energies Article
Maximum Power Extraction from a Partially Shaded PV System Using an Interleaved Boost Converter Hassan M. H. Farh 1,2, *, Mohd F. Othman 1 , Ali M. Eltamaly 3,4 1 2 3 4 5
*
and M. S. Al-Saud 2,5
Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Kuala Lumpur 54100, Malaysia;
[email protected] Electrical Engineering Department, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia;
[email protected] Electrical Engineering Department, Mansoura University, Mansoura 35516, Egypt;
[email protected] Sustainable Energy Technologies Center, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia Saudi Electricity Company Chair in Power System Reliability and Security, King Saud University, Riyadh 11421, Saudi Arabia Correspondence:
[email protected] or
[email protected]; Tel.: +966-50-050-7630
Received: 23 July 2018; Accepted: 17 September 2018; Published: 24 September 2018
Abstract: The partially shaded photovoltaic (PSPV) condition reduces the generated power and contributes to hot spot problems that may lead to breakdown of shaded modules. PSPV generates multiple peak, one global one and many other local peaks. Many efficient, accurate and reliable maximum power point tracker (MPPT) techniques are used to track the global peak instead of local peaks. The proposed technique is not limited to global peak tracking, but rather it is capable of tracking the sum of all peaks of the PV arrays using an interleaved boost converter (IBC). The proposed converter has been compared with the state of the art conventional control method that uses a conventional boost converter (CBC). The converters used in the two PSPV systems are interfaced with electric utility using a three-phase inverter. The simulation findings prove superiority of the PSPV with IBC compared to the one using CBC in terms of power quality, reliability, mismatch power loss, DC-link voltage stability, efficiency and flexibility. Also, IBC alleviates partial shading effects and extracts higher power compared to the one using CBC. The results have shown a remarkable increase in output generated power of a PSPV system for the three presented scenarios of partial shading by 61.6%, 30.3% and 13%, respectively, when CBC is replaced by IBC. Keywords: partially shaded photovoltaic; conventional boost converter; interleaved boost converter; maximum power point tracker; utility grid; mismatch loss
1. Introduction Solar photovoltaic (PV) energy systems are considered as some of the most promising options of the renewable generation systems (RGSs) which are clean, abundant, noise free and friendly to the environment compared to the conventional energy resources such as natural gas, fossil fuel, coal, etc. For these reasons, RGSs, especially solar and wind, are attracting interest all over the world. In addition, tracking the maximum power from these RGSs and choosing a suitable power electronics converter that matches the utility grid requirements are considered to be a hot development area as it can improve the system’s efficiency, reliability, power quality and flexibility [1–4]. Partial shading (PS) occurs when some cells or modules of a PV system are partially or totally shaded due to aging, damage, dust, moving clouds during the day or neighboring buildings and towers. Some reasons may appear with time and cause PS after the installation of the PV energy system. The shaded PV modules have a negative effect on the generated output power and overall
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efficiency of the PV system. Furthermore, hot-spot and thermal breakdown problems may occur, where the of protection of the PVFurthermore, modules using bypass diodes is inevitable [5–8]. Under partial shading efficiency the PV system. hot-spot and thermal breakdown problems may occur, conditions (PSCs), the of P-V one global peakis (GP) and many peakspartial (LPs) where the protection thecharacteristic PV modulescontains using bypass diodes inevitable [5–8].local Under instead of the unique peak the under conditions as shown in the P-V(GP) characteristic Figure 1. shading conditions (PSCs), P-Vuniform characteristic contains one global peak and many of local peaks Conventional MPPT techniques Hill Climbing (HC), Perturbinand (P&O), and (LPs) instead of the unique peak such underasuniform conditions as shown the Observe P-V characteristic of Incremental Conductance (IC) techniques [9–15] are quite simple to implement and acceptable in tracking the Figure 1. Conventional MPPT such as Hill Climbing (HC), Perturb and Observe (P&O), unique MPP under uniform conditions. they are efficientand in tracking theinGP under and Incremental Conductance (IC) [9–15]However, are quite simple to not implement acceptable tracking PSCs as they not uniform have the ability and intelligence to not distinguish and GP. the unique MPPdo under conditions. However, they are efficient inbetween tracking LPs the GP under Additionally, solar irradiance with rapid fluctuations can cause these MPPT techniques to track the PSCs as they do not have the ability and intelligence to distinguish between LPs and GP. Additionally, MPP irradiance direction inaccurately [16–20]. Thecan power losses ofMPPT the PVtechniques system duetototrack PSCsthe orMPP inaccurate GP solar with rapid fluctuations cause these direction tracking is extraordinarily high, and may of the generated power. GP Consequently, inaccurately [16–20]. The power losses of exceed the PV 70% system duetotal to PSCs or inaccurate tracking is tracking the GPhigh, is of interest inexceed order to70% achieve high power efficiency, lessConsequently, power losses, and high the output extraordinarily and may of the total generated power. tracking GP power [21]. in order to achieve high power efficiency, less power losses, and high output power [21]. is of interest
Figure Figure 1. 1. P-V P-V characteristics characteristics of of partially partially shaded shaded photovoltaic photovoltaic (PSPV) (PSPV) arrays. arrays.
In efficient In recent recent years, years, many many studies studies have have been been carried carried out out to to track track the the GP GP instead instead of of LPs LPs using using efficient soft computing techniques to improve the maximum power extracted and overall efficiency [22–32]. soft computing techniques to improve the maximum power extracted and overall efficiency [22–32]. These tracking speed, speed, efficiency, efficiency, These techniques techniques differ differ in in terms terms of of simplicity, simplicity, cost, cost, design, design, performance, performance, tracking robustness and accuracy. In addition, each technique has its own merits and demerits. For example, robustness and accuracy. In addition, each technique has its own merits and demerits. For example, Titri Titri et et al. al. proposed proposed aa new new bio-inspired bio-inspired (BI) (BI) technique technique called called ant ant colony colony optimization optimization based based on on aa new new pheromone update (ACO_NPU) to track the GP under PSC [22]. The obtained ACO_NPU MPPT pheromone update (ACO_NPU) to track the GP under PSC [22]. The obtained ACO_NPU MPPT was was analyzed, analyzed, investigated investigated and and compared compared to to conventional conventional the the P&O P&O MPPT MPPT technique technique and and MPPT MPPT artificial artificial intelligence such as artificial neural network (ANN), fuzzyfuzzy logic controller (FLC), intelligence(AI)-based (AI)-basedtechniques techniques such as artificial neural network (ANN), logic controller artificial neural fuzzy interface (ANFIS) and fuzzy logic genetic algorithm (FL-GA) MPPT techniques. (FLC), artificial neural fuzzy interface (ANFIS) and fuzzy logic genetic algorithm (FL-GA) MPPT It was also compared with the BI particle swarm optimization and ACO. The results showed techniques. It was also compared with the BI particle swarm(PSO) optimization (PSO) and ACO. The superior performance of BI methods like ACO, and PSO in terms of convergence speed, accuracy, results showed superior performance of BI methods like ACO, and PSO in terms of convergence stability and robustness the other hand, PSO IPSOtechnique, [23–25] is IPSO used speed, accuracy, stability[22]. and On robustness [22]. On an theimproved other hand, antechnique, improved PSO for tracking the for GP tracking accurately without due tooscillation the cooperation [23–25] is used theand GPalmost accurately andoscillation almost without due toand the competition cooperation between particles. It updates the particle’s speed and position continuously to track the GP through and competition between particles. It updates the particle’s speed and position continuously to track sending the optimal duty cycle to the DC-DC converter [23,26–29]. Finally, the[23,26–29]. researchers in [30–33] the GP through sending the optimal duty cycle to the DC-DC converter Finally, the proved the effectiveness of the AI techniques such as ANN, FLC, genetic algorithm (GA) and hybrid researchers in [30–33] proved the effectiveness of the AI techniques such as ANN, FLC, genetic techniques (e.g., and neuro-fuzzy or ANFIS (e.g., and FL optimized or byANFIS GA) inand terms accuracy,by quick algorithm (GA) hybrid techniques neuro-fuzzy FLof optimized GA)response, in terms flexibility, power consumption and implementation simplicity. In spite of the capability of accuracy, quick response, flexibility, power consumption and implementation simplicity.of Inthese spite modern MPPT techniques to track the GP, it is still lower than the sum of all individual peaks of of the capability of these modern MPPT techniques to track the GP, it is still lower than the sum ofthe all PSPV system. Anofinterleaved boost converter (IBC) boost interfaced with(IBC) multi-PV arrayswith is one of the individual peaks the PSPV system. An interleaved converter interfaced multi-PV most solutions mitigatesolutions PS effectsto and enhance ability toenhance extract the power arrayseffective is one of the mosttoeffective mitigate PSthe effects and themaximum ability to extract available from the whole PSPV system, which are newly introduced in this paper. Using IBC, the whole the maximum power available from the whole PSPV system, which are newly introduced in this PV system performance is improved in terms of power quality, reliability, DC-link voltage stability paper. Using IBC, the whole PV system performance is improved in terms of power quality, reliability, and overall efficiency. It can usedefficiency. for high voltage, high power applications in DC-link voltage stability andbe overall It can behigh usedcurrent, for highand voltage, high current, and high different industrial purposes. In addition, IBC has many attractive features such as: (i) minimal input power applications in different industrial purposes. In addition, IBC has many attractive features
such as: (i) minimal input current ripples; (ii) boosting the output voltage to higher levels; (iii)
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current ripples; (ii) boosting the output voltage to higher levels; (iii) reducing the thermal stresses on the devices; (iv) lower current stress on the power switches and inductance hence; reducing the passive components size; (v) higher output power and efficiency; and (vi) higher power density [34–39]. In one of the earliest works on interleaved DC-DC converters they were used over 40 years ago to design a power supply for the Jet Propulsion Laboratory [40]. Benyahia et al. investigated the P&O MPPT performance with IBC for fuel cell generators supplying electricity to a power train [41]. In another study, Arango et al. proposed asymmetrical interleaved DC-DC converters and a voltage multiplier cells combined together (boost, buck-boost and flyback-based) for PV and fuel cell applications to achieve high output voltage and ripple reduction in the generator and load [42]. However, variable DC-link voltage was generated and two DC-DC converters were used for each PV array that resulted in total cost increase. A study by Deihimi et al. also investigated the performance of variable IBC (series-connected) but it interfaced with multi energy sources of different outputs [43]. Although variable IBC provides higher voltage gains in addition to a wide range of applications from low to high voltage/power, the DC-link voltage is unstable (variable) [44]. Hence, the whole system will operate in asymmetric condition and the maximum power generated from PSPV cannot be captured. Therefore, variable IBC is not able to mitigate and fix the DC-link voltage variations. As a result, it is not preferred to be applied with the PSPV system where the irradiance of all PV modules/strings/arrays is different, and the output voltage/current of each DC-DC converter is not the same. Hence, fixed IBC is the best choice to enhance the stability of DC-link voltage. Recently, many literature studies [45–55] have been done to prove the superiority of the interleaved DC-DC converters compared to the CBC with constant input power in terms of ripples, energy savings, efficiency, steady state, electromagnetic emission, and reliability. For example, the researchers in [47,50,52] have shown the possibility of using IBC with PV in terms of reliability evaluation, ripple reduction and faster transient response. However, they performed their studies on standalone PV without PS in order to highlight the IBC performance where the input power is constant, which is different under PSCs. On the other hand, the researchers in [43,45,46,48,53] demonstrated the possibility of using IBC for high voltage applications compared to the CBC, whereas, Rehman et al. introduced a detailed comparisons of interleaved DC-DC converter topologies in terms of cost, reliability, flexibility and efficiency that can be used in renewable energy applications [54]. The latter proved that buck and boost are more reliable, less cost and more efficient while Cuk and single-ended primary-inductor converter (SEPIC) converters are more flexible than others as they are ripple free and able to increase or decrease the output voltage. Finally, Ngai-Man et al. proved the better performance of a two-phase IBC using the SiC diodes compared to IBC using the Si diodes in addition to high efficiency and high power density [55]. This is supported by the study of Mouli et al. which revealed that higher power density was obtained with SiC IBC (2.5 times) compared to the Si IBC interfaced with the 10-kW PV for tracking the MPP [56]. On the basis of this comprehensive literature review, the study shown in this paper may be counted as the first study to show the improvement of PSPV system performance in case of PSC using IBC. It is an effective and efficient solution, not only to remedy the PS effects but also to extract the summation of individual maximum power available from each PV array branches which is greater than the GP tracked from the PSPV system with CBC. The performance of IBC interfaced with multi partially shaded photovoltaic (PSPV) arrays interconnected to the utility grid—which has never been done before—will be analyzed and investigated in this paper. To achieve this purpose, performance comparisons between the proposed PSPV system with IBC and another PSPV system with CBC have been carried out and investigated in terms of power quality, reliability, mismatch power loss and overall efficiency. Also, future enlargements of the PV system can be easily adopted where multi-PV arrays can be added easily as an add-on option with their own boost converter into the existing PV system. Finally, the adequacy of whether the variable or fixed interleaved DC-DC converter is adequate or not to PSPV grid connected will be investigated. As a result, the best IBC topology to achieve the DC-link voltage regulation and extract the maximum power available from the whole PSPV system
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of 18 interfaced with the utility grid is determined and presented. The findings of this study can4 open the door for the PV designers and researchers to adopt IBC that interfaced with the PSPV system to can open the door for the PV designers and researchers to adopt IBC that interfaced with the PSPV maximize the output power generated. system to maximize the output power generated.
2. Description of the PSPV Systems with and without IBC 2. Description of the PSPV Systems with and without IBC 2.1. Grid-Connected PSPV Energy System with CBC 2.1. Grid-Connected PSPV Energy System with CBC Figure 2 shows a PV energy conversion system, where the PV array is connected to the utility 2 ) and Figure 2 shows a PV energy conversion system,towhere PV array is connected the utility grid through CBC and three-phase inverter. Inputs the PVthe array are Sun irradiance to (W/m 2) and ◦ grid through CBC and three-phase inverter. Inputs to the PV array are Sun irradiance (W/m cell temperature ( C). Three PV arrays WITH three different radiations are used to represent the PSCs. cell (°C). Three multiple PV arrayspeaks WITHare three differentthree radiations used represent the PSCs. As atemperature consequence of PSCs, generated; peaks;are and theto occurrence of the GP As a consequence of PSCs, multiple peaks are generated; three peaks; and the occurrence of the GP is at different places of the P-V curve. Three different shading patterns with three different cases is at different of the P-V curve. shading patterns with are three different cases (Case 1; GP at places the beginning, Case 2; GPThree at thedifferent middle, Case 3; GP at the end) used successively. (Case 1; GP at thepattern beginning, GP at the middle, Caseby3;the GPsecond at the end) are used successively. The first shading (GP Case at the2;beginning) is followed shading pattern (GP at the The first which shading (GP beginning) is followed bythe theend) second shading (GP at the middle) is pattern followed by at thethe last shading pattern (GP at as shown in pattern Figure 3. Each PV middle) which 54 is followed by the and last shading pattern (GP the end) shown in Figure Each PV array contains parallel strings 5 series modules per at string withas a peak power of 50 3. kW; hence array contains 54 parallel stringsfrom and 5the series modules per string with peak power of PSPV 50 kW;system, hence the maximum power available whole PV energy system is a150 kW. In this the maximum power available from the whole PV energy system is 150 kW. In this PSPV system, the the improved or deterministic PSO (DPSO) is used as an efficient GP tracker to track the GP power. improved or deterministic PSO is used as an efficient GP tracker to track GP power. This This goal has been achieved via(DPSO) searching the optimal duty cycle of the CBC thatthe extracts the GP as goal has been achieved via searching the optimal duty cycle of the CBC that extracts the GP as shown shown in Figure 3. Nevertheless, tracking the GP power does not mean that the maximum power in Figure from 3. Nevertheless, tracking GP power does notpower mean is that the maximum power available available the PSPV system has the been achieved. The GP always less than the summation of from the PSPV hasfrom beenthe achieved. The GP power always less than the summation of maximum powersystem available individual arrays of PSPVisenergy system which will be discussed maximum power available from theThe individual arrays of index, PSPV energy system determines which will be discussed in the simulation results section. mismatch loss MML which the relation in the simulation results section. Thewhole mismatch loss MML which determines the relation between the maximum power of the system andindex, the sum of all peaks can give an indication between maximum whole system and the sum of all peaks about thethe power quality.power It can of be the calculated mathematically as follows [7]: can give an indication about the power quality. It can be calculated mathematically as follows [7]: Maximum Power of the whole system MML = M aximum Power of the whole system (1) N M ML = N (1) P ( i ) ∑ Pmax( i )
1
max
1
where, ii is is the the index index for for PV PV modules is the where, modules and and N N is the total total number number of of PV PV modules/arrays. modules/arrays.
Figure 2. Multi-PV grid-connected system with conventional boost converter (CBC). Figure 2. Multi-PV grid-connected system with conventional boost converter (CBC).
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Figure 3. Three different partial shading cases of the PV arrays under study.
Figure Figure 3. 3. Three Three different different partial partial shading shading cases cases of of the the PV PV arrays arrays under under study. study.
2.2. Grid-Connected PSPV Energy System with IBC 2.2. Grid-Connected Grid-Connected PSPV PSPV Energy Energy System System with with IBC IBC 2.2. Multi-PV arrays which are interconnected to the utility grid through IBC and pulse width Multi-PV arrays which are interconnected interconnected to the utility grid through IBC behind and pulse pulse width modulation voltage source converter (PWM-VSC)to arethe shown in grid Figure 4. The idea using IBC Multi-PV arrays which are utility through IBC and width modulation voltage source converter (PWM-VSC) are shown in Figure 4. The idea behind using interfaced with multi-PV arrays is to reduce the ripple current, quality,using regulate modulation voltage source converter (PWM-VSC) are shown in improve Figure 4.the Thepower idea behind IBC IBC interfaced with multi-PV arrays is to reduce the ripple current, improve the power quality, regulate the DC-link voltage, and enable the use of independent MPPT control of each PV array to achieve interfaced with multi-PV arrays is to reduce the ripple current, improve the power quality, regulate the DC-link DC-link voltage, and power enableand the use use of independent independent MPPT control of this eachproposed PV array arrayPV to achieve achieve higher output generated increase the overall MPPT efficiency. Also, system the voltage, and enable the of control of each PV to higher output generated power and increase the overall efficiency. Also, this proposed PV system remedies and alleviates PS effects related tothe theoverall maximum power Also, of the this system and itsPV efficiency. higher output generatedthe power and increase efficiency. proposed system remedies and alleviates the PS effects related to the maximum power of the system and its efficiency. Each PV and arrayalleviates works at MPP that to is the being trackedpower by a separate MPPand tracker through remedies theitsPSown effects related maximum of the system its efficiency. Each PV at at its its own MPP that is being trackedtracked by a separate MPP tracker through providing the works duty cycle to its own boost converter. Different cycles are provided for each Each PVarray array works own MPP that is being byduty a separate MPP trackerproviding through the duty to its own Different duty cyclesfor are provided for to each branch ofeach the branch ofcycle the where separate tracker P&O is used each PV array track itsfor unique providing theIBC duty cycleaboost to its converter. ownMPP boost converter. Different duty cycles are provided IBC where a separate MPP tracker P&O is used for each PV array to track its unique MPP as shown in MPP asof shown in Figure Hence, the proposed withfor IBC works at its MPP anditsthe total branch the IBC where 4. a separate MPP tracker multi-PV P&O is used each PV array to track unique Figure 4. Hence, the proposed multi-PV with IBC works at its MPP and the total maximum power maximum power this PSPV system ismulti-PV the summation of works all peaks which greater MPP as shown in delivered Figure 4. by Hence, the proposed with IBC at its MPPisand the than total delivered by this PSPV system is the summation of all peaks which is greater than the GP tracked from the GP tracked from the previous PSPV system with CBC as will be shown later in the simulation maximum power delivered by this PSPV system is the summation of all peaks which is greater than the previous PSPV system with CBC as will be shown results the GP section. tracked from the previous PSPV system with later CBC in as the willsimulation be shownresults later insection. the simulation results section.
Figure 4. 4. Multi-PV Multi-PV arrays arrays with with interleaved interleaved boost boost converter converter (IBC) (IBC) interfaced interfaced the the utility utility grid. grid. Figure
Figure 4. Multi-PV arrays with interleaved boost converter (IBC) interfaced the utility grid.
The simulations of the two PSPV energy systems with and without IBC are carried out using MATLAB/Simulink (ver2016, MathWorks, Natick, MA, USA). The same three PV-arrays with the
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The simulations of the two PSPV energy systems with and without IBC are carried out using MATLAB/Simulink (ver2016, MathWorks, Natick, MA, USA). The same three PV-arrays with the same characteristics and inputs (Irradiance and temperature) of the previous PSPV system with CBC are used here to investigate, analyze and compare the response and performance of the two proposed PV systems. The purpose of these comparisons and analysis is to determine the best choice of a boost converter to deal with the PS in terms of output power generated, power quality, DC-link voltage stability and participation of PS mitigation. The inverter active and reactive power output can be controlled according to the following equations [57]:
√ Pout =
3 m a Vdc Vsys √ sin(δ) 2 2XT
√ Qout =
Vsys 3 Vdc Vsys √ cos(δ) − XT 2 2XT
(2) 2 (3)
where; Vsys is the utility voltage, XT is the reactance between the inverter and utility system, Vdc is the DC-link voltage and δ is the inverter voltage angle. 3. Maximum Power Point Tracking under Partial Shading Conditions 3.1. Particle Swarm Optimization Technique The particle swarm optimization (PSO) technique represents one of the most efficient BI techniques. It can track the GP accurately with low oscillation. The GP tracking depends on the particle’s velocity and position which are renewed and updated to track the GP instead of LPs by sending the duty cycle to the boost converter [22–25]. Each particle in the swarm has mainly two variables; the position vector xi k and the velocity vector vi k and the new position can be calculated as follows [23]: x i k +1 = x i k + v i k +1
(4)
The new position of the particle is determined through calculating the velocity using current position xi k , particle velocity vi k , and global best position Gbest as follows: vi k+1 = ωvi k + c1 r1 Pbest i − xi k + c2 r2 Gbest − xi k
(5)
where, ω is the inertia weight that determines the research area. It can be set to constant value (0.5) or variable to accelerate the GP tracking [24]. c1 and c2 are the acceleration coefficients where, c1 is self-confidence and c2 is swarm-confidence. The range of c1 varies from 1.5 to 2 while the range of c2 varies from 2 to 2.5 [58]. Authors in [23] used the duty cycles of the DC-DC converter as the positions of the PSO particles. The PSO algorithm begins the search by sending initial duty cycles to the DC-DC converter and the obtained PV voltage and current are used to compute the Pbest and Gbest values as shown in the PSO flowchart in Figure 5. The new duty cycles are computed using the velocity and position equations, based on Equations (4) and (5). Some authors [27–29,59,60] used the conventional PSO which is able to handle PSCs and track the GP accurately, but they discovered that it is low during the steady state oscillations [24]. As a result, others in [25,61] have added some modifications to it. Later an improved or a deterministic PSO (DPSO) was proposed to improve the tracking capability of the conventional PSO, where the random number in the velocity equation is removed as follows [25]: vi k+1 = ωvi k + Pbest i − xi k + Gbest − xi k
(6)
vi k+1 = ωvi k + Pbest i + Gbest − 2xi k
(7)
vi k +1 = ω vi k + ( Pbest i − xi k ) + ( Gbest − xi k ) Energies 2018, 11, 2543
vi k +1 = ω vi k + ( Pbest i + Gbest − 2 xi k )
(6) 7 of(7) 18
Figure5.5. The The Flowchart Flowchart of of deterministic deterministicparticle particleswarm swarmoptimization optimization(DPSO) (DPSO)based basedmaximum maximumpower power Figure point tracker (MPPT). point tracker (MPPT).
The The DPSO DPSO has has many many advantages advantages compared compared to to the the conventional conventional PSO PSO such such as as simple simple structure, structure, more more satisfactory satisfactory performance performance and and furthermore furthermore aa consistent consistent solution solution can can be be achieved achieved for for smaller smaller number parameter needs to be tuned (the(the inertia weight). Additionally, the numberofofparticles. particles.Also, Also,only onlyone one parameter needs to be tuned inertia weight). Additionally, DPSO has faster tracking speed, robust, and almost zero steady-state oscillation compared to HC or the DPSO has faster tracking speed, robust, and almost zero steady-state oscillation compared toany HC other MPPT techniques [25]. On the other et al. proved of or any other MPPT techniques [25]. Onhand, the Soltani other hand, Soltani the et superiority al. proved performance the superiority conventional PSO, IPSO, quantum inspired PSO, QPSO, vector evaluated PSO, VEPSO and PSO with performance of conventional PSO, IPSO, quantum inspired PSO, QPSO, vector evaluated PSO, time varying coefficients, techniques in terms of fast response andinhigh accuracy VEPSO and acceleration PSO with time varying PSOTVAC acceleration coefficients, PSOTVAC techniques terms of fast compared to the conventional P&O technique. conventional has the Also, fastestconventional response among response and high accuracy compared to the Also, conventional P&OPSO technique. PSO all PSO techniques and PSOTVAC is more accurate in tracking the GP than others [61]. According to the literature [23,25,26,28,29,62–64], the results proved the significant performance of the BI techniques especially PSO, cuckoo search optimization (CSO), Modified firefly (MFA) and ACO to track the GP in all cases of PS in terms of convergence speed, accuracy, stability and robustness. As a result, the
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has the fastest response among all PSO techniques and PSOTVAC is more accurate in tracking the GP than others [61]. According to the literature [23,25,26,28,29,62–64], the results proved the Energies 2018, 11, 2543 8 of 18 significant performance of the BI techniques especially PSO, cuckoo search optimization (CSO), Modified firefly (MFA) and ACO to track the GP in all cases of PS in terms of convergence speed, accuracy, stability and robustness. As a result, the maximum power extraction from the gridmaximum power extraction from the grid-connected PSPV energy system with CBC is carried out connected PSPV energy system with CBC is carried out using DPSO technique. The DPSO logic steps using DPSO technique. The DPSO logic steps used in the simulation is summarized as follows: used in the simulation is summarized as follows:
•• ••
•• ••
Step Step11(DPSO (DPSOinitialization): initialization):Send Sendthe theinitial initialduty dutycycles cyclesto toCBC CBCof ofthe thePSPV PSPVsystem systemone oneby byone one and andcollect collectthe therelated relatedpower powervalues. values. Step Step22(Updating (Updatingthe thevelocity velocityand andposition positionofofparticles): particles): Update Update the theposition positionand andvelocity velocityfor for each eachparticle particleusing usingEquations Equations(4), (4),and and(7), (7),respectively, respectively,and andconsequently consequentlyget getthe thenew newvalues valuesof of duty dutycycles. cycles. Step the new values of duty cycles to the PSPV system and and collect the Step33(Fitness (Fitnessevaluation): evaluation):Send Send the new values of duty cycles to the PSPV system collect related power values. the related power values. Step44Evaluate Evaluatethe thePP best,i,, G Gbest best and position (duty (duty cycles), cycles), then; then;go goback back Step and their their associated associated particle’s position best,i toStep Step2.2. to
3.2. 3.2.Perturb Perturband andObserve ObserveTechnique Technique The from thethe grid-connected PSPV energy system with IBC becan tracked easily Themaximum maximumpower power from grid-connected PSPV energy system withcan IBC be tracked and efficiently using P&O technique. As shown in Figure in 4, independent MPP tracker is easily and efficiently using P&O technique. Aspreviously shown previously Figure 4, independent MPP used for each PV array to track its unique MPP. Multi-PV arrays interfaced with IBC does not only tracker is used for each PV array to track its unique MPP. Multi-PV arrays interfaced with IBC does alleviate mitigate themitigate negativethe effects of PSeffects but also that each PV array branch not onlyand alleviate and negative ofguarantees PS but also guarantees that each PVworks array at its own MPP and the total maximum power extracted from this system is the sum of all peaks branch works at its own MPP and the total maximum power extracted from this system is the sum of Tracking the maximum frompower the multi-PV is achieved ofindividual all peaks ofarrays. individual arrays. Tracking the power maximum from thearrays multi-PV arrays is through achieved controlling the duty cycles of the IBCofseparately where three different cycles are cycles sent from the through controlling the duty cycles the IBC separately where three duty different duty are sent three MPP trackers. from the three MPP trackers. The MPPT uses the the operating voltage perturbation of theof array observes the output TheP&O P&Obased based MPPT uses operating voltage perturbation the and array and observes the power If the power increased the last voltage increment, the next then perturbation outputvariation. power variation. If the power with increased with the last voltagethen increment, the next must be kept in the be same as shown in Figure 6. On the other hand, if the hand, voltage increment perturbation must keptdirection in the same direction as shown in Figure 6. On the other if the voltage reduces the reduces power, the perturbation be reversed. is achieved whenis increment thenext power, the next must perturbation mustThe be maximum reversed. power The maximum power dachieved /d = 0 [65,66]. Figure 7 shows the flow chart of P&O technique. when 𝑑 /𝑑 = 0 [65,66]. Figure 7 shows the flow chart of P&O technique. 𝑃 𝑉 P V dp =0 dv
dp 0 dv
Figure 6. P-V characteristic of the PV array. Figure 6. P-V characteristic of the PV array.
dp 0 dv
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Measure V(t), I(t)
Calculate P(t)
Yes
P(t)-P(t-1) =0 No
No
V(t)-V(t-1) ˂ 0
No
Yes
P(t)-P(t-1) ˃ 0
Yes
V(ref)= V + ∆V
Yes
V(t)-V(t-1) ˃ 0
No
V(ref)= V - ∆V
Return
Figure Theflow flow chart of of Perturb and Observe (P&O) technique. Figure 7. 7.7. The Observe (P&O) technique. Figure The flowchart chart ofPerturb Perturb and and Observe (P&O) technique.
4. Simulation Results and Discussion 4. Simulation Results and Discussion
4. Simulation Results and Discussion The two different grid-connected PSPV PSPV systems are simulated in in MATLAB/Simulink (V2016). TheThe twotwo different grid-connected MATLAB/Simulink (V2016). different grid-connected PSPVsystems systems are are simulated simulated in MATLAB/Simulink (V2016). The first PV system consists of three PSPV arrays having the same characteristics with a total The The first first PV system consists of three arraysarrays havinghaving the same with a total PV system consists of PSPV three PSPV thecharacteristics same characteristics with maximum a total maximum power of 150 kW. Three different shading patterns are selected to cover all possible PSC power of 150 kW. Three different shading patterns are selected to cover all possible PSC casesPSC (GP at maximum power of 150 kW. Three different shading patterns are selected to cover all possible cases (GP at the beginning, GP at the middle and GP at the end). Each PV array consists of five seriesthe beginning, GP at the middle and GP at the end). Each PV array consists of five series-connected cases (GP atmodules the beginning, GP at the54 middle and GP at the end). array five seriesconnected per string and parallel strings. The I-V &Each P-V PV curves ofconsists each PVofarray are modules per string and 54 parallel strings. The I-V & P-V curves of each PV array are shown in Figure connected modules per string and 54 parallel strings. The I-V & P-V curves of each PV are 8 shown in Figure 8 and the main characteristic of the module used (CRM185S156P-54 Sunperfectarray Solar, in Figure 8 and the main characteristic of the module used (CRM185S156P-54 Sunperfect Solar, and shown the main characteristic of the module used (CRM185S156P-54 Sunperfect Solar, 3101 N 1st St #107, 3101 N 1st St #107, San Jose, CA, USA) is shown in Table 1. 3101 N 1st St #107, San Jose, CA, USA) is shown in Table 1. San Jose, CA, USA) is shown in Table 1.
Figure 8. I-V and P-V characteristics of the PV array under study.
Figure I-Vand andP-V P-Vcharacteristics characteristics of Figure 8. 8. I-V of the the PV PVarray arrayunder understudy. study.
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For comparison purposes, the power circuit and inputs of the two PSPV systems are the same, except for the DC-DC converter. The first PSPV system contains three PSPV arrays is interconnected to the grid through CBC and three-phase inverter as shown previously in Figure 2. DPSO technique is used to track the GP via sending the duty cycle to the CBC, whereas, the second PV system contains the same three PSPV arrays interconnected to the grid through IBC and three-phase inverter as shown previously in Figure 4. A separate P&O MPPT tracker is used to track the peak power for each PV array individually and the total power generated from this system is equal to the summation of all peaks also shown previously in Figure 4. In addition, a fixed IBC (parallel) is used not only to share the currents among inductors but also to regulate and stabilize the DC-link voltage. Hence, IBC performed well compared to CBC in terms of power generated, efficiency, reliability, flexibility, reduction in size and total cost of the generated power. Also, future enlargements of the PV system can be adopted where multi-PV arrays can be added easily as an add-on option with their own boost converter into the existing PV system. Therefore, the incorporation of the IBC instead of CBC under partial shading will attain more technical and economical benefits. Table 1. The electrical characteristics of Sunperfect Solar CRM185S156P-54 module. Maximum power (Pmax ) Cells per Module Open-circuit voltage (Voc ) Short-circuit current (Isc ) Voltage at maximum power point (VMPP ) Current at maximum power point (IMPP )
185.22 W 54 32.2 V 7.89 A 25.2 V 7.35 A
Different radiation on each PV array generates different power from one PV array to another and multiple peaks will be generated as shown in Table 2. A comparison between the actual power captured with the theoretical one for the three different PS cases is shown in Table 2. The theoretical power is the summation of individual peaks power of the three PV arrays. The actual power generated equals to the GP power in the case of the first PSPV system with CBC, whereas the actual power generated equals to the summation of individual peaks of the three PV arrays in the case of the second PSPV system with IBC which is higher than GP in all cases of PS as shown in Table 2. On the other hand, MML is calculated based on Equation (1) for the two PSPV systems for comparison purposes. As the MML increases, the actual generated power from the PV system also increases and vice versa. Therefore, improving the MML represents a priority to extract high output power generated and improve the power quality. Tracking the GP instead of LPs will improve the MML, but does not guarantee the extraction of the maximum power available from the whole PV system. The proposed PV system with IBC works at its MPP and each PV array works at its own MPP, the MML is 100% regardless of whether PS occurred or not as shown in Table 2. Table 2. Mismatch loss comparisons of the three PS different cases with and without IBC. PS Cases
Case 1 (GP at the Beginning)
Case 2 (GP in the Middle)
Case 3 (GP at the End)
Ir (W/m2 )
MP (kW)
Ir (W/m2 )
MP (kW)
Ir (W/m2 )
MP (kW)
1000 400 200
50 20.6 10.2
800 400 700
40.5 20.6 35.6
1000 700 900
50 35.6 45.3
PV arrays
PV array 1 PV array 2 PV array 3
With CBC
Theoretical Power (kW) Actual Power (kW) MML
80.8 50 38.5%
96.7 74 40.5%
130.9 116 44.8%
With IBC
Theoretical Power (kW) Actual Power (kW) MML
80.8 80.8 100%
96.7 96.7 100%
130.9 130.9 100%
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Figure 9a shows both the theoretical and actual powers generated from the PV system with CBC, Figure 9a shows both both the theoretical and actual powers generated from the PV system with CBC, whereas Figure 9b shows the theoretical and actual powers generated from the PV system with whereas Figure 9b shows both the theoretical and actual powers generated from the PV system with IBC. It is concluded that there is a significant reduction in the actual power generated from the PSPV IBC. It iswith concluded that theretois the a significant reduction in contrast, the actualthe power generated thepowers PSPV system CBC compared theoretical power. In theoretical andfrom actual system with CBC compared to with the theoretical power. In contrast, theoretical and actual powers generated from the PV system IBC are almost of equal values.the Hence, the overall efficiency and generated from the PV system with IBC are almost of equal values. Hence, the overall efficiency and the PV system reliability with IBC are improved. Figure 10 shows the actual power generated from the system reliability withand IBCIBC are for improved. Figure power generated the the PV PSPV system with CBC the three cases10 of shows PS (GPthe at actual the beginning, GP at thefrom middle PSPV system with CBC and IBC for the three cases of PS (GP at the beginning, GP at the middle and GP and GP at the end). Fortunately, the actual power generated from the PSPV system with IBC is higher at end).30.3% Fortunately, therespectively, actual powercompared generatedto from systemfrom withPSPV IBC issystem higherwith by 61.6%, bythe 61.6%, and 13%, thethe onePSPV generated CBC 30.3% 13%, respectively, compared the one generated system thepower three for theand three PSCs, respectively. This to emphasizes that thefrom PSPVPSPV system withwith IBCCBC has for high PSCs, This emphasizes that thepower PSPV system IBClosses has high power quality through qualityrespectively. through harvesting high generated and lowwith power under PSCs. This can help harvesting generated power andthe lowchallenges power losses under can helpsystem and support and supporthigh effectively in overcoming that face thePSCs. radial This distribution such as effectively in overcoming thethe challenges that face thehow radial system such as the continuous the continuous growth of load demand and to distribution supply it through renewable distributed growth of the load demand and how to supply it through renewable distributed generation. generation.
Pact. (kW) Pth. (kW)
Pact.: Actual power (kW) Pth.: Theoretical power (kW)
(116 kW, 400 V) (74 kW, 260 V)
(50 kW, 120 V)
(a)
Pact.: Actual power (kW) Pth.: Theoretical power (kW)
PPV (kW)
Pact. (kW) Pth. (kW)
(b) Figure 9. 9. The from the the PSPV: PSPV: (a) (a) With With CBC; CBC; (b) (b) With WithIBC. IBC. Figure The maximum maximum power power available available from
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140 140 120 120 100 100 80 8060
6040 4020
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Pact. (kW) with CBC Pact. (kW) with CBC
80.8 80.8
50 50
Pact. (kW) with IBC Pact. (kW) with IBC 96.7 96.7
130.9 130.9 116 116
74 74
20 0 0
Case 1 (GP at the beginning) Case 2 (GP in the middle) Case 1 (GP at the beginning) Case 2 (GP in the middle)
Case 3 (GP at the end) Case 3 (GP at the end)
Figure10. 10. The The actual from thethe PSPV system withwith CBC CBC and IBC thefor three of cases PS. Figure actualpower powergenerated generated from PSPV system andforIBC thecases three of PS. 10. The actual power generated from the PSPV system with CBC and IBC for the three cases of PS. Figure
Duty cycles Duty cycles
Figure 11 shows the three different duty cycles (D1, D2 and D3) that are sent to the IBC as illustrated previously in three Figuredifferent 3. Each duty duty cycles cycle tracks theand peak power of its own PV array Figure 11 11 shows the the (D1, D2 D2 D3) that are are sent to the the IBC as as Figure shows three different duty cycles (D1, and D3) that sent to IBC individually and the total generated powerduty is thecycle summation of allpeak peaks. Figure 12 shows the DCillustrated previously in Figure 3. Each tracks the power of its own PV array illustrated previously in Figure 3. Each duty cycle tracks the peak power of its own PV array link voltageand (IBC output voltage) which is almostsummation equal to theofreference voltage value; 500 the V. Hence, individually allall peaks. Figure 12 12 shows DC-link individually and the the total total generated generatedpower powerisisthe the summation of peaks. Figure shows the DCfixed IBC enhances the stability and regulation of the DC-link voltage which improves the power voltage (IBC output voltage) which is almost equal to the reference voltage value; 500 V. Hence, fixed link voltage (IBC output voltage) which is almost equal to the reference voltage value; 500 V. Hence, quality and stability of theand system. The DC-link is voltage regulated and controlled through the three IBC enhances the stability regulation of thevoltage DC-link which improves the power fixed IBC enhances the stability and regulation of the DC-link voltage which improves the quality power duty cycles while the active and reactive power control are controlled through the modulation index and stability of the system. The DC-link voltage is regulated and controlled through the three duty quality and stability of the system. The DC-link voltage is regulated and controlled through the three and duty cycles as shown inreactive Figurespower 12 andcontrol 13. Ourare findings revealed the superiority in performance cycles while the active and controlled through the modulation index and duty cycles while the active and reactive power control are controlled through the modulation index of multi PSPV with IBC compared toand PSPV with CBC in terms of generated power, reliability, DC-linkof duty cycles as shown in Figures 12 13. Our findings revealed the superiority in performance and duty stability cycles asand shown in Figures 12 and 13. Our findings revealed the superiority in performance voltage flexibility. multi PSPV power, reliability, reliability, DC-link DC-link of multi PSPVwith withIBC IBCcompared comparedtotoPSPV PSPVwith withCBC CBCin in terms terms of of generated generated power, voltage stability and flexibility. voltage stability and flexibility.
D1 D2 D3 D1
D2 D3
Figure 11. The three duty cycles to the IBC.
Figure Figure11. 11.The Thethree threeduty dutycycles cyclesto tothe theIBC. IBC.
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Figure DC-link voltage the IBC and of the inverter. Figure 12. The DC-link voltageofof ofthe theIBC IBC and and the the modulation modulation index (ma) of of thethe inverter. Figure 12. 12. TheThe DC-link voltage modulationindex index(ma) (ma) inverter.
(a) (a)
(b) (b) Figure 13. The active and reactive power of the utility grid: (a) Active power (kW); (b) Reactive power
Figure The activeand and reactive reactive power thethe utility grid:grid: (a) Active power (kW); (b)(kW); Reactive Figure 13. 13. The active powerofof utility (a) Active power (b)power Reactive (VAr). (VAr). power (VAr).
5. 5. Conclusions Conclusions 5. Conclusions Partial shading (PS) reduces the generated power from PV systems considerably compared to Partial shading reduces generated power from PVsystems systemsconsiderably considerablycompared compared to to the Partial shading (PS)(PS) reduces thethe generated power from PV the generation during healthy conditions. Bypass diodes are connected across each PV module the generation during healthy conditions. Bypass diodes are connected across each PV module to to generation during healthy conditions. Bypass diodes are connected across each PV module to protect protect protect the the shaded shaded modules modules or or arrays arrays from from destruction destruction due due to to hot-spot hot-spot effect. effect. In In this this case, case, multiple multiple
the shaded modules or arrays from destruction due to hot-spot effect. In this case, multiple peaks (one GP and many LPs) are generated. Tracking the GP power using efficient soft computing techniques
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based on MPPT does not guarantee the extraction of the maximum power available from the PSPV system with CBC. Therefore, the main goal of this study is to propose an effective and efficient solution using IBC, which is not limited to mitigate or alleviate PS effects but also to extract the maximum power available from the whole PSPV system with 100% MML. The second aim of this study is to investigate the performance of IBC interfaced with the PSPV grid-connected compared to the one using CBC. Multi PSPV arrays with IBC using P&O MPP tracker can extract the maximum power available of the whole PV system which is equal to the summation of all peaks of the PV arrays. Whereas, multi PSPV arrays with CBC can extract the GP using DPSO MPP tracker which is lower than the maximum power available from the whole system. The most obvious finding to emerge from this study is that, the power generated from the PSPV system can be increased by 61.6% (Case 1; GP at the beginning), 30.3% (Case 2; GP in the middle) and 13% (Case 3; GP at the end) respectively from the PSPV system by adopting IBC instead of CBC. The results of this investigation have shown that the IBC guarantees the extraction of the maximum power available from the PSPV system with 100% MML, which cannot be attained using CBC. Consequently, an overall efficiency improvement of the presented system was obviously achieved. Furthermore, sharing the input current among the inductors using IBC enhances the PV system’s reliability and efficiency. As a result, significant reduction in size and cost is achieved. In addition, power losses can reach 70% of the total generated power with CBC under PSCs, whereas IBC guarantees the extraction of the maximum power available from the PSPV system. Hence, IBC enhances the power quality and reliability of the PSPV system. On the other hand, fixed IBC is similar to the parallel circuit where it enhances the stability of the DC-link voltage. These findings show the superior performance of the proposed PSPV with IBC system compared to the PSPV with CBC in terms of generated power, power quality (less power losses), reliability, efficiency and flexibility. Author Contributions: Conceptualization, H.M.H.F. and A.M.E.; Methodology, H.M.H.F., M.F.O. and A.M.E.; Software, H.M.H.F., A.M.E. and M.F.O.; Validation, H.M.H.F., A.M.E. and M.F.O.; Formal Analysis, H.M.H.F., A.M.E., M.F.O. and M.S.A.-S.; Investigation, H.M.H.F., A.M.E., M.F.O. and M.S.A.-S.; Resources, H.M.H.F., M.F.O. and A.M.E.; Data Curation, H.M.H.F., A.M.E. and M.F.O.; Writing—Original Draft Preparation, H.M.H.F., M.F.O. and A.M.E.; Writing—Review & Editing, H.M.H.F., M.F.O., A.M.E. and M.S.A.-S.; Visualization, H.M.H.F., A.M.E. and M.F.O.; Supervision, M.F.O and A.M.E.; Project Administration, A.M.E.; Funding Acquisition, A.M.E. Funding: The authors extend their appreciation to the Deanship of Scientific Research at King Saud University, Riyadh, Saudi Arabia for funding this work through research group No (RG-1439-66). Conflicts of Interest: The authors declare no conflict of interest.
Nomenclature xi k vi k ω c1 and c2 VPV (i) IPV (i) PPV (i) dP /dV IMPP VMPP MP Ir MML PSPV GP LPs MPPT IBC CBC
Position vector of PSO; Velocity vector of PSO; Inertia weight; The acceleration coefficients; PV voltage for each particle; PV current for each particle; PV output power for each particle; Slope of the P-V curve; Current at maximum power point; Voltage at maximum power point; Maximum power generated; irradiance (W/m2 ); Mismatch loss index; Partially Shaded Photovoltaic; global peak; local peaks; Maximum Power Point Tracker; Interleaved Boost Converter; and Conventional Boost Converter.
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