Massimo Vitelli

Optimization of perturb and observe maximum power point tracking method

Maximum power point tracking (MPPT) techniques are used in photovoltaic (PV) systems to maximize the PV array output power by tracking continuously the maximum power point (MPP) which depends on panels temperature and on irradiance conditions. The issue of MPPT has been addressed in different ways in the literature but, especially for low-cost implementations, the perturb and observe (P&O) maximum power point tracking algorithm is the most commonly used method due to its ease of implementation. A drawback of P&O is that, at steady state, the operating point oscillates around the MPP giving rise to the waste of some amount of available energy; moreover, it is well known that the P&O algorithm can be confused during those time intervals characterized by rapidly changing atmospheric conditions. In this paper it is shown that, in order to limit the negative effects associated to the above drawbacks, the P&O MPPT parameters must be customized to the dynamic behavior of the specific converter adopted. A theoretical analysis allowing the optimal choice of such parameters is also carried out. Results of experimental measurements are in agreement with the predictions of theoretical analysis.

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

Worst-case tolerance design by genetic algorithms

An evolutionary approach to worst-case circuit tolerance design is presented in this paper. Thanks to an appropriate choice of the fitness function and of the reproduction operators, the algorithm is able to explore a wide sub-region of the space of parameters without any prior knowledge about position and size of the region of acceptability. Vertex analysis has been used to check the feasibility of any candidate tolerance region. For this reason, if, as for a large part of cases, the region of acceptability is convex and simply connected, the algorithm ensures an optimal design with 100% yield. The search for a central design in the feasible region,. namely for a set of parameters central values and tolerances that make the circuit the most tolerant to uncertainties, is driven by the optimization of the objective function of interest for the designer as, for example, the per-unit circuit cost. Features and limitations of the approach are discussed by means of two examples.

Design and Optimization of a Maximum Power Point Tracking controller for a PV battery charger

In this paper the design criteria for a Maximun Power Point Tracking (MPPT) controller of a dc-dc converter for photovoltaic (PV) applications are presented. The switching converter matches a single panel with a battery and performs the maximum power point tracking at the batterys terminals instead that at the panels output. Comparisons among analytic results, simulations and experimental measurements on a laboratory prototype are presented and discussed.

Time-domain analysis of switching converters based on a discrete-time transition model of the spectral coefficients of state variables

In this paper, a new method for the large-signal time-domain analysis of switching converters is presented. It is based on a discrete-time transition model for the coefficients of time-domain spectral form of state variables describing the behavior of the converter between each pair of switching instants. The variables controlling the zero-current and zero-voltage switching instants are represented by finite-order approximating polynomials, whose zeros are determined by means of a fastly convergent interval analysis technique; the analysis of synchronous commutations is carried out by means of the compensation theorem. In order to illustrate the effectiveness and accuracy of the proposed method the example of a regulated dc-dc converter is given.

TEODI: PV MPPT based on the Equalization of the Output operating points in correspondence of the forced Displacement of the Input operating points

A new analog Maximum Power Point Tracking (MPPT) technique which is particularly suitable for Distributed Maximum Power Point Tracking Applications (DMPPT) is presented and discussed. Its main advantages are simplicity of implementation, absence of memory and multiplication operations, high MPPT efficiency and the intrinsic capability to attenuate the effect, on the PV voltage, of 100/120 Hz disturbances coming from the grid.

Optimized tolerance design of feedback compensation networks for voltage regulators

A reliable yield evaluation tool, useful for circuit tolerance design, is presented in this paper. It is based on a recursive divide-and-conquer algorithm that verifies the feasibility of each subset of the tolerance region (TR) under test. Such a check is performed by means of interval arithmetic (IA), thus giving a high robustness and reliability to the method and supplying a lower bound and all upper bound for the yield value pertinent to the tolerance region under test. Thanks to the use of IA, the method allows detecting possible unfeasibility pockets included in the designed TR. Such a circumstance occurs if the design problem shows a nonconvex and not simply connected region of acceptability and this fact has not been accounted for during the TR optimization design stage. Any portion of the boundaries of the region of acceptability that is included in the tolerance region is identified and the analysis is refined across it. The technique proposed in the paper has been applied to the tolerance design of two different possible realizations of the feedback control network of a voltage-mode regulated DC-DC converter.

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.

Resistive losses of conductors carrying SMPS current waveforms

Switch-mode power supplies (SMPS) generate distorted nonsinusoidal current waveforms flowing into conductors (wires, striplines, windings), which cause ohmic losses mainly ruled by the skin-effect. Skin effect is traditionally studied in the frequency domain; most studies on the effects of distorted SMPS current waveform are devoted to examine the so-called high-frequency effects, namely the behavior of components and systems at the switching frequency and its harmonics, considering a virtual sinusoidal steady-state operation at each frequency of the range under study. In this paper skin-effect has been studied in the time-domain by means of a formulation based on a magnetic vector potential A and on a scalar potential φ. The obtained results show that the equivalent per-unit length resistance of conductors carrying typical SMPS nonsinusoidal current waveforms depend both on switching frequency and duty-cycle and is rather different from DC and AC sinusoidal equivalent resistances.