Giovanni Spagnuolo

Power Electronics and Control Techniques for Maximum Energy Harvesting in Photovoltaic Systems

“... very innovative ... [a] rigorous analytical treatment starting from the modeling of the PV field and the power converter stages as well as the dynamics of the overall system, including MPPT control. This in-depth analytical description allows the design of power converters and DMPPT algorithms improving the overall efficiency of the whole PV system operating under mismatching conditions.” —Francesc Guinjoan, Polytechnic University of Catalonia

Perturb and observe MPPT technique robustness improved

In presence of rapidly changing atmospheric conditions, the perturb and observe (P&O) maximum power point tracking (MPPT) algorithm can be confused due to the fact that it is not able to distinguish the variations of the photovoltaic array output power caused by the duty cycle modulation from those ones caused by the irradiance variation. In this paper, it is shown that the negative effects associated to such a drawback can be greatly reduced if the magnitude of the duty-cycle perturbations is customized to the dynamic behavior of the specific dc-dc converter adopted to realize the P&O MPPT. As an example, a boost battery charger has been studied.

A multivariable MPPT algorithm for granular control of photovoltaic systems

In this paper a novel approach to the Maximum Power Point Tracking (MPPT) in distributed PhotoVoltaic (PV) applications is proposed. It is useful when the granular control of the PV field is applied by adopting a dc/dc converter for each PV module. It consists of a single digital controller implementing a multivariable MPPT algorithm based on the Perturb and Observe (P&O) approach, acting on the dc/dc converters dedicated to each PV module and with their output terminals put in series connection. The control strategy only requires a single current sensor on the dc bus, so that classical PV modules current sensing is avoided. PSIM simulations confirm the advantages offered by the proposed approach.

Photovoltaic modules diagnostic: An overview

Diagnostic functions will be making the difference in photovoltaic systems. The need of a daily, monthly and yearly quantification of the energy produced by a plant is a feature required by the customers for comparing the actual performances of their system with the expected values in order to quantify the real return on investment time. In some cases, monitoring facilities are offered by the producers of the power processing system but some companies also offer power production monitoring as a service. The power and energy monitoring is a first step towards a more complete diagnosis of the photovoltaic modules and prognosis about the expected lifetime, which would be welcome by the market. The modules productivity is a too coarse information for understanding the problems affecting the modules and for performing the right repairing. Thus, new and even more advanced diagnostic algorithms must be developed in order to monitor the status of the cells and to predict failures before they lead to a significant reduction on the energy produced by the module. Such failures might be not only due to cells malfunctioning, but also to faults of the bypass diode the module is equipped with. This might happen due to repeated shadowing or to lightning. In this paper the techniques for photovoltaic modules diagnosis proposed in the recent literature are overviewed. The main features of some commercial products are also given. Some elements to be used as a starting point for the development of algorithms for diagnostic and prognostic purposes at module level are proposed.

Photovoltaic Sources Modeling

This comprehensive guide surveys all available models for simulating a photovoltaic (PV) generator at different levels of granularity, from cell to system level, in uniform as well as in mismatched conditions. Providing a thorough comparison among the models, engineers have all the elements needed to choose the right PV array model for specific applications or environmental conditions matched with the model of the electronic circuit used to maximize the PV power production.

A vectorial MPPT algorithm for distributed photovoltaic applications

In this paper a novel multi variable maximum power point tracking algorithm is introduced. The method is suitable for distributed photovoltaic applications and, in contrast with the concept of using a power optimizer for each module working independently from the others, the architecture used in this paper is based on the adoption of a centralized controller for distributed DC/DC converters. The technique uses a vectorial control of the converters that perturbs the operating points of all the DC/DC converters at one time and observes the power transferred to the DC link. Simulation results confirm that the proposed technique performs better than other multi variable controls presented in recent literature.

Load matching of photovoltaic field orientation in stand-alone distributed power systems

The problem of optimizing the photovoltaic field orientation in stand-alone photovoltaic-hydrogen-powered distributed power systems (PHP-DPS) is treated in this paper. The system is supposed to be composed of a photovoltaic field, as energy source, and of a hydrogen energy backup subsystem including a hydrolyser, a hydrogen tank and a PEM fuel cell. Given the characteristics of the solar panels, of the switching converters and of the backup subsystem, three different load profiles have been considered with three typical irradiation diagrams corresponding to as many different typical days in a year. For each case study, the best photovoltaic field orientation, which involve the minimum number of panels to ensure the load power and energy requirements, has been found. Results of simulations allows to single the best configuration out, both whenever the system is supposed to work all the year round and if its operating period does not include winter. The paper puts in evidence that panels orientations chosen according to the load time profile allow to reduce the plant cost, in terms of number of panels and backup size, and to save some amount of energy that is not processed by the backup subsystem. To this regard, the paper also highlights that the best design of a stand-alone PHP-DPS maximizes the flux of energy that goes straight from source to load, as the energy production matches the load needs as much as possible. This objective is particularly important in PHP-DPS that are characterized by a low efficiency back-up path.

Analysis of switching-invariant characteristics of soft-switching cells

In this paper, a model representing the switching invariant properties of soft-switching cells is presented. On the basis of the application of the compensation theorem and of the adoption of the switching cell modeling approach, a cause-effect model of the behavior of six families of switching cells in hard and soft commutations is formulated. Thanks to such model the consequences of the commutation of any switching device (SD) of a cell on the state of all the other SDs is easily allowed in analytical form by exploiting the symbolic toolboxes of the world-wide known software package MATLAB(R).