Amélioration de la productivité et de la fiabilité d’un système photovoltaïque sous ombrage partiel

Abstract

Researchers agree that a partially shaded photovoltaic module still presents significant challenges, particularly with respect to reliability and power output. Indeed, several technical issues having a direct impact on the performance of the photovoltaic system must be deepened and rethought. The aim of this research is, therefore, to re-examine the operation of a photovoltaic module in the context of total or partial shading. This reflection will focus in particular on the following four main themes: a better understanding of cell behavior in the second quadrant of IV characteristic, detection of shading by measuring the dynamic parameters of cells, protection against hot spots and the tracking of the global power point under different shading scenarios. We will address, in a first step, the classification of solar cells as well as the study of constraints on shaded cells. Constraints appear mainly during operation in the second quadrant Reversepolarized, these cells consume part of the energy produced by the lighted cells. We will also demonstrate the limitations of bypass diodes in preventing hot spots. For the second step, measurement of the dynamic parameters of the cells, in order to identify those that are shaded, is detailed. A complete procedure has been developed and tested in the laboratory. The obtained results are very promising. However, this method will not be retained for the detection of shading due to the difficulty of real-time implementation. The next step focuses on protection against hot spots. To this end, we have chosen a strategy that provides the best possible protection by isolating shaded subgroups. However, disconnection poses significant challenges, such as detecting the start and end of shading and the maximum power point tracking.While being built using simple and standard components, the electronic circuit we introduce can meet these challenges. Another element was considered in our study. It is related to the analysis of heat stress in shaded cells when applying global power search rules. The algorithms found in the literature are complex. They involve, in many cases, heuristic methods that are not only demanding in terms of computing power but also subject to the risks of divergence. What is proposed in this fourth step is a new approach called "Voltage Clamping Method". This procedure is original and is a complement to the widely used techniques of fractional short-circuit current (FSCC) and fractional open-circuit voltage (FOCV). It is easy to implement and gives results that are sufficiently precise and very fast. Indeed, in a reduced number of steps, it is possible to achieve an accurate characterization of the shading situation, which makes it possible to locate all the locals and global maximum power points. It can work in conjunction with active hot spots protection techniques without causing thermal stress to the shaded cells, which is a great advantage.

Date	7 Aug 2020
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Ambrish Chandra (Supervisor) & Ahmed Cheriti (Co-supervisor)