Fabrication of dc–dc converter using nanocrystalline Mn–Zn ferrites

Abstract

The microwave–hydrothermal method has been successfully used for synthesis of nanocrystalline Mn–Zn ferrites which are used for high frequency applications. The nanopowders were characterised using X-ray diffraction and TEM. The nanopowders were annealed using microwaves at 600°C/10 min. The frequency dependence of dielectric constant ?′ was measured in the range from 10 Hz to 1·3 GHz, and initial permeability μ _i was measured in the range from 10 Hz to 1 MHz. The total power loss was measured at 100 kHz and 200 mT on the annealed samples. Conductor embedded ferrite transformers were fabricated, and output power P _o, efficiency η and temperature increase ΔT were measured at sinusoidal voltage of 25 V with frequency 1 MHz. The transformer efficiency η was found to be high, and surface rise of temperature ΔT is very low.     

Highly efficient maximum power point tracking using DC–DC coupled inductor single-ended primary inductance converter for photovoltaic power systems

Solar photovoltaics (PVs) have nonlinear voltage–current characteristics, with a distinct maximum power point (MPP) depending on factors such as solar irradiance and operating temperature. To extract maximum power from the PV array at any environmental condition, DC–DC converters are usually used as MPP trackers. This paper presents the performance analysis of a coupled inductor single-ended primary inductance converter for maximum power point tracking (MPPT) in a PV system. A detailed model of the system has been designed and developed in MATLAB/Simulink. The performance evaluation has been conducted on the basis of stability, current ripple reduction and efficiency at different operating conditions. Simulation results show considerable ripple reduction in the input and output currents of the converter. Both the MPPT and converter efficiencies are significantly improved. The obtained simulation results validate the effectiveness and suitability of the converter model in MPPT and show reasonable agreement with the theoretical analysis.     

Interleaved soft-switched active-clamped L–L type current-fed half-bridge DC–DC converter for fuel cell applications

In this paper, an interleaved soft-switched active-clamped L–L type current-fed half-bridge isolated dc–dc converter has been proposed. The L–L type active-clamped current-fed converter is able to maintain zero-voltage switching (ZVS) of all switches for the complete operating range of wide fuel cell stack voltage variation at full load down to light load conditions. Active-clamped circuit absorbs the turn-off voltage spike across the switches. Half-bridge topology maintains higher efficiency due to lower conduction losses. Soft-switching permits higher switching frequency operation, reducing the size, weight and cost of the magnetic components. Interleaving of the two isolated converters is done using parallel input series output approach and phase-shifted modulation is adopted. It reduces the input current ripple at the fuel cell input, which is required in a fuel cell system and also reduces the output voltage ripples. In addition, the size of the magnetic/passive components, current rating of the switches and voltage ratings of the rectifier diodes are reduced.     

Online humidification diagnosis of a PEMFC using a static DC–DC converter

This paper deals with the online checking of the humidification of a Proton Exchange Membrane Fuel Cell (PEMFC). Indeed, drying or flooding can decrease the performance of the PEMFC and even lead to its destruction. An online humidification diagnosis can allow a real-time control. A good indicator of the membrane humidification state is its internal resistance. As known, the membrane ionic conductivity increases with the membrane water content. This resistance can be calculated at high frequency by dividing the voltage variation by the current variation. The proposed scheme makes use of measurements of current and voltage ripples coming from the association of a static DC–DC converter and the fuel cell. The experiment thus consists in computing the internal resistance in wet and dry conditions.     

Modeling and control of a push–pull converter for photovoltaic microinverters operating in island mode

This paper presents the modeling and control of a push–pull converter integrated into a two-stage photovoltaic microinverter operating in island mode without backup energy storage components (batteries). A push–pull small signal model is presented, from which they are derived all transfer functions needed to implement the controllers that regulate the output current, input voltage and output voltage interacting with the MPPT algorithm. A significant contribution of the paper is the proposal of an innovative control structure that simultaneously regulates in island mode both the ac voltage and the dc voltage of the panels, in order to place it in the best operation point. Such operation point is calculated by a specific control loop that interacts with the MPPT algorithm. To validate the proposed concept, simulations in PSIM™ were carried out.     

High voltage step-up integrated double Boost–Sepic DC–DC converter for fuel-cell and photovoltaic applications

In this paper, an integrated double boost SEPIC (IDBS) converter is proposed as a high step-up converter. The proposed converter utilizes a single controlled power switch and two inductors and is able to provide high voltage gain without extreme switch duty-cycle. The two inductors can be coupled into one core for reducing the input current ripple without affecting the basic DC characteristic of the converter. Moreover, the voltage stresses across all the semiconductors are less than half of the output voltage. The reduced voltage stress across the power switch enables the use of a lower voltage and R_DS-ON MOSFET switch, which will further reduce the conduction losses. Whereas, the low voltage stress across the diodes allows the use of Schottky rectifiers for alleviating the reverse-recovery current problem, leading to a further reduction in the switching and conduction losses. A detailed circuit analysis is performed to derive the design equations. A design example for a 100-W/240 V_dc with 24 V_dc input voltage is provided. The feasibility of the converter is confirmed with results obtained from simulation and an experimental prototype.     

FC/UC hybridization for dynamic loads with a novel double input DC–DC converter topology

Due to the fact that the environmental issues have become more serious recently, interest in renewable energy systems, such as, fuel-cells (FCs) has increased steadfastly. Among many types of FCs, proton exchange membrane FC (PEMFC) is one of the most promising power sources due to its advantages, such as, low operation temperature, high power density and low emission. However, using sole PEMFC for dynamic loads may not be feasible to satisfy the peak demand changes. Therefore, hybridizing PEMFC and an energy storage system (ESS) decreases the FC cost and improves its performance and life. Ultra-capacitor (UC) is the most powerful candidate to hybridize with PEMFC for dynamic loads. The DC–DC converter is the key enabling technology for hybridization of PEMFC and UC. Generally, the efficiency and performance of hybridization is largely limited by the converter topology employed for the mentioned hybridization. Integrating each source (PEMFC and UC) with a DC–DC converter is not feasible in terms of cost, performance, and control. Due to the above mentioned reasons, an attractive converter topology which can combine PEMFC and UC is strongly required. In this regard, the objective of this study is to design and simulate a novel double input DC–DC converter based on current additivity concept, in order to combine two different types of energy systems (PEMFCs and UCs).     

A high-flexibility DC load for fuel cell and solar arrays power sources based on DC–DC converters

In this paper, a flexible DC load to test and evaluate current–voltage characteristics of fuel cells stacks and photovoltaic modules based on DC–DC converters is proposed. The load features are simple structure, scalability, low cost, and its possibility to emulate an arbitrary load profile. The measure of the desired characteristics of fuel cells and photovoltaic modules further includes high speed of response and high fidelity. A comparison between conventional methods and the proposed one is also provided. Experimental results show the usefulness of the DC load proposed.     

Nonlinear stability analysis and a new design methodology for a PEM fuel cell fed DC–DC boost converter

The dynamical behaviour of a fuel cell feeding a boost converter is studied in this paper. A nonlinear model of the combined system is derived including the effect of the switching action of the converter. Using Filippov's theory, it is possible to analytically study the bifurcation patterns of the system and to demonstrate that the system loses stability through a period doubling bifurcation. To overcome this instability, we inject a high frequency sinusoidal signal into the system that forces the system to remain stable while at the same time retaining its basic slow scale properties (like the steady state error). This controller is simple to implement and does not require any special hardware. The stability analysis and new controller design method presented in this paper allow for the re-design of the converter to stabilize circuit operation with a substantially reduced inductor size, reducing the size and cost of the converter while maintaining its average currents and voltages and other circuit steady-state behaviour characteristics. The results are confirmed by using numerical and analytical tools.     

Posicast control within feedback structure for a DC–DC single ended primary inductor converter in renewable energy applications

In this paper, modeling, analysis, design, simulation and control of a single ended primary inductor converter (SEPIC) are discussed for renewable energy applications. Because the traditional control methods such as proportional–integral–derivative (PID) and classical half-cycle Posicast controllers based on feedforward are sensitive to noise and variations in natural frequency, a Posicast control with feedback structure is proposed and designed to reduce or rejection undesirable sensitivity greatly, to suppress measurement noise and to eliminate the overshoot in the output response. The SEPIC converter is modeled using average value modeling analysis. Dynamic modeling and simulation are accomplished using MATLAB Simulink? 7.2.     

A high voltage ratio and low stress DC–DC converter with reduced input current ripple for fuel cell source

A new single-switch non-isolated dc–dc converter with high-voltage gain and reduced semiconductor voltage stress is proposed in this paper. The proposed topology is derived from the conventional boost converter integrated with self-lift Sepic converter for providing high voltage gain without extreme switch duty-cycle. The reduced voltage stress across the power switch enables the use of a lower voltage and R_DS-ON MOSFET switch, which will further reduce the conduction losses. Moreover, the low voltage stress across the diodes allows the use of Schottky rectifiers for alleviating the reverse-recovery current problem, leading to a further reduction in the switching and conduction losses. Furthermore, the “near-zero” ripple current can be achieved at the input side of the converter which will help improve the fuel cell stack life cycle. The principle of operation, and theoretical are performed. Experimental results of a 100 W/240 V_dc output with 24 V_dc input voltage are provided to evaluate the performance of the proposed scheme.     

Techno-economic evaluation of off-grid hybrid photovoltaic–diesel–battery power systems for rural electrification in Saudi Arabia—A way forward for sustainable development

The burning of depleting fossil fuels for power generation has detrimental impact on human life and climate. In view of this, renewable solar energy sources are being increasingly exploited to meet the energy needs. Moreover, solar photovoltaic (PV)–diesel hybrid system technology promises lot of opportunities in remote areas which are far from utility grid and are driven by diesel generators. Integration of PV systems with the diesel plants is being disseminated worldwide to reduce diesel fuel consumption and to minimize atmospheric pollution. The Kingdom of Saudi Arabia (K.S.A.) being endowed with high intensity of solar radiation, is a prospective candidate for deployment of PV systems. Also, K.S.A. has large number of remote scattered villages. The aim of this study is to analyze solar radiation data of Rafha, K.S.A., to assess the techno-economic feasibility of hybrid PV–diesel–battery power systems to meet the load requirements of a typical remote village Rawdhat Bin Habbas (RBH) with annual electrical energy demand of 15,943 MWh. Rafha is located near RBH. The monthly average daily global solar radiation ranges from 3.04 to 7.3 kWh/m². NREL's HOMER software has been used to perform the techno-economic evaluation. The simulation results indicate that for a hybrid system composed of 2.5 MWp capacity PV system together with 4.5 MW diesel system (three 1.5 MW units) and a battery storage of 1 h of autonomy (equivalent to 1 h of average load), the PV penetration is 27%. The cost of generating energy (COE, US$/kWh) from the above hybrid system has been found to be 0.170$/kWh (assuming diesel fuel price of 0.1$/l). The study exhibits that the operational hours of diesel generators decrease with increase in PV capacity. The investigation also examines the effect of PV/battery penetration on COE, operational hours of diesel gensets. Concurrently, emphasis has been placed on: un-met load, excess electricity generation, percentage fuel savings and reduction in carbon emissions (for different scenarios such as: PV–diesel without storage, PV–diesel with storage, as compared to diesel-only situation), COE of different hybrid systems, etc. The decrease in carbon emissions by using the above hybrid system is about 24% as compared to the diesel-only scenario.     

Development of trimetallic Ni–Cu–Zn anode for low temperature solid oxide fuel cells with composite electrolyte

Trimetallic alloys of Ni_0.6Cu_0.4−xZn_x (x = 0, 0.1, 0.2, 0.3, 0.4) have been investigated as promising anode materials for low temperature solid oxide fuel cells (SOFCs) with composite electrolyte. The alloys have been obtained by reduction of Ni_0.6Cu_0.4−xZn_xO oxides, which are synthesized by using the glycine–nitrate process. Increasing the Zn content x decreases the particle sizes of the oxides at a given sintering temperature. Fuel cells have been constructed using lithiated NiO as cathode and as-prepared alloys as anodes based on the composite electrolyte. Peak power densities are observed to increase with the increasing Zn addition concentration into the anode. The maximum power density of 624 mW cm⁻² at 600 °C, 375 mW cm⁻² at 500 °C has been achieved for the fuel cell equipped with Ni_0.6Zn_0.4 anode. A.c. impedance results show that the resistances dramatically decrease with increasing temperatures under open circuit voltage state. Both cathodic and anodic interfacial polarization resistances increase with the amplitude of applied DC voltage. Possible reaction process for H₂ oxidation reaction at anode based on composite electrolyte has been proposed for the first time. The stability of the fuel cell with Ni_0.6Cu_0.2Zn_0.2 composite anode has been investigated. The results indicate that the trimetallic Ni_0.6Cu_0.4−xZn_x anodes are considerable for low temperature SOFCs.     

Development of a power management unit for small portable direct borohydride fuel cell–NiMH battery hybrid system

In this study, a small portable fuel cell/battery hybrid system has been developed. The system consists of a single portable direct borohydride/peroxide fuel cell (DBPFC), NiMH battery and power management unit (PMU). The battery has been used as a primary power source and has been discharged at constant load. When its state of charge is reduced, the DBPFC charges the battery and powers the load simultaneously. A DC–DC Boost converter has been used as a PMU. The DBPFC has provided the total power of 0.21 Wh into the system during the charge. During this experimental study fuel (NaBH₄) efficiency of 37% has been achieved in the hybrid system, while the system efficiency has been calculated as 34.5%.     

Electroplated Zn–Ni nanocrystalline alloys as an efficient electrocatalyst cathode for the generation of hydrogen fuel in acid medium

Energy conversion and renewable energy are the valuable research fields for the future of the energy. Synthesis of electroplated thin film of low cost elements and their alloys is promising nanomaterials for energy conversion. Electroplating of Zn–Ni alloys were performed using natural products such as cysteine and gluconate under direct current and ultrasound waves. The morphological and crystalline structures of the electroplated Zn–Ni alloys were examined using scanning electron microscopy, SEM, and X-ray diffraction techniques, XRD. The chemical composition of the electroplated Zn–Ni alloys was determined using energy dispersive X-ray analysis, EDX. The morphological structures of electroplated Zn–Ni alloys changed from smooth to coral reef-like and granular structures with the increase of Zn wt%. Electrocatalysis of the hydrogen evolution reaction using the electroplated Zn–Ni alloys was studied in 0.5 M H₂SO₄ medium by the cathodic polarization and electrochemical impedance spectroscopy, EIS. The electroplated Zn–9.5Ni cathode of cubic γ-brass arrangement exhibits the highest rate of hydrogen evolution reaction.     

Research of ZnMn spinel electrode material for aqueous secondary batteries

ZnMn complex oxides have been prepared by the organic acid complex method. X-ray diffraction (XRD) analyses show that the major product is a ZnMn spinel phase. The capacity of the sample is above 200 mAh g⁻¹ on cycling in aqueous LiOH electrolyte, but deep-discharge has great influence on the cycling property of the sample. XRD analysis shows that Li⁺ ions are intercalated into and extracted from the ZnMn spinel lattice during the discharge and charge process.     

Life duration of Ni–MH cells for high power applications

Intensive research and development carried out at SAFT Research [1], [2] has shown that limitation of Ni–MH battery life duration can be directly linked to AB₅ alloy corrosion in the negative electrode. A mathematical model taking into account these results has been developed in order to predict battery life as a function of the conditions of utilisation: cycle and calendar life [3].However, the degradation of the negative electrode is the consequence of two phenomena: surface corrosion of the active alloy and decrepitation of alloy particles during cycling. Up to now, only the kinetic law controlling the evolution of the thickness of the corrosion layer could have been quantified [3]. On the other hand, the kinetic law of decrepitation could not be directly measured, but is only fitted by determining the total amount of corrosion.Thus, an in situ method suitable to quantify the electrochemical surface of the alloy has been developed. Therefore, electrochemical impedance spectroscopy (EIS) has been used to follow the degradation of the negative electrode, as a function of depth of discharge (DOD) during cycling. Alloy corrosion measurements and scanning electron microscope (SEM) analyses have been performed to confirm the validity of the method. It has been found that decrepitation is nearly zero for low levels of low DOD (5%).     

Development of Ti–Cr–Mn–Fe based alloys with high hydrogen desorption pressures for hybrid hydrogen storage vessel application

Three series of Ti–Cr–Mn–Fe based alloys with high hydrogen desorption plateau pressures for hybrid hydrogen storage vessel application were prepared by induction levitation melting, as well as their crystallographic characteristics and hydrogen storage properties were investigated. The results show that all of the alloys were determined as a single phase of C14-type Laves structure. As the Fe content in the TiCr_1.9−xMn_0.1Fe_x (x = 0.4–0.6) alloys increases, the hydrogen absorption and desorption plateau pressures increase, and the hydrogen storage capacity and plateau slope factor decrease respectively. The same trends are observed when increasing the Mn content in the TiCr_1.4−yMn_yFe_0.6 (y = 0.1–0.3) alloys, except for the plateau slope factor. Compared with the stoichiometric TiCr_1.1Mn_0.3Fe_0.6 alloy, the titanium super-stoichiometric Ti_1+zCr_1.1Mn_0.3Fe_0.6 (z = 0.02, 0.04) alloys have larger hydrogen storage capacities and lower hydrogen desorption plateau pressures. Among the studied alloys, Ti_1.02Cr_1.1Mn_0.3Fe_0.6 has the best overall properties for hybrid hydrogen storage application. Its hydrogen desorption pressure at 318 K is 41.28 MPa, its hydrogen storage capacity is 1.78 wt.% and its dissociation enthalpy (ΔH_d) is 16.24 kJ/mol H₂.     

Comparison of Cu–Mn and Mn–Co spinel coatings for solid oxide fuel cell interconnects

Electrophoretic deposition (EPD) of protective coatings on solid oxide fuel cell (SOFC) interconnects is an efficient method to mitigate ‘chromium poisoning’, which is a primary reason for degradation of fuel cell performance. Cu–Mn spinels and Mn–Co spinels are the most widely used materials for such coatings. In this study, four spinel coatings were examined; CuMn₂O₄, CuNi_0.2Mn_1.8O₄, MnCo₂O₄, and MnFe_0.34Co_1.66O₄. The coatings were evaluated on multiple criteria; including phase stability, microstructural stability, conductivity, Cr gettering ability, ability to act as a diffusion barrier to outward chromium and inward oxygen diffusion, and the ability to limit the increase in the area specific resistance (ASR) during high temperature oxidation exposures. The results showed that, while different coatings have best individual characteristics, overall CuNi_0.2Mn_1.8O₄ was the best candidate for the coatings operating in the intermediate temperature range due to its best sinterability, highest conductivity, lowest ASR, phase stability over the operational temperature range, lower cost and good resistance to outward chromium and inward oxygen diffusion.