Investigation On Grid-Connected Power Converter For Wind Power Generation System

Due to the increasing demand for energy and problems with fossil fuels such as high price and environmental pollutants emission and exploitation of a half of discovered resources, the necessity to find durable and clean energy sources such as wind power forced the researches to focus on more efficient harnessing of energy, or improving the quality and controllability of captured power. In general, most of recent wind power generation systems are connected to the local or global power grid via an electrical power conversion system, which mostly consists of two converters namely Generator-Side and Grid-Side converters. Therefore, the issues related to each of which has its own importance for overall system improvement and optimization.Variable speed wind power DFIG-based generation system is connected to power grid via an electrical conversion system that is basically an AC-DC-AC electrical power converter, which operates at rotor side withfrequency. However, grid-side converter works at c ovnarsitaabnlte -vvoollttaaggee aanndd cvoanrisatbanlet frequency. Although operational conditions of these two converters are different, their topologies and basic functions have some similarities. Thus, some of the techniques and concepts are applicable to both converters with some modifications.In this thesis dissertation, the investigation and research is focused on the grid-connected converter and different issues for this converter as a part of variable speed wind power generation system, especially for DFIG-based system. This converter has to operate with reverse power direction (i.e. DC-to-AC conversion) for super-synchronous speed region, which leads to bi-directional or four-quadrant operation capability of converter. The most effective converter that fits for such kind of application is a well-known full-bridge three-phase VSI (Voltage Source Inverter) converter with IGBT (Insolated Gate Bipolar Transistor) modules, which can be used in wind power generation system or other general purpose utilizations such as ASD (Adjustable Speed Drive), Active Rectifiers, AC power supplies, and so forth. This system consists of a full bridge PWM (Pulse Width Modulation) Regenerative Rectifier or so-called VSC (Voltage Source Converter) that connected to PCC (Point of Common Connection) at the power utility grid through a passive interface circuitry.Thus, objective of this project is to improve the functionality and efficiency, and mitigate the drawbacks of a variable speed generation system or ASG (Adjustable Speed Generator) in conjunction with a DFIG (Double Fed Induction Generator), which is frequently named as Variable-Speed/Constant Frequency (VSCF) generation system. This research is mostly focused on the grid-side AC-to-DC regenerative rectifier that connects the rotor side converter to the power utility grid.The first issue that is discussed in this research for grid-connected converter is the design and analysis of the interface between conversion system and power grid. The LCL filter topology is adopted due to its advantages compared to LC filter such as smaller inductor size, good dynamic response, compactness, cost-effectiveness and...