Fabio Di Napoli

Monitoring and Diagnostics of PV Plants by a Wireless Self-Powered Sensor for Individual Panels

In this paper, an innovative sensor suited to perform real-time measurements of operating voltage and current, open-circuit voltage, and short-circuit current of string-connected photovoltaic (PV) panels is presented. An effective disconnection system ensures that the sensor does not affect the behavior of the string during the measurement phase and offers many benefits like the automatic detection of bypass events; moreover, the sensor does not require additional cables thanks to a wireless communication and a power supply section based on energy harvesting. An extensive experimental campaign is performed to prove the reliability and usefulness of the sensor for continuous monitoring of PV plants. The capability to detect faults and accurately localize malfunctioning panels in a PV string is highlighted.

Accurate Maximum Power Tracking in Photovoltaic Systems Affected by Partial Shading

A maximum power tracking algorithm exploiting operating point information gained on individual solar panels is presented. The proposed algorithm recognizes the presence of multiple local maxima in the power voltage curve of a shaded solar field and evaluates the coordinated of the absolute maximum. The effectiveness of the proposed approach is evidenced by means of circuit level simulation and experimental results. Experiments evidenced that, in comparison with a standard perturb and observe algorithm, we achieve faster convergence in normal operating conditions (when the solar field is uniformly illuminated) and we accurately locate the absolute maximum power point in partial shading conditions, thus avoiding the convergence on local maxima.

Maximum Power Point Tracking Algorithm for Grid­tied Photovoltaic Cascaded H­bridge Inverter

Abstract In this article, a maximum power point tracking algorithm properly adapted for a gridtied photovoltaic multi-level inverter is presented. The inverter structure is based on a singlephase cascaded Hbridge configuration, where each power cell is supplied by an individual photovoltaic panel. The dedicated maximum power point tracking algorithm is based on a suitable hysteresis band, which defines the proper boundaries for maximum power point tracking references to ensure both stable inverter operation and maximum photovoltaic power extraction. The inverter control method is a mixed staircase pulse-width modulation based on a sorting algorithm. Some experimental tests have been performed by using a laboratory prototype of a singlephase fivelevel photovoltaic cascaded Hbridge inverter, which is controlled by means of dSPACE realtime hardware platform (ds1006, dSPACE GmbH, Paderborn, Germany), where the control section is implemented on a field-programmable gate array (Xilinx Virtex5, Xilinx, Inc., San Jose, CA). The experimental results confirm that the proposed control is able to efficiently track the maximum power point while assuring good performance in terms of harmonic distortion and power factor in both standard and mismatch conditions.

FPGA implementation of an adaptive modulation method for a three-phase grid-tied PV CHB inverter

This work deals with an optimal control strategy for a three-phase grid-tied photovoltaic (PV) cascade H-bridge inverter. The main challenge for the control of this system topology derives from the inherent power imbalance among the phases as well as from the different power levels of the H-bridge cells in each phase leg. The power imbalance among the phases is compensated by the injection of a proper zero-sequence voltage. The power distribution among the cells of each phase could be affected by uneven irradiance and temperature conditions of PVGs (PV Generators). This latter issue is addressed by means of an adaptive modulation method especially suited to manage unequal dc sources, while assuring stable circuit operation and maximizing the power extraction through a dedicated MPPT (Maximum Power Point Tracking) algorithm. The digital controller is developed and tested in Matlab/Simulink environment integrated with XSG (Xilinx System Generator), thus allowing an easy transfer on FPGA embedded in dSPACE real-time platform. Simulations and experimental results prove the validity of the proposed design and control approach.

Real time monitoring of solar fields with cost/revenue analysis of fault fixing

This paper proposes a monitoring approach based on single string real-time measurements. An electronic board was developed able to sense string voltage and string current along with open circuit voltage and short circuit current of a selected solar panel belonging to the string. Acquired information allowed real time monitoring of the power actually produced by each string. At the same time, information gained from the monitored solar panel allowed the definition of a production target which is dynamically compared with the actual value. Each string is both compared with stored data regarding the string itself, in order to identify performance degradation during time, and with all the other strings, in order to immediately identify an underperforming string. Experiments performed on a medium size solar field allowed the evaluation of energy losses attributable to underperforming strings. The conversion of energy losses into money losses can be adopted to quantify the revenues of fault fixing.

Experimental comparison between an “information based” MPPT algorithm and standard P&O in both partial shading and uniform illumination

In this paper a maximum power point tracking algorithm able to drive the operating point of a partially shaded photovoltaic system toward the global maximum power point is analyzed. The algorithm exploits detailed information about the electrical parameters of all solar panels forming the solar system gained by means of a distributed sensor network, which monitors the operation of the solar field at a very high granularity level. Data collected by the monitoring system are exploited to reconstruct the power voltage curve of the photovoltaic system, thus recognizing the presence of multiple local maxima and their exact voltage position. Experiments performed on a pilot solar filed equipped with the sensor network evidence the reliability of the analyzed approach. A convergence time of about 2.5 s was achieved independently of illumination conditions and, in case of partial shadowing, an increment of 90 W (50% more) with respect to a standard tracking algorithm.