1,548 research outputs found
A fractional open circuit voltage based maximum power point tracker for photovoltaic arrays
No full textA Unified Approach to Maximum Power Point Tracking and I-V Curve Determination of Photovoltaic Arrays from Real-time Measurements
No full textIn recent years we have seen a considerable increase in the installed capacity of Photovoltaic (PV) power generating plants worldwide. This increase is primarily attributed to the decrease in the cost of installation and the awareness towards the sustainable power generation. However, the efficiency of the PV modules is still low. The Current vs. Voltage (I-V) characteristics of the PV generators is non-linear and changes with irradiance and temperature. For optimal utilization of PV sources, Maximum Power Point Trackers (MPPTs) are used. When the array is under uniform illumination, there is a single peak on the Power vs. Voltage (P-V) curve of the PV array. This peak is easily tracked by conventional MPPTs. However, under Partial Shading Conditions (PSC), multiple peaks appear on the P-V curve. Out of these, there is one Global Peak (GP) while the others are Local Peaks (LP). When the MPPT algorithm is trapped at LP, considerable power loss occurs. Special MPPTs are designed for finding the GP when the array is under PSC. It is also important to periodically find the I-V curve of the array under the field conditions for monitoring and control of the PV generators. For this purpose, specialized tests are performed. During these tests, the generation of power from the PV arrays is halted. Similarly, the speed of performance of these tests is also important as the environmental conditions may change quickly during finding of the curve. Any change in the surroundings during the performance of finding the characteristic curve may affect the results. In this thesis, two algorithms are proposed that perform the MPP tracking and measurement of the I-V curve under any kind of irradiance. The first algorithm performs these tasks by using the module voltages as the parameter. In the second method, the input filter capacitor of buck or buck-boost converter is used. Simulation and experimental results confirm the performance of the proposed methods
A maximum power point tracker for module integrated PV systems under rapidly changing irradiance conditions
No full textPerturb and Observe (P&O) method is a commonly employed technique in module integrated maximum power point tracking (MPPT) system. But the method suffers from the problems of oscillations around the maximum power point (MPP) during the steady state. Various methods have been reported in the literature to overcome the problem of oscillations around the MPP in the steady state. These methods perform well in the regions with uniform irradiance from the sun throughout the day. However, in the regions with highly variable irradiance due to stochastic cloud cover and cyclonic activity, the P&O based MPPTs with no steady state oscillations do not operate properly due to their slow response to the changing irradiance. This paper proposes a P&O based MPPT which tracks the MPP of a PV module in the face of varying irradiance. Simulation results show that the proposed algorithm quickly tracks the MPP. The results also show that the proposed method has 99.92% efficiency in the steady state operation. The proposed algorithm is simple to implement as no additional hardware is required for its implementation
How much is the advisable self-sufficiency of aggregated prosumers with photovoltaic-wind power and storage to avoid grid upgrades?
No full textThis paper defines, with respect to the consumption, the maximum value of self-sufficiency that can be reached by users, who decide to install photovoltaic (PV) modules, wind turbines and electrochemical storage. The primary goal of the aggregated users, who become prosumers, is assumed the achievement of the best match between power profiles of loads and power profiles of generators. Such best match is obtained thanks to an appropriate procedure to design the sizes of generators and storages. In this procedure, power ratings of PV and wind generators and energy capacities of batteries are chosen to attain the highest levels of self-consumption and the lowest power exchange with the grid according to the load profile. Thus, the upgrade of transformers and lines is avoided and there are benefits for both prosumers and grid operators. The simulation results are very realistic, because the inputs, in terms of irradiances for PV modules, wind speeds for turbines and powers for loads, are accurate measurements. The return on investments is estimated according to current costs and market rules. The results can be useful to plan the future electricity mix in the Mediterranean areas
A module voltage based maximum power point tracking algorithm for photovoltaic arrays under partial shading conditions
No full textMultiple peaks in the Power vs. Voltage (P-V) characteristics of Photovoltaic (PV) arrays appear due to partial shading. Conventional Maximum Power Point Tracking (MPPT) algorithms fail to track the Global Peak (GP) among the Local Peaks (LP). Special MPPT techniques are applied for tracking the GP under partial shading conditions. Various schemes reported in the literature perform blind scanning of the P-V curve in order to find the GP. This type of scanning takes a long time during which the array is not operated at the MPP. This causes a considerable amount of power loss. In this paper an MPPT algorithm is proposed which quickly tracks the GP of a partially shaded PV array. The algorithm avoids blind and unnecessary scanning of the P-V curve by finding the total number of peaks after tracking the peak nearest to the open circuit voltage (Voc). The tracking process is accelerated through the use of modified versions of the Perturb and Observe (P&O) algorithm
An efficient maximum power point tracking algorithm for photovoltaic arrays under partial shading conditions
No full textVarious peaks in the Power vs. Voltage (P-V) characteristic curve of Photovoltaic (PV) arrays appear due to the effects of partial shading. Conventional Maximum Power Point Trackers (MPPTs) may be unable to track the Global Peak (GP) among the Local Peaks (LP). For tracking the GP under partial shading conditions it is important to develop special MPPTs. In commercially available MPPTs, blind scanning of the P-V curve is performed in order to find the GP. This type of scanning takes various seconds during which the array is not operated at the MPP. In this paper an MPPT algorithm is proposed which quickly takes the operating point of a PV to the GP under uniform and partial shading conditions. The presence of partial shading and the number of peaks is determined from the operating voltage of the modules. The voltage at which the peaks in the P-V curve are located is also determined from the module voltages
A variable step size perturb and observe based MPPT for partially shaded photovoltaic arrays
No full textSocial media use for public health campaigning in a low resource setting: the case of waterpipe tobacco smoking
No full textProbability bounds on the peak intensity of optical ultrashort light pulse CDMA
No full textIncludes bibliographical references (p. 14).Caption title.Research supported by the NSF. NSF-ECS-8519058 Research supported by the ARO. DAAL03-86-K-0171 Research supported by Bellcore.by Emmanouel A. Varvarigos and Jawad A. Salehi
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