المؤلفون / Authors
الملخص / Abstract
الكلمات المفتاحية / Keywords
File partitions
1-Introduction
2-Materials and Methods
3-Results and Discussions
4-CONCLUSION
5-References |
Control And Reliability Assessment of a Double Stage Grid-Connected Pv System: A Case Study of Adrar Region |
| تقييم التحكم والموثوقية لنظام الكهروضوئية المتصل بالشبكة على مرحلتين: دراسة حالة لمنطقة أدرار |
| الناشر : جامعة دمشق |
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ZEMITTE Seddik , HAMOUDA Messaoud, ARAMA Fatima Zohra, LAIDI Abdallah, BELBALI Abdelkarim, MAATALLAH Elabbes |
| الصديق زميط، مسعود حمودة، فاطمة الزهراء عرامة، عبد الله العايدي،عبد الكريم بلبالي،العباس معطالله |
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Abstract
This paper discusses the control and reliability assessment of a double-stage grid-connected PV system: a case study of the Adrar region (Southwest of Algeria), which uses a DC-DC boost converter and the DC/AC inverter (VSC) to generate power for the utility grid. The model represents the main components of the power system in the region of Kaperten (72 km north of Adrar), including integrating the 3 MW photovoltaic power plant and examining the effi-ciency and reliability of the control applied to this system. The paper starts with a description of the system. In this section we have defined and summarized each system component taken separately. The system is then presented in MATLAB/SIMULINK. We presented a maximum power point tracking (PO-MPPT) method included in a DC/DC converter and used to track the PV plant's maximum pow-er. Finally, in order to connect the PV array to the grid and control the output voltage of the DC/DC converter, a three-level DC/AC inverter (VSC) is employed. The simu-lation study demonstrates how changes in solar irradiance can affect a photovoltaic system's output power and the control effectiveness and dynamic behavior of a grid-connected photovoltaic system in different operating conditions
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Keywords: Grid-connected PV system, MPPT, Renewable energy, Adrar power system. |
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الملخص:
تناقش هذه الورقة تقييم التحكم والموثوقية لنظام الكهروضوئية المتصل بالشبكة على مرحلتين: دراسة حالة لمنطقة أدرار (جنوب غرب الجزائر) ، والتي تستخدم محول تعزيز DC-DC وعاكس DC / AC (VSC) لتحويل التيار المستمر لتيار متردد من أجل دمجه في الشبكة. يمثل النموذج المكونات الرئيسية لنظام الطاقة في منطقة كابرتن (72 كم شمال أدرار) ، بما في ذلك دمج محطة الطاقة الكهروضوئية 3 ميجاوات وفحص كفاءة وموثوقية التحكم المطبق على هذا النظام. تبدأ الورقة بوصف النظام. في هذا القسم قمنا بتعريف وتلخيص كل مكون من مكونات النظام بشكل منفصل. ثم يتم تقديم النظام في MATLAB / SIMULINK. قدمنا طريقة تتبع الحد الأقصى لنقطة الطاقة (PO-MPPT) المضمنة في محول DC / DC وتستخدم لتتبع الطاقة القصوى لمحطة الكهروضوئية. أخيرًا، من أجل توصيل مجموعة PV بالشبكة والتحكم في جهد الخرج لمحول DC / DC ، يتم استخدام عاكس DC / AC ثلاثي المستويات (VSC). توضح دراسة المحاكاة كيف يمكن للتغييرات في الإشعاع الشمسي أن تؤثر على طاقة خرج النظام الكهروضوئي وفعالية التحكم والسلوك الديناميكي لنظام كهروضوئي متصل بالشبكة في ظروف تشغيل مختلفة.
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الكلمات المفتاحية: ذمج الطاقة الشمسية، محطة كابرتن الكهروضوئية، ماتلاب، الطاقات المتجددة. |
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1-Introduction |
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Future energy demand is increasing rapidly, whereas conventional energy resources are reducing. Hence, the world searches for other energy sources. There are many sources of renewable energies, such as; Wind energy, Solar PV, Fuel Cell, Hydropower, Biomass, Geothermal, Tidal, and Wave energy. This type of renewable energy aims to address the rising energy demand and mitigate the climate and environmental impacts of fossil fuels[1] . However, this type of energy source is characterized by continuous change and sometimes sudden interruption because it is directly related to the weather, which is characterized by intermittency[2]. Thus, it is vital to investigate and assess the effects of climate change on the energy produced by these alternative energy sources. In this paper, we examine the impact of climatic changes in terms of temperature and irradiance on the output of a 3-megawatt photovoltaic power plant located in the Kaperten region of southwest Algeria in order to provide an overview of the station's contribution to the region's energy supply under various operating conditions.
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Photovoltaic electricity comes from converting solar energy into DC current through a cell based on semiconductor material called the photoelectric effect. Solar energy is not available during the night; it is necessary to supply stand-alone photovoltaic systems with batteries that make it possible to store electricity and recover it in time. However, only between 9 and 17 % of solar energy is effectively converted into electrical energy[3]. Thus, maximum power point tracking (MPPT) is an essential component of a grid-connected solar PV system to ensure that the maximum possible power is always taken from the PV panel and supplied to the AC grid under all circumstances[4]. |
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A photovoltaic generator is the association of photovoltaic cells in series or parallel to obtain the desired electrical characteristics such as power, current and voltage. The operation of the photovoltaic cell depends on the level of solar illumination and the cell's temperature[5]. Many publications in the literature examine the effects of meteorological conditions on the output and effectiveness of solar power plants from various perspectives. |
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the researchers in [6] demonstrates the modeling and simulation of a grid-connected PV system using the Perturb and Observe MPPT Algorithm to inject extracted power into the grid. whereas [7] addresses the Design of a Grid Connected Photovoltaic Power Electronic Converter where the Perturb and Observe MPPT algorithm is used to monitor the maximum power point, allowing the system to operate at its optimum ratings for a given ecological conditions. |
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The primary disadvantage of solar energy-based electrical power generation is that it is not constant throughout the day, as atmospheric conditions are always changing[8]. |
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The MPPT regulator is used to extract the optimum amount of power from the PV cell and transfer it to the load[9]. |
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Approximately 20 MPPT techniques have been developed over the past two decades. Some of these techniques/methods are : Hill climbing, Perturb and observe (P&O) , Incremental conductance (IncCond) , Fractional open circuit voltage (Voc), Fractional short circuit current (Isc) , Ripple correlation control (RCC), Fuzzy logic control (FLC), DC link capacitor droop control etc[10]. |
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The aim of this paper is to ensure the reliability and assessment of the solar power plant in the Kapertan region, southwestern Algeria, under different operating conditions (temperature - irradiation). |
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The rest of the paper is organized into the following sections: Section 2 provides a description of the test system and its compounds. Section 3 presents the results and discussion. Finally, Section 4 concludes this paper.
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2-Materials and Methods |
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2-1 Description of Test System |
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The Kaberten PV plant, connected to the 30 kV distribution network, has a peak power of 3 MW. The plant is comprised of three standard 1 MW fields. Each field is separated into two sub-fields that generate 0.5 MW apiece. Each sub-fields has its own conversion station, a transformer station and a solar module field. Figure 1 shows the location of the station on the map of Algeria. |
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Table (1) : Characteristics of some station components
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Fig 1. Site of the Kaperten photovoltaic power plant |
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Fig 2. Temperature Curve of adrar region |
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Fig 3. Test system in Matlab/simulin.
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2-2 Designing of PV array in Simulink |
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There are many models for representing photovoltaic panels. This study uses the ready-made model from MATLAB/Simulink library. We select the module type to obtain the required power and then determine the number of strings connected in series and parallel. |
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Fig 4. Module interface in Matlab/Simulink |
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The characteristics I(V) and P(V) will show four different curves in response to a change in irradiance. It should be noted that an increase in solar illumination causes a rise in the value of the short-circuit current, while the open-circuit voltage value is slightly affected. |
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Fig5. Influence of irradiation on the current-voltage characteristic at T=25C° |
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Fig6.Influence of irradiation on the power-voltage characteristic at T=25C°
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2-2-1 DC/DC boost converter |
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A Boost converter is used to convert a DC voltage into another DC voltage of higher value it essentially consists of a switch based on semiconductor material placed in parallel with the dc power source. , a diode D, an inductor and a capacitor, figure 7 shows the equivalent diagram of the boost converter. |
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Fig 7. shows the equivalent diagram of the boost converter |
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A capacitor CPV is connected in parallel to the output of the PV array to ensure it appears to operate the boost converter as a voltage source. |
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2-2-2 Calculation of Boost Inductor and DC link Capacitor |
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The system is designed for connection to a 30 KV (line-to-line ) grid. This indicates that the DC link voltage must sufficiently ensure this AC output. The DC link voltage is determined by : |
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2-3 Filter as Grid Interface |
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In this design, an LCL filter is used to connect the inverter to the grid. As an inverter is based on switching devices and gating signals in the form of pulses must be supplied to the switches, the output current may include significant harmonic disturbances that tend to degrade power quality. |
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Using the following equations, we can design L_i, ∁ , L_g values : |
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To determine the grid side inductance, |
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To calculate the value of the capacitor, we use the following equation.:
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Where, |
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P : is the single-phase power |
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ω_grid: is the rotational frequency of grid = 314.2 rad/s,
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According to [11], a damping resistor should be added in series with the LCL filter capacitor to improve the filter's efficacy. It is acquired by, |
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C_(f ): is the filter capacitor, |
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ω_(0 ): represents the resonance frequency of the LCL filter, which can be determined by, |
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2-4 P&O MPPT algorithm |
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The perturb and observe (P&O) algorithm is the most prevalently used control strategy for the MPPT algorithm for the PV generator. It has a basic structure, low cost, is simple to apply, has a reduced number of parameters, allows for the introduction of enhancements, and may result in top-tier effectiveness.[12]This algorithm depends on determining the relationship between the output power of a PV module and its voltage. According to Fig.8, which depicts the behavior of the solar panel indicating MPP and its operating principle, the observed change in PV power is as follows: When the operating point of the PV module is on the left side of the curve (P/V is positive), which indicates that the PV module output power is increasing, the voltage perturbation should be increased[13]. |
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Fig.8: Characteristic power-voltage of the photovoltaic generator |
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Fig.9: Diagrammatic representation of the P&O algorithm
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2-5 VSC Inverter |
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The three-level VSC converter maintains an 840V dc bus voltage with a unity power factor. The control system employs two control loops, one of which regulates the dc link voltage to +/420V. Id and Iq grid currents are governed by an internal control loop (active and reactive current components). Id current reference is the output of the external controller for dc voltage. Iq current reference is set to zero to preserve a power factor of unity. The Vd and Vq voltage outputs of the current controller are transformed into three modulating signals Uref abc that the pulse-width modulation (PWM) three-level pulse generator uses. The sample time for the voltage and current controllers, as well as the PLL synchronization unit, is 100 microseconds in the control system. Pulse generators of dc-dc boost and VSC converters employ a sample time of 1s to generate PWM waveforms with the requisite precision[14]. |
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Fig.10: Simulink model of VSC main controller. |
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2-6 PWM Generation |
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Pulse Width Modulation is now used to send pulses to the six switches in the inverter based on the desired voltage reference signals Vd_des and Vq_des. These signals come from the current controller. the phase angle from the PLL is used to change these wanted voltage references back to their natural frame, which is three-phase quantities. As a carrier wave, a triangular wave is used. The gate pulses for the MOSFET switches of the inverter are made by comparing the desired voltage waves to the carrier wave[15]. |
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3- Results and Discussions |
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In this part, we present the simulation results for only one subfield of the kabertan plant with a capacity of 0.5 MW under different climatic conditions. Simulation of the proposed system is carried out in Matlab/Simulink environment. |
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In the first section, we change the irradiation as follows (1000, 500, 200, 1000) while maintaining the temperature in standard conditions of 25°. In the second part, we change the temperature as follows (50°, 40°, 25°, 10°) while maintaining the irradiance in the standard conditions of 1000 w/m. |
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Case 1 : variation of irradiance |
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Fig.11: Output current of the PV. |
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Fig.12: The voltage generated by the PV arrays. |
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Fig.13: powers generated/injected into the grid. |
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Fig.14: reactive power . |
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Fig.15: DC link voltage Vdc.
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-Figure 11 shows the output current of the PV We observe that as the amount of radiation decreases, so does the amount of current generated by the solar panels. |
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-As for the voltage, it is relatively unaffected in the initial stage (Ir = 1000 W/m2), but some oscillation appears when the irradiation decreases to 200 W/m2.(fig.12). |
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-Figure 13 shows The active powers generated from the PV and injected into the grid. We observe that the decrease in irradiation has a direct effect on the power generated by the station, as the power decreases with the reduction in irradiation and return |
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- from (fg.15) In the case of decreasing irradiance, the dc link voltage fluctuates, which effects the inverter's performance. However, the dc link voltage recovers to its nominal value when the irradiance returns to 1000 W/m2. |
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Case 2 : variation of temperature |
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Fig.16: Output current of the PV. |
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Fig.17: The voltage generated by the PV arrays. |
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Fig.18: The powers generated/injected into the grid. |
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Fig.19: reactive power . |
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Fig.20 : DC link voltage Vdc. |
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- In this case, we keep the irradiation value constant (Ir=1000 w/m2) and we change the temperature . |
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-Figure 16 shows the output current of the pv , We observe that the current generated by the PV panels is not significantly affected by variations in temperature, while the voltage approaches its nominal value when the temperature is close to 25°. |
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- The value of the energy generated by the PV panels is affected by the temperature, it is in the best case at the temperature of 25°(fig.18). |
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4-CONCLUSION |
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This paper discusses the control and reliability assessment of a double-stage grid-connected PV system: a case study of the Adrar region (Southwest of Algeria), we use the Perturb and Observe MPPT Algorithm to inject the power extracted from a photovoltaic array .The inverter's control allows for the unitary power factor, maintaining constant DC bus voltage, and syncing the grid and PV at the same frequency and phase. under various weather circumstances. The obtained results show the effect of different climatic conditions on the energy produced from the station, where the lack of irradiation negatively affects the efficiency of the solar panels. The best performance of the PV panels was in the case of temperatures 25°. |
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In future work, I plan to implement other forms of MPPT controllers or optimize them using metaheuristics, as well as investigate the impact of climate on the stability of the power system. |
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5-References
[1] Y. Himri et al., “Overview of the Role of Energy Resources in Algeria’s Energy Transition,” Energies, vol. 15, no. 13, 2022, doi: 10.3390/en15134731.
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[11] X. Wei, L. Xiao, Z. Yao, and C. Gong, “Design of LCL filter for wind power inverter,” Proc. 2010 World Non-Grid-Connected Wind Power Energy Conf. WNWEC 2010, pp. 106–111, 2010, doi: 10.1109/WNWEC.2010.5673156.
[12] D. P. Mishra, K. K. Rout, S. Mishra, M. Nivas, R. K. P. R. Naidu, and S. R. Salkuti, “Power quality enhancement of grid-connected PV system,” Int. J. Power Electron. Drive Syst., vol. 14, no. 1, pp. 369–377, 2023, doi: 10.11591/ijpeds.v14.i1.pp369-377.
[13] M. A. Salem, Y. A. G. Atia, and O. M. Arafa, “Improved MPPT control for single-phase grid-connected PV system,” Int. J. Power Energy Convers., vol. 12, no. 1, pp. 1–22, 2021, doi: 10.1504/IJPEC.2021.113037.
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