurrent controller for step change in the source current isillustrated as shown in Fig. 10 and 11. The range of stepchange in the d-axis for the source current locatedbetween 3A and 6A, while the q-axis reference current isadjusted to equal zero as seen in Fig. 10. The step changein the q-axis for reference current occurs in the range of(-5A to -2A) and the d-axis reference current is adjustedto equal zero as illustrated in Fig. 11. The current

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i*d

id iq

PI

Vgd

+ + +

+ +

+

Vgq -L

θ L id iq

+ i*q = 0

+ -

iq

id

dq

dq abc

SVPWM

Vdc Vdc

V*

V*

L

L

L

ia

ib

ic

Vgd

Vgq

Grid angle detemination

θ

abc dq

Vgb

Vgc

Vga oc

oE

Go

PI

V3(010) V2(110)

b

V5(001)

V1(100)

a,

V6(101)

V4(011)

c

Sector 5

Sector 4

Sector 3

Sector 2

Sector 1

Sector 6

V0(000)

V7(111)

Vref

J. Eng. Applied Sci., 15 (6): 1407-1420, 2020

Fig. 8: The selected pattern for the simulation system of the connected grid

Fig. 9: Simulation results of grid voltage and (pll) gridangle

Fig. 10: Simulation results of tracking in the (d-q) framefor the step change of the (Id) reference and the(Id) measured

controller characterized as quick and has a settleddynamic response for the step change for the current.From Fig. 12, the currents of the system have beensimulated and the emulation results of step changereaction for the three phase current are sketched accordingto the abc frame in the d-axis reference current, it can beeasy to realize that the controller features a quick, steadydynamic reaction for the step changes of the current.

Fig. 11: Simulation results of tracking in the (d-q) framefor the step change of the (Id) reference and the(Iq) measured

Fig. 12: Simulation outcome of the step change reactionfor the three-phase current

Hardware implementation: This study presents theenforcement of whole structure loops used for execute theexperimental procedures for the photovoltaic system asexplained in Fig. 13, also the required components andelements to establish the system of PV panels connectedto the grid to perform the experimental operation, whenthe modern technology is mentioned it is necessary todiscuss the great role of the inverter as significant part inthe PV systems, the interaction with a device like inverterrequires variable knowledge of the electrical circuitsand computer technology, electronic devices testing and

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0.00 0.02 0.04 0.06 0.08 0.10

Time (sec)

200

100

0.00

-100 V

olte

(V

) 2

(rad

)

va vb vc 2

Cur

rent

(A

)

8

6

4

2

\

0

0.0 0.01 0

Time (sec

.02 0.03 0.04 0.05 0.

Id Id

c)

06 0.07 0.08 0.09 0.1

d-ref Iq-ref

10

Iq

Time (sec)

0.0 0.02 0.04 0.06 0.08 0.10

Cur

rent

(A

)

1

0

-1

-2

-3

-4

-5

Id Id-ref Iq Iq-ref

Time (sec)

Cur

rent

(A

)

6 4 2 0

-2 -4 -6 0 0.0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

Ia Ib Ic I-ref

J. Eng. Applied Sci., 15 (6): 1407-1420, 2020

Fig. 13: Comprehensive overview of physical components

Fig. 14: Block diagram of executed single stage grid connected PV

designing the suitable programming to simulate theexperimental results. This study includes two basicssections the first section concerning about the laboratoryempiricist circuits which serve the whole system while thesecond section consists of the laboratory results andconclusions.

Figure 14 shows the PV system tied to the grid usingthree-phase inverter, this scheme consists of PV panels,three phase-inverter, power filter, dSPACE device,computer and oscilloscope device.

The execution of the hardware: The main circuits thatcompose the whole PV systems varies between the PV

panels, the sensors circuits, interactions loop, controlcircuits, all of these circuits are connected to the outlets ofthe dSPACE or the inverter. Each circuit has its specificfunction where the variation of the excited signals such asvoltage and current consequently become necessary tohave feedback for these signals, the level shifter whichacts as interacting circuits between the signals of PWMand inverter.

Photovoltaic system: The arrangement of the PV panelswhich consists of 12 modules and connected in seriesorder, the characteristics of the PV panel are shown inTable 1.

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Three-phase grid

Step-up transformer

Current sensors circuitFilter

Voltage sensors circuit

Oscilloscope

Computer with control desk

form dSPACE

dSPACE MicroLabBox

1202

Opt-couple circuit

IR2110 driver circuit

Inverter circuit

Power supply

Interfa

Voltage sensor

DC contactor

acing circuit

r Vdc Current sensor Idc

C Rsens

3

DSPACE MicroLab1202

Opto-isolator

MOSFET driver ICc

S6 S2 S4

S1 S3 S5

phase inverter powe

bBox

InPWM

PWM

VS

PWM C

V

FilteV U W

er circuit

nterfacing circuit

Voltage and currentSensing circuit

Iac Vac Transf

er

AC contactor

former

Grid

CB

J. Eng. Applied Sci., 15 (6): 1407-1420, 2020

Fig. 15: Basic opt-coupler circuit

Table 1: Electrical charteristics of a PV moduleParameter ValueNumber of series cells 12Maximum power rating 250 WOpen circuit Voltage (Voc) 37.4 VShort circuit current (Isc) 8.63 AMaximum power Voltage (Vmp) 30.7 VMaximum power current (Imp) 8.15 A

Suggested designing for the inverter: The inverter is avery important electronically equipment, the function ofthe inverter is to convert the DC signals to AC signals.The generated voltage of the inverter has two forms, thefirst form is the (AC) voltage (e.g., sine wave and squarewave) and the second form is the sine modulation(modulation sine wave). Semiconductor industry iscommonly used in the power devices like the inverter,MOSFET, IGBT, transistor or thyristor. The two kinds ofthe generated signals for the PV connected three-phaseinverters are: the low power and the medium power canbe applied by the usage of square wave output signal. Thehigh-power implementation is done by using the sinewaves output signal.

Opto coupler: The used opto-coupler in this circuitcharacterized by rapid, continuously switching and it isflexible to be easily triggered even with the smallvoltages. The gate drivers function is to obtain the signalpulses from the controlling board and then amplifythose signals in order to reach the required level of theswitching, the power circuits and the circuits ofcontrollers can be secluded by usage of the IGBTs andopt isolators loops. The generated (PWM) signal whichcome from the dSPACE of the inverters controllingswitches must be isolated away from the basic DC powerby usage of the device of TLP250 photo transistor couplerfor isolation as explained in Fig. 15.

As seen from figure, the circuit consists of sixopt-couplers which are connected. The resistance functionis to restrict the current in signal.

Fig. 16: IR2110 driver circuit

Fig. 17: Inverter circuit

MOSFET driver circuit: The suggested gate driver inthis circuit is the IR2110 of the international rectifier.With 14 pins pack the IR2110 has high voltage and speedpower, the MOSFET and IGBT drivers with high and lowside referenced output channels. The circuit of the IGBTor MOSFET driver which is explained in the circuit of thehardware components is shown in Fig. 16.

Function of inverting circuit: The main function of theinverting circuits to convert the income dc voltage to anac voltage. It also comes with pull-up, pull-down andactivated optocoupler circuit which can be operated byusing dSPACE unit. The voltage source inverter VSItakes a DC bus voltage and uses six switches arranged inthree-phase legs. From the middle of each phase legcomes from the line, the voltage on these lines must be abalanced three-phase sinusoidal waveform. This isachieved by a controlled switching to the gate of theIGBTs as shown in Fig. 17. In VSIs, the input voltage ismaintained constant and the amplitude of the outputvoltage is independent of the nature of the load. But theoutput current waveform as well as magnitude dependsupon nature of load impedance. Three-phase VoltageSource Inverters (VSIs) are more common for providingadjustable frequency power to industrial applications ascompared to single phase inverters.

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Fig. 18: dSPACE MicroLabBox (1202) controller

Table 2: The used element of the designed circuitComponent DescriptionIGBT IRG4PC50UDIGBT DRIVER IR2110Photo coupler TLP250

Table 3: The IGBT featuresCharacteristics ValuesDevice IGBTType IRG4PH50UDCurrent rating (ic) 24 AVoltage rating (VCES) 1200 VVCE (on) typ. 2.78 VVGE 15 V

In this research, the selected type of inverter is thethree-phase inverter; this type is proposed to achieve theoperation of controlling the designed circuit, the usedelements are detailed in Table 2 and also the IGBTfeatures are mentioned in Table 3.

dSPACE MicroLabBox: The proposed circuit of PWMcircuit has been executed by using the dSPACEMicroLabBox (1202) as shown in Fig. 18. The dSPACEis one of the most important components in the moderntechnology. Where it characterized as it can performvariable calculations. Furthermore, it can examine, detect,collect data and process multi functions which serves thewhole system. Platform for laboratory use, MicroLabBoxthat offers high computing power and comprehensivefunctionalities. MicroLabBox makes creating, optimizingand testing controllers and implementing data acquisitionapplications easy and cost-efficient for both industry andacademia.

Voltage sensor: In order to estimate the generatedvoltages of the grid three voltage sensors are needed andthe fourth sensor is used for estimating the voltage of thedc junction. The used sensors characterized are hall-effectsensors which has been made by LEM. Figure 19illustrates the design scheme for the sensors of the voltageand its connection method.

Fig. 19: Photo of the implemented voltage sensor board

Fig. 20: Photo of the implemented current sensor board

Fig. 21: Three-phase calculated voltages and angle (θ)of the grid (gauge v = 100 v/div, θ = 2 rad/div,t = 10 msec/div)

Current sensor: Three current sensors used to measurethe current injected to grid and one to measure DC currentof PV. Each current sensor can measure up to 25A. Thesensors are hall-effect sensors and are manufactured byLEM. The circuit of the implemented current sensor cardis shown in Fig. 20.

RESULTS AND DISCUSSION

As explained in Fig. 21, the simulation results ofdetecting the grid theta angle (θ) and the three-phase

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Fig. 22: Laboratory results for the (PWM) switchingmodels for the space vector during the firstsector

Fig. 23: Laboratory results for the (PWM) switchingmodels for the space vector during the secondsector

voltages, it is illustrated that the angle theta can bedetermined between 0° and 360°. The simulation resultsfrom Fig. 22-27 shows the laboratory results of thepulsated signals starting from the first sector and endingwith the sixth sector.

The active response of the current controller isexplained in Fig. 28. Values of ki = 300 and kp = 50. Therange of step change in the d-axis for the source currentlocated between 3A and 6A while the q-axis referencecurrent is adjusted to equal zero, the PI controller featuresa quick and steady response and the generated current isfree of excrescent or under shooting, the active responseof PI when the step change in the q-axis for referencecurrent occurs in the range of (-5A to -2A) and the d-axisreference current is adjusted to equal zero, the resultsshown in Fig. 29 can confirm that the proposed system iscapable of controlling both of reactive and activepower. Figure 30 shows the current of the d-axis referenceand the generated current of the three phase forsource current step changing, the figure also show up thestrength of the implemented controller to pursuit thequick alterations which occurs in the source currentwhilst the source current of the q-axis is adjusted to equalzero.

Fig. 24: Laboratory results for the (PWM) switchingmodels for the space vector during the thirdsector

Fig. 25: Laboratory results for the (PWM) switchingmodels for the space vector during the fourthsector

Fig. 26: Laboratory results for the (PWM) switchingmodels for the space vector during the fifthsector

Processing of active and reactive power: There are twostages of the experiments conclusions, the first section isthe results of steady state which ensure the suitableoperation for the suggested controller, the second stageis the transient operation which expose the flexibility ofthe system for observing and follow the changes thatoccurs in the reference orders.

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Fig. 27: Laboratory results for the (PWM) switchingmodels for the space vector during the sixthsector

Fig. 28: Dynamic reaction for the current controller in theframe of dq for step change (Id) reference(gauge: I = 5 A/div, t = 10 msec/div)

Fig. 29: Dynamic reaction for the current controller in theframe of dq for step change (Iq) reference(gauge: I = 5 A/div, t = 10 msec/div)

Operation of steady state: The graphs shown inFig. 31-33 explain the laboratory results for the procedureof the steady state. These graphs explain the receivedactive and reactive power into grid, the graphs recordeddifferent conditions for the current and the voltage for thephase (A). In graph shown in Fig. 31 illustrate the statueof the power factor unity. While Fig. 32 shows the zerostate of the power factor, the angel measurement betweenthe voltage and the current of phase (A) is 90°, the

Fig. 30: Step change of generated three phase currentand (Id) reference (gauge: I = 5 A/div, t = 10msec/div)

Fig. 31: Experimental stage for the steady state ofthe power factor unit process [Scale: V = 150V/div, I = 5 A/div, P = 1000 W/div, t = 20msec/div]

Fig. 32: Experimental stage for the steady state whenthe power factor equals zero [Scale: V = 150V/div, I = 5 A/div, P = 1000 W/div, t = 20msec/div]

operation of the power factor delay of 0.7 is shownin Fig. 33 whereas the active and reactive power areevenness whilst the current of phase (A) has a 45º laggingabout the voltage of phase (A).

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Fig. 33: Experimental stage for the steady state at theprocedure of power factor 0.7 lagging [Scale:V = 150 V/div, I = 5 A/div, P = 1000 W/div,t = 20 msec/div]

Fig. 34: Laboratory results for the changing step for theactive power whereas the reactive power = 0,[Scale: V: 150 V/div, I: 5 A/div, P: 1000 W/div,t: 20 msec/div]

Transitional period: The process of the transientresponse includes the readings and information and dataof the active and reactive power, the graph of Fig. 34shows the transient response in the case of changing stepfor the active power in the meanwhile there is noinjection for the reactive power, the current which hasbeen injected is in phase with the voltage phase graph ofFig. 35 explains the changing step in reactive power in themeanwhile there is no injection for the active power, thecurrent which has been injected is 90º lag by the voltageof the grid. Figure 36 illustrate the performance of thesystem during the changing of step for the reactive power,after the changing step both of active and reactive powerare equal, the procedure is switched from the power factorunity to the power factor (45º) lag and that happens afterthe changing step for the reactive power source. Figure 37explains the step change for the reactive and active powerwhich transferred from the power factor unity to theprocedure of power factor by 0.7 lag.

Fig. 35: Laboratory results for changing step for thereactive power whereas the value of the activepower = 0 [Scale: V: 150 V/div, I: 5 A/div,P: 1000 W/div, t: 20 msec/div]

Fig. 36: Laboratory results of the changing step for thereactive power where the active power has fixedvalue [Scale: V: 150 V/div, I: 5 A/div, P: 1000W/div, t: 20 msec/div]

Fig. 37: Laboratory results of changing step for the activeand reactive power from power factor unit to(0.7 lag) power factor process [Scale: V: 150V/div, I: 5 A/div, P: 1000 W/div, t: 20 msec/div]

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CONCLUSION

This study has presented a three-phase designedinverter connected to PV system which has features of ahigh performance and clean produced energy. A model ofthree-phase designed inverter connected to the grid hasbeen established and supplied with suitable programmingcircuits. The controlling task consists of two basicscontrol circuits as follow; the current control circuit andthe dc-link voltage circuit, the PI controller function is todominate the active and reactive power. The proposedtechnique for the executed system has been exposed toseries of procedures like measurements, testing, analysis,simulation using (MATLAB/Simulink), designing anddeveloping of circuits, recording and detecting results andnotes, sketching and comparing resulted values for theexperimental results. Eventually, the injection of powerinto the grid, power factor unit and pure sinusoidalcurves have been represented using waveforms andMATLAB/Simulink. Moreover, all the previous processesproved that the selected technique for executing thesystem has been designed and implemented in a verygood approach.

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