Photovoltaic panels have nonlinear characteristics. Therefore, there is only one point where the output power from photovoltaic panel at its maximum. This point is called the maximum power point (MPP). There are many of the maximum power point search algorithms in literature. The simplest methods are the open circuit voltage (OCV), the short circuit current (SCC), the perturb and observe method or the incremental conductance method. The most complicated methods use neutral networks or genetic algorithms. The maximum power point current depends on the short circuit current. However, to measure the short circuit current, the photovoltaic panel must be disconnected from the load. Some of methods use an additional module that represents the whole solar panel. The short circuit current depends on the solar irradiation mainly. Therefore, by the measurement of the irradiation the maximum power point current can be estimated. In this work the hybrid method that uses the solar irradiation measurement to determine the initial operating point and then the perturb and observe algorithm for the final seeking is used. The smaller initial seeking error, the smaller perturbation step of the perturb and observe method can be used and the seeking time is shorter. Therefore, in the testing algorithm the solar sensor is the critical element. In this article the linear and nonlinear light sensors in the short circuit current are tested. The integrated sensors like linear BH1603FVC, OPT3001IDNPRQ1, VEML6030 or nonlinear ISL29009 through phototransisors like TEPT4400, photodiode like BPW21 or photoresistor like GL5516 are compared.
Solar panels are devices that convert solar irradiation directly into the electrical power without any mechanical parts. The efficiency of solar cells is between 8-20% depending of manufacturer technology so it is important to use all available energy. On the voltage-current characteristics of the photovoltaic panel is a special point called the maximum power point. To find this special point special devices called the maximum power point trackers are used. If we connect each series of solar cells with bypass diodes to avoid the negative effect of the partial shading or the differences in the photovoltaic panel parameters, local maximum power points can appear. Therefore, the special algorithm that can track the real maximum power point must be used in the maximum power point tracker. In this work, the three-channel step down converter with the algorithm that uses the temperature and light measurement is designed and tested.
Proc. SPIE. 9898, Photonics for Solar Energy Systems VI
KEYWORDS: Optical sensors, Detection and tracking algorithms, Sensors, Solar cells, Manufacturing, Temperature sensors, Light sources and illumination, Diodes, Solar system, Solar radiation, Temperature metrology, Correlation function
Solar cells have low efficiency and non-linear characteristics. To increase the output power solar cells are connected in more complex structures. Solar panels consist of series of connected solar cells with a few bypass diodes, to avoid negative effects of partial shading conditions. Solar panels are connected to special device named the maximum power point tracker. This device adapt output power from solar panels to load requirements and have also build in a special algorithm to track the maximum power point of solar panels. Bypass diodes may cause appearance of local maxima on power-voltage curve when the panel surface is illuminated irregularly. In this case traditional maximum power point tracking algorithms can find only a local maximum power point. In this article the hybrid maximum power point search algorithm is presented. The main goal of the proposed method is a combination of two algorithms: a method that use temperature sensors to track maximum power point in partial shading conditions and a method that use illumination sensor to track maximum power point in equal illumination conditions. In comparison to another methods, the proposed algorithm uses correlation functions to determinate the relationship between values of illumination and temperature sensors and the corresponding values of current and voltage in maximum power point. In partial shading condition the algorithm calculates local maximum power points bases on the value of temperature and the correlation function and after that measures the value of power on each of calculated point choose those with have biggest value, and on its base run the perturb and observe search algorithm. In case of equal illumination algorithm calculate the maximum power point bases on the illumination value and the correlation function and on its base run the perturb and observe algorithm. In addition, the proposed method uses a special coefficient modification of correlation functions algorithm. This sub-algorithm uses the error value between calculated and real maximum power point and on its base modifies correlation function coefficients.
Proc. SPIE. 9526, Modeling Aspects in Optical Metrology V
KEYWORDS: Optical sensors, Detection and tracking algorithms, Sensors, Solar cells, Computer simulations, Temperature sensors, Light sources and illumination, Temperature metrology, Correlation function, Optical power tracking algorithms
Disadvantages of photovoltaic panels are their low efficiency and non-linear current-voltage characteristic. Therefore it is necessary to apply the maximum power tracking systems which are dependent on the sun exposure and temperature. Trackers, that are used in photovoltaic systems, differ from each other in the speed and accuracy of tracking. Typically, in order to determine the maximum power point, trackers use measure of current and voltage. The perturb and observe algorithm or the incremental conductance method are frequent in the literature. The drawback of these solutions is the need to search the entire current-voltage curve, resulting in a significant loss of power in the fast-changing lighting conditions. Modern solutions use an additional measurement of temperature, short-circuit current or open circuit voltage in order to determine the starting point of one of the above methods, what decreases the tracking time. For this paper, a sequence of simulations and tests in real shading and temperature conditions for the investigated method, which uses additional light sensor to increase the speed of the perturb and observe algorithm in fast-changing illumination conditions was performed. Due to the non-linearity of the light sensor and the photovoltaic panel and the influence of temperature on the used sensor and panel characteristics, we cannot directly determine the relationship between them. For this reason, the tested method is divided into two steps. In the first step algorithm uses the correlation curve of the light sensor and current at the maximum power point and determines the current starting point with respect of which the perturb and observe algorithm is run. When the maximum power point is reached, in a second step, the difference between the starting point and the actual maximum power point is calculated and on this basis the coefficients of correlation curve are modified.
Proc. SPIE. 9516, Integrated Optics: Physics and Simulations II
KEYWORDS: Photovoltaics, Optical sensors, Detection and tracking algorithms, Sensors, Solar cells, Temperature sensors, Light sources and illumination, Evolutionary algorithms, Temperature metrology, Correlation function
The main disadvantage of PV panels is their low efficiency and non-linear current-voltage characteristic. Both of the above depend on the insolation and the temperature. That is why, it is necessary to use the maximum power point search systems. Commonly used solutions vary not only in complexity and accuracy but also in the speed of searching the maximum power point. Usually, the measurement of current and voltage is used to determine the maximum power point. The most common in literature are the perturb and observe and incremental conductance methods. The disadvantage of these solutions is the need to search across the whole current-voltage curve, which results in a significant power loss. In order to prevent it, the techniques mentioned above are combined with other methods. This procedure determines the starting point of one of the above methods and results in shortening the search time. Modern solutions use the temperature measurement to determine the open circuit voltage. The simulations show that the voltage in the maximum power point depends mainly on the temperature of the photovoltaic panel, and the current depends mainly on the lighting conditions. The proposed method uses the measurement of illuminance and calculates the current at the maximum power point, which is used as a reference signal in power conversion system. Due to the non-linearity of the light sensor and of the photovoltaic panel, the relation between them cannot be determined directly. Therefore, the proposed method use the modified correlation function to calculate current corresponding to the light.