Abstract

Photovoltaic (PV) energy, which has proven to be environmentally friendly and sustainable compared to traditional energy sources, has gained widespread attention in recent years. The grid-tied PV energy conversion system has become a preferred choice for renewable power generation since it does not need energy storage devices. In this dissertation, an advanced stateof-the-art PV energy system is developed. This includes a high-efficiency zero-voltage zerocurrent switching DC/DC converter with active voltage clamping for power loss minimization, a multiphase interleaved power conversion system with cascade control for power rating expansion, a modified maximum power point tracking (MPPT) scheme with improved accuracy and dynamic response, a novel active frequency drift anti-islanding detection met hod with grid code compliances, and a laboratory prototype PV energy system for performance evaluation and verification. Various soft switched DC/DC converters for PV applications are investigated. A new gating scheme for the converter with active voltage clamping that results in zero-voltage and zerocurrent switching (ZVZCS) is proposed. The operating principles of the proposed converter are presented and its performance is investigated. To increase the power rating of the PV converters, a multi-channel DC/DC converter system, consisting of multiple units of parallel converters and operating in an interleaved mode, is developed. A new cascade control method is proposed, where the PV array voltage is controlled by a master converter and the active current sharing is implemented by the remaining slave converters. The performance of the new control method under varying temperature and irradiance levels are analyzed and verified by simulation in the Matlab/Simulink platform. Various MPPT algorithms are investigated and their performance with rapid changes in irradiance and temperature are compared. A detailed simulation of the algorithms is carried out, and an experimental setup is developed. The islanding phenomenon in renewable energy systems is examined, and an improved active anti-islanding detection method that can detect islanding with less total harmonic distortion compared to the conventional methods is proposed. The rms value and the Fourier series coefficients of the current waveform of the proposed method are obtained and used to derive the operational characteristics of the method.

Highlights

  • 1.1 Introduction TheSun generates 3.8x1020 MW of electromagnetic energy, some of which reaches us as solar energy

  • At the instant of island, if the real power generated by the inverter (Pinv) is not equivalent to the power absorbed by the load (Pload), the amplitude of the voltage at point of common coupling (PCC) will vary

  • Another type of converter is the phase-shifted zero-voltage switching full-bridge converter (ZVSFB), which uses the parasitic components of the circuit to achieve Zero-Voltage Switching (ZVS)

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Summary

Introduction

1.1 Introduction TheSun generates 3.8x1020 MW of electromagnetic energy, some of which reaches us as solar energy. Quasi-resonant or multiresonant converters work in a narrower frequency range, but their high component stress makes them unsuitable for high power and high voltage applications [85]. Another type of converter is the phase-shifted zero-voltage switching full-bridge converter (ZVSFB), which uses the parasitic components of the circuit to achieve ZVS. A parallel DC/DC conversion system is shown, where multiple units of DC/DC converters are connected in parallel to increase the power rating of the PV energy systems and a DC/AC inverter is used to deliver the PV energy to the grid. The frequency drift can be detected with the boundary limits

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