Pitch Control of Wind Turbine through PID, Fuzzy and adaptive Fuzzy-PID controllers

As the penetration of the wind energy into the electrical power grid is extensively increased, the influence of the wind turbine systems on the frequency and voltage stability becomes more and more significant. Wind turbine rotor bears different types of loads; aerodynamic loads, gravitational loads and centrifugal loads. These loads cause fatigue and vibration in blades, which cause degradation to the rotor blades. These loads can be overcome and the amount of collected power can be controlled using a good pitch controller (PC) which will tune the attack angle of a wind turbine rotor blade into or out of the wind. Each blade is exposed to different loads due to the variation of the wind speed across the rotor blades. For this reason, individual electric drives can be used in future to control the pitch of the blades in a process called Individual Pitch Control. In this thesis work, an enhanced pitch angle control strategy based on fuzzy logic control is proposed to cope with the nonlinear characteristics of wind turbine as well as to reduce the loads on the blades. A mathematical model of wind turbine (pitch control system) is developed and is tested with three controllers -PID, Fuzzy, and Adaptive Fuzzy-PID. After comparing all the three proposed strategies, the simulation results show that the Adaptive Fuzzy-PID controller has the best performance as it regulates the pitch system as well as the disturbances and uncertain factors associated with the system

Gendered Spaces in the Arab World

Gender spacing is an important concept in sociology. It refers to the process of segregating individuals and the use of physical spaces based on gender. There are considerable variations in gender roles and the sphere of activities between societies. This research paper describes the gendered spaces in the Arab world. It explores the critical causes of gender-specific use of physical spaces and changing trends in Arab societies. Traditionally, in most societies in the Arab world, women are given only a supportive or submissive role. While men use and control spaces in public spheres, the home is the sphere of activities for women. Social structuring and religious values are important reasons for the spatial segregation of males and females. However, the sphere of activities of women and their roles are getting changed. Several Arab states put considerable efforts to diffuse gendered spaces. Palestinian territory, Egypt, Kuwait, Jordan, Yemen, and the UAE are some of the examples where women are encouraged to occupy spaces in public spheres. Advanced education, changes in attitudes and perceptions, and women empowerment activities are significant reasons for diffusing gendered spaces in the Arab world

An investigation into the influence of land-use, social networks and information and communication technologies on destination choice for social activities

Information and Communication Technologies (ICT) enable individuals to travel more flexibly. The choice of location for social activities has become very flexible. In addition to this, land-use characteristics also play a vital role in the location of social activities. This work aims to analyse the influence of land-use characteristics, ICT use, and social networks in the destination choices for face-to-face social activities of university students during both weekdays and weekends. Students from the two different campuses of the Instituto Superior Técnico were presented with an online questionnaire, which was intended to collect information about their use of ICT and social networks, in addition to their travel characteristics and socio-demographics. Emphasis was made upon capturing the characteristics of social networks and ICT usage. Information on land-use characteristics was obtained from secondary sources. Factor analysis was initially carried out to extract factors related to the use of ICT and social networks; these were later used to model the destination choice for social activities. The alternatives considered for destination choice included: home or the vicinity thereof, university or the vicinity thereof, other locations (further away from home and university), and evenly spread locations – having no specific priority for any of the other three locations considered. The analysis was performed separately for travel during weekdays and weekends so that an understanding of the differences and similarities in behaviour during these different time periods could be garnered. A multinomial logit model was estimated to model this choice. The results point to the relevance of land-use characteristics, the location of close friends, and modes of interaction. Individuals residing in more accessible central, and denser areas, were more likely to have activities distributed evenly across the city. These results stress the relevance of accessibility in allowing larger and more diverse spaces to be used for social activities

Areas of triangles between two parallel lines with same base are equal : proof(?) by paper folding

There are many methods to prove that the areas of triangles between two parallel lines and with the same base length are equal. Here, we are discussing the proof using a paper folding method. We give the geometric reasoning of the proof and follow it up with the implications of this in the paper folding activity. During the paper folding activity, some geometrical properties are used intuitively, and the questions alongside will serve to stimulate both observation as well as reasoning and deductive skills in the students. We hope that this approach illustrates that results which are observed during the paper folding are based on beautiful and rigorous mathematics

DC-Link Current Harmonic Mitigation via Phase-Shifting of Carrier Waves in Paralleled Inverter Systems

DC-connected parallel inverter systems are gaining popularity in industrial applications. However, such parallel systems generate excess current ripple (harmonics) at the DC-link due to harmonic interactions between the inverters in addition to the harmonics from the PWM switching. These DC-link harmonics cause the failure of fragile components such as DC-link capacitors. This paper proposes an interleaving scheme to minimize the current harmonics induced in the DC-link of such a system. First, the optimal phase-shift angle for the carrier signal is investigated using the analytical equations, which provides maximum capacitor current ripple cancellation (i.e., at the main switching frequency harmonic component). These optimally phase-shifted switching cycles lead to variations of the output current ripples, which, when summed together at the DC-link, result in the cancellations of the DC-link current ripples. The results show that when the carrier waves of the two inverters are phase-shifted by a 90° angle, the maximum high-frequency harmonic ripple cancellation occurs, which reduces the overall root-mean-square (RMS) value of the DC-capacitor current by almost 50%. The outcome of this proposed solution is a cost-effective DC-harmonics mitigating strategy for the industrial designers to practically configure multi-inverter systems, even when most of the drives are not operating at rated power levels. The experimental and simulation results presented in this paper verify the effectiveness of the proposed carrier-based phase-shifting scheme for two different configurations of common DC connected multi-converter systems

Effect of Unipolar and Bipolar SPWM on the Lifetime of DC-link Capacitors in Single-Phase Voltage Source Inverters

This paper explores the impact of different modulation techniques on the lifetime of DC-link capacitors for different modulation indices and varying operating power of voltage source inverter system. The conducted analysis show that the capacitor lifetime improves when using unipolar Sinusoidal pulsewidth modulation (SPWM), which introduces the highest lifetime for DC-link capacitors when a single unit voltage source inverter is used. Likewise, for two paralleled voltage source inverter unit' topology, both units using unipolar SPWM, having the same switching frequency produces the least thermal stress on the capacitor and consequently giving the highest lifetime

Outcomes of Middle Turbinate Flap in the Reconstruction of Non-tumorous Ventral Skull Base Defects - an Institutional Review

Objective: Middle turbinate (MT) flap, based on the branches of sphenopalatine artery is one of the commonest mucosal flaps used in endoscopic skull base surgery. The objective of this study is to analyze the outcomes of the MT flap in the reconstruction of non-tumorous ventral skull base defects.Methods: A retrospective review of patients was done from 2010-19. Patients who underwent reconstruction for non-tumorous ventral skull base defects using middle turbinate (MT) flap were included in the study. The parameters assessed include patient demography, primary etiology, site of the defect, size of the defect, graft materials used, outcomes and postoperative complications.Results: A total of 13 patients who met the study criteria were included. Three (23.07%) of the patients had meningo-encephalocele, while the remaining 10 (76.93%) had CSF fistula. Isolated foveal defect (53.8%) was the most common site involved, followed by isolated cribriform, combined cribriform-foveal and combined foveal-planar defects. Graft materials used were fascia lata, fat and septal cartilage. MT flap was successfully harvested in 11 (84.6%) patients, with successful outcome in 10/11 patients. Hypoplastic MT was present in two patients, who subsequently required Hadad flap for defect closure. No major complications were reported in the postoperative period.Conclusion: The MT flap is effective in the reconstruction of selective skull base defects. Appropriate surgical technique and expertise are required for successful harvest. Further studies are required to analyze its outcomes in various skull base defects