1,720,983 research outputs found
An efficient MPPT algorithm for partially shaded PV strings
No full textUnder partial shading conditions, several power peaks (maximum power points - MPPs) are presented on the P-V curve of a photovoltaic system, hindering the effectiveness of typical maximum power point tracking (MPPT) algorithms, due to possible convergence to a local suboptimal MPP. In this paper, a global MPPT (GMPPT) method for PV strings is proposed, which exploits the theoretical MPP characterization to detect the shading conditions and estimate all MPPs on the P-V curve. The calculations performed do not involve unnecessary operating point variations and output power fluctuations. The proposed method is designed for PV strings illuminated at two irradiance levels and only needs the standard voltage and current sensors of the DC/DC converter
A MPPT algorithm for partial shading conditions employing curve fitting
No full textStandard maximum power point tracking (MPPT) algorithms often fail to locate the global maximum of a photovoltaic (PV) system under partial shading conditions, while other more sophisticated approaches usually involve extra perturbation of the operating point, which entails undesired output power fluctuation. In this paper, a new MPPT method is introduced, which continuously detects the shading parameters and estimates all power peaks (MPPs) on the P-V curve, guaranteeing continuous operation at the global maximum. The algorithm applies least squares (LSQ) curve fitting (CF) to measurements at the current MPP, utilizing the inherent ripple, without the need for additional perturbation on the operating point. The calculations performed are entirely mathematical and no extra measurement equipment is required, such as irradiance or temperature sensors. The method is designed for PV strings illuminated at two irradiance levels
Enhanced MPPT control of a two-stage grid-connected PV system under fast-changing irradiance conditions
No full textIn this paper, an enhanced Maximum Power Point Tracking (MPPT) strategy for a two-stage gridconnected PV system is proposed, which enables accurate tracking of the maximum power point irrespective of the rate of change in solar irradiance levels. The analysis is performed both in the frequency and time domains, using a suitable linearized model of the system. A comparative assessment of the proposed MPPT strategy versus a conventional Perturbation and Observation (P&O) method is carried out for operation under trapezoidal irradiance profiles.<br/
A method for the analytical extraction of the single-diode PV model parameters
No full textDetermination of PV model parameters usually requires time consuming iterative procedures, prone to initialization and convergence difficulties. In this paper, a set of analytical expressions is introduced to determine the five parameters of the single-diode model for crystalline PV modules at any operating conditions, in a simple and straightforward manner. The derivation of these equations is based on a newly found relation between the diode ideality factor and the open circuit voltage, which is explicitly formulated using the temperature coefficients. The proposed extraction method is robust, cost-efficient, and easy-to-implement, as it relies only on datasheet information, while it is based on a solid theoretical background. Its accuracy and computational efficiency is verified and compared to other methods available in the literature through both simulation and outdoor measurements.</p
Evaluation of PV inverter control schemes under distorted and variable frequency grid conditions
No full textA partial shading detection technique for MPPT algorithms in PV systems
No full textIn this paper, a simple algorithmic enhancement for MPPT methods is introduced, which mathematically determines if the PV system is shaded, thus avoiding unnecessary curve scanning to locate the global maximum if it is unshaded. The proposed technique improves the overall efficiency and applies to any PV system at any irradiance distribution, using only a common temperature sensor
Power balance control for a two-stage solar inverter with Low Voltage Ride Through capability
No full textThe latest grid codes require the renewable energy sources (RES) to provide ancillary services during fault and post fault conditions. More specifically, in case of a short-duration voltage dip, the grid-tied photovoltaic (PV) system should stay connected and support the grid by injecting reactive power. However, meeting these requirements during voltage sags is a challenge for two-stage systems, due to the power imbalance between the dc/dc converter and the inverter, resulting in dc-link voltage excursions and output current overshoots. In this paper, a power balance control scheme is proposed, by which, a successful low voltage ride through (LVRT) and smooth dclink voltage variation are achieved, while the output current is kept within the predefined limits. Two reactive power injection strategies are investigated that exhibit different dynamic response during voltage sags. The effectiveness of the proposed LVRT control is verified though simulations of a 2 kVA solar system
An algorithm to detect partial shading conditions in a PV system
No full textMultiple local maxima (MPPs) are presented on the P-V curve of a PV system under partial shading conditions. In general, standard maximum power point tracking (MPPT) algorithms have trouble locating the global maximum, leading often to suboptimal operation at a local MPP, and thus to decreased efficiency. In commercial inverters, this situation is mitigated by performing periodically scans of the characteristic curve to relocate the global MPP. However, this procedure entails fluctuation of the power output, as well as, short-term power losses. To limit these implications, a simple algorithm is introduced in this paper, which mathematically determines whether a PV system is partially shaded or not, thus avoiding unnecessary curve scans at uniform illumination. The proposed method needs only datasheet information and a temperature sensor, while it is applicable to any PV topology, multiple irradiance levels and is readily implemented as an enhancement to any existing MPPT algorithm.</p
An explicit pv string model based on the lambert w function and simplified mpp expressions for operation under partial shading
No full textIn this paper, a reformulation of the widely used one-diode model of the photovoltaic (PV) cell is introduced, employing the Lambert W function. This leads to an efficient PV string model, where the terminal voltage is expressed as an explicit function of the current, resulting in significantly reduced calculation times and improved robustness of simulation. The model is experimentally validated and then used for studying the operation of PV strings under partial shading conditions. Various shading patterns are investigated to outline the effect on the string I-V and P-V characteristics. Simplified formulae are then derived to calculate the maximum power points of a PV string operating under any number of irradiance levels, without resorting to detailed modeling and simulation. Both the explicit model and the simplified expressions are intended for application in shading loss and energy yield calculations.</p
Partial shading analysis of multistring PV arrays and derivation of simplified MPP expressions
No full textIn this paper, the electrical response of a partially shaded photovoltaic (PV) array, comprising several strings connected in parallel, is investigated. The PV array is simulated by employing an enhanced version of the widely used single-diode model, reformulated in an explicit manner employing the Lambert W function. The multiple maximum power points (MPPs) that appear on the P-V characteristic of the array in partial shading conditions are analyzed, in terms of their number and properties. Simplified empirical expressions are then derived to calculate the voltage, current, and power for each local MPP, at any irradiance level and temperature, using only datasheet information, in a most simple and straightforward manner, without resorting to detailed modeling and simulations. The derived formulae are validated using both simulation and experimental results
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