الفهرس 
CHAPTER 1: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Renewable energies have great potential and can fulfill the world’s current energy demand. They have the potential to increase market diversity, ensure long-term sustainable energy supply, and reduce regional and global atmospheric emissions. The most important renewable energy resources are wind and solar photovoltaic (PV) energy which can be captured anywhere and can be converted directly into electric power.
PV energy appears to be quite attractive for electricity generation due to its lack of noise, no emissions, scale flexibility, and low maintenance requirements. The most common wind turbine generator is a doubly-fed induction generator (DFIG). It has back-to-back converters that are rated at about 25%–30% of the generator’s rating. It also has four-quadrant active and reactive power capabilities, as well as variable speed operation via the rotor-side converter (RSC) and grid-side converter (GSC). In comparison to a system based on a fully fed synchronous generator with a full-rated converter, this system has lower converter costs and lower power losses.
Although the DFIG-based wind turbine is the most widely used wind generator topology, it is extremely sensitive to grid disturbances. The DC-link voltage may surpass the allowable limits due to over-voltages, causing the wind power plant to get tripped by the protection system. Another issue related to wind power generation is wind uncertainty, which can cause power fluctuation at the generator output.
Thus, this thesis focused on a novel concept of integrating a DFIG wind turbine and a PV / battery energy storage system (BESS). The proposed hybrid DFIG/PV-BESS system evaluates the ability of a PV-BESS to regulate the DFIG output power. The proposed methodology is based on integrating the PV-BESS system into the DC-link of a DFIG back-to-back converter to achieve optimal power management and good behavior, resulting in improved overall system performance under variable solar radiation and wind speed conditions. The proposed new system has several advantages: the overall costs are minimized due to the elimination of the PV Inverter. The circulating power flow in the DFIG system has been reduced. This reduces overall system losses and improves overall system efficiency. The Minimization of the day-to-day variation in grid-injected power. The proposed configuration and control scheme integrates a PV source and a DFIG-based wind energy source elegantly and cost-effectively.
The main objective of the thesis is to present an optimal design, control, and power management of grid-connected DFIG-based WECS using a hybrid PV-BESS system connected to the DFIG through the DC-link of the back-to-back converter.
In the first stage, a new control methodology for a 1.5 MW DFIG-based WECS is carried out using an optimized fuzzy logic controller (OFLC). The proposed strategy is to optimize the FLC scaling factors by applying Particle Swarm Optimization (PSO), Grey Wolf Optimizer (GWO), Moth-Flame Optimization (MFO), and Multi-Verse Optimization (MVO) algorithms. Two FLC units are proposed; the first one is the FLC unit to control the DC-link voltage (Vdc) of the back-to-back converter. This controller has a single-input -single-output (SISO) fuzzy membership function and is applied to adjust the Vdc according to the grid requirements and gives a good behavior under variable wind speed with smooth & stable transition from low to high. The other FLC is a multi-input multi-output (MIMO) controller to control the d-q component of rotor and stator currents.
The second stage is to provide a new strategic optimal design and control for the wind PV-BESS system. PV array with a boost DC-DC converter is used in the proposed system and the MFO-FLC method has been implemented as an MPPT technique under variable solar radiation conditions. In addition, an optimized constant-current constant-voltage (CC-CV) MIMO-FLC controller for BESS charging and discharging control is carried out using the PSO, GWO, MFO, and MVO techniques to obtain an optimal performance, which makes the system more stable and gives the best results. This methodology’s main aim is to maintain a constant DC-link voltage without affecting variation in wind speed, keep the stator and rotor currents stable and smooth under changing conditions, and maintain stabilization of active power with slight fluctuations compared to the overshoot of active power under conventional control. MATLAB/ SIMULINK® platform is used to verify the design and control of the proposed system.
The operation of the proposed controller is tested under variable wind speed to investigate the DFIG behavior in case of transition from low to high gust. The simulation results demonstrated the effectiveness of the optimized control methodology under variable solar radiation and wind speed conditions. The simulation results are clarified, with an explanation for different cases that occur during operation. The active power transferred to the grid through the grid side converter of the DC-link is smoothed and maximized while preserving a constant DC-link voltage during transient and steady-state conditions. It is noticed from the results that the proposed modified hybrid wind/PV-BESS energy conversion system exhibits good behavior under variable solar radiation and wind speed conditions. And also, maintaining active power as stable as possible during disturbances in the system.