POWER LOSS COMPARISON OF SINGLE AND TWO STAGE GRID CONNECTED PHOTOVOLTAIC SYSTEMS CONNECTED WITH MICROGRID

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1 International Journal of Electrical Engineering & Technology (IJEET) Volume 9, Issue 4, July- August 2018, pp , Article ID: IJEET_09_04_012 Available online at ISSN Print: and ISSN Online: Journal Impact Factor (2016): (Calculated by GISI) IAEME Publication POWER LOSS COMPARISON OF SINGLE AND TWO STAGE GRID CONNECTED PHOTOVOLTAIC SYSTEMS CONNECTED WITH MICROGRID Mohammad Kalimullah Research Scholar, Deptt of EE, Jamia Millia Islamia (A central University), New Delhi, India ABSTRACT In this paper, the power loss based on double line frequency voltage ripple (DLFVR), steep solar radiation change and DLFVR, rapid DC load change and DLFVR, finite operating voltage scope and DLFVR, and comprehensive loss factor amalgamation has been analyzed and compared for grid connected solar photovoltaic (SPV) single stage and two stage system. The SPV system in single stage and double stage operating on Maximum power point fluctuated by these loss components. An additional maximum power point tracker used in double stage SPV system nullifies the effects of loss components but the tracker diminishes the system performance nearly about 2.5%. In grid connected SPV system with single stage, the power loss due to these loss components is also nearly 2.5% but this system has the merit of saving equipments and hence reduces the expenditure and under certain operating voltage scope, the overall system efficiency does not reduce more. This power loss comparison has been studied and reported in MATLAB simulation environment. Keywords: power loss, solar radiation and MATLAB. Cite this Article: Mohammad Kalimullah, Power Loss Comparison of Single and Two Stage Grid Connected Photovoltaic Systems Connected With Microgrid: International Journal of Electrical Engineering & Technology, 9(4), 2018, pp INTRODUCTION Photovoltaic (PV) grid-connected systems based on a two-stage configuration have been widely studied. They can draw maximum power from PV modules and inject the power into utility grid with unity power factor or they can rectify the ac source to replenish and regulate the dc bus. However, the loss factors, such as operational conditions, components, and grid voltage, will deviate effective PV output power [1]. In a grid-connected PV system (GCPVS), PV power varies with operational conditions, such as irradiance, temperature, light incident angle, reduction of sunlight transmittance on glass of module, and shading [2] [5], [12], [13] editor@iaeme.com

2 Mohammad Kalimullah These factors have been investigated in detail and the authors have presented diagnosis methods to estimate the reduction of PV power. Moreover, a special condition, snow coverage, has been also discussed [6], which was compared with other coverage situations such as shading and dirt. Then, another loss factors, such as components, solar cell serial resistance, and capacity loss in PV batteries, have been reported [3], [7], [8], [19], which are related to the cells themselves. During system operation, there are loss factors such as double line-frequency voltage ripple (DLFVR) due to ac grid [9], [10], [14] [17] and fast irradiance variation [11], causing deviation from the maximum power points (MPPs) and also resulting in power loss. However, these factors have not been taken into account in power loss comparison for both single-stage and two-stage GCPVS. Here our endeavor is to present power loss comparison according to five loss factors that might deviate the operating points from the MPPs. First, in this we have conducted modeling of solar cells and numerical analysis including I V characteristics of PV modules to derive the effect of DLFVR on both single-stage and two stage GCPVS. Then, it performs power loss analysis due to fast irradiance variation. Moreover, a single-stage PV system will penalize its output power under certain operating voltage ranges, while it can save an MPPT stage. In a PV dc-distributed system, its dc-bus voltage is regulated by the bidirectional inverter within V (380±20 V), and dc appliance and equipment can be connected to the dc bus directly. Thus, this study chooses fast dc load variation and limited operating voltage range as two of the loss factors. Since the effect of DLFVR exists all the time, In this work I have presented the five loss factors as DLFVR, fast irradiance variation + DLFVR, fast dc load variation + DLFVR, limited operating voltage range + DLFVR, and overall loss factor combination. Cost and T&D Losses: Solar PV is some years away from true cost competitiveness and from being able to compete on the same scale as other energy generation technologies. Adding to the cost are T&D losses that at approximately 40 percent make generation through solar energy sources highly unfeasible. However, the government is supporting R&D activities by establishing research centers and funding such initiatives. The government has tied up with world-renowned universities to bring down the installation cost of solar power sources and is focusing on up gradation of substations and T&D lines to reduce T&D losses. Land Scarcity: Per capita land availability is very low in India, and land is a scarce resource. Dedication of land area near substations for exclusive installation of solar cells might have to compete with other necessities that require land. Funding of initiatives like National Solar Mission is a constraint due to India's inadequate financing capabilities. The finance ministry has explicitly raised concerns about funding an ambitious scheme like NSM. Manufacturers are mostly focused on export markets that buy Solar PV cells and modules at higher prices thereby increasing their profits. Many new suppliers have tie-ups with foreign players in Europe and United States thereby prioritizing export demand. This could result in reduced supplies for the fast-growing local market. The lack of closer industry-government cooperation for the technology to achieve scale. The need for focused, collaborative and goals driven R&D to help India attain technology leadership in PV. The need for a better financing infrastructure, models and arrangements to spur the PV industry and consumption of PV products. Training and development of human resources to drive industry growth and PV adoption. The need for intra-industry cooperation in expanding the PV supply chain, in technical information sharing through conferences and workshops, in collaborating with BOS (balance of systems) manufacturers and in gathering and publishing accurate market data, trends and projections. The need to build consumer awareness about the technology, its economics and right usage. Complexity of subsidy structure & involvement of too many agencies like MNRE, IREDA, SNA, and electricity board and electricity regulatory commission makes the development of solar PV projects editor@iaeme.com

3 Power Loss Comparison of Single and Two Stage Grid Connected Photovoltaic Systems Connected With Microgrid difficult. Land allotment & PPA signing is a long procedure under the Generation Based Incentive scheme. 2. SYSTEM DESIGN The objective of this project is to simulate a model of Single stage and two stages Grid Connected Photo-Voltaic System and Compare the Power loss in both. It also involves the harmonic analysis of Single Stage and Two Stage with and without battery. All the models have been simulated in MATLAB-Simulink and the simulation results have been presented in the following report SYSTEM CONFIGURATION OF PROPOSED MODEL Figure 2.1 proposed model. Figure 2.2 circuit configuration of a single stage GCPVS. The circuit configuration of a single-stage GCPVS is shown in Fig 2.2 When the system reaches the maximum power point Pmpp under a specific irradiance, its PV voltage vpv and current ipv become constant and equal to Vmpp and Impp, respectively. However, the effect of DLFVR on the deviation of PV voltage away from Vmpp will cause power loss, which can be expressed as ( ) ( ) ( ) (4) ( ) (5) (6) editor@iaeme.com

4 Mohammad Kalimullah Here, is the line period and Ts is the switching period of the full-bridge inverter. In general, an inverter system is operated by a current control at fixed frequency 1/Ts. Figure 2.3 circuit configuration of a two-stage GCPVS with a boost converter functioning as an MPPT Circuit configuration, with a boost converter functioning as an MPPT, of a two-stage GCPVS is shown in Fig 2.3. With the boost converter, the operating voltage v pv of the PV modules can be lower than the dc-link voltage v link. For comparing both single-stage and twostage systems, inverter parameters are kept identical. The expression of the PV current i pv is the same as solar current output, and the variation of the PV voltage v pv is ( ) ( ) ( ) (7) Before the next perturbation of maximum power point tracking, it is necessary to regulate the average value of i Lb equaling the MPP current I mpp. Table 2.1 Specifications of the 220-W Solar Module (Apos Series Ap-220) Parameter Value Peak Power (+/-5%) 225 Rated Voltage Rated Current 7.77 Open Circuit Voltage Short Circuit Current 8.20 Temperature Coefficient of Voltage %/ Temperature Coefficient of Current 0.07 %/ Table 2.2 Operating Conditions of the Two Pv Systems Operating Condition /System Type Single-Stage GCPVS Two-Stage GCPVS Irradiance 1000 W/ 1000 W/ Temperature T PV Capacitor 8*470 µf 8*470 µf DC-Link Capacitor N/A 20 Inverter Switching Freg 20 khz 20 khz Boost Switching Freq N/A 20 khz Inverter Inductor 2.5 mh 2.5 mh Boost Inductor N/A mh editor@iaeme.com

5 Power Loss Comparison of Single and Two Stage Grid Connected Photovoltaic Systems Connected With Microgrid 3. SIMULATION MODEL AND RESULT OF TEST SYSTEM 3.1. DOUBLE LINE FREQUENCY VOLTAGE RIPPLE (DLFVR) Figure 3.1 PV array voltage vpv in a single-stage GCPVS when capacitor Cpv is fixed at 8*470 μf. Figure 3.2 PV array output power p pv in a single-stage GCPVS when capacitor C pv is fixed at 8*470 μf. For the operating conditions shown in Table 2.2, we can obtain the waveforms of PV array voltage v pv and PV array output power p pv with MATLAB. The waveforms of v pv and p pv can be simulated, as shown in Fig. 3.1 & 3.2, in which the system is operated with C pv = 8*470 μf. It can be observed that the magnitude of p pv is not constant, and its swing is much larger. The power loss due to double line-frequency in a single-stage PV system is about 3.5 W or 0.06% under C pv = 8*470 μf Figure 3.3 p pv in a two-stage GCPVS when a PV capacitor C link is fixed at 8*470 μf and C pv is 470 μf. For a two-stage GCPVS, the dc-link capacitor Clink is fixed to 8*470 μf. Fig. 3.3 shows the ripple waveform of dc-link voltage v link, PV array voltage v pv, and its output power p pv editor@iaeme.com

6 Mohammad Kalimullah with C pv = 470 μf. The voltage ripple of v pv and the power ripple are almost zero mainly due to switching-frequency, hence the ripple effect can be ignored. Therefore, we can select PV capacitor C pv =470 μf, which is sufficient enough to filter out the effect of DLFVR FAST IRRADIANCE VARIATION + DLFVR Figure 3.4 V pv in a single-stage GCPVS when fast irradiance variation is 100 W/m 2 /16.6 ms. Figure 3.5 p pv in a single-stage GCPVS when fast irradiance variation is 100 W/m 2 /16.6 ms First, we consider that the speed of cloud is 30 m/s passing over PV arrays, and its corresponding irradiance variation ΔSi /Δt being about 100 W/m 2 /16.6 ms and the PV array temperature being unchanged over one line cycle (1/60 Hz). According to the power loss analysis of fast irradiance variation, the ripple waveforms of PV voltage v pv and PV output power p pv can be simulated as shown in Fig. 3.4 & 3.5. For a large PV capacitor C pv, the change of v pv is only 3.8 V, and the power loss is 3.67 W or 0.07%. Because the change of V mpp during 100 W/m 2 is only 2 V, the operating voltage does not deviate from the MPP significantly. Therefore, the effect of fast irradiance variation on a single-stage GCPVS is not significant FAST DC LOAD VARIATION + DLFVR Figure 3.6 PV array output power under fast dc load variation in a single-stage GCPVS editor@iaeme.com

7 Power Loss Comparison of Single and Two Stage Grid Connected Photovoltaic Systems Connected With Microgrid Figure 3.7 PV array output power under fast dc load variation in a two-stage GCPVS. For common dc home appliances, some like air conditioners consume high power above 500 W per set and others like lamps and computers just consume low power, below 300 W. In the following, we assume that a set of dc load includes two air conditioners (the maximum power is 2000 W), ten lamps (about 400 W), two computers (about 500 W), and the rising times of their power are 3 min, 1 ms, and 0.5 ms, respectively. That is, the fastest power variation is 1 kw/ms. Moreover, the operating conditions, C pv = 8*470 μf for a single-stage GCPVS, and Clink = 8*470 μf and C pv = 470 μf for a two-stage GCPVS, are selected. The simulated results can be obtained with parameters P dc = 1000 W and T rise = 1 ms, as shown in Figs. 3.6 & 3.7. The power loss caused by a deviation from the MPP under fast dc load variation is 7.77 W on average or 0.13% in a single-stage GCPVS and 0.12 W or 0.002% in a two-stage GCPVS as shown in fig 3.6 & OVERALL LOSS FACTOR Figure 3.8 PV array output power under overall loss factor combination in a single-stage GCPVS. Since all of the loss factors are not independent, combing them together to calculate overall power loss is necessary. Moreover, this analysis just focuses on a single-stage PV system, because the effects due to fast irradiance variation + DLFVR and fast\ dc load\ variation + DLFVR are very insignificant in a two-stage PV system and the effect due to limited operating voltage range + DLFVR does not exist in the two-stage case. Fig. 3.8 shows the PV array output power under overall loss factor combination and with the operational parameters of Si = 600 W/m 2, T = 60 C, P mpp = 3028 W, V mpp = 336 V, ΔSi = 100 W/m 2 /16.6 ms, P dc = 1000 W, T rise = 1 ms, and the operating voltage fixed to 360 V for a single-stage GCPVS. The average power loss over one line period is W or 2.34% editor@iaeme.com

8 Mohammad Kalimullah Table 3.1 of power loss in percentage Single stage GCPVS Two Stage GCPVS DLFVR 0.06 % 0 Fast Irradiance Variation + DLFVR.07 % 0 Fast DC Load Variation + DLFVR.13 % 0 Overall Loss Factors Combination 2.34 % 0 Boost Converter Loss % Inverter Loss 2 % 2 Total Loss 4.34 % % 4. CONCLUSION Numerical analysis along with MATLAB simulation has been presented here to simulate power-loss caused due to deviation from the MPPs. Power loss is primarily due to the loss factors such as double line frequency voltage ripple, fast irradiance change + DLFVR, fast dc load change + DLFVR, limited operating voltage limit + DLFVR, and cumulative combination of both on single-stage GCPVS and two-stage GCPVS. Analysis and simulation technique of the power loss has been shown in the dissertation report, which provides engineers of world a direction for making a model of PV arrays and performing the power loss analysis. As per the loss analysis, the total power loss occurred in single-stage GCPVS is almost close to a two-stage GCPVS, while in a single-stage one can eliminate the cost of boost converter. That is, from a point of efficiency, cost, and system configuration and size, a single-stage GCPVS is feasible in dc-distribution system and grid-connected applications if the operating voltage range is properly chosen. It has been also verified with the measured inverter output power from the two systems. With the introduction of battery in single stage and two stage grid connected photovoltaic systems harmonic content is significantly reduced but introduction of battery will increase the cost involved in the whole system. REFERENCES [1] T.-F.Wu, C.-H. Chang, Y.-D. Chang, and K.-Y. Lee, Power loss analysis of gridconnection photovoltaic systems, in Proc. Power Electronics and Drive Systems (PEDS) Conf., pp , [2] T.A.Huld, M. Suri,R. P.Kenny, and E. D. Dunlop, Estimating PV performance over large geographical regions, in Proc. 31st IEEE. Photovoltaic. Spec. Conf., pp , [3] N. Okada, S. Yamanaka, H. Kawamura, and H. Ohno, Diagnostic method of performance of apvmodulewith estimated power output in considering four loss factors, in Proc. 31st IEEE Photovoltaic. Spec. Conf., pp , [4] R. Suzuki, H. Kawamura, S. Yamanaka, H. Ohno, and K. Naito, Loss factors affecting power generation efficiency of a PV module, in Proc. 29th IEEE. Photovoltaic. Spec. Conf., pp , [5] N. Okada, S. Yamanaka, H. Kawamura, and H. Ohno, Energy loss of photovoltaic system caused by irradiance and incident angle, in Proc. 3rd IEEE Photovoltaic Energy Convers. World. Conf., pp , [6] Y. Ueda, K. Kurokawa, T. Itou, K. Kitamura, Y. Miyamoto, M. Yokota, and H. Sugihara, Performance ratio and yield analysis of grid connected clustered PV systems in Japan, in Proc. 4th IEEE Photovoltaic Energy Convers. World. Conf., pp , [7] W.-M. Wu, X.-L. Wang, P. Geng, and T.-H. Tang, Efficiency analysis for three phase grid-tied inverter, in Proc. IEEE Ind. Technol. Int. Conf. (ICIT), pp. 1 5, editor@iaeme.com

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