Cascade sliding mode maximum power point tracking controller for photovoltaic systems

Introduction. Constant increases in power consumption by both industrial and individual users may cause depletion of fossil fuels and environmental pollution, and hence there is a growing interest in clean and renewable energy resources. Photovoltaic power generation systems are playing an important role as a clean power electricity source in meeting future electricity demands. Problem. All photovoltaic systems have two problems; the first one being the very low electric-power generation efficiency, especially under low-irradiation states; the second resides in the interdependence of the amount of the electric power generated by solar arrays and the ever changing weather conditions. Load mismatch can occur under these weather varying conditions such that maximum power is not extracted and delivered to the load. This issue constitutes the so-called maximum power point tracking problem. Aim. Many methods have been developed to determine the maximum power point under all conditions. There are various methods, in most of them based on the well-known principle of perturb and observe. In this method, the operating point oscillates at a certain amplitude, no matter whether the maximum power point is reached or not. That is, this oscillation remains even in the steady state after reaching the maximum power point, which leads to power loss. This is an essential drawback of the previous method. In this paper, a cascade sliding mode maximum power point tracking control for a photovoltaic system is proposed to overcome above mentioned problems. Methodology. The photovoltaic system is mainly composed of a solar array, DC/DC boost converter, cascade sliding mode controller, and an output load. Two sliding mode control design strategies are joined to construct the proposed controller. The primary sliding mode algorithm is designed for maximum power point searching, i.e., to track the output reference voltage of the solar array. This voltage is used to manipulate the setpoint of the secondary sliding mode controller, which is used via the DC-DC boost converter to achieve maximum power output. Results. This novel approach provides a good transient response, a low tracking error and a very fast reaction against the solar radiation and photovoltaic cell temperature variations. The simulation results demonstrate the effectiveness of the proposed approach in the presence of environmental disturbances.Вступ. Постійне збільшення енергоспоживання як промисловими, так і індивідуальними користувачами може призвести до виснаження запасів викопного палива та забруднення навколишнього середовища, тому зростає інтерес до чистих та відновлюваних джерел енергії. Фотоелектричні системи виробництва електроенергії відіграють важливу роль як екологічно чисте джерело електроенергії для задоволення майбутніх потреб в електроенергії. Проблема. Усі фотоелектричні системи мають дві проблеми; по-перше, дуже низька ефективність вироблення електроенергії, особливо в умовах низького опромінення; друга полягає у взаємозалежності кількості електроенергії, що виробляється сонячними батареями, та постійно мінливих погодних умов. У цих погодних умовах, що змінюються, може відбутися невідповідність навантаження, так що максимальна потужність не буде витягнута і передана в навантаження. Ця проблема є так званою проблемою відстеження точки максимальної потужності. Мета. Було розроблено безліч методів визначення точки максимальної потужності за будь-яких умов. Існують різні методи, здебільшого засновані на відомому принципі збурення та спостережень. У цьому методі робоча точка коливається з певною амплітудою, незалежно від того, досягнуто точку максимальної потужності чи ні. Тобто це коливання залишається навіть у стійкому стані після досягнення точки максимальної потужності, що призводить до втрати потужності. Це значний недолік попереднього способу. У цій статті для подолання вищезазначених проблем пропонується каскадне керування відстеженням точки максимальної потужності в режимі ковзання для фотоелектричної системи. Методологія. Фотоелектрична система в основному складається з сонячної батареї, перетворювача постійного струму, що підвищує, каскадного контролера ковзного режиму та вихідного навантаження. Дві стратегії проєктування керування ковзним режимом об'єднані для побудови пропонованого контролера. Алгоритм первинного ковзного режиму призначений для пошуку точки максимальної потужності, тобто для відстеження вихідної опорної напруги сонячної батареї. Ця напруга використовується для управління уставкою вторинного контролера ковзного режиму, який використовується через перетворювач постійного струму, що підвищує, для досягнення максимальної вихідної потужності. Результати. Цей новий підхід забезпечує хорошу перехідну характеристику, низьку помилку відстеження та дуже швидку реакцію на сонячне випромінювання та коливання температури фотогальванічного елемента. Результати моделювання демонструють ефективність пропонованого підходу за наявності збурень довкілля

Indirect adaptive fuzzy finite time synergetic control for power systems

Introduction. Budget constraints in a world ravenous for electrical power have led utility companies to operate generating stations with full power and sometimes at the limit of stability. In such drastic conditions the occurrence of any contingency or disturbance may lead to a critical situation starting with poorly damped oscillations followed by loss of synchronism and power system instability. In the past decades, the utilization of supplementary excitation control signals for improving power system stability has received much attention. Power system stabilizers (PSS) are used to generate supplementary control signals for the excitation system in order to damp low-frequency oscillations caused by load disturbances or short-circuit faults. Problem. Adaptive power system stabilizers have been proposed to adequately deal with a wide range of operating conditions, but they suffer from the major drawback of requiring parameter model identification, state observation and on-line feedback gain computation. Power systems are nonlinear systems, with configurations and parameters that fluctuate with time that which require a fully nonlinear model and an adaptive control scheme for a practical operating environment. A new nonlinear adaptive fuzzy approach based on synergetic control theory which has been developed for nonlinear power system stabilizers to overcome above mentioned problems. Aim. Synergetic control theory has been successfully applied in the design of power system stabilizers is a most promising robust control technique relying on the same principle of invariance found in sliding mode control, but without its chattering drawback. In most of its applications, synergetic control law was designed based on an asymptotic stability analysis and the system trajectories evolve to a specified attractor reaching the equilibrium in an infinite time. In this paper an indirect finite time adaptive fuzzy synergetic power system stabilizer for damping local and inter-area modes of oscillations for power systems is presented. Methodology. The proposed controller design is based on an adaptive fuzzy control combining a synergetic control theory with a finite-time attractor and Lyapunov synthesis. Enhancing existing adaptive fuzzy synergetic power system stabilizer, where fuzzy systems are used to approximate unknown system dynamics and robust synergetic control for only providing asymptotic stability of the closed-loop system, the proposed technique procures finite time convergence property in the derivation of the continuous synergetic control law. Analytical proofs for finite time convergence are presented confirming that the proposed adaptive scheme can guarantee that system signals are bounded and finite time stability obtained. Results. The performance of the proposed stabilizer is evaluated for a single machine infinite bus system and for a multi machine power system under different type of disturbances. Simulation results are compared to those obtained with a conventional adaptive fuzzy synergetic controller

Cascade sliding mode maximum power point tracking controller for photovoltaic systems

Introduction. Constant increases in power consumption by both industrial and individual users may cause depletion of fossil fuels and environmental pollution, and hence there is a growing interest in clean and renewable energy resources. Photovoltaic power generation systems are playing an important role as a clean power electricity source in meeting future electricity demands. Problem. All photovoltaic systems have two problems; the first one being the very low electric-power generation efficiency, especially under low-irradiation states; the second resides in the interdependence of the amount of the electric power generated by solar arrays and the ever changing weather conditions. Load mismatch can occur under these weather varying conditions such that maximum power is not extracted and delivered to the load. This issue constitutes the so-called maximum power point tracking problem. Aim. Many methods have been developed to determine the maximum power point under all conditions. There are various methods, in most of them based on the well-known principle of perturb and observe. In this method, the operating point oscillates at a certain amplitude, no matter whether the maximum power point is reached or not. That is, this oscillation remains even in the steady state after reaching the maximum power point, which leads to power loss. This is an essential drawback of the previous method. In this paper, a cascade sliding mode maximum power point tracking control for a photovoltaic system is proposed to overcome above mentioned problems. Methodology. The photovoltaic system is mainly composed of a solar array, DC/DC boost converter, cascade sliding mode controller, and an output load. Two sliding mode control design strategies are joined to construct the proposed controller. The primary sliding mode algorithm is designed for maximum power point searching, i.e., to track the output reference voltage of the solar array. This voltage is used to manipulate the setpoint of the secondary sliding mode controller, which is used via the DC-DC boost converter to achieve maximum power output. Results. This novel approach provides a good transient response, a low tracking error and a very fast reaction against the solar radiation and photovoltaic cell temperature variations. The simulation results demonstrate the effectiveness of the proposed approach in the presence of environmental disturbances

Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease

Reaching phase free adaptive fuzzy synergetic power system stabilizer

International audienc

Non-communicable health risks during mass gatherings

Mass gatherings (MGs) have been associated with high rates of morbidity and mortality from non-communicable diseases, accidents, and terrorist attacks, thus posing complex public health challenges. We assessed the health risks and public health responses to MGs to identify an evidence-based framework for public health interventions. Human stampedes and heat-related illnesses are the leading causes of mortality. Minor traumatic injuries and medical complaints are the main contributors to morbidity and, particularly, the need for onsite medical care. Infrastructure, crowd density and mood, weather, age, and sex determine the risks to health. Many predictive models for deployment of medical resources are proposed, but none have been validated. We identified the risks for mortality and morbidity during MGs, most efficient public health interventions, and need for robust research into health risks for non-communicable diseases during MGs