Evaluation of DC-link voltage ripple in seven-phase PWM voltage source inverters

The analysis of dc-link inverter current and voltage ripple is important for the optimization of the input components, mainly the dc-link capacitor. In this paper reference is made to two-level seven-phase PWM voltage source inverters with balanced load, typically multiphase ac motors. The peakto-peak amplitude of the dc-link voltage switching ripple within the fundamental period is analytically determined as a function of operating conditions: modulation index, output currents amplitude and phase angle. The maximum of voltage switching ripple is also derived in order to design the dc-link capacitor. The two most popular inverter modulation techniques are considered: sinusoidal PWM and centered PWM (CPWM, equivalent to space vector modulation, SVM). A comparison between them is made in terms of the dc voltage switching ripple envelope. Numerical simulations are carried out by Matlab/Simulink in order to verify the analytical results

Evaluation of DC-link voltage ripple in five-phase PWM voltage source inverters

This paper presents the analysis of the DC-link voltage switching ripple in five-phase PWM voltage source inverters with balanced load. The analysis is particularly important for the design and selection of a DC-link capacitor making it possible to meet desired electrical performance of the inverter system. Simple and practical equation for designing the DC-link capacitor is proposed relating the value of capacitance to the maximum value (peak-to-peak) of the DC-link voltage ripple. The amplitude of the DC-link voltage switching ripple is analytically derived as a function of modulation index, and the amplitude of the output current and phase angle. In order to show peak-to-peak voltage ripple distribution, different diagrams are introduced. Reference is made to continuous symmetric centred PWM modulation (i.e., space vector modulation SVM). In order to verify proposed developments, simulations have been carried out by Matlab/Simulink considering full range of modulation index and output phase angle

SOIL EROSION EVALUATION IN THE RASTOCKI POTOK WATERSHED OF MONTENEGRO USING THE EROSION POTENTIAL METHOD

Soil erosion is the most important factor of land degradation worldwide, causing significant environmental problems in the region of South East Europe also. We studied soil erosion processes in the RastockiPotok Watershed of Montenegro using the Erosion Potential Method (EPM) of Gavrilovic, which is created in Yugoslavia and is the most suitable on catchment level for the watershed management needs in this Region. The peak discharge (Qmax) is calculated on 150 m3s-1 and there is a possibility for large flood waves to appear in the studied basin. According to our analysis, the coefficient fs, (portion under forest) is 0.45; ft (grass) is 0.41 and fg (bare land) is 0.14 and the coefficient of the river basin planning, Xa, is 0.52. Real soil losses, Gyr, were calculated on 1472m3yr-1, specific 250m3km-2yr-1. The value of the Z coefficient of 0.488 indicates that the studied watershed belongs in the Destruction Category III: the erosion process is medium. This study confirmed the findings of the other Balkan researchers that the EPM method of Professor Gavrilovic is a useful tool for calculating sediment yield in the South East Europe

An Output Ripple-Free Fast Charger for Electric Vehicles Based on Grid-Tied Modular Three-Phase Interleaved Converters

An off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide ripple-free output current in the typical EV batteries voltage range is presented in this article. The proposed configuration is based on modular three-phase interleaved converters and supplied by the low-voltage ac grid. The ac/dc interleaved three-phase active rectifier is composed of three standard two-level three-phase converter modules with a possibility to slightly adjust the dc-link voltage level in order to null the output current ripple. A modular interleaved dc/dc converter, formed by the same three-phase converter modules connected in parallel, is used as an interface between the dc link and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities. The effect of coupling on the individual input/output inductors and total input/output current ripples has been investigated as well, considering both possible coupling implementations, i.e., inverse and direct coupling. Numerical simulations are reported to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, including the proposed control strategy aimed to null the ripple of the output current. Experimental results are provided by a reduced scale prototype of the output stage to verify the ripple-free output current operation capability

Evaluation of DC-link voltage switching ripple in multiphase PWM voltage source inverters

This paper presents a generalized approach towards the dc-link voltage switching ripple analysis in two-level multiphase PWM voltage source inverters with balanced load. Since voltage ripple is one of the crucial sizing criteria for dc-link capacitor, simple and practical equation for designing the dc-link capacitor, based on the maximum (peak-to-peak) value of the dc-link voltage ripple, has been proposed for multiphase inverters. The amplitude of the dc-link voltage switching ripple is analytically derived as a function of operating conditions. The effect of the number of phases on the dc-link capacitor size is investigated as well. It is found that considering the same total output current, the dc-link capacitor size is reduced increasing the number of phases up to seven. However, from the point of view of dc-link capacitor size, there are no benefits of further increasing the number of phases. Reference is made to two commonly used modulation strategies – sinusoidal PWM and continuous symmetric centered PWM (i.e., space vector). The mathematical models derived aim to provide precise dc-link capacitor sizing and hence improve the power density of the whole system. Comparison of different phase numbers has been made. Proposed theoretical developments are verified by simulation and experimental tests

DC-link low-frequency current and voltage ripple analysis in multiphase voltage source inverters with unbalanced load

Inverter’s performance and operating mode may be negatively affected by inverter input (dc-link) current and voltage ripple. It is a common experience that even theoretically balanced loads with perfectly balanced supply voltages, such as multiphase ac motors supplied by PWM inverters, in practice show a certain degree of current unbalance, in the range of a few percent, which introduces a low-frequency instantaneous power oscillation. This reflects in current and voltage low-frequency ripple on the dc-link inverter side (i.e., at the double-fundamental frequency). A possible method to analyze this matter is through the symmetric sequence components. In particular, based on the first negative current sequence component and by considering the equiva-lent dc-link impedance calculated at the dominant double-fundamental frequency, the amplitude of the corresponding dc-link voltage ripple component is calculated in this paper for a general multiphase load. Finally, the design of the dc-link capacitor in multiphase inverters is proposed considering requirements referred to the double-fundamental dc voltage ripple. The feasibility of proposed developments has been verified for three-, five- and seven-phase inverters by both numerical simulations and comprehensive experimental tests, always showing a good matching

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery