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FPGA Based Implementation of MPPT Algorithms for Photovoltaic System under Partial Shading Conditions
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FPGA Based Implementation of MPPT Algorithms for Photovoltaic System under Partial Shading Conditions A. Senthilvel , K.N. Vijeyakumar , B. Vinothkumar PII: DOI: Reference:
S0141-9331(19)30714-8 https://doi.org/10.1016/j.micpro.2020.103011 MICPRO 103011
To appear in:
Microprocessors and Microsystems
Received date: Revised date: Accepted date:
23 December 2019 25 January 2020 29 January 2020
Please cite this article as: A. Senthilvel , K.N. Vijeyakumar , B. Vinothkumar , FPGA Based Implementation of MPPT Algorithms for Photovoltaic System under Partial Shading Conditions, Microprocessors and Microsystems (2020), doi: https://doi.org/10.1016/j.micpro.2020.103011
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
FPGA Based Implementation of MPPT Algorithms for Photovoltaic System under Partial Shading Conditions 1*
A. Senthilvel, 2Dr.K.N.Vijeyakumar and 3Dr.B.Vinothkumar
1*
Assistant Executive Engineer, Tamilnadu Generation and Distribution Corporation, Pollachi. E-mail: [email protected]
2
Associate Professor, Department of Electronics and Communication Engineering, Dr. Mahalingam College of Engineering and Technology, Pollachi. E-mail: [email protected] 3
Associate Professor, Department of Electrical and Electronics Engineering, Dr. Mahalingam College of Engineering and Technology, Pollachi. E-mail: [email protected]
ABSTRACT In Photovoltaic (PV) systems, Maximum power point (MPPT) tracking has emerged as a crucial element of that guarantees PV arrays maximum power output in all environmental conditions. Almost regularly there is a shadowing effect that occurs on the PV arrays. This is done either in a manner that is partial or almost complete coverage through trees, poles, towers, building nearby or even passing clouds. Almost often there is a shadowing impact that happens on the PV arrays. This is often done either in a manner that is partial or almost complete coverage through trees, poles, towers, building nearby or even passing clouds. Under these conditions, multiple peaks occurs that increase the complexity of the PV characteristics which in turn results in difficulty in tracking Global Peak (GP). Therefore the proposed Periodic Power Hunt (PPH) MMPT technique permits in overcoming those problems which include lower observation efficiency under Partial Shading Conditions (PSCs) like in perturbing and observe (P&O) MPPT. The proposed PPH scheme PV array under PSCs shows various completed peaks. The tracking performance is also compared with P&O-MPPT algorithms. The control technique doesn‟t have any affect of explicit operating environments and
results in better performance than ancient strategies with solar power harvesting. The FPGA based experimental implementation of proposed PPH MPPT solution in such a technique that does not involve particular measurement of open circuit voltage or short circuit current. I.INTRODUCTION The need for renewable resources of energy has multiplied on account of the results of global warming and the insufficiency of resources like fossil fuels [1], [2]. Therefore the most important source amongst the list of renewable resources is radiation [3]. Solar radiation alone is believed to be the only such resource that potentially will address this demand for energy consumption and should be considered as a feasible replacement. The major position of PV Power Generators is to convert solar radiation energy into electrical energy. This transformation takes place without any moving components in particular. There are precise voltage levels for the complete electrical grid. These are comparatively higher than those that have maximum voltage. It is due to single silicon-based PV cell. PV modules are formed by serially connecting PV cells which are used to interface PV power generators with the grid. It is found that individual PV module‟s voltage is too low. So it cannot be used as a grid-connected PV power generator. Development of generators takes place through the serial and parallel affiliation of the photovoltaic modules. This affiliation is formed to extract an adequate voltage level, similarly increase the generator nominal power [26]. The series affiliation of the photovoltaic cells is vulnerable to the probable mismatching power loss. This happens as long as the characteristics of the cells vary or if the cells are not working in uniform conditions. The current of the complete series affiliation are limited by the PV cell with the low short circuit (SC)
current [4]. Short circuit currents sometimes disagree on account of the many technical or environmental factors. The PV power generator‟s part shading impacted on account of clouds, trees, buildings, etc. may leads to uneven SC currents. In partial shading conditions, if one PV cell of the generator is shaded the it may consist of serially-connected shaded cells and it is observed that SC current of the shaded cell is less than PV power generator. Hence assume, shaded cells are reverse biased to make up connection in series. As an outcome, it results in hot spots within the shaded cell and further results in harm within the cell [5]. Prevention of PV cells from unfavorable degradation because of hot spots, PV modules producers as a consequence have installed bypass diodes connections. PV cells are in anti-parallel with it [6]. If PV cell is shaded, it will become reverse biased. The excess current in the shaded cell are bypassed by the bypass diodes connected in anti-parallel with it. Some bypass diodes may start to conduct in non-uniform situations such as Partial shading condition (PSC).In PSC Multiple maxima are shown in the power–voltage (P–V) curve of PV module which is shown in Fig. 1. In this situation, the PV power generator‟s maximum power extraction process is not direct one. This is produced due to one local maximum power point (MPP) with low voltages and another at high voltages. The efficiency of PV system can be improved by using various MPPT methods including Incremental Conductance (IC) [10], Hill Climbing (HC) [7] and Perturb and Observe (P&O) [7]–[9]. Perturbation is used by HC technique in the duty ratio of the power converter. P&O technique also used perturbation in
operating voltage of PV system [7]–[9]. These two techniques result in delivering oscillations at MPP. This is primarily due to perturbation which changes almost on a continual basis. These changes occur in both directions and are aimed for sustaining MPP and lead to power loss. The perturbation rate and perturbation size that have been analytically presented in [9] are the two influencing parameters. These influencing parameters are applicable in the P&O algorithm. Reducing the number of these oscillations helps in delivering module efficiency and improvement. The IC technique suggested [10] results in reducing the number of oscillations. However it does not completely reduce the oscillations. Techniques deploying P&O and IC here are shown as failure in achieving time intervals that have been considered as one that change the atmospheric surroundings [11], [12]. Some improvised IC algorithms have been suggested to enhance capability of MPP tracking that occurs in the fast-changing irradiance level and load [13], [14]. For attaining a fast MPP tracking response, the suggested study here proposes a simple trigonometric rule [15]. The I–V curve and load line relationship can be derived using this method. The dynamic MPPT controller that is used to facilitate PV systems is evaluated. It is found that under fast-varying insolation the PSCs have been suggested here [16]. This essentially is a scanning method which enables to define the capacity of panel‟s maximum power-deliver at the panel‟s specific operating state. Main objective of this work is to assure GP through PSCs. This is done to highlight the issues generated in output power of PV. The issues include low tracking efficiency and oscillations. Various optimization techniques like Grey Wolf Optimization (GWO) [19], firefly optimization algorithm [18], Particle Swarm Optimization (PSO) [17], etc have been utilized in varied applications. Here the MPPT has been deployed for the purpose of high tracking efficiency
under PSCs. However, these meta-heuristic MPPT algorithms have drawbacks such as complex implementation feasibility and higher cost. This research work proposes a MPPT method with efficient tracking performance under PSCs. It has an advantage of easy implementation and reduced cost. Since the functions of various components can be integrated onto the same chip, FPGAs offer lower implementation cost than DSPs that can perform only DSP-related computations. In addition, FPGAs can provide equivalent or higher performance with the customization potential of an ASIC. As FPGAs can also be reprogrammed at any time, repairs can be performed in-situ while the system is running providing a high degree of robustness. Beside robustness, this re-programmability can also provide a high level of flexibility: the proposed PPH MPPT control system can be easily updated or modified even when it is running The paper is organized as, Section discusses about the PV system characteristics in PSC. It also describes the curves I - V and P - V of partially shaded modules. Section III gives the procedure of proposed PPH P&O and MPPT. Section IV and V shows the experimental results by using FPGA. Section VI concludes the work. II. CHARACTERISTICS OF A PV SYSTEM UNDER PSCS A. PV Cell Basic Characteristics Equivalent single diode model is used to represent a cell of PV [7]. For suggested model in evaluation, symbols and their respective terminology has been specified below: Constant source of PV is given by
;
The diode connected in parallel with current source is represented by D;
All inherent components resistance‟s sum in the path of current is given by and it should be low; The leakage resistance across P-N junction is given by Difference between diode current
and it should be high;
and photocurrent
is given by I and it
is given by, (1) Where, saturation current is given by
,
Ideality factor of diode is given by a, represents Boltzmann‟s constant, Electron charge is given by q, Temperature is represented by T in kelvin, and Count of cells connected in series is given by
.
B. System Description Different PV modules form a serially and sequentially interlinked PV array. This series arrangement produces higher and parallel voltage, which helps to enhance the current. During PSCs, the P–V characteristics curve observes numerous peaks, i.e. local and global maximum points owing to bypass diodes existence, with the existence of linked bypass diode. During PSCs, the hot spot occurrence can be reduced by connecting bypass diode parallel to PV module. The shaded module corresponds to a load as opposed to a power generation means. Figs. 1 and 2 demonstrate the two distinct PV arrays considered here. Fig. 1 shows the configuration which contains serially connected four modules (4S configuration). It has two dissimilar shading patterns. It includes its P–V curves. PV configuration, two modules are serially arranged in second stage. Finally, it is connected parallel to another two modules which are serially configured s (2S2P
configuration). Fig. 2 shows both contain dissimilar pattern shading including P– V curves.
(a)
(c)
(b)
(d)
Fig.1: 4S Configuration Under Various Patterns of Shading (a) Pattern 1 (b) P-V curve under Pattern 1. (c) Pattern 2 (d) P-V curve under Pattern 2
(a)
(c)
(b)
(d)
Fig.2: 2S2P Configuration Under Various Patterns of Shading (a) Pattern 3 (b) P-V Curve Under Pattern 3. (c) Pattern 4 (d) P-V Curve Under Pattern 4. III. P&O and Proposed PPH MPPT ALGORITHM A. Perturb and Observe (P&O) Algorithm This algorithm basically brings its basic structure on the basis of the periodic measurement of panel voltage and current of PV ( percent output power
and
) to compute
of PV.
The operating point of a system can be varied by perturbing (increasing or decreasing) power converter‟s switching duty cycle (D). The variation in output power is measured as
.
When there is an increase in power, MPP is pursued. So perturbation must remain as status co for the consecutive stage. If it does not happen perturbation must be reversed. Until MPP is reached [15] process repetition takes place and flow chart of the P&O algorithm shows this and it is shown in Fig.3.
Fig.3: Flow Chart of P&O Algorithm B. Proposed PPH MPPT Algorithm Suggested Here This is the most efficient method; PSC power is tracked using MPPT. According to this method, current and voltage of PV panel are measured periodically to estimate the output power percentage of PV. Using this value output power variation and voltage variation are observed. Considering the positive power variation and negative voltage variation, duty cycle D rises further and in turn raises the power until MPP or the maximum power point is achieved. The duty ratio increases till it‟s at the count, and is zero value of differential power by differential Voltage. The maximum value is compared with single-cell current limit, if it is greater than the power tracked in local power then duty cycle is increased to track global power. Otherwise the duty cycle is allowed to settle and power will be reduced.
The power of individual Cell (2) Where
is maximum PV power, count of parallel and serially connected cell
of a panel is represented by
.
Here steady-state error is nearly equivalent to 0.66% with 0.005 step size for duty cycle for suggested algorithm with boost converter. From this power per duty cycle
is calculated. (3)
The maximum count
is calculated using the following equation. (4)
Fig.4: Flow chart of Proposed PPH MPPT Algorithm
IV. SIMULATION RESULTS MPPT algorithm for PSCs was carefully analyzed and evaluated. P&O MPPT algorithms are used to compare the evaluation. The implementation process was conducted for the above two algorithms based on PSCs. The insolation level of 4S and 2S2P are changing rapidly. A,
= 17.5 V, and
= 50 W,
= 21.8 V,
= 3.20
= 2.90 A. In the pattern 1 and 2 current, voltage and
power in the 4S configuration has been suggested for P&O MPPT. A dedicated computer program is developed in MATLAB for proposed PPH based MPPT in both cases with the help of Simulink and State flow tool boxes. The simulation results are discussed now. With respect to pattern 1 where the simulation study has been conducted, for the suggested MPPT its working has been clearly shown in Fig. 5 and Fig. 6 demonstrates the functioning of P&O MPPT algorithm and its capacity to monitor the 119.4 W GP. However given this state P&O MPPT have steady-state oscillations. Or in other words operating point is starts to oscillate around MPP. These oscillations result in power loss and decrease the speed of algorithm response and PV system efficiency. Fig. 11 and Fig. 12 shows shading pattern 4 as suggested in the MPPT and P&O algorithms. The suggested MPPT converges to the 95.5 W GP but P&O MPPT converges to 79.2 W LP. This is because, it cannot distinguish GPs and local. It results in steady-state oscillations.
(c) Fig.5: Simulation results of proposed PPH MPPT in 4S configuration pattern 1
(c)
Fig.6: Simulation results of P&O MPPT for 4S configuration pattern 1
(c)
Fig.7: Simulation results of proposed PPH MPPT for 4S configuration pattern 2
(c)
Fig.8: Simulation results of P&O MPPT in 4S configuration pattern 2 In the pattern 3 and 4 power, voltage, and current for the 2S2P configuration has been suggested for P&O MPPT. With respect to pattern 3 where the simulation study has been conducted, for the suggested MPPT its working has been clearly
shown in Fig.9. In Fig. 10 P&O MPPT algorithms have been clearly shown. This allows tracking of GP of 142.5 W, however in this state P&O MPPT is seen to have steady-state oscillations. Or in other words operating point is starting to oscillate to MPP. These oscillations produces power loss and slow down speed of algorithm response and PV system efficiency. Fig. 11 and Fig. 12 shows shading pattern 4as suggested in the MPPT and P&O algorithms. The suggested MPPT converges to the 102.6 W GP, but P&O MPPT converges to 75.8 W. This is because, it cannot distinguish GPs and local. It results in steady-state oscillations.
(c) Fig.9: Simulation results of proposed PPH MPPT in 2S2P configuration pattern 3
(c) Fig.10: Simulation results of P&O MPPT for 2S2P configuration pattern 3
(c) Fig.11: Simulation results of proposed PPH MPPT for 2S2P configuration pattern 4
(c) Fig.12: Simulation results of P&O MPPT for 2S2P configuration pattern 4 V. FPGA BASED EXPERIMENTAL RESULTS Maximum power produced by the boost converter at a specific duty ratio produced by the design tool Quartus II of Altera is simulated and afterward programmed to FPGA (which acts as MPPT Controller) using Byte blaster II cable. The VHDL code representing the block function is written in the Quartus II Text Editor. The Quartus II also can be used to compile the VHDL code. When the compilation is finished and no error, that code can be convert into block symbol file. The “Create/Update” command used to create a Block Symbol File (.bsf) from a VHDL design file, and then incorporate it into a Block Design File (.bdf).For the purpose of authenticating suggested GWO-based MPPT effectiveness several experiments were done. 2S2P and 4S configurations are used to conduct experimentation on actual PV array.
(a)
(b) Fig.13: PROPOSED PPH MPPT METHOD‟s Experimental results in 4S CONFIGURATION (a) Pattern 5. (b) Pattern 6
(a)
(b) Fig.14: PROPOSED PPH MPPT METHOD‟s Experimental result in 2S2P CONFIGURATION (a) Pattern 7. (b) Pattern 8.
Table1: Proposed PPH MPPT method‟s performance comparison in 4s configuration Pattern used
GP in Watts
TRACK efficiency
For Shading Pattern 5
108.2W/75.5V 75.7 1.41 106.74W
98.65%
Pattern 6
76.33W/35.8V 35.1 2.13
97.94%
74.76W
Table 2: Proposed PPH MPPT method‟s performance comparison in 2s2p configuration Pattern used
GP in Watts
TRACK efficiency
For Shading Pattern 7 Pattern 8
76.7 W/17.9V 37.7 V 2.44 91.99W 52.3 W/38V
18.4 V 4.15 76.36W
98.28% 98.02%
The four series(4S) configuration is obtained by two pattern with different irradiation conditions as Pattern 1 and Pattern 2, as well as Two series two parallel (2S2P) configuration is obtained by two pattern with different irradiation conditions as Pattern 3 and Pattern 4. Four (50 W) solar modules manufactured by Sukam are used for experimentation. The ratings of the modules are P_mpp = 50 W, I_mpp = 2.90 A , I_sc = 3.20 A ,V_oc = 21.8 V, and V_mpp= 17.5 V. For partial shading, transparent sheets were placed having varying shapes on PV modules. VI. CONCLUSION This research paper proposed PPH an innovative MPPT algorithm to extract maximum power for PV Systems and also it could locate the MPP for any environmental variations including partial shading condition and large fluctuations of insolation. This extraction will optimize their functioning and enable them to work with simpler implementations and lowered costs under PSCs.Simulation
experimentation is done to evaluate the overall performance of proposed PPH technique. Overall performance of MPPT was reviewed and it is compared with current MPPT P&O algorithm technique. Hence based on the results obtained from simulation and several experimental analyses, proposed PPH MPPT approach is capable of tracking GP under PSCs efficiently. Additionally, the efficiency of the proposed PPH MPPT tracking is comparatively higher when reviewed with the present P&O MPPT under PSCs state which is obtained as 98.5%. The proposed PPH MPPT algorithm implementation FPGA, study shows the improved performance of execution time and consequently reducing the MPPT settling error. REFERENCES [1]
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AUTHOR BIOGRAPHY A.SENTHILVEL is an Executive Engineer working in Tamil Nadu Distribution & Generation Corporation. He pursued his Diploma in Electrical & Electronic Engineering at Nachimuthu Polytechnic college Pollachi in 1981. He also continued his B.E electrical & electronics engineering degree at PSG college Coimbatore in 1989 by working part time at Sathiyamangalam. He also pursued his Masters degree in Applied Electronics at Dr. Mahalingam College of Engineering & Technology, Pollachi in 2011. He joined at TNEB as Technical Assistant in 1984.With his hard work and determination to work he has been promoted as Assistant Engineer and was on helm at Ambarampalayam, Kinathukadavu, Pollachi, Podanur, Thiruvanamalai between 1990 to 2005.Later he got promoted as Assistant Executive Engineer at 2005 and served as Assistant Executive Engineer till 2016. Further promotion has made him to serve as an Executive Engineer at Coimbatore and with further transfer he is on helm as Executive Engineer Pollachi.
K. N. Vijeyakumar is currently with Dr. Mahalingam College of Engineering and Technology, Pollachiworking as Associate Professor in the Department of Electronics and Communication Engineering since 30.12.2013. Formerly, he was working as Lecturer in Anna University, Coimbatore from September-2007 to September-2008 and as Assistant Professor in Anna University Regional Centre, Coimbatore from October-2008 to December-2013. He completed Masters in Engineering at Government College of Technology, Coimbatore, Tamilnadu in the year 2007 and PhD in the area of VLSI in the Faculty of Information and Communication Engineering from Anna University, Chennai, in the year 2013. His area of research include FPGA based signal and image processing system design, Analog and Mixed Signal IC design ,Low power Processor design for signal and image processing, Approximate computing . His publications include 3 books,27 international journals and 57 conferences in the areas of ASIC design, VLSI design, Digital system design and Approximate Computing. Currently he is working with ISRO sponsored research project on “High End Analog IC design”.
Vinoth Kumar Bojan received B.E. degree in Electrical & Electronics Engineering from the Bharathiar University, India, in 2002, M.E(Applied Electronics) and Ph.D degree in Information and Communiation Engineering from Anna University, India in 2005 and 2015 respectively. He has 14 years of teaching and research experience. He is currently working as an Associate Professor, in Department of Electrical and Electronics Engineering, Dr. Mahalingam College of Engineering & Technology, Pollachi, India since 2017. His current research interest includes FPGA based system design, medical image processing, soft computing and pattern recognition.
FPGA Based Implementation of MPPT Algorithms for Photovoltaic System under Partial Shading Conditions A. Senthilvel , K.N. Vijeyakumar , B. Vinothkumar PII: DOI: Reference:
S0141-9331(19)30714-8 https://doi.org/10.1016/j.micpro.2020.103011 MICPRO 103011
To appear in:
Microprocessors and Microsystems
Received date: Revised date: Accepted date:
23 December 2019 25 January 2020 29 January 2020
Please cite this article as: A. Senthilvel , K.N. Vijeyakumar , B. Vinothkumar , FPGA Based Implementation of MPPT Algorithms for Photovoltaic System under Partial Shading Conditions, Microprocessors and Microsystems (2020), doi: https://doi.org/10.1016/j.micpro.2020.103011
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
FPGA Based Implementation of MPPT Algorithms for Photovoltaic System under Partial Shading Conditions 1*
A. Senthilvel, 2Dr.K.N.Vijeyakumar and 3Dr.B.Vinothkumar
1*
Assistant Executive Engineer, Tamilnadu Generation and Distribution Corporation, Pollachi. E-mail: [email protected]
2
Associate Professor, Department of Electronics and Communication Engineering, Dr. Mahalingam College of Engineering and Technology, Pollachi. E-mail: [email protected] 3
Associate Professor, Department of Electrical and Electronics Engineering, Dr. Mahalingam College of Engineering and Technology, Pollachi. E-mail: [email protected]
ABSTRACT In Photovoltaic (PV) systems, Maximum power point (MPPT) tracking has emerged as a crucial element of that guarantees PV arrays maximum power output in all environmental conditions. Almost regularly there is a shadowing effect that occurs on the PV arrays. This is done either in a manner that is partial or almost complete coverage through trees, poles, towers, building nearby or even passing clouds. Almost often there is a shadowing impact that happens on the PV arrays. This is often done either in a manner that is partial or almost complete coverage through trees, poles, towers, building nearby or even passing clouds. Under these conditions, multiple peaks occurs that increase the complexity of the PV characteristics which in turn results in difficulty in tracking Global Peak (GP). Therefore the proposed Periodic Power Hunt (PPH) MMPT technique permits in overcoming those problems which include lower observation efficiency under Partial Shading Conditions (PSCs) like in perturbing and observe (P&O) MPPT. The proposed PPH scheme PV array under PSCs shows various completed peaks. The tracking performance is also compared with P&O-MPPT algorithms. The control technique doesn‟t have any affect of explicit operating environments and
results in better performance than ancient strategies with solar power harvesting. The FPGA based experimental implementation of proposed PPH MPPT solution in such a technique that does not involve particular measurement of open circuit voltage or short circuit current. I.INTRODUCTION The need for renewable resources of energy has multiplied on account of the results of global warming and the insufficiency of resources like fossil fuels [1], [2]. Therefore the most important source amongst the list of renewable resources is radiation [3]. Solar radiation alone is believed to be the only such resource that potentially will address this demand for energy consumption and should be considered as a feasible replacement. The major position of PV Power Generators is to convert solar radiation energy into electrical energy. This transformation takes place without any moving components in particular. There are precise voltage levels for the complete electrical grid. These are comparatively higher than those that have maximum voltage. It is due to single silicon-based PV cell. PV modules are formed by serially connecting PV cells which are used to interface PV power generators with the grid. It is found that individual PV module‟s voltage is too low. So it cannot be used as a grid-connected PV power generator. Development of generators takes place through the serial and parallel affiliation of the photovoltaic modules. This affiliation is formed to extract an adequate voltage level, similarly increase the generator nominal power [26]. The series affiliation of the photovoltaic cells is vulnerable to the probable mismatching power loss. This happens as long as the characteristics of the cells vary or if the cells are not working in uniform conditions. The current of the complete series affiliation are limited by the PV cell with the low short circuit (SC)
current [4]. Short circuit currents sometimes disagree on account of the many technical or environmental factors. The PV power generator‟s part shading impacted on account of clouds, trees, buildings, etc. may leads to uneven SC currents. In partial shading conditions, if one PV cell of the generator is shaded the it may consist of serially-connected shaded cells and it is observed that SC current of the shaded cell is less than PV power generator. Hence assume, shaded cells are reverse biased to make up connection in series. As an outcome, it results in hot spots within the shaded cell and further results in harm within the cell [5]. Prevention of PV cells from unfavorable degradation because of hot spots, PV modules producers as a consequence have installed bypass diodes connections. PV cells are in anti-parallel with it [6]. If PV cell is shaded, it will become reverse biased. The excess current in the shaded cell are bypassed by the bypass diodes connected in anti-parallel with it. Some bypass diodes may start to conduct in non-uniform situations such as Partial shading condition (PSC).In PSC Multiple maxima are shown in the power–voltage (P–V) curve of PV module which is shown in Fig. 1. In this situation, the PV power generator‟s maximum power extraction process is not direct one. This is produced due to one local maximum power point (MPP) with low voltages and another at high voltages. The efficiency of PV system can be improved by using various MPPT methods including Incremental Conductance (IC) [10], Hill Climbing (HC) [7] and Perturb and Observe (P&O) [7]–[9]. Perturbation is used by HC technique in the duty ratio of the power converter. P&O technique also used perturbation in
operating voltage of PV system [7]–[9]. These two techniques result in delivering oscillations at MPP. This is primarily due to perturbation which changes almost on a continual basis. These changes occur in both directions and are aimed for sustaining MPP and lead to power loss. The perturbation rate and perturbation size that have been analytically presented in [9] are the two influencing parameters. These influencing parameters are applicable in the P&O algorithm. Reducing the number of these oscillations helps in delivering module efficiency and improvement. The IC technique suggested [10] results in reducing the number of oscillations. However it does not completely reduce the oscillations. Techniques deploying P&O and IC here are shown as failure in achieving time intervals that have been considered as one that change the atmospheric surroundings [11], [12]. Some improvised IC algorithms have been suggested to enhance capability of MPP tracking that occurs in the fast-changing irradiance level and load [13], [14]. For attaining a fast MPP tracking response, the suggested study here proposes a simple trigonometric rule [15]. The I–V curve and load line relationship can be derived using this method. The dynamic MPPT controller that is used to facilitate PV systems is evaluated. It is found that under fast-varying insolation the PSCs have been suggested here [16]. This essentially is a scanning method which enables to define the capacity of panel‟s maximum power-deliver at the panel‟s specific operating state. Main objective of this work is to assure GP through PSCs. This is done to highlight the issues generated in output power of PV. The issues include low tracking efficiency and oscillations. Various optimization techniques like Grey Wolf Optimization (GWO) [19], firefly optimization algorithm [18], Particle Swarm Optimization (PSO) [17], etc have been utilized in varied applications. Here the MPPT has been deployed for the purpose of high tracking efficiency
under PSCs. However, these meta-heuristic MPPT algorithms have drawbacks such as complex implementation feasibility and higher cost. This research work proposes a MPPT method with efficient tracking performance under PSCs. It has an advantage of easy implementation and reduced cost. Since the functions of various components can be integrated onto the same chip, FPGAs offer lower implementation cost than DSPs that can perform only DSP-related computations. In addition, FPGAs can provide equivalent or higher performance with the customization potential of an ASIC. As FPGAs can also be reprogrammed at any time, repairs can be performed in-situ while the system is running providing a high degree of robustness. Beside robustness, this re-programmability can also provide a high level of flexibility: the proposed PPH MPPT control system can be easily updated or modified even when it is running The paper is organized as, Section discusses about the PV system characteristics in PSC. It also describes the curves I - V and P - V of partially shaded modules. Section III gives the procedure of proposed PPH P&O and MPPT. Section IV and V shows the experimental results by using FPGA. Section VI concludes the work. II. CHARACTERISTICS OF A PV SYSTEM UNDER PSCS A. PV Cell Basic Characteristics Equivalent single diode model is used to represent a cell of PV [7]. For suggested model in evaluation, symbols and their respective terminology has been specified below: Constant source of PV is given by
;
The diode connected in parallel with current source is represented by D;
All inherent components resistance‟s sum in the path of current is given by and it should be low; The leakage resistance across P-N junction is given by Difference between diode current
and it should be high;
and photocurrent
is given by I and it
is given by, (1) Where, saturation current is given by
,
Ideality factor of diode is given by a, represents Boltzmann‟s constant, Electron charge is given by q, Temperature is represented by T in kelvin, and Count of cells connected in series is given by
.
B. System Description Different PV modules form a serially and sequentially interlinked PV array. This series arrangement produces higher and parallel voltage, which helps to enhance the current. During PSCs, the P–V characteristics curve observes numerous peaks, i.e. local and global maximum points owing to bypass diodes existence, with the existence of linked bypass diode. During PSCs, the hot spot occurrence can be reduced by connecting bypass diode parallel to PV module. The shaded module corresponds to a load as opposed to a power generation means. Figs. 1 and 2 demonstrate the two distinct PV arrays considered here. Fig. 1 shows the configuration which contains serially connected four modules (4S configuration). It has two dissimilar shading patterns. It includes its P–V curves. PV configuration, two modules are serially arranged in second stage. Finally, it is connected parallel to another two modules which are serially configured s (2S2P
configuration). Fig. 2 shows both contain dissimilar pattern shading including P– V curves.
(a)
(c)
(b)
(d)
Fig.1: 4S Configuration Under Various Patterns of Shading (a) Pattern 1 (b) P-V curve under Pattern 1. (c) Pattern 2 (d) P-V curve under Pattern 2
(a)
(c)
(b)
(d)
Fig.2: 2S2P Configuration Under Various Patterns of Shading (a) Pattern 3 (b) P-V Curve Under Pattern 3. (c) Pattern 4 (d) P-V Curve Under Pattern 4. III. P&O and Proposed PPH MPPT ALGORITHM A. Perturb and Observe (P&O) Algorithm This algorithm basically brings its basic structure on the basis of the periodic measurement of panel voltage and current of PV ( percent output power
and
) to compute
of PV.
The operating point of a system can be varied by perturbing (increasing or decreasing) power converter‟s switching duty cycle (D). The variation in output power is measured as
.
When there is an increase in power, MPP is pursued. So perturbation must remain as status co for the consecutive stage. If it does not happen perturbation must be reversed. Until MPP is reached [15] process repetition takes place and flow chart of the P&O algorithm shows this and it is shown in Fig.3.
Fig.3: Flow Chart of P&O Algorithm B. Proposed PPH MPPT Algorithm Suggested Here This is the most efficient method; PSC power is tracked using MPPT. According to this method, current and voltage of PV panel are measured periodically to estimate the output power percentage of PV. Using this value output power variation and voltage variation are observed. Considering the positive power variation and negative voltage variation, duty cycle D rises further and in turn raises the power until MPP or the maximum power point is achieved. The duty ratio increases till it‟s at the count, and is zero value of differential power by differential Voltage. The maximum value is compared with single-cell current limit, if it is greater than the power tracked in local power then duty cycle is increased to track global power. Otherwise the duty cycle is allowed to settle and power will be reduced.
The power of individual Cell (2) Where
is maximum PV power, count of parallel and serially connected cell
of a panel is represented by
.
Here steady-state error is nearly equivalent to 0.66% with 0.005 step size for duty cycle for suggested algorithm with boost converter. From this power per duty cycle
is calculated. (3)
The maximum count
is calculated using the following equation. (4)
Fig.4: Flow chart of Proposed PPH MPPT Algorithm
IV. SIMULATION RESULTS MPPT algorithm for PSCs was carefully analyzed and evaluated. P&O MPPT algorithms are used to compare the evaluation. The implementation process was conducted for the above two algorithms based on PSCs. The insolation level of 4S and 2S2P are changing rapidly. A,
= 17.5 V, and
= 50 W,
= 21.8 V,
= 3.20
= 2.90 A. In the pattern 1 and 2 current, voltage and
power in the 4S configuration has been suggested for P&O MPPT. A dedicated computer program is developed in MATLAB for proposed PPH based MPPT in both cases with the help of Simulink and State flow tool boxes. The simulation results are discussed now. With respect to pattern 1 where the simulation study has been conducted, for the suggested MPPT its working has been clearly shown in Fig. 5 and Fig. 6 demonstrates the functioning of P&O MPPT algorithm and its capacity to monitor the 119.4 W GP. However given this state P&O MPPT have steady-state oscillations. Or in other words operating point is starts to oscillate around MPP. These oscillations result in power loss and decrease the speed of algorithm response and PV system efficiency. Fig. 11 and Fig. 12 shows shading pattern 4 as suggested in the MPPT and P&O algorithms. The suggested MPPT converges to the 95.5 W GP but P&O MPPT converges to 79.2 W LP. This is because, it cannot distinguish GPs and local. It results in steady-state oscillations.
(c) Fig.5: Simulation results of proposed PPH MPPT in 4S configuration pattern 1
(c)
Fig.6: Simulation results of P&O MPPT for 4S configuration pattern 1
(c)
Fig.7: Simulation results of proposed PPH MPPT for 4S configuration pattern 2
(c)
Fig.8: Simulation results of P&O MPPT in 4S configuration pattern 2 In the pattern 3 and 4 power, voltage, and current for the 2S2P configuration has been suggested for P&O MPPT. With respect to pattern 3 where the simulation study has been conducted, for the suggested MPPT its working has been clearly
shown in Fig.9. In Fig. 10 P&O MPPT algorithms have been clearly shown. This allows tracking of GP of 142.5 W, however in this state P&O MPPT is seen to have steady-state oscillations. Or in other words operating point is starting to oscillate to MPP. These oscillations produces power loss and slow down speed of algorithm response and PV system efficiency. Fig. 11 and Fig. 12 shows shading pattern 4as suggested in the MPPT and P&O algorithms. The suggested MPPT converges to the 102.6 W GP, but P&O MPPT converges to 75.8 W. This is because, it cannot distinguish GPs and local. It results in steady-state oscillations.
(c) Fig.9: Simulation results of proposed PPH MPPT in 2S2P configuration pattern 3
(c) Fig.10: Simulation results of P&O MPPT for 2S2P configuration pattern 3
(c) Fig.11: Simulation results of proposed PPH MPPT for 2S2P configuration pattern 4
(c) Fig.12: Simulation results of P&O MPPT for 2S2P configuration pattern 4 V. FPGA BASED EXPERIMENTAL RESULTS Maximum power produced by the boost converter at a specific duty ratio produced by the design tool Quartus II of Altera is simulated and afterward programmed to FPGA (which acts as MPPT Controller) using Byte blaster II cable. The VHDL code representing the block function is written in the Quartus II Text Editor. The Quartus II also can be used to compile the VHDL code. When the compilation is finished and no error, that code can be convert into block symbol file. The “Create/Update” command used to create a Block Symbol File (.bsf) from a VHDL design file, and then incorporate it into a Block Design File (.bdf).For the purpose of authenticating suggested GWO-based MPPT effectiveness several experiments were done. 2S2P and 4S configurations are used to conduct experimentation on actual PV array.
(a)
(b) Fig.13: PROPOSED PPH MPPT METHOD‟s Experimental results in 4S CONFIGURATION (a) Pattern 5. (b) Pattern 6
(a)
(b) Fig.14: PROPOSED PPH MPPT METHOD‟s Experimental result in 2S2P CONFIGURATION (a) Pattern 7. (b) Pattern 8.
Table1: Proposed PPH MPPT method‟s performance comparison in 4s configuration Pattern used
GP in Watts
TRACK efficiency
For Shading Pattern 5
108.2W/75.5V 75.7 1.41 106.74W
98.65%
Pattern 6
76.33W/35.8V 35.1 2.13
97.94%
74.76W
Table 2: Proposed PPH MPPT method‟s performance comparison in 2s2p configuration Pattern used
GP in Watts
TRACK efficiency
For Shading Pattern 7 Pattern 8
76.7 W/17.9V 37.7 V 2.44 91.99W 52.3 W/38V
18.4 V 4.15 76.36W
98.28% 98.02%
The four series(4S) configuration is obtained by two pattern with different irradiation conditions as Pattern 1 and Pattern 2, as well as Two series two parallel (2S2P) configuration is obtained by two pattern with different irradiation conditions as Pattern 3 and Pattern 4. Four (50 W) solar modules manufactured by Sukam are used for experimentation. The ratings of the modules are P_mpp = 50 W, I_mpp = 2.90 A , I_sc = 3.20 A ,V_oc = 21.8 V, and V_mpp= 17.5 V. For partial shading, transparent sheets were placed having varying shapes on PV modules. VI. CONCLUSION This research paper proposed PPH an innovative MPPT algorithm to extract maximum power for PV Systems and also it could locate the MPP for any environmental variations including partial shading condition and large fluctuations of insolation. This extraction will optimize their functioning and enable them to work with simpler implementations and lowered costs under PSCs.Simulation
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AUTHOR BIOGRAPHY A.SENTHILVEL is an Executive Engineer working in Tamil Nadu Distribution & Generation Corporation. He pursued his Diploma in Electrical & Electronic Engineering at Nachimuthu Polytechnic college Pollachi in 1981. He also continued his B.E electrical & electronics engineering degree at PSG college Coimbatore in 1989 by working part time at Sathiyamangalam. He also pursued his Masters degree in Applied Electronics at Dr. Mahalingam College of Engineering & Technology, Pollachi in 2011. He joined at TNEB as Technical Assistant in 1984.With his hard work and determination to work he has been promoted as Assistant Engineer and was on helm at Ambarampalayam, Kinathukadavu, Pollachi, Podanur, Thiruvanamalai between 1990 to 2005.Later he got promoted as Assistant Executive Engineer at 2005 and served as Assistant Executive Engineer till 2016. Further promotion has made him to serve as an Executive Engineer at Coimbatore and with further transfer he is on helm as Executive Engineer Pollachi.
K. N. Vijeyakumar is currently with Dr. Mahalingam College of Engineering and Technology, Pollachiworking as Associate Professor in the Department of Electronics and Communication Engineering since 30.12.2013. Formerly, he was working as Lecturer in Anna University, Coimbatore from September-2007 to September-2008 and as Assistant Professor in Anna University Regional Centre, Coimbatore from October-2008 to December-2013. He completed Masters in Engineering at Government College of Technology, Coimbatore, Tamilnadu in the year 2007 and PhD in the area of VLSI in the Faculty of Information and Communication Engineering from Anna University, Chennai, in the year 2013. His area of research include FPGA based signal and image processing system design, Analog and Mixed Signal IC design ,Low power Processor design for signal and image processing, Approximate computing . His publications include 3 books,27 international journals and 57 conferences in the areas of ASIC design, VLSI design, Digital system design and Approximate Computing. Currently he is working with ISRO sponsored research project on “High End Analog IC design”.
Vinoth Kumar Bojan received B.E. degree in Electrical & Electronics Engineering from the Bharathiar University, India, in 2002, M.E(Applied Electronics) and Ph.D degree in Information and Communiation Engineering from Anna University, India in 2005 and 2015 respectively. He has 14 years of teaching and research experience. He is currently working as an Associate Professor, in Department of Electrical and Electronics Engineering, Dr. Mahalingam College of Engineering & Technology, Pollachi, India since 2017. His current research interest includes FPGA based system design, medical image processing, soft computing and pattern recognition.