73 research outputs found
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
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
A 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
Evaluation of PV inverter control schemes under distorted and variable frequency grid conditions
No full textAn 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
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
Power reserves control for PV systems with real-time MPP estimation via curve fitting
No full textIn order for a photovoltaic (PV) system to provide a full range of ancillary services to the gird, including frequency response, it has to maintain active power reserves. In this paper, a new control scheme for the dc/dc converter of a two-stage PV system is introduced, which permits operation at a reduced power level, estimating the available power (maximum power point-MPP) at the same time. This control scheme is capable of regulating the output power to any given reference, from near-zero to 100% of the available power. The proposed MPP estimation algorithm applies curve fitting on voltage and current measurements obtained during operation to determine the MPP in real time. This is the first method in the literature to use the nonsimplified single-diode model for the determination of the MPP and the five model parameters while operating at a curtailed power level. The developed estimation technique exhibits very good accuracy and robustness in the presence of noise and rapidly changing environmental conditions. The effectiveness of the control scheme is validated through simulation and experimental tests using a 2-kW PV array and a dc/dc converter prototype at constant and varying irradiance conditions
Energy models for photovoltaic systems under partial shading conditions: a comprehensive review
No full textThe partial shading phenomenon and its implications on the electrical response and energy yield of photovoltaic (PV) systems have received increased attention in the last years. In order to study, foresee and mitigate such effects, several energy models are proposed in the bibliography, presenting different degrees of complexity, accuracy and applicability. This study presents an overview of the state of the art in the development of models for PV systems under partial shading conditions. Alternative modelling approaches are analysed, highlighting their advantages and shortcomings and models available in the literature are reviewed and classified according to important attributes, related to their accuracy and implementability. Current research trends, as well as topics that warrant further investigation, are identified and discussed
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