An Enhanced DC-Bus Voltage-Control Loop for Single-Phase Grid-Connected DC/AC Converters

© 1986-2012 IEEE. This paper presents a method to enhance the dc-bus voltage-control loop of a single-phase grid-connected dc/ac converter, which improves its responses in terms of oscillation on its dc-bus voltage as well as its output ac current. Conventionally, the double-frequency (2-f) ripple is reduced by using a large electrolyte capacitor, which increases the cost and size of the system. A state-of-the-art approach is to use a notch filter (NF) to block the 2-f ripple in the voltage-control loop. This can significantly reduce the capacitor size. The existing presentations of this method, however, do not integrate the internal dynamics of the NF into consideration. This paper proposes a new way of implementing the NF, which allows integration of its internal variables into the control loop. The resulted system exhibits enhanced transient responses at both the dc-bus voltage and the output ac current. The proposed method is analyzed in detail and its effectiveness is verified through simulations and experimental results

An enhanced control system for single-phase inverters interfaced with weak and distorted grids

© 2019 IEEE. This paper presents an enhanced current controller for improving the performance of a class of single-phase grid-connected inverters operating in weak and distorted grid conditions. An inverter designed to operate at normal (strong or stiff and clean) grid conditions may not perform satisfactorily during weak and distorted grid conditions. One major reason is the interfering dynamics of the synchronization or phase-locked loop (PLL). This paper proposes an enhanced control structure for a popular class of single-phase inverters to address this problem. The proposed idea is to include the PLL state variables into the main inverter controller thereby minimizing the undesirable interactions of the PLL with the other components. A method for optimally designing the controller gains is also proposed. Compared to the conventional one, the proposed controller is shown to have a more robust performance over a substantially wider range of weak and distorted grid conditions. Extensive simulation and experimental results are presented to validate the proposed controls

A Multifunctional Single-Phase EV On-Board Charger with a New V2V Charging Assistance Capability

© 2013 IEEE. This paper presents the design and implementation of a single-phase multifunctional electric-vehicle (EV) on-board charger with an advanced vehicle-to-vehicle (V2V) functionality for emergency roadside charging assistance situations. Using this function, an EV is able to charge from another EV in case of an emergency when the battery is flat and there is no access to a charging station. The designed EV charger can support the proposed V2V function with rated power and without the need for an additional portable charger. It can also provide conventional functions of vehicle-to-grid (V2G), grid-to-vehicle (G2V), the static synchronous compensators (STATCOM) and active power filter (APF) (i.e. reactive power support, and harmonics reduction). All the functions are addressed in the control part through the sharing of existing converters in an all-in-one system. The proposed EV charger is designed and simulated in MATLAB/Simulink, and a laboratory prototype is also implemented to validate its key functions

Cyber attacks in smart grid - Dynamic impacts, analyses and recommendations

© 2020 Institution of Engineering and Technology. All rights reserved. Cyber attacks can cause cascading failures and blackouts in smart grids. Therefore, it is highly necessary to identify the types, impacts and solutions of cyber attacks to ensure the secure operation of power systems. As a well-known practice, steady-state analysis is commonly used to identify cyber attacks and provide effective solutions. However, it cannot fully cover non-linear behaviours and cascaded blackouts of the system caused by dynamic perturbations, as well as provide a postdisturbance operating point. This study presents a novel approach based on dynamic analysis that excludes the limitations of the steady-state analysis and can be used in the events of various cyber attacks. Four types of common attacks are reviewed, and their dynamic impacts are shown on the IEEE benchmark model of the Western System Coordinating Council system implemented in MATLAB Simulink. Then, recommendations are provided to enhance the security of the future smart power grids from the possible cyber attacks

A Fast Time-Domain Current Harmonic Extraction Algorithm for Power Quality Improvement Using Three-Phase Active Power Filter

© 2013 IEEE. Harmonic current estimation is the key aspect of Active Power Filter (APF) control algorithms to generate a reference current for harmonic compensation. This paper proposes a novel structure for harmonic current estimation scheme based on Trigonometric Orthogonal Principle (TOP) and Self Tuning Filter (STF). The key advantages of the proposed method are its simplicity, low computational burden and faster execution time in comparison to the conventional harmonic current estimation approaches. The TOP method provides a simple and fast approach to extract the reference current, while STF provides a simplified structure to generate the required synchronization signal that eliminates the need of a Phase Locked Loop (PLL) algorithm for synchronization. As a result, it exhibits less complexity in implementation and less consumption of microcontroller's resources; thus, the proposed method can be implemented using a low-cost microcontroller. It is shown in the paper that the proposed method provides 10 times gain in processing speed as compared to the conventional DQ method. The proposed approach is analyzed in detail, and its effectiveness and superior performance are verified using simulation and experimental results

Enhanced wheat yield by biochar addition under different mineral fertilization levels

Climate change and global warming have worldwide adverse consequences. Biochar production and its use in agriculture can play a key role in climate change mitigation and help improve the quality and management of waste materials coming from agriculture and forestry. Biochar is a carbonaceous material obtained from thermal decomposition of residual biomass at relatively low temperature and under oxygen limited conditions (pyrolysis). Biochar is currently a subject of active research worldwide because it can constitute a viable option for sustainable agriculture due to its potential as a long-term sink for carbon in soil and benefits for crops. However, to date, the results of research studies on biochar effects on crop production show great variability, depending on the biochar type and experimental conditions. Therefore, it is important to identify the beneficial aspects of biochar addition to soil on crop yield in order to promote the adoption of this practice in agriculture. In this study, the effects of two types of biochar from agricultural wastes typical of Southern Spain: wheat straw and olive tree pruning, combined with different mineral fertilization levels on the growth and yield of wheat (Triticum durum L. cv. Vitron) were evaluated. Durum wheat was pot-grown for 2 months in a growth chamber on a soil collected from an agricultural field near Córdoba, Southern Spain. Soil properties and plant growth variables were studied in order to assess the agronomic efficiency of biochar. Our results show that biochar addition to a nutrientpoor, slightly acidic loamy sand soil had little effect on wheat yield in the absence of mineral fertilization. However, at the highest mineral fertilizer rate, addition of biochar led to about 20–30 % increase in grain yield compared with the use of the mineral fertilizer alone. Both biochars acted as a source of available P, which led to beneficial effects on crop production. In contrast, the addition of biochar resulted in decreases in available N and Mn. A maximum reduction in plant nutrient concentration of 25 and 80% compared to nonbiochar-treated soils for N and Mn, respectively, was detected. This fact was related to the own nature of biochar: low available nitrogen content, high adsorption capacity, and low mineralization rate for N; and alkaline pH and high carbonate content for Mn. Our results indicate that biochar-based soil management strategies can enhance wheat production with the environmental benefits of global warming mitigation. This can contribute positively to the viability and benefits of agricultural production systems. However, the nutrient–biochar interactions should receive special attention due to the great variability in the properties of biochar-type materials

Senescent Cells in Growing Tumors: Population Dynamics and Cancer Stem Cells

Tumors are defined by their intense proliferation, but sometimes cancer cells turn senescent and stop replicating. In the stochastic cancer model in which all cells are tumorigenic, senescence is seen as the result of random mutations, suggesting that it could represent a barrier to tumor growth. In the hierarchical cancer model a subset of the cells, the cancer stem cells, divide indefinitely while other cells eventually turn senescent. Here we formulate cancer growth in mathematical terms and obtain predictions for the evolution of senescence. We perform experiments in human melanoma cells which are compatible with the hierarchical model and show that senescence is a reversible process controlled by survivin. We conclude that enhancing senescence is unlikely to provide a useful therapeutic strategy to fight cancer, unless the cancer stem cells are specifically targeted

Frontal Bone Remodeling for Gender Reassignment of the Male Forehead: A Gender-Reassignment Surgery

Gender-reassignment therapy, especially for reshaping of the forehead, can be an effective treatment to improve self-esteem. Contouring of the cranial vault, especially of the forehead, still is a rarely performed surgical procedure for gender reassignment. In addition to surgical bone remodeling, several materials have been used for remodeling and refinement of the frontal bone. But due to shortcomings of autogenous bone material and the disadvantages of polyethylene or methylmethacrylate, hydroxyapatite cement (HAC) composed of tetracalcium phosphate and dicalcium phosphate seems to be an alternative. This study aimed to analyze the clinical outcome after frontal bone remodeling with HAC for gender male-to-female reassignment. The 21 patients in the study were treated for gender reassignment of the male frontal bone using HAC. The average age of these patients was 33.4 years (range, 21–42 years). The average volume of HAC used per patient was 3.83 g. The authors’ clinical series demonstrated a satisfactory result. The surgery was easy to perform, and HAC was easy to apply and shape to suit individual needs. Overall satisfaction was very high. Therefore, HAC is a welcome alternative to the traditional use of autogenous bone graft for correction of cranial vault irregularities

The role and scope of practice of midwives in humanitarian settings:a systematic review and content analysis

Abstract Background Midwives have an essential role to play in preparing for and providing sexual and reproductive health (SRH) services in humanitarian settings due to their unique knowledge and skills, position as frontline providers and geographic and social proximity to the communities they serve. There are considerable gaps in the international guidance that defines the scope of practice of midwives in crises, particularly for the mitigation and preparedness, and recovery phases. We undertook a systematic review to provide further clarification of this scope of practice and insights to optimise midwifery performance. The review aimed to determine what SRH services midwives are involved in delivering across the emergency management cycle in humanitarian contexts, and how they are working with other professionals to deliver health care. Methods Four electronic databases and the websites of 33 organisations were searched between January and March 2017. Papers were eligible for inclusion if they were published in English between 2007 and 2017 and reported primary research pertaining to the role of midwives in delivering and performing any component of sexual and/or reproductive health in humanitarian settings. Content analysis was used to map the study findings to the Minimum Initial Service Package (MISP) for SRH across the three phases of the disaster management cycle and identify how midwives work with other members of the health care team. Results Fourteen studies from ten countries were included. Twelve studies were undertaken in conflict settings, and two were conducted in the context of the aftermath of natural disasters. We found a paucity of evidence from the research literature that examines the activities and roles undertaken by midwives across the disaster management cycle. This lack of evidence was more apparent during the mitigation and preparedness, and recovery phases than the response phase of the disaster management cycle. Conclusion Research-informed guidelines and strategies are required to better align the scope of practice of midwives with the objectives of multi-agency guidelines and agreements, as well as the activities of the MISP, to ensure that the potential of midwives can be acknowledged and optimised across the disaster management cycle