Giovanni Petrone

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.

Distributed Maximum Power Point Tracking of Photovoltaic Arrays: Novel Approach and System Analysis

One of the major drawbacks of photovoltaic (PV) systems is represented by the effect of module mismatching and of partial shading of the PV field. Distributed maximum power point tracking (DMPPT) is a very promising technique that allows the increase of efficiency and reliability of such systems. Modeling and designing a PV system with DMPPT is remarkably more complex than implementing a standard MPPT technique. In this paper, a DMPPT system for PV arrays is proposed and analyzed. A dc and small-signal ac model is derived to analyze steady-state behavior, as well as dynamics and stability, of the whole system. Finally, simulation results are reported and discussed.

Reliability Issues in Photovoltaic Power Processing Systems

Power processing systems will be a key factor of future photovoltaic (PV) applications. They will play a central role in transferring, to the load and/or to the grid, the electric power produced by the high-efficiency PV cells of the next generation. In order to come up the expectations related to the use of solar energy for producing electrical energy, such systems must ensure high efficiency, modularity, and, particularly, high reliability. The goal of this paper is to provide an overview of the open problems related to PV power processing systems and to focus the attention of researchers and industries on present and future challenges in this field.

Predictive & Adaptive MPPT Perturb and Observe Method

The perturb and observe (P&O) best operation conditions are investigated in order to identify the edge efficiency performances of this most popular maximum power point tracking (MPPT) technique for photovoltaic (PV) applications. It is shown that P&O may guarantee top-level efficiency, provided that a proper predictive (by means of a parabolic interpolation of the last three operating points) and adaptive (based on the measure of the actual power) hill climbing strategy is adopted. The approach proposed is aimed at realizing, in addition to absolute best tracking performances, high robustness and promptness both in sunny and cloudy weather conditions. The power gain with respect to standard P&O technique is proved by means of simulation results and experimental measurements performed on a low power system. Besides the performance improvements, it is shown that the proposed approach allows possible reduction of hardware costs of analog-to-digital (A/D) converters used in the MPPT control circuitry.

A Technique for Improving P&O MPPT Performances of Double-Stage Grid-Connected Photovoltaic Systems

In double-stage grid-connected photovoltaic (PV) inverters, the dynamic interactions among the DC/DC and DC/AC stages and the maximum power point tracking (MPPT) controller may reduce the system performances. In this paper, the detrimental effects, particularly in terms of system efficiency and MPPT performances, of the oscillations of the PV array voltage, taking place at the second harmonic of the grid frequency are evidenced. The use of a proper compensation network acting on the error signal between a reference signal provided by the MPPT controller and a signal that is proportional to the PV array voltage is proposed. The guidelines for the proper joint design of the compensation network (which is able to cancel out the PV voltage oscillations) and of the main MPPT parameters are provided in this paper. Simulation results and experimental measurements confirm the effectiveness of the proposed approach.

A Fast Current-Based MPPT Technique Employing Sliding Mode Control

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.

Optimized one-cycle control in photovoltaic grid connected applications

The use of one-cycle control (OCC) for maximum power point tracking (MPPT) and power factor correction (PFC) in grid connected photovoltaic (PV) applications is discussed. Circuit and operating parameters of the one cycle-based controller of a cost-effective single-stage inverter are optimized in order to obtain the best performances of the system under different irradiance levels. Firstly, design constraints are formulated which allow to get a very efficient OCC operation in terms of power extracted from the PV array, stability, and PFC. Afterwards, such constraints are used to perform the parametric optimization of the one cycle controller by means of suitable heuristic approaches. Various selection criteria of the best parameters set under different conditions are discussed and applied. Finally, a customized perturb and observe (P&O) control is applied to the optimized one cycle controlled single-stage inverter in order to perform a real MPPT in presence of varying irradiance conditions. Subjects described here are covered by the Italian Patent Application SA2005A000014-13.07.2005 and PCT Application PCT/IT2005/000747-20.12.2005

Maximum Power Point Tracking in a One-Cycle-Controlled Single-Stage Photovoltaic Inverter

In this paper, the design of the one-cycle controller of a single-stage inverter for photovoltaic applications is carried out by means of a multiobjective strategy to optimize inverter performance at both high and low insolation levels. Design constraints that account for different weather conditions are adopted. The optimization algorithm also provides useful information concerning the system sensitivity with respect to each of the controller parameters. This allows the design of a maximum power point tracking perturb and observe controller that significantly improves inverter performance. Experimental measurements confirm the predictions of theoretical and simulation results.

A Multivariable Perturb-and-Observe Maximum Power Point Tracking Technique Applied to a Single-Stage Photovoltaic Inverter

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.

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