Solar photovoltaic energy generation and conversion --from devices to grid integration

Abstract

Solar photovoltaic (PV) energy is becoming an increasingly important part of the world's renewable energy. In order for effective energy extraction from a solar PV system, this research investigates solar PV energy generation and conversion from devices to grid integration. First of all, this dissertation focuses on I-V and P-V characteristics of PV modules and arrays, especially under uneven shading conditions, and considers both the physics and electrical characteristics of a solar PV system in the model development. The dissertation examines how different bypass diode arrangements could affect maximum power extraction characteristics of a solar PV module or array. Secondly, in order to develop competent technology for efficient energy extraction from a solar PV system, this research investigates typical maximum power point tracking (MPPT) control strategies used in solar PV industry, and proposes an adaptive and close-loop MPPT strategy for fast and reliable extraction of solar PV power. The research focuses especially on how conventional and proposed MPPT methods behave under highly variable weather conditions in a digital control environment. A computational experiment system is developed by using MatLab SimPowerSystems and Opal-RT (real-time) simulation technology for fast and accurate investigations of the maximum power extraction under high frequency switching conditions of power converters. A hardware experiment system is built to compare and validate the conventional and the proposed MPPT methods in a more practical condition. Advantages, disadvantages and properties of different MPPT techniques are studied,evaluated, and compared. Thirdly, in order to develop efficient and reliable energy conversion technologies, this dissertation compares the energy extraction characteristics of a PV system for different converter configurations. A detailed comparison study is conducted to investigate what enhancements and impacts can be made by using different bypass diode schemes. It is found that compared to micro-converter based PV systems, the central converter scheme with effective bypass diode connections could be a simple and economic solution to significantly enhance PV system efficiency, reliability and performance. Lastly, the development of coordinated control tools for next-generation PV installations, along with energy storage units (ESU), provides flexibility to distribution system operators. The objective of the control of this hybrid PV and energy storage system is to supply the desired active and reactive power to the grid and at the same time to maintain the stability of the dc-link voltage of the PV and energy storage system through coordinated control of power electronic converters. This research investigates three different coordinated control structures and approaches for grid integration of PV array, battery storage, and supercapacitor (SC). In addition, other applications including single-phase Direct- Quadrature (DQ) control and ramp rate limit control are presented in this dissertation. Index Terms - solar photovoltaic, semiconductor physics, I-V characteristics, P-V characteristics, bypassing diodes, uneven shading, power electronic converters, maximum power point tracking, digital control, computational and hardware-based experiments, battery and supercapacitor, control coordination, single-phase DQ control, and ramp rate control.