Improved power quality operation of symmetrical and asymmetrical multilevel inverter using invasive weed optimization technique

Low switching frequency pulse width modulation (PWM) technique for modulation and control of multilevel inverter in medium voltage high power applications is preferred in order to reduce the switching losses. In this context, a multilevel inverter operated with Selective harmonics minimization PWM technique offers better quality waveform at reduced switching losses. After the Fourier series analysis, the system of non-linear simultaneous transcendental equations is obtained. These equations are then solved to obtain switching angles to have certain low order harmonics at minimum value and regulation in the fundamental voltage magnitude. In this paper, a novel invasive weed optimization (IWO) technique is proposed to compute switching angles. The proposed technique can compute switching angles for both symmetrical and asymmetrical multilevel inverters. Thus it has superiority over well-known optimization techniques such as GA, PSO, DE, and ACO, etc. Moreover, in certain modulation index ranges, it provides faster convergence and accurate results which have been demonstrated in the paper. The computational results have been verified with the experimental result on the prototype developed in the laboratory. The field programming gate arrays (FPGA) based controller is used to implement the proposed technique. The hardware results have been found in close agreement with the computed results. 2022This publication was made possible by NPRP grant #[ 13S-0108-20008 ] from the Qatar National Research Fund (A member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. The APC of the paper is funded by the Qatar National Library , Doha, Qatar.Scopu

A review of optimization approaches for controlling water-cooled central cooling systems

Buildings consume a large amount of energy across all sectors of society, and a large proportion of building energy is used by HVAC systems to provide a comfortable and healthy indoor environment. In medium and large-size buildings, the central cooling system accounts for a major share of the energy consumption of the HVAC system. Improving the cooling system efficiency has gained much attention as the reduction of cooling system energy use can effectively contribute to environmental sustainability. The control and operation play an important role in central cooling system energy efficiency under dynamic working conditions. It has been proven that optimization of the control of the central cooling system can notably reduce the energy consumption of the system and mitigate greenhouse gas emissions. In recent years, numerous studies focus on this topic to improve the performance of optimal control in different aspects (e.g., energy efficiency, stability, robustness, and computation efficiency). This paper provides an up-to-date overview of the research and development of optimization approaches for controlling water-cooled central cooling systems, helping readers to understand the new significant trends and achievements in this area. The optimization approaches have been classified as system-model-based and data-based. In this paper, the optimization methodology is introduced first by summarizing the key decision variables, objective function, constraints, and optimization algorithms. The principle and performance of various optimization approaches are then summarized and compared according to their classification. Finally, the challenges and development trends for optimal control of water-cooled central cooling systems are discussed

Optimal design of a composite active aeroelastic wing

The primary aim of this research was to design a Seamless Aeroelastic Wing (SAW) structure applicable to a lightweight Unmanned Aerial Vehicle (UAV). Therefore the study focused on optimal design of a SAW structure by utilising the maximum aeroelastic beneficial effect. Although similar to the Active Aeroelastic Wing (AAW) and relevant to the Flapless Air Vehicle Integrated Industrial Research (FLAVIIR), the major difference from them is that a SAW will function as an integrated one piece lifting and control surface. It is designed to produce a desirable wing camber for control by deflecting a hinge-less flexible trailing edge (TE) part instead of a traditional control surface. Attention was firstly paid on the design of a hinge-less flexible trailing edge control surface and the actuation mechanism applicable for a light-weight aircraft (UAV). The proposed mechanism in the SAW TE section has two innovative design features: an open sliding TE and a curved beam and disc actuation mechanism. This type of actuated TE section allows for the SAW having a smooth camber change in a desirable shape with minimum control power demand. This design concept has been simulated numerically and its feasibility has been demonstrated by a test model. The wing structure for a small scale UAV is likely to be over designed in terms of strength, stiffness and weight due to manufacturing constraints. For the optimal wing design, the investigation was conducted in two stages. In the first stage, effort was made to design and model an optimised composite wing box for a minimum weight and maximum flutter speed. Both analytical and numerical methods were used for structural stress, vibration and aeroelastic analyses. In the second stage, the study focused on integrating the TE actuation mechanism with the optimised wing box for detailed understanding of the structure. A finite element analysis was conducted to simulate the SAW TE to ensure that structural strength requirements were satisfied. Furthermore, a study was carried out on the structural dynamic behaviour of the SAW TE section under the aerodynamic pressure to demonstrate its dynamic stability. Hence, the outcome of this research shows that a feasible SAW design for a UAV can be achieved.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The acquisition and maintenance of antibodies to merozoite antigens of Plasmodium falciparum and their role in protective immunity to malaria

Measurement of antibodies at a single time point in malaria-endemic populations and associating them with protection and susceptibility has given insight into the development and maintenance of the immune response to malaria. Immunity to malaria is a dynamic process that takes place over a number of years in different stages, which implies that antibody measurement at a single time point may not adequately encompass acquisition of immunity. Antibody responses to merozoite antigens (AMA 1 and MSP2) were measured in 300 children aged 0-10 years twice a year for three years. Each child was followed up on a weekly basis for episodes of malaria. Factors affecting antibody responses at each time point and antibody contributions to protection from malaria were investigated, and the association between functional activity of anti-AMA 1 antibodies and protection was assessed. Anti-AMA 1 and anti-MSP2 antibody responses were dependent on the amount of prior and ongoing exposure and paralleled the decline in malaria transmission that occurred during the study period. High antibody responses were generated after 2-3 episodes of parasitemia and were likely to drop on further exposure. There was no evidence for polarisation of IgG responses to AMA 1. The association between antibody responses and protection/risk of malaria was dependent on both the sample time and analysis method used. Antibody responses to AMA 1(W2mef) were associated with an increased risk of malaria over the study period. Antibodies to MSP2(3D7) may be associated with protection from malaria. Antibodies to a functional invasion inhibitory epitope of AMA 1(3D7) were rare but associated with protection from malaria. Longitudinal assessment of antibody levels gives a more complete picture of acquisition and maintenance of malaria immunity. Antibodies can be both a measure of protection or susceptibility. These findings enrich knowledge on acquisition of immunity and will impact vaccination development and immunisation strategies