Designing the optimal number of active branches in a multi-branch buck-boost converter

The given research is aimed at the mathematical modeling and synthesis of the electrical equivalent circuit of an electrochemical device as an element of an electrical circuit. Mathematical modeling is completed in the result of a systematic study of the concentration and electric fields in a two-electrode electrochemical system. The object of study is considered to be linear with constant parameters. The object sizes are considered to be insignificant that’s why the electric current density on the electrodes surface is assumed to be equally distributed. Diffusion in the electrolyte becomes the limiting stage of electrode processes in the system with a finite mass transfer rate. The Laplace operator method is used as a research method, it is used to calculate the voltage at the electrodes of an electrochemical device. The mathematical model of an electrochemical device has been developed in the run of the system study and an electrical equivalent circuit has been synthesized, which contains infinite number of parallel branches including active and reactive elements. Besides, analytical formulas have been obtained that can be used in the process of calculation individual discrete parameters on these branches. In case of engineering calculations, the number of branches in the electrical equivalent circuit can be limited with the finite number, specified by accuracy of the calculations. It should be also mentioned that as a result of the study, it has become possible to synthesize all kinds of particular characteristics of an electrochemical device as well as the opportunity to study the dynamics of various transition processes in it.

Current harmonized improvement method: A concept of the optimal electrical array configuration of thermoelectric modules for minimizing the mismatch loss of a thermoelectric generator

An experiment was conducted to characterize the growth and yield performance of narrow-leafed sweet blue lupin varieties (Lupinus angustifolius L.) in northwestern Ethiopia. The experiment was laid out in a randomized complete block design with 4 replications and included 7 varieties (Bora, Probor, Sanabor, Vitabor, Haags blaue, Borlu and Boregine). Data on days to flowering and to maturity, flower color, plant height, numbers of leaflets, branches and pods per plant, pod length, number of seeds per pod, forage dry matter (DM) yield, grain yield and 1,000-seed weight were recorded. The results showed that plant height, number of branches per plant, forage DM yield, number of seeds per pod, grain yield and 1,000-seed weight varied significantly (P<0.01) among varieties. The highest forage DM yield at 50% flowering (2.67 t/ha), numbers of pods per plant (16.9) and of seeds per pod (4.15), grain yield (1,900 kg/ha) and 1,000-seed weight (121 g) were obtained from the Boregine variety. The tallest plants and greatest number of branches per plant were recorded from varieties Sanabor and Bora, respectively. Correlation analysis showed that the major factor affecting forage DM yield was plant height, while plant height, days to maturity and number of seeds per pod had the greatest influence on grain yield. The best performing variety was Boregine followed by Sanabor and Bora. These varieties seem promising for the development of sustainable forage production strategies with limited external inputs. However, future research should be conducted on the improvement of their agronomy and the possibility of their utilization as protein supplements using narrow-leafed sweet blue lupin forage or grain, as well as testing of promising varieties in diverse locations.

Forward converter with active clamp is a suitable topology for a low output voltage and high output current DC-DC power supply module. The topology can be used in a resonant transition manner to obtain a low voltage over the main switch at turn-on instant. A low voltage can be obtained by adjusting the magnitude of the magnetizing current of the transformer and the delay between the two primary side switches. An increased magnetizing current, however, increases conduction losses in the primary side of the converter and may consume the advantage gamed in the switching losses. The converter can also be easily used for self-driven synchronous rectification. However, pursue for low switching losses for the primary side switch may deteriorate performance of the self-driven synchronous rectifiers, particularly at high loads. This paper presents a study of the applicability and advantage of the use of the resonant transition hi forward with active clamp and self-driven synchronous rectifiers. The emphasis is on the comparison of the achieved efficiency with different voltage levels over the primary switch prior to turning on. Measurement results show that, at low loads, a reduced voltage level improves the efficiency but, on the other hand, at high loads the advantage is not so significant, or it may be totally lost, mainly due to the increased losses of the self-driven synchronous rectifiers. The paper includes discussion on the effect of the magnetizing inductance on the efficiency of the converter and the optimal voltage level at which the primary switch should be turned on. Measurement results from a 3.4 V 30 A prototype converter are included.

The effect of switching losses on the efficiency of a switch mode power converter and methods adopted for its improvement using an energy recovery lossless snubber has been presented. A comparative analysis of various types of soft switching techniques along with effects of dissipative and nondissipative snubbers on efficiency of the converter has been carried out before zeroing in on the selected scheme. The selected snubber serves the dual function of a turn-on and turn-off snubber and thereby reducing the switching losses both during turn-on and turn-off transients, resulting in improved efficiency of the converter. A detailed design procedure of the snubber for high-power applications taking into account various effects such as diode reverse recovery, diode voltage stress, and minimum and maximum duty cycle limits, has been presented in this paper. Importance of practical aspects in layout to minimize wiring inductance is also highlighted. A high-power prototype of buck converter has been developed to experimentally validate the theoretical design and analytical observations.

Background: Climate change is a major challenge faced by the agricultural sector all over the world. Different adaptation and mitigation strategies are used to cope with these weather aberrations. Growing climate resilient crops and cultivars suitable for different regions is one of the adaptation strategy. Leguminous crops are well known for their resilience, adaptation and tolerance to adverse conditions, among these crops cluster bean is a hardy and drought tolerant crop extremely suitable for warm tropical regions. Hence identification and improvement of selected genotypes of cluster bean have paramount importance for combating the challenges possessed by the changing climatic scenario. Methods: Thirty accessions of cluster bean were evaluated during 2018. The experiment was laid out in randomized block design with two replications. Statistical analysis was employed for estimation of correlation and path coefficients. Result: The correlation analysis revealed that pod yield/plant had positive significant correlation with number of branches, number of pod clusters/plant, number of pods/plant and days to first harvest hence, selection of accessions having higher mean values for these traits could improve yield in cluster bean. Path analysis revealed that number of pods/plant had maximum positive direct effect on pod yield/plant followed by number of branches and plant height. Thus, while attempting selection for higher pod yield in cluster bean, number of pods per plant, number of branches and plant height have to be taken into account.

In this paper, we propose a single-input dual-output (SIDO) DC-DC converter designed by switched capacitor (SC) techniques. Unlike conventional SC converters, the proposed converter can provide nine kinds of two stepped- up and/or stepped-down output voltages without changing circuit topology. This paper also presents a novel analysis method to estimate properties of the SC SIDO converters, because few studies have been done on the theoretical analysis of the multi-output SC converters. Unlike the traditional state-space averaging method, the proposed method can derive the power efficiency and output voltages without complex matrix calculations. The simulation program with integrated circuit emphasis (SPICE) simulation shows the following results: (1) more than 82% efficiency is obtained over a range of output power from 0.1W to 1W with conversion ratios of 1/2 and 3/2 and (2) the proposed analysis method will be helpful to estimate the power efficiency and output voltages of the SC SIDO converter, because theoretical results are in good agreement with SPICE simulated results. Furthermore, experiment on a breadboard shows the validity of the proposed SC SIDO topology. Normal 0 0 2 false false false EN-US JA X-NONE In this paper, we propose a single-input dual-output (SIDO) DC-DC converter designed by switched capacitor (SC) techniques. Unlike conventional SC converters, the proposed converter can provide nine kinds of two stepped- up and/or stepped-down output voltages without changing circuit topology. This paper also presents a novel analysis method to estimate properties of the SC SIDO converters, because few studies have been done on the theoretical analysis of the multi-output SC converters. Unlike the traditional state-space averaging method, the proposed method can derive the power efficiency and output voltages without complex matrix calculations. The simulation program with integrated circuit emphasis (SPICE) simulation shows the following results: (1) more than 82% efficiency is obtained over a range of output power from 0.1W to 1W with conversion ratios of 1/2 and 3/2 and (2) the proposed analysis method will be helpful to estimate the power efficiency and output voltages of the SC SIDO converter, because theoretical results are in good agreement with SPICE simulated results. Furthermore, experiment on a breadboard shows the validity of the proposed SC SIDO topology. Normal 0 0 2 false false false EN-US JA X-NONE

The recovery voltage method based on dielectric response is a non-destructive electrical diagnostic method used to diagnose the insulation state of transformer oil paper. In response to the difficulty in determining the number of equivalent circuit branches based on the recovery voltage method, this paper uses a mathematical model of recovery voltage to analyze the relationship between the mathematical expression of recovery voltage and branch parameters. A recovery voltage decomposition method is proposed to separate the recovery voltage sub-curves represented by each polarized branch, thereby determining the number of equivalent circuit branches and solving the problem of difficult selection of equivalent circuit branches. Example verification shows that using the recovery voltage decomposition method can truly confirm the number of polarization branches in the equivalent circuit and accurately reflect the insulation aging condition of transformers.

In this paper, a novel zero voltage transition (ZVT) boost converter is proposed, and the overall efficiency of the converter is predicted with an artificial neural network (ANN) model. In the proposed converter, the main switch is turned on by ZVT and turned off by zero voltage switching (ZVS). Also, the other semiconductor elements operate by soft switching (SS). Besides, the proposed snubber cell has the bidirectional direct power transfer feature. The theoretical analyzes of the converter are verified by an prototype having 50 VDC input voltage, 100 VDC output voltage, 250 W output power, and 100 kHz switching frequency. The overall efficiency of the converter in hard switching (HS) condition is increased from 87.2% to 95.4% thanks to proposed snubber cell. Moreover, the efficiency of converter at HS operation is estimated with ANN. For this estimation, 110 efficiency values are obtained based on the different switching frequency and the output power values. When the actual efficiency measurements and the estimation results obtained with the ANN model are compared, it is seen that the results overlap and is obtained very close result to the truth by ANN. Thus, owing to the ANN model, the semiconductor power elements will not need to be operated at high frequencies and overheating, and the damaging to the elements will be prevented. Finally, the efficiency curve measurement of the converter takes long time in the experimental study when it takes highly short time as a few minutes in the estimation with ANN.

An approximate approach for calculating the inductance coefficients of an electric circuit containing a number of branches is derived from the definition of an inductance coefficient of a single loop. An equivalent circuit is then developed to calculate the current distribution when lightning strikes a launch tower system. A numerical example is given. The computed results are consistent with the results of test measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Growing demand for more efficient power converters, corresponding with increased renewable energy generation, is necessitating high performance semiconductor power devices. Though most power devices are currently made from silicon (Si), these devices are approaching their theoretical performance limits as they suffer from high conduction and switching losses under harsh operating conditions. Wide bandgap (WBG) semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) contain superior materials allowing power devices to operate efficiently at higher blocking voltages, switching frequencies, and junction temperatures. The objective of this research is to design a highly efficient non-isolated dc-dc buck-boost converter with a hybrid Cascode GaN-FET/SiC-Schottky diode power device for residential PV applications. The performance and efficiency of the converter with this combination of power devices is compared against a common Si-MOSFET/Si-diode. The switching behavior of each device is evaluated, as well as energy loss when the switch current is increased. Total power loss and efficiency are assessed at varying switching frequencies, output power levels, and load currents. The hybrid Cascode GaN-FET/SiC-Schottky diode improves the switching performance, reduces power loss, and increases the efficiency of the buck-boost converter.

This paper presents a novel design procedure to improve the efficiency of the LLC resonant converter for photovoltaic (PV) applications. State of the art LLC resonant converter operates either in buck or boost mode by operating at a switching frequency higher or lower than the resonant frequency respectively. However, such operation of the converter at a switching frequency other than the resonant frequency may result in increased turn off losses for MOSFET, conduction losses, and hard commutation for the rectifier diodes which reduces the efficiency of the converter. In this paper, a design procedure is proposed where the converter operates very close to the resonant frequency (10% margin) in buck and boost mode of operation to improve the efficiency of the converter. The design procedure mainly involves the control of the transformer tap ratio such that the converter operates near the resonant frequency. Since the transformer tap changing control is slow in nature, the proposed control strategy is mainly suited for photovoltaic application where the input voltage to the converter does not change rapidly during the daytime. The transformer tap control is suggested based on the historical data for solar energy, i.e. recorded temperature and solar irradiance. On changing the transformer tap ratio according to the input voltage, the switching frequency is observed to be moving towards the resonant frequency of the LLC resonant converter. Simulations for both the boost and buck mode operation of the resonant tank of the converter are performed, and with the proposed control higher efficiency is achieved for PV applications.

High-step-up dc/dc converters are widely required in grid-connected applications with renewable energy sources. An extremely high-ratio step-up nonisolated dc/dc converter, in the form of a harmonics-boosted resonant converter, is proposed in this paper. This proposed converter consists of a high-frequency dc/ac inverter stage that is followed by a passive ac/dc rectifier stage connected in cascade. Conventionally, such a dc/ac inverter is designed to output a pure sinusoidal ac voltage with an amplitude several times the amplitude of the input voltage. However, for the proposed converter, the harmonics-boosted inverter stage is designed to contain selected voltage harmonics that significantly boost the amplitude of its output voltage. This greatly increases the overall gain of the converter. The adopted ac/dc stage is a diode-capacitor rectifier, which is of high efficiency and easily extendable to increase the voltage gain. Importantly, the proposed converter involves only one active switch. With only one active switch, the driver's loss is minimized and the converter's control is simplified. Zero-voltage switching is applied to reduce the switching loss, which also allows the converter to operate efficiently at high frequency, and thus can be designed for high power density. The optimal design of the two converter stages and their combined voltage gain is investigated and reported. Besides, a design guideline of the proposed converter is provided. A prototype of a 57-time harmonics-boosted resonant converter with 3.3 V input voltage, 500 kHz switching frequency, and 21 W output power, is built. The experimental result shows that the achieved converter's efficiency is as high as 88.6%.

Renewable energy sources are fluctuating depending on the availability of the energy source. For this reason, energy storage is becoming more important and bidirectional fuel cells represent an attractive technology. Fuel cells require high-current low-voltage dc-dc or dc-ac converters as power interface to the grid. In power electronics, the converter efficiency is characterized at fixed operating voltage for various output power. This type of characterization is not suitable for fuel cells, since as the power from the fuel cell increases, the cell voltage decreases. This paper analyses how the fuel cell I-V characteristics influences the power electronics converter efficiency and their consequence on the overall system. A load-dependent efficiency curve is presented based on experimental results from a 6 kW dc-dc converter prototype including the most suitable control strategy which maximizes the dc-dc conversion efficiency.

Switched reluctance generators (SRGs) are widely used in wind power generation. However, due to the natural tendency of SRG, there are always nonnegligible conflicts to achieve high efficiency and low output voltage ripple at the same time. This creates difficulties for the high-performance of SRG. Thus, a multi-objective optimization control strategy is proposed in this paper to improve the static performance of SRG. The proposed control strategy contains following steps. First, in order to gain the maximum output power range at different rotor speeds, the turn-off angle is optimized off-line by simulated annealing algorithm (SAA). The optimized results are fitted as a function of rotor speed for on-line regulating; then, a closed-loop controller is built, and the reference current is regulated according to the difference between actual output power and required output power. Second, a multi-objective function is constructed as the evaluation result of SRG performance, which takes system efficiency, output voltage ripple and power converter loss into consideration. In the end, the turn-on angle is tuned by SAA according to the real-time multi-objective evaluation result. The proposed control strategy can be flexibly applied to SRGs with different structures and avoids the disadvantage of single-objective optimization. The simulation and experiments results show that the overall performance of SRG is improved.