Engineering Science and Technology, an International Journal 23 (2020) 1058–1067

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Engineering Science and Technology,an International Journal

journal homepage: www.elsevier .com/locate / jestch

Full Length Article

Solar PV-BES in distribution system with novel technique for DC voltageregulation

https://doi.org/10.1016/j.jestch.2020.01.0042215-0986/� 2020 Karabuk University. Publishing services by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

⇑ Corresponding author.E-mail addresses: giranaveen@yahoo.com, naveen_6150024@nitkkr.ac.in

(N. Gira).

Peer review under responsibility of Karabuk University.

Naveen Gira ⇑, Anil Kumar DahiyaElectrical Engineering Department, National Institute of Technology, Kurukshetra, 136119, India

a r t i c l e i n f o a b s t r a c t

Article history:Received 4 September 2019Revised 31 December 2019Accepted 22 January 2020Available online 10 February 2020

Keywords:Solar photovoltaic (SPV)Battery energy storage (BES)Reactive powerDistribution systemDC link voltage

The incremental penetration of solar photovoltaic (SPV) is creating voltage related issues in the distribu-tion system. The problem gets complicated during the peak load demand and peak generation from SPV.This article proposes the real time implementation of SPV and Battery energy storage (BES) to regulatethe DC link voltage and to compensate reactive power while supplying active power to local load in gridconnected operation. The DC voltage regulation controller is derived using the curve fitting toolbox inSimulink (MATLAB) software. The combined operation of SPV and BES is investigated to sure that voltageprofile of the distribution system is improved. Variations in PV generation and load are considered to ver-ify the efficacy of the proposed scheme. Further, simulation is carried out in real time environment usingreal time (OPAL-RT) simulator. The results demonstrate that the reactive power compensation capabilityof SPV, combined with BES, is very effective to improve the voltage profile while supplying active powerto the local loads.� 2020 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC

BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

There is ever-increasing demand for energy on one handwhereas on the other hand the fossil fuels available on our planetare depleting at a faster rate than earlier. Therefore, the renewableenergy sources are becoming viable alternate to the conventionalenergy sources with technological improvements. Solarphotovoltaic-based electricity is in particular, gaining momentumover the last decade. Rooftop based distributed generation is a sig-nificant part of the overall scenario in the developed and mostdeveloping countries. The future growth scenario for rooftop SPVin India is as in Fig. 1. This trend shows that reasonably gooddemand will be met from rooftop SPV by 2022, as per the clean cli-mate commitments [1]. However, total rooftop SPV potential con-sidering the market dynamics such as supply, demand, andconsumer acceptability is 124 GW [2].

The incentives provided by the government coupled with grow-ing awareness among the consumers are making SPV a popularalternate for distributed generation. SPV based power generationcan contribute to the grid capacity and thus defer the requirement

to invest in grid expansion. The voltage regulation at the customerpoint improves with the distribution generation.

However, the high-penetration of renewable energy in to thedistributed generation brings certain technical challenges to powersystem engineers. Active power supplied from SPV into the distri-bution system can make the voltage level rise. This problembecomes severe in the midday when SPV generation is maximum.In addition, the peak load condition in the distribution systemcauses the voltage variations. Tap changer transformer is utilizedto control the voltage [3]. However, fast on-load tap changer(OLTC) with the definite time setting is implemented in distribu-tion substations [4]. Besides, frequent tap changing of transformerresults in increased feeder losses and transformer stress.

The grid voltage can also be kept within acceptable limits bySPV power curtailment, which may not be appropriate, as the sub-stantial amount of energy will be lost. Reactive power control canalso be utilized to maintain the voltage profile. Various researchstudies are considered on diverse integrated and distributed reac-tive control techniques [5–8]. Stetz et al. suggest independent con-verters to improve voltage utilizing their reactive capability, whichalso limits the active power supply resulting in generator revenueloss [9]. Moreover, the reactive power compensation to maintainthe voltage is not as effective in low voltage distribution systemas in high and medium voltage systems. Therefore, in distributionsystem, a more appropriate approach is essential to keep the volt-age level within acceptable limits.

Fig. 1. Solar rooftop projected targets of government of India.

Fig. 2. Block diagram of the complete test setup.

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Utilizing the energy storage to store the extra energy generatedrather than curtailing it is a suitable alternate to remove the over-voltage issue [10]. In this case, BES is suitable due to compact sizesand can perform the task of maintaining the voltage profile in dis-tribution systems. This can be done by shifting the charging of BESat the time when load is minimum and SPV generation is maxi-mum. The BES can be discharged as and when the load increasesand the SPV generation diminish. The voltage issues caused bySPVs at the consumers point are countered using energy storage.Super capacitors based energy storage is suitable for the lowenergy density and high power applications. However, BES is idealfor high energy and long duration applications such as residentialloads. The control scheme for SPV-BES is designed to work as con-trolled current source working in phase with grid supply in thisstudy. Hugihara et al. have suggested synchronized regulator forlarge as well as small commercial loads and utilized concentratedgrid level storage with complicated regulation methods [11]. How-ever, it is not a viable solution in distribution system due to highlosses and complicated regulation methods.

BES is also suitable in the regulation of variable output of SPVdue to partial shading and cloud transients. SPV along with BEScan be utilized to improve the active power supply from SPVaffected by partial shading. Taking into consideration the cloudingand seasonal fluctuation, the SPV capability is required to berescheduled. Coordinated control of SPV-BES is proposed in thiswork for voltage control in distributed systems. Distributed con-trols are placed in each location to counter the requirement ofmetering setup.

This paper proposes the coordinated regulation of active poweralong with reactive power compensation of grid-tied SPV-BES. TheMPPT algorithm is integrated in the control scheme to extract thepeak power output from SPV at any instance under the variableoperating conditions. Curve fitting toolbox in Simulink (MATLAB)is used to derive the controller equation for a novel DC voltage reg-ulator. Variations in solar irradiance and load changes are also sim-ulated to verify the effectiveness of the proposed system. Inaddition, reactive power compensation is utilized to improve thevoltage profile. The simulation is done in MATLAB/Simulink envi-ronment first and then in OPAL-RT based real time simulation tovalidate the proposed scheme.

Fig. 3. The Single diode solar cell equivalent circuit.

2. System description and modelling

Grid-tied SPV-BES configuration: The SPV-BES connected withgrid is displayed in Fig. 2. The SPV is joined with the DC link capac-itor via DC/DC converter. The BES is also coupled to the DC link

capacitor through buck-boost DC/DC converter. The DC side ofthe structure is connected to the AC side using DC/AC converter.Variable AC loads are coupled at point of common coupling(PCC). The control structure measures the voltages at PCC and gridside and currents at load and SPV-BES side. The signals are fed tothe controller to perform energy flow management. The well-known mathematical models are explained below.

2.1. SPV model

The single-diode PV cell equivalent model comprises a currentsource connected in shunt with the diode and series, parallel resis-tances, namely Rs, Rsh, as displayed in Fig. 3. The PV output current(I0) and reverse saturation current (Irr) are represented in eq. (1)and eq. (2), respectively.

The saturation current of diode (Id) depends on the operatingtemperature of solar panel, as given in Eq. (3).

Fig. 4. Power versus voltage characteristics of solar cell at different solar irradiance.

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Io ¼ Ipv � Id expq Vop þ I0Rs� �NsAKTak

� �� 1

� �ð1Þ

Irr ¼ Iscr

expð qVocKANsTrk

Þ � 1h i ð2Þ

Id ¼ IrrTak

Trk

� 3

expqEg

AK

� 1Trk

� 1Tak

� ð3Þ

where I0, Ipv, Id, Irr, Ish, Iscr, Isc are PV output current, PV current,diode saturation current, reverse saturation current, shunt current,module short circuit current and short circuit current, respectively.Vop, VOC are PV output voltage and open circuit voltage, respec-tively. Tak, Trk are actual temperature (�K) and reference tempera-ture (⁰K), respectively. Rs, Rsh are series resistance and shuntresistance, respectively. A is diode ideality factor, Ns is number ofcells in series, K is Boltzmann constant (1.38065*10�23 JK�1), q ischarge of electron (1.6021*10�19 C), and Eg is band gap energy ofmaterial used (1.12 eV (Si)). The detailed specifications of the solarPV panels used is given in Table 1.

The SPV array is joined to the DC link capacitor via a DC/DCboost converter. The function of this converter is to achieve maxi-mum power from SPV. The SPV array consists of solar modules.Solar modules when joined in series arrangement strings and arefurther joined in parallel as an array [12]. The power voltage char-acteristic of the SPV is given in Fig. 4. At varying operating irradi-ance, the maximum output point of the SPV lies on differentpower voltage curves. It is also evident from the power voltagecurve that in certain operating irradiance, the output from SPV var-ies according to the voltage.

To make best use of the SPV energy, the SPV needs to function atmaximum power point. This is achieved by varying the outputvoltage of SPV utilizing boost converter. The maximum powerpoint tracking (MPPT) techniques are extensively developed andreported in various researches. Perturb and observe (P&O) methodis implemented in this work. The solar irradiance is varied to showthe operation of SPV in full day operation. The solar irradianceincreases around noon and then drops in afternoon. The tempera-ture is kept constant for the simulation. It is observed that the SPVvaries its voltage under solar irradiance variation. As the graph inFig. 4. displays, the power output tracks the variation in solarirradiance.

2.2. Battery model

The irregular nature of renewable energy based electricitysources emphasised the requirement of storage technologies tolevel the power gap in the grid. In this research, BES is connectedto the grid-tied SPV system at DC link through buck-boost DC con-verter for the discharging and charging of BES.

VBAT ¼ VOB � RbIb � KQ

Q � Ribdt

þ Be�AR

ibdt

�ð4Þ

SOC ¼ 100� 1�RibdtQ

� ð5Þ

Table 1Technical specifications of the PV panels.

Parameters Values

PV output power at MPP (kW) 4.03Open circuit voltage (Volts) 36.3Short circuit current (Amperes) 3.18Cells per module (Nos.) 60Parallel Strings (Nos.) 3Series coupled modules per string (Nos.) 16

where VOB is the battery open circuit voltage, Rb is battery internalresistance, Ib is the discharging current of the battery, Q is totalcapacity of battery (2.1 kWh), K is polarization voltage, A is expo-nential capacity, and B is exponential voltage. The battery dischargecharacteristic of Simulink (MATLAB) based model is displayed inFig. 5.

The crucial factors to depict the behavior of BES are the terminalvoltage and state of charge (SOC) as given in Eqs. (4) and (5) [13]:

2.3. Interlinking converter model

The DC/AC converter is described in Fig. 6. The converter can becontrolled to supply variable active power while compensatingreactive power between grid and SPV-BES.

The reactive power compensation helps in maintaining voltageprofile at the distribution point. The mathematical modelling of theAC part of the converter is given in eq. (6).

Vi ¼ V 0g þ If Rf þ Lf

dIfdt

ð6Þ

where V’g and Vi are the grid voltage vector and converter voltage

with respect to the micro grid side, correspondingly; Lf the filterinductance; If the inverter yield current vector; Rf the correspondingreactance. The converter output active and reactive powers are givenin eq. (7) and (8), respectively.

P ¼ 32Re V 0

gI�f

h i¼ 3

2V 0

gaIfa þ V 0gbIfb

�ð7Þ

Q ¼ 32Im V 0

gI�f

h i¼ 3

2V 0

gaIfa � V 0gbIfb

�ð8Þ

The dynamic behavior of LC filter capacitor can be expressed byEq. (9).

CfdVc

dt¼ If � IL ð9Þ

where Vdc is DC link capacitor voltage, IL is value of load current, Cf

is the value of filter capacitor. The mathematical representation ofthe DC/AC converter is explained in Eq. (10).

Vi ¼ Vdc þ If Rf þ LfdIfdt

ð10Þ

3. Control diagrams of the suggested setup

The control of the entire setup is displayed along with variouscomponents of the setup are explained separately in the followingsections.

Fig. 5. The discharge characteristics of BES.

Fig. 6. The single line diagram of interlinking converter in grid connected mode.

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3.1. DC/DC boost converter controller

The MPPT is executed using the DC/DC boost converter con-nected to the SPV. The variation of irradiance of SPV will resultin the relative deviation in the output power of SPV. The efficiencyof system increases when the SPV power is maintained at maxi-mum power point. There are numerous methods to implementMPPT by varying the duty cycle (D) of the DC/DC boost converter.These methods include Perturb and observe (P&O), IncrementalConductance, Neural Network and Fuzzy Logic [14,15]. In thiswork, P&O MPPT technique is used due to this being simple toimplement.

Effectiveness of MPPT algorithm used in this research is show-cased in Fig. 7. And Fig. 12(e). The solar irradiation when reducedfrom 1000 W/m2 to 550 W/m2, tracking of MPP is given inFig. 12(e).

The voltage (Vpv) and current (Ipv) variations are measured andthen the measurements are fed to the P&O algorithm. Accordingly,D for DC/DC boost converter is calculated. The variation in D resultsin variation of output voltage, which in turn will change the outputpower. The output power is tracked using these small perturba-tions as explained in the algorithm given in Fig. 8.

Fig. 7. MPP tracking at various solar irradiance.

3.2. Battery charging and discharging control

The lead acid battery is utilised to accumulate and supplyenergy. The battery will be charged from the solar energy whensolar irradiance is higher than a certain value. This value is deter-mined by the SPV voltage measurement. The battery is coupledwith the DC link capacitor via a DC/DC buck-boost converter as dis-played in Fig. 9. Lbat is battery inductance, S1 and S2 are the switch-ing devices of DC/DC converter, Vb is the battery voltage, C is theDC link capacitor, and Vdc is the DC link voltage.

The battery discharges when the SPV is incapable to supply theloads under reduced irradiance. The converter permits the energyto flow in both direction i.e. to the battery and from the battery.The control strategy of this buck boost converter is displayed inFig. 10. The DC link voltage is maintained in different scenarios.This voltage (V*dc) is taken as reference voltage. When referencevoltage is compared to the actual voltage (Vdc) of the battery, cur-rent signal (I*bat) is generated from the novel controller. This cur-rent signal is compared with the actual battery current (Ibat).Accordingly, the switching signals are generated by pulse widthmodulation (PWM) technique. SOC* and SOC are the referenceSOC and battery SOC, respectively.

3.3. Voltage source converter control

In the grid tied mode, the PV-battery based setup is able tomaintain the DC link voltage using the DC/DC converter. The DC/AC converter works to deliver a stable AC voltage for the loads con-nected at the PCC. The capacitor voltage is maintained for thestable operation of the setup. The DC voltage controller is basedon the equations derived from the curve fitting toolbox ofMATLAB/Simulink [16–18]. The Curve Fitting Toolbox is a combi-nation of M-fie functions and graphical user interfaces (GUIs)based on the MATLAB environment. The toolbox offers severalmethods, comprising parametric fit. A dedicated equation demar-cated by the designer to cater the explicit curve fitting require-ments, can be utilised to achieve a parametric fit. The toolboxgives an approximation with declared accuracy of the actual con-troller. The controller performance is evaluated using the parame-ters such as the mean squared error (MSE) and the approximationaccuracy. The choice measures of curve fitting technique is subjec-tive to fit goodness factors. The results of fitting the data are rela-tively reliable which can be considered as a standard. The toolboxis utilised in this work in place of the conventional controller (PI orPID). In addition, the toolbox can be used to replace these con-trollers having the advantages of pre-knowledge of accuracy ofthe controller. However, the designer must have the data to design

Fig. 8. P&O method MPPT control diagram of the SPV.

Fig. 9. The circuit diagram representation of boost converter (DC/DC buck-boost).

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the controller, which is the limitation of the curve fitting method.The graphical user interface (GUI) of curve fitting toolbox is dis-played in Fig. 11.

The equation derived using the curve fitting toolbox is Eq. (11)

f xð Þ ¼ a1 � sin b1 � xþ c1ð Þ ð11Þ

where coefficients (with 95% confidence bounds), a1 = 2454 (2436,2471), b1 = 0.0004076 (0.0004047, 0.0004105), c1 = �5.01*10�7

(�5.159*10�7, �4.861*10�7).The fit goodness factors are:Steady state error (SSE) = 0.03569 and R-square = 1, and root

mean square error = 0.00138.The exchange of power is monitored using the current flowing

in and out of the converter and the voltage at grid and the PCC.

Fig. 10. Battery charge/disch

The function of the static compensator (STATCOM) system is toregulate the flow of power from the DC to AC side and vice versa.The flow of power is controlled using a well-known dq referencecontroller [19], as displayed in Fig. 12. The grid voltage, grid cur-rent, and DC voltage are taken as the input parameters to the con-troller. The phase-locked loop (PLL) is applied to evaluate the angle(h) for determining the dq parameters. The difference of instanta-neous voltage and desired voltage values is used to find out thecurrent reference IQ*. To regulate DC link voltage, the value of DClink voltage is observed and related to the voltage reference Vdc,the current reference ID* is actuated. The mathematical productof IQ* and ID* with cos h and sin h, respectively is used to computerequired the real component of current Ir*. The required imaginarycomponent of current Ii* can also be attained by mathematical pro-duct of IQ* and ID* with cos (h + 2p/3) and sin (h + 2p/3), respec-tively. The real and imaginary components of PV-STATCOMcurrent are deducted from required IQ* and ID* to check the currentvariations. Then, the output signals (VSabc) generated from currentregulator are supplied to pulse width modulator to produce the fir-ing pulses of the converter switches. The q-axis component is usedfor voltage regulation and reactive power compensation. The d-axis component is utilized to retain the constant DC voltagethrough active power control [20].

The reactive power control signal is generated according to thegrid parameters as given in eq.

Qref ¼VG � VGN

VGN� 100 � k var ð12Þ

where VG is the measured voltage of grid, kvar is the reactive powercompensation coefficient, and VGN is the reference voltage of grid.

arge controller diagram.

Fig. 11. The curve fitting GUI of Simulink (MATLAB) software.

Fig. 12. Block diagram representation of the PV-Battery controller diagram based on synchronous reference frame (SRF) theory.

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The grid voltage is used in the reactive power compensation as thereference value. Accordingly, this voltage when dips at PCC, itresults in the reactive power compensation from the PV-BES andthe voltage rise results in the reactive power consumption. This fea-ture of the PV-BES setup helps to improve the operation of grid interms of power quality. The detailed response of proposed con-troller is seen in the results section.

4. Results and discussion

As described in the previous section, the controller enables thePV-battery setup to not only supply active power but also compen-sate reactive power at PCC. The PV-battery setup is working in thegrid-tied mode of operation for the entire simulation.

Time instant t1: AC load of 6 + j0.8 kVAR is increased to 10 + j1.2kVAR. The solar PV output is maximum at this instant, so the con-troller generates the signal to charge the battery.

Time instant t2: The load is switched down to the previous val-ues of 6 + j0.8 kVAR from 10 + 1.2 kVAR with the constant solarirradiance level of 1000 W/m2.

Time instant t3: The reactive load remains unchanged whileactive load is switched to 10 kW from 6 kW.

Time instant t4: The reactive load is increased to 1.2 kVAR from0.8 kVAR in order to display the reactive power compensationcapability of the setup, keeping the active power at 10 kW.

Time instant t5: Solar irradiance is ramped down from 1000 W/m2 to 550 W/m2 to demonstrate that battery supplies the requiredactive power when solar PV is working at a lower capacity due tolow irradiance level. The solar PV current drops as evident fromFig. 13(g). However, the battery current increases to meet thepower demand at PCC. Also, changes in SOC of the battery is dis-played in the Fig. 13(h).

Time instant t6: The AC load is decreased to 6 + j0.8 kVAR from10 + j1.2 kVAR.

4.1. Simulation results

In order to display the capabilities of the proposed setup, thecomplex cases are demonstrated with various load conditionsand operation modes. The level of solar irradiance ramps downfrom 1000 W/m2 to 550 W/m2 at time instant t5 to demonstratethe operation of setup in variable solar irradiance. The detailed

Fig. 13. Graphs highlighting the simulation results of the test setup. (a) Three-phase ac voltage at PCC (b) Single phase (R-phase) voltage at PCC (c) Three phase AC current atPCC (d) Single phase AC current at PCC (e) Active power (f) Reactive power (g) SPV and battery current (h) DC link voltage (i) Battery % SOC (j) Frequency (k) Output voltage ofDC/AC converter (l) Voltage THD at PCC.

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Fig. 14. (a) Setup Architecture. (b) Test setup.

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results highlighting the system performance are displayed inFig. 13. The zoomed in waveforms of three phase AC voltage andsingle-phase AC voltage are displayed in Fig. 13(a) and Fig. 13(b),respectively. The graph shows that the voltage waveforms aresmooth and without harmonics. Three-phase AC current andsingle-phase AC current waveforms are displayed in the Fig. 13(c) and (d), respectively, highlighting the switching of loads atPCC. The current waveforms display that the filtering equipmentwoks effectively in removing the fluctuations caused by theswitches of DC/AC converter. Active and reactive power graphsare displayed in Fig. 13(e) Fig. 13(f), respectively. The load is variedat various time instants to display the compensation capability ofthe proposed system. SPV and battery current are exclusively dis-played in the Fig. 13(g). The graph shows that the battery is able toswitch from charging to discharging mode as per the requirementsof loads and availability of SPV.

The DC link voltage remains constant for most part of simula-tion period under variable operating conditions as displayed inthe Fig. 13(h). However, there is some minor fluctuation in DC linkvoltage at the switching of loads. The battery SOC varying fromcharging to discharging at time instant t5 is displayed in Fig. 13(i). The battery charge controller is capable to sense the dip inSPV output and subsequently operate the battery to supply thepower requirements. The supply frequency is displayed in Fig. 13(j), which highlights that the system remains stable under suddenchanges in operating conditions.

Single-phase voltage waveform of DC/AC converter is displayedin Fig. 13(k). The output of converter passes through the passive fil-ter connected between the converter and the PCC. The total har-monic distortion (THD) of the single-phase AC voltage at PCC isdisplayed in the Fig. 13(l). As the graph displays, the THD of con-verter voltage is well within the IEEE limits [21].

4.2. Hardware in loop OPAL-RT based results

In this section, the simulation results validation is executed inthe RTS of OPAL-RT. The RT simulators are gaining importance tovalidate the performance of complex power system [22–30]. Thesuggested setup is developed in RT-LAB environment of OPAL-RT,utilizing RT toolbox of MATLAB/Simulink, as illustrated in Fig. 14

(a). The laboratory setup of the OPAL-RT system is displayed inFig. 14(b). It comprises of a host computer and a RT system target.

In the proposed setup, host computer having 4 GB RAM, a 64-bitoperating system, and an Intel core (TM) i7 processor is utilized.Test setup is designed in MATLAB/Simulink 2013b software onhost computer, loaded on Opal-RT-OP5700 using the RT-LAB inter-face. The simulation is carried out to acquire the RT results asworthy as actual prototype results. The exchange of data betweenhost computer and RTDS setup is done using the ether-net cable.Three-phase voltage waveform is displayed in Fig. 15(a). The wave-form displays that the voltage output of the proposed system isvery near to pure sinusoidal, which is the essential requirementfor grid connected renewable energy sources. Zoomed in waveformof three-phase AC current at the time instant t2 is displayed inFig. 15(b). The current reduces to nearly half of the previous valuein accordance with the reduction in loads. Three-phase AC currentand single-phase AC current are displayed in the Fig. 15(c) andFig. 15(d), respectively displaying the load switching at varioustime instants. Active power and reactive power graphs are dis-played in Fig. 15(e) and Fig. 15(f), respectively. The effectivenessof the proposed system to compensate the variable load is dis-played in the graphs. Active power requirements on the grid arereduced considerably with the use of hybrid system.

SPV and battery current is displayed in Fig. 15(g). The graphhighlights the ability of battery to supply power as per the require-ments of the load and the availability of SPV power. The DC linkvoltage and AC voltage frequency are displayed in Fig. 15(h). Thefrequency remains stable while the DC link voltage has acceptablefluctuations at the switching instants. The output sin and cos asobtained from the PLL are displayed in Fig. 15(i). The PLL outputis used to extract the dq components from the measured signals.Single-phase AC voltage prior to passive filter is displayed inFig. 15(j). The converter supply voltage passes through the passivefilter and the voltage out of the passive filter is close to pure sinu-soidal. The variation in solar irradiance is displayed in Fig. 15(k).Solar irradiance is varied to display the capability of battery con-troller. The battery controller is able to switch from charging todischarging mode when the SPV power is fully available. THD ofvoltage at PCC is displayed in Fig. 15(l). The graph displayed herehighlights that the voltage THD is well within the IEEE require-ments [18].

Fig. 15. Graphs highlighting the hardware in loop real time results of the test setup. (a) Three-phase AC voltage at PCC (b) Three phase (zoomed in) current at t2 (c) Threephase AC current at PCC (d) Single phase ac current at PCC (e) Active power (f) Reactive power (g) SPV and battery current (h) DC link voltage and frequency (i) Sin-Cos fromPLL (j) Output voltage of DC/AC converter (k) Variation in solar irradiance (l) Voltage THD at PCC.

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5. Conclusion

In this work, a control strategy, derived from the curve fittingmethod in MATLAB/Simulink, has been proposed for a grid con-nected SPV-Battery hybrid system. The main contribution of thecontrol strategy is to operate the grid connected hybrid systemin stable manner under varying operating conditions. In addition,the capability of hybrid system to compensate reactive powerhas also been utilised to improve the system stability and powerquality. Effective discharging and charging of battery have alsobeen verified in grid-connected mode under variable load condi-tions and variable power generation. The results have authenti-cated that the suggested hybrid system structure and the relatedcontrol has the prospective applications in present renewableenergy based grid advancements.

Declaration of Competing Interest

The authors declare that they have no known competing finan-cial interests or personal relationships that could have appearedto influence the work reported in this paper.

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