Research on a grid-connected power inversion technique for photovoltaic systems with maximum power point tracking

Abstract

This thesis presents research results on a grid-connected power inversion technique for photovoltaic (PV) systems with maximum power point (MPP) tracking. The proposed MPP methods not only are simple and elegant, but also can globally locate the MPP under wide insolation conditions. They do not approximate the panel characteristics but have the ability to track the NIPP under a large insolation change. Furthermore, an integrated inverter with MPP tracking for grid-connected PV systems is presented. It inverts a shaped output current from the PV panel to the grid that complies with the IEEE standard on Recommended Practice for Utility Interface of Photovoltaic (PV) Systems (IEEE Std 929-2000), and provides a unity power factor. The contents of this thesis are as follows. In Chapter I, the impact of PV technologies will be discussed. Then, the need of MPP tracking and the existing MPP tracking methodologies, such as the power matching scheme, curve-fitting techniques, etc., will be reviewed. Moreover, the need of an inverter to convert the energy from the PV panels to the electricity fed to the grid will be discussed, followed by some comparisons of existing inverter topologies. In Chapter 2, the operating principles of the proposed MPP tracking method using the Switching Frequency Modulation Scheme (SFMS), .will be described. Different operating topologies will be discussed. Its tracking capability will be verified experimentally with a 10W PV panel under a controlled experimental setup. Also, performances under the steady state and in a large-signal insolation change will be evaluated. Moreover, a comparative study of different operating topologies using SFMS will be given. The feasibility of using other types of dc/dc converters, such as buck, boost converters, and so on, will be investigated. Their respective experimental performances will also be studied. In Chapter 3, a self-oscillatory MPP tracker will be proposed. Its underlying operating principles - duty perturbation - will first be reviewed. Then, the small-signal modeling of the SEPIC dc/dc converter and different parts of the tracker will be studied. Based on the derived models, the tracker controller will be designed to make the overall system self-oscillate. Also the technique of duty perturbation will be applied to achieve MPP tracking. Detailed design procedures will be given. The theoretical predictions will be verified with experimental results using a l00W PV Panel. In Chapter 4, an integrated inverter with MPP tracking for grid-connected PV systems will be proposed. This inverter is perturbation-based using the SFMS. Theoretical predictions and experimental performances will be studied. In Chapter 5, a detailed examination of the integrated inverter mentioned in Chapter 4 will be investigated. This includes modeling, analysis and discussion of some design-related issues. In Chapter 6, conclusions of the research and some suggestions for further studies will be given.

Date of Award	15 Feb 2005
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Shu Hung Henry CHUNG (Supervisor)