Grid Connected Doubly Fed Induction Generator Based Wind Turbine under LVRT

This project concentrates on the Low Voltage Ride Through (LVRT) capability of Doubly Fed Induction Generator (DFIG) wind turbine. The main attention in the project is, therefore, drawn to the control of the DFIG wind turbine and of its power converter and to the ability to protect itself without disconnection during grid faults. It provides also an overview on the interaction between variable speed DFIG wind turbines and the power system subjected to disturbances, such as short circuit faults. The dynamic model of DFIG wind turbine includes models for both mechanical components as well as for all electrical components, controllers and for the protection device of DFIG necessary during grid faults. The viewpoint of this project is to carry out different simulations to provide insight and understanding of the grid fault impact on both DFIG wind turbines and on the power system itself. The dynamic behavior of DFIG wind turbines during grid faults is simulated and assessed by using a transmission power system generic model developed and delivered by Transmission System Operator in the power system simulation toolbox Digsilent, Matlab/Simulink and PLECS.

Development of a microgrid with renewable energy sources and electrochemical storage system integration

Beside the traditional paradigm of "centralized" power generation, a new concept of "distributed" generation is emerging, in which the same user becomes pro-sumer. During this transition, the Energy Storage Systems (ESS) can provide multiple services and features, which are necessary for a higher quality of the electrical system and for the optimization of non-programmable Renewable Energy Source (RES) power plants. A ESS prototype was designed, developed and integrated into a renewable energy production system in order to create a smart microgrid and consequently manage in an efficient and intelligent way the energy flow as a function of the power demand. The produced energy can be introduced into the grid, supplied to the load directly or stored in batteries. The microgrid is composed by a 7 kW wind turbine (WT) and a 17 kW photovoltaic (PV) plant are part of. The load is given by electrical utilities of a cheese factory. The ESS is composed by the following two subsystems, a Battery Energy Storage System (BESS) and a Power Control System (PCS). With the aim of sizing the ESS, a Remote Grid Analyzer (RGA) was designed, realized and connected to the wind turbine, photovoltaic plant and the switchboard. Afterwards, different electrochemical storage technologies were studied, and taking into account the load requirements present in the cheese factory, the most suitable solution was identified in the high temperatures salt Na-NiCl2 battery technology. The data acquisition from all electrical utilities provided a detailed load analysis, indicating the optimal storage size equal to a 30 kW battery system. Moreover a container was designed and realized to locate the BESS and PCS, meeting all the requirements and safety conditions. Furthermore, a smart control system was implemented in order to handle the different applications of the ESS, such as peak shaving or load levelling.

Numerical and physical modelling of axially loaded piles for offshore wind turbines

The scope of the thesis is to broaden the knowledge about axially loaded pipe piles, that can play as foundations for offshore wind turbines based on jacket structures. The goal of the work was pursued by interpreting experimental data on large-scale model piles and by developing numerical tools for the prediction of their monotonic response to tensile and compressive loads to failure. The availability of experimental results on large scale model piles produced in two different campaigns at Fraunhofer IWES (Hannover, Germany) represented the reference for the whole work. Data from CPTs, blow counts during installation and load-displacement curves allowed to develop considerations on the experimental results and comparison with empirical methods from literature, such as CPT-based methods and Load Transfer methods. The understanding of soil-structure interaction mechanisms has been involved in the study in order to better assess the mechanical response of the sand with the scope to help in developing predictive tools of the experiments. A lack of information on the response of Rohsand 3152 when in contact with steel was highlighted, so the necessity of better assessing its response was fulfilled with a comprehensive campaign of interface shear test. It was found how the response of the sand to ultimate conditions evolve with the roughness of the steel, which is a precious information to take account of when attempting the prediction of a pile capacity. Parallel to this topic, the work has developed a numerical modelling procedure that was validated on the available large-scale model piles at IWES. The modelling strategy is intended to build a FE model whose mechanical properties of the sand come from an interpretation of commonly available geotechnical tests. The results of the FE model were compared with other predictive tools currently used in the engineering practice.

The Influence of Baseline Metabolic Rate and Exercise Training on Cardio-Respiratory Dynamics

Speeding the VO2 kinetics results in a reduction of the O2 deficit. Two factors might determine VO2 kinetics: oxygen delivery to muscle (Tschakovsky and Hughson 1999) and a muscle 'metabolic inertia' (Grassi et al. 1996). Therefore, in study 1 we investigated VO2 kinetics and cardiovascular system adaptations during step exercise transitions in different regions of the moderate domain. In study 2 we investigated muscle oxygenation and cardio-pulmonary adaptations during step exercise tests before, after and over a period of training. Study 1 methods: Seven subjects (26 ± 8 yr; 176 ± 5 cm; 69 ± 6 kg) performed 4 types of step transition from rest (0-50W; 0-100W) or elevate baseline (25-75W; 25-125W). GET and VO2max were assessed before testing. O2 uptake and were measured during testing. Study 2 methods: 10 subjects (25 ± 4 yr; 175 ± 9 cm; 71 ± 12 kg) performed a step transition test (0 to 100 W) before, after and during 4 weeks of endurance training (ET). VO2max and GET were assessed before and after of ET (40 minutes, 3 times a week, 60% O2max). VO2 uptake, Q and deoxyheamoglobin were measured during testing. Study 1 results: VO2 τ and the functional gain were slower in the upper regions of the moderate domain. Q increased more abruptly during rest to work condition. Q τ was faster than VO2 τ for each exercise step. Study 2 results: VO2 τ became faster after ET (25%) and particularly after 1 training session (4%). Q kinetics changed after 4 training sessions nevertheless it was always faster than VO2 τ. An attenuation in ∆[HHb] /∆VO2 was detectible. Conclusion: these investigations suggest that muscle fibres recruitment exerts a influence on the VO2 response within the moderate domain either during different forms of step transition or following ET.