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The nine papers in this special section focus on photovoltaic module and sub-module level power electronics. Grid connected photovoltaic energy systems have experienced an explosive growth over the last decade, with a cumulative installed capacity surpassing the 400 GW milestone as of 2017. Among PV system configurations, distributed module-level converter architectures can lead to a higher energy yield by mitigating partial shading, persistent shading (soiling, snow, bird droppings, and fallen leaves), mismatch, and aging, through a higher maximum power point tracking (MPPT) efficiency. Also, distributed electronics might be the key for implementing diagnostic and prognostic actions at a module level. Among these configurations, microinverters (also known as ac-module inverter), which connect a single PV module to the grid, and PV power optimizers, which are dc–dc converters performing the MPPT function at a module level, have attracted the academic and industrial interest in the last decade. So much so, that both microinverters and dc–dc power optimizers are commercialized by tens of companies around the world, with a great variety of circuit topologies, which comprise combinations of one or more power stages, interleaved converters, resonant converters, topologies with and without isolation, etc. [ABSTRACT FROM AUTHOR]

In the last five years, the desire to improve the control of photovoltaic (PV) arrays working in mismatched conditions has stimulated substantial research and development. Recent research has revived the previously discounted idea of changing the electrical connection between the PV modules according to their operating conditions and load requests. The switching matrix is reliable and allows the additional cost of module-level switching converters to be avoided and also maintains high efficiency under infrequent mismatched conditions. The PV array electrical reconfiguration also enables the best load matching between the PV source and its varying load. Such issues are discussed in this article with an overview of the main aspects introduced in the technical literature. [ABSTRACT FROM PUBLISHER]

Photovoltaic (PV) systems are one of the main actors in distributed power generation. In particular, in urban contexts, the PV generators can be subjected to mismatching phenomena due to the different orientation of the modules with respect to the sun rays or due to shadowing. In these cases, the maximum power point tracking (MPPT) function must be designed carefully. In this paper, architecture, including one dc/dc converter for each PV generator, is considered. The converters' output terminals are series connected to a high-voltage dc bus, where also a bidirectional dc/dc converter managing the power from/to a storage device is plugged. The functional constraints deriving from the dc/dc converters' connection, the mismatching phenomena, the MPPT capabilities of the inverter, connected with its input terminals at the dc bus, are taken into account in order to determine the best operating point of the system as a whole. The real-time constrained optimization problem is solved by using the particle swarm optimization method, which needs the knowledge of the actual current versus voltage curve of each PV generator. The practical impact of this need is also discussed in the paper. The feasibility and the performances of the proposed approach are experimentally validated by using a laboratory prototype. [ABSTRACT FROM PUBLISHER]

In this paper, the procedure for designing a sliding-mode controller for maximum power point tracking photovoltaic (PV) applications is proposed. It is applied to a single-ended primary inductor converter, thus to a fourth-order topology, but it can be extended to a wide class of converters suitable for PV applications. The reachability and existence conditions give rise to a number of design inequalities that add to the classical steady-state conditions in order to have the desired closed-loop converter's performances. The superiority of the control technique over the classical tracking methods is analytically demonstrated through the procedure proposed in this paper. The analytical results have been validated by means of both simulations and experiments. [ABSTRACT FROM PUBLISHER]

Sliding mode is a control technique that is widely employed in switching converter applications. Such a nonlinear 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 converter's 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. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel maximum power point tracking (MPPT) technique aimed at maximizing the power produced by photovoltaic (PV) systems. The largest part of the MPPT approaches presented in the literature are based on the sensing of the PV generator voltage. On the contrary, in this paper, a current-based technique is proposed: the sensing of the current in the capacitor placed in parallel with the PV source is one of the innovative aspects of the proposal. A dual control technique based on an inner current loop plus an outer voltage loop allows to take profit of the fast current tracking capability of the inner current loop while the voltage loop benefits from the logarithmic dependency of the PV voltage on the irradiation level. The features of the proposed algorithm, particularly in terms of tracking of irradiation variations and disturbance rejection, are supported by theoretical analysis, simulations, and experimental results. The technique described in this paper is patent pending. [ABSTRACT FROM PUBLISHER]

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In this paper, a novel maximum power point tracking algorithm based on the perturb-and-observe (P&O) technique is introduced. The novelty of the approach is represented by the perturbation of more control variables, rather than just one. This allows the increase of the power extracted from the photovoltaic (PV) field as compared to the case of perturbation of a single control variable. The proposed technique overcomes the limitations of any existing tracking technique dedicated to PV arrays exhibiting a unique maximum power point, thus not only of the P&O approach, whenever dynamic constraints ensuring the correct system behavior must be fulfilled too. The proposed multivariable approach is described by means of its application to a single-stage one-cycle controlled PV inverter. [ABSTRACT FROM AUTHOR]

The articles in this special section focus on photovoltaic power systems (PVS). The market for photovoltaic power systems has increased exponentially, but the government subsidies have been reduced dramatically in recent years. The return of the investment mainly relies on selling the energy produced during the PV plant lifetime. Thus, the PV system must be designed and controlled properly in order to ensure its lifetime and reliability but also new features are required: 1) real-time monitoring of the energy production; 2) on-site diagnostic functions; and 3) estimation of the residual life. The degradation of electronic components and PV cells can be accelerated by various unpredictable and unavoidable phenomena. [ABSTRACT FROM PUBLISHER]