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An hybrid digital-analog sliding mode controller for photovoltaic applications
No full textSliding mode is a control technique that is widely employed in switching converter applications. Such a non-linear control technique, which is commonly implemented by means of analog circuitry only, forces the switches commutations by comparing a reference signal with a combination of signals acquired on the converter itself. In this way, the control action and the switching modulation are integrated in a single functional block. In this paper the implementation of the sliding mode controller in a low cost digital device is discussed. The proposed approach profits from features offered by some digital devices, e.g. the dsPic33FJ16GS502 family from Microchip Technology Inc., in order to make the implementation simple. In the paper, the aspects related to the accuracy of the comparison between the signals required by the sliding mode controller are discussed. Moreover, the elaboration time needed to calculate the signals that drive the converters switching devices is the subject of an in-depth analysis. The techniques proposed in the paper have been validated by means of simulations and through experimental results performed on a switching dc/dc converter for photovoltaic applications
Perturb and Observe MPPT algorithm with a current controller based on the sliding mode
No full textIn this paper acurrentcontroller is used to reject the 100-Hz oscillation of the voltage of the photovoltaic field taking place in any grid connected system. With respect to the classical linear voltage control the current-basedsliding-mode approach ensures a wider regulation band but, unfortunately, in presence of a fast irradiance variation the sliding conditions might be violated, so that the operating point, which should be the maximum power point, might not be the expected one. In order to prevent such a drawback, an appropriate voltage compensation loop is used to interface the current-basedslidingmode with the Maximum Power Point Tracking algorithm. Simulation and experimental results confirm the goodness of the proposed algorithm
Sliding mode control of DC/DC switching converters for photovoltaic applications
Full text link2011 - 2012The maximum power point tracking (MPPT) is one of the most important features of a system that
process the energy produced by a photovoltaic generator must hold. It is necessary, in fact, to
design a controller that is able to set the value of voltage or current of the generator and always
ensure the working within its maximum power point. This point can considerably change its
position during the day, essentially due to exogenous variations, then sunshine and temperature. The
MPPT techniques presented in literature and adopted in commercially devices operate a voltage
control of the photovoltaic generator and require careful design of the control parameters. It is in
fact complex obtain high performance both in stationary that strongly variable conditions of
sunshine without a careful choice of some parameters that affect in both conditions the performance
of the algorithm for the MPPT. In this thesis has been addressed the analysis of an innovative
current-based MPPT technique: the sensing of the current in the capacitor placed in parallel with the
photovoltaic source is one of the innovative aspects of the proposal. The controller is based on a
nonlinear control technique called ”sliding mode” of which has been developed an innovative
model that allow to obtain a set of conditions and enable the designing of the controller with
extreme simplicity. The model also allow to demonstrate how the performance of this MPPT
control tecnique are independent not only from the characteristics and operating conditions of the
photovoltaic generator, but also by the parameters of the switching converter that implements the
control. This property allows a significantly simplification in the designing of the controller and
improve the performance in presence of rapid changes of the irradiance. An approach to the
dynamic analysis of a class of DC/DC converters controlled by a sliding mode based maximum
power point tracking for photovoltaic applications has been also presented. By referring to the boost
and SEPIC topologies, which are among the most interesting ones in photovoltaic applications, a
simple analytical model is obtained. It accounts for the sliding mode technique that allows to
perform the maximum power point tracking of the photovoltaic generator connected at the
converters input terminals. Referring to the previous approach, a correction term allowing to have
an increased accuracy of the model at high frequencies has been also derived. The control technique
proposed has been implemented by means of low cost digital controller in order to exploit the
potential offered by the hardware device and optimize the performance of the controller. An
extensive experimental analysis has allowed to validate the results of the research. The laboratory
measurements were conducted on prototypes of DC/DC converters, boost and SEPIC, carried out
by Bitron SpA. There are a considerable experimental tests both in the time and in the frequency
domain , both using source generator in laboratory than photovoltaic panels. The results and
theoretical simulations have found a large validation through laboratory measurements. [edited by Author]XI n.s
Reducing the hardware requirements in FPGA based controllers: a photovoltaic application
No full textSistemas fotovoltaicos monofásicos experimentan oscilaciones de voltaje debido a la diferencia entre la potencia promedio generada y la potencia instantánea inyectada a la red. Estas oscilaciones de voltaje degradan la producción de potencia. Este artículo propone una solución para mitigar las oscilaciones propagadas a las terminales del generador, la cual minimiza los recursos de hardware requeridos para implementar la técnica de compensación de un dispositivo FPGA, permitiendo su coexistencia con algoritmos de control adicionales en un solo dispositivo. La efectividad de la solución se valida experimentalmente, y sus requerimientos de hardware se contrastan con soluciones basadas en plataformas comerciales
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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