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Issues in Design of Maximum-Power-Point-Tracking Control – Power Electronics Perspective

Research output: Book/ReportDoctoral thesisMonograph

Details

Original languageEnglish
PublisherTampere University of Technology
Number of pages106
ISBN (Electronic)978-952-15-4213-8
ISBN (Print)978-952-15-4194-0
Publication statusPublished - 5 Oct 2018
Publication typeG4 Doctoral dissertation (monograph)

Publication series

NameTampere University of Technology. Publication
Volume1571
ISSN (Print)1459-2045

Abstract

This thesis provides a comprehensive study of the dynamic characteristics and operation of maximum-power-point-tracking (MPPT) dc-dc converters, especially for those parts that concern the MPPT-control design. The study concentrates on the widely-utilized heuristic perturb-based MPPT algorithms and their design constraints when equipped with photovoltaic-interfacing converter. The main objective is to provide an explicit formulation of the input-power dynamics of the photovoltaic-generator-interfacing dcdc converter for addressing the MPP-tracking control. The dynamics introduce design constraints for the aforementioned MPPT-control algorithms and provide tools for deterministic MPPT design.

A photovoltaic (PV) generator has nonlinear current-voltage characteristics with a particular maximum power point (MPP), which depends on the environmental factors such as temperature and irradiation. Thus, to ensure the maximization of the power extracted from the PV source, the interfacing power converter must be capable of controlling its parameters, i.e., changing its input voltage and current levels based on the MPP of the PV generator. That is done by implementing an MPPT controller, which generates the reference control signal for the interfacing converter. Despite the way of implementation, the fundamental operation is to nd the electrical operating point, i.e., the voltage and the current, at which the PV generator either generates the maximum power or follows a given power reference at every time instant. However, the dynamic characteristics of a photovoltaic generator are determined by the environmental conditions as well as the dynamics of the interfacing converter, which creates limitations for the MPPT-control design. It has been noticed recently that the characteristic curve of a PV generator can be separated into three dierent operation regions each having their distinct characteristics. Thus, to ensure reliability and eciency of a maximum-power tracking, all of these regions should be analyzed separately and choose the condition corresponding to the slowest settling dynamics of the PV system. Up to now, that is not completely recognized, and deterministic analytical models are missing to provide design guidelines for the MPPT-control design.

This thesis presents a detailed dynamic model for PV-generator power dynamics in case of open-loop and closed-loop-operated switched-mode dc-dc converter. Two common design examples of closed-loop-operated converters were provided, where the closed-loop dynamics of the converter was slow and fast by adjusting the control bandwidth and phase margin of the feedback loop. With the developed models, a proper evaluation of the MPPT control imposed by the converter dynamics was presented. Thus, previously developed design guidelines were revised, or new guidelines were established.

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