Discontinuous Mode Operation Research Articles

Outstanding productions of peroxymonosulfuric acid combining tailored electrode coating and 3D printing

In this work, the combination of a tailored design of electrode and electrochemical cell to produce peroxymonosulfuric acid (PMSA), also known as Caro's acid, is evaluated. For the electrode, a customized coating of BDD was deposited onto a niobium substrate. This electrode exhibited a good reproducibility and efficiency in the production of PMSA, thus promoting direct oxidation of sulfuric acid into Caro's acid and preventing the action of scavengers. The electrochemical cell was manufactured after the application of computer-aided design (CAD) combined with computational fluid-dynamics (CFD) simulation and 3D printing. The prototype, with an area of 25sqcm and a designed flowrate of 48 L/h, has been characterized with the evaluation of mass transfer coefficients and RDT curves, which demonstrate an outstanding performance with mass transport coefficients over 3·10−5 m s−1 without turbulence promoter. The cell equipped with the electrodes was tested in the production of Caro's acid enabling a remarkable production of 200 mM of peroxymonosulfuric acid in discontinuous operation mode with a coulombic efficiency (57.2 %) and energy Efficiency (10.67 mmolA−1 h−1). These values outperform the previous state-of-the-art works done in the field for undivided cells operated in discontinuous mode. The results obtained were successfully fitted to a phenomenological model for the generation of Caro's acid.

A Nonintrusive Digital Current Sensing Method for DC–DC Converters With Wide Load Range

Current estimators for dc-dc converters reduce the requirement of current transducers (e.g. sense resistor, Hall sensor) which may be either expensive, invasive, and (or) require additional signal conditioning circuits. High-frequency inductor currents within dc-dc converters can be estimated instantaneously using voltage measurements taken at its terminals. The voltage measurement at the switching terminal of the inductor is assisted by a comparator, whose output state is related to the corresponding voltage magnitude. This paper presents a novel unified current estimation method in which a single comparator is required to detect the switch node status both in continuous and discontinuous modes of operation. The other measurements required for this method include sensing dc voltage magnitudes, which are essential measurements for a regulated dc-dc converter system; hence the proposed methodology can be easily integrated into existing digital control schemes. The proposed approach has been applied to first-order dc-dc converters and has been validated using a laboratory prototype of a digitally controlled boost converter system using an FPGA.

A Unified Analysis of DC–DC Converters’ Current Stress

There is always a need to analyze current signals generated by various DC–DC converters. For example, to determine the current stress experienced by semiconductor devices and to evaluate active and reactive power consumption in converters. The study demonstrates that the shape of a current signal dictates the analytical expressions required to determine the average and RMS values of a signal as well as the RMS value of the ripple of that signal. The study also shows that current signals can be treated as composite waveforms comprising various combinations of trapezoidal, rectangular, and triangular pulses. The current literature lacks a unified approach to analyze current stresses in DC–DC converters. This study will propose a unified and generalized analytical technique that is applicable to any type of DC waveform that can be treated as a composite waveform made up of a combination of triangular, rectangular, or trapezoidal sections or sub-intervals. Furthermore, the rectangular and triangular pulses are shown to be a special kind of trapezoidal pulse. This provides the basis for a very broad generalization of current signals’ analysis based on the analysis of a trapezoidal pulse. Additionally, a method for the direct evaluation of signals’ ripple RMS content is developed. This is unlike in the current literature where it is necessary to evaluate the signal’s average and RMS values before ripple content can be evaluated. The technique developed is applicable to continuous and discontinuous conduction modes of operation.

Electrodialysis with Bipolar Membranes for the Sustainable Production of Chemicals from Seawater Brines at Pilot Plant Scale.

Environmental concerns regarding the disposal of seawater reverse osmosis brines require the development of new valorization strategies. Electrodialysis with bipolar membrane (EDBM) technology enables the production of acid and base from a salty waste stream. In this study, an EDBM pilot plant with a membrane area of 19.2 m2 was tested. This total membrane area results much larger (i.e., more than 16 times larger) than those reported in the literature so far for the production of HCl and NaOH aqueous solutions, starting from NaCl brines. The pilot unit was tested both in continuous and discontinuous operation modes, at different current densities (200-500 A m-2). Particularly, three different process configurations were evaluated, namely, closed-loop, feed and bleed, and fed-batch. At lower applied current density (200 A m-2), the closed-loop had a lower specific energy consumption (SEC) (1.4 kWh kg-1) and a higher current efficiency (CE) (80%). When the current density was increased (300-500 A m-2), the feed and bleed mode was more appropriate due to its low values of SEC (1.9-2.6 kWh kg-1) as well as high values of specific production (SP) (0.82-1.3 ton year-1 m-2) and current efficiency (63-67%). These results showed the effect of various process configurations on the performance of the EDBM, thereby guiding the selection of the most suitable process configuration when varying the operating conditions and representing a first important step toward the implementation of this technology at industrial scale.

Analysis and Design Considerations of a Buck-Boost Energy Recovery-Based Power Converter for SRM Drive

This article presents the development of a dynamic model and a design approach for the recently proposed buck-boost energy recovery circuit (BBERC) based power converter for a switched reluctance motor (SRM). The advantage of an increased demagnetization voltage in reducing the commutation torque ripple is analyzed using analytical and simulation-based studies. Though there have been several studies on the steady state behavior of the energy recovery stage in the literature, the dynamics of the same have never been investigated. An equation-based small signal model to describe the dynamic behavior of the energy recovery stage is proposed, which can be used to estimate the overshoots and oscillations in the inductor current and capacitor voltage during the dynamics. This article also evaluates the effects of discontinuous conduction mode (DCM) of operation of the BBERC on the drive performance, which has also not been addressed in the prior art. Furthermore, a method for the design of the energy recovery stage considering the continuous conduction of the energy recovery inductor is proposed. Additionally, the advantages of BBERC are reemphasized by comparing it with other energy recovery-based topologies such as energy efficient C-dump converter (EECDC). The analyses presented in this article are validated with experiments and simulations.

Study of subcritical water scale-up from laboratory to pilot system for brewer’s spent grain valorization

The feasibility of an industrial-scale subcritical water (SW) system by scaling up from laboratory to pilot scale in a discontinuous operation mode has been investigated regarding the valorization of brewer´s spent grain (BSG). The subcritical water treatment (SWT) of BSG at the pilot scale in a discontinuous mode at 170 °C and 22 min, resulted in the release of 56% of the total carbohydrates present in the BSG. A total pentose yield of 78% was achieved (18% as monomer and 82% as oligomer). The concentration of inhibitors in the hydrolysate was relatively low, 0.22 g/L, 0.31 g/L, and 0.13 g/L of furfural and acetic and formic acids respectively. Other high-value compounds were obtained, such as 6.5 g peptides/L (64% protein yield), 21 mg free amino acids/g protein (2.17% aa yield), and a total phenolic content (TPC) of 17.84 mg GAE/g dry BSG. In general, the results showed good reproducibility when scaling up from laboratory to pilot SW process. Good reproducibility of the scale-up was found for the release yield of arabinoxylo-oligomers, and gluco-oligomers from BSG, also for the protein yield and the release of free amino acids. However, the xylo-oligomers yield was 13% higher at the lab scale than at the pilot scale and higher concentrations of monomers and phenolic compounds were found in the SW hydrolysates obtained at the lab scale. Differences in the preheating time in both systems seem to have an effect on the hydrolysis yield of some the biopolymers. SWT modified the composition of the residual solid, as a decrease in the concentration of hemicellulose and an increase in the glucan content was observed, which may enhance the digestibility of the solid improving a further enzymatic release of glucose from the remaining solid. • Subcritical water treatment allows an integral valorization of brewer´s spent grain. • Structural components were recovered as peptides and oligomers by subcritical water. • The protein and amino acids yields were similar at lab- and pilot- scales. • The sum of carbohydrates released as oligomers were similar at both scales. • Heating rate greatly affected the monosaccharides yield and TPC in the hydrolysates.

A Novel Single Phase Grid Connected Transformer-Less Solar Micro-Inverter Topology With Power Decoupling Capability

A novel transformer-less micro-inverter topology suitable for interfacing a 35 V, 220 W solar PV module to a single phase 220–230 V ac grid is proposed in this paper. It employs only six switches, out of which two switches operate at high frequency, three at line frequency and one switch at high frequency during the negative half cycle of the grid voltage. The micro-inverter is operated in discontinuous conduction mode of operation for all possible operating conditions to achieve high gain as well as negligible turn on losses for the high frequency switches. In this topology the negative terminal of the PV module is shorted with the grid neutral which makes the magnitude of the leakage current flow to be zero. The power decoupling between the dc and ac sides is inherent in this topology, and it is achieved without incorporating any active power decoupling circuit. Thin film capacitors are utilized to improve the reliability of the micro-inverter. The detailed analyses of the proposed micro-inverter are carried out. The effectiveness of the proposed scheme is verified by performing detailed simulation studies. A 220 W laboratory prototype of the proposed micro-inverter is fabricated, and detailed experimental studies are carried out to confirm the viability of the proposed scheme.

Non-Inverting Quadratic Buck–Boost Converter with Common Ground Configuration for Supercapacitor Applications

This article presents a novel buck–boost converter-based topology suitable for supercapacitors and grid-connected solar PV system applications. The proposed converter can handle a wide range of voltage variations at the input side, making it ideal for extracting most of the energy from supercapacitors or a solar PV system connected to the input side of the converter. The output voltage of the converter is non-inverting which makes the control easier. The design of passive components, continuous mode operation, and discontinuous mode operation are all thoroughly discussed. A low-power hardware prototype of three hundred watts is developed and tested in the laboratory to validate the theoretical aspects of the converter.

New Multi-Leg Converter for DC Microgrid with Two Duty Cycles

In recent times, important contributions and the incorporation of renewable sources, such as photovoltaic, fuel cells, etc., are the main reasons for the popularity of DC microgrids. Integrating renewable sources into the microgrid requires high-voltage, high-efficiency DC-to-DC converters. Without modification, traditional converters are not suitable for achieving the required voltage in microgrid applications, due to the requirement for a large duty cycle, inductor resistance, voltage rating of switches, reverse recovery of the diode, high current rating inductors, etc. Various converters based on the circuitry of voltage multipliers, switched inductors/capacitors, coupled inductors, transformers, etc., have been proposed in the literature and have their drawbacks. In this paper, to realize significant voltage gain with two duty cycle controls, a new multi-leg (ML) converter is recommended as a solution for use in DC microgrids. The converter is designed by incorporating multiple legs into the boost converter. The implications of the proposed converter are reduced device voltage stress, small inductors and capacitors, two-duty cycle control, triple mode operation, single-stage conversion, etc. The proposed converter’s power circuits, mode of operation, and design equations of the converter are presented. The non-ideal model of the proposed converter is discussed, and efficiency is analyzed. The effect of unequal insurance on the operation of the converter is discussed. Comparative studies of converters are provided to draw attention to the benefits of the converter. The results of the experiments are shown to prove that the analysis and performance of the converter are correct. The discontinuous mode of operation and unequal inductance case of the converter are studied with the help of a simulation model.

Power Management Unit for Solar Energy Harvester Assisted Batteryless Wireless Sensor Node

This work describes an energy-efficient monolithic Power Management Unit (PMU) that includes a charge pump adapted to photovoltaic cells with the capability of charging a large supply capacitor and managing the stored energy efficiently to provide the required supply voltage and power to low energy consumption wireless sensor nodes such as RFID sensor tags. The proposed system starts-up self-sufficiently with a light source luminosity equal to or higher than 500 lux using only a 1.42 cm2 solar cell and integrating an energy monitor that gives the ability to supply autonomous sensor nodes with discontinuous operation modes. The system occupies an area of 0.97 mm2 with a standard 180 nm CMOS technology. The half-floating architecture avoids losses of charging the top/button plate of the stray capacitors in each clock cycle. Measurements’ results on a fabricated IC exhibit an efficiency above 60% delivering 13.14 W over 1.8 V. The harvested energy is enough to reach the communication range of a standard UHF RFID sensor tag up to 21 m.

Modified High Gain DC-DC Converter with APICs for Microgrid

This paper proposes a nonisolated high voltage gain DC-DC converter. The active–passive inductor cells (APICs) makes the converter topology expandable, and it also helps in providing a high gain quality at lower duty cycles. The proposed converter is suitable for high gain applications mainly necessitating microgrid as well as integration of renewable energy sources into the existing grid infrastructure. The merits of the converter can be attributed to the ability to achieve high gain and low current stress and switching losses on power electronic switches. The proposed converter is analyzed in both continuous and discontinuous modes of operation, the efficiency is calculated and simulation results substantiate the operation of the converter.

An Isolated Multilevel DC–DC Converter Topology With Hybrid Resonant Switching for EV Fast Charging Application

This article proposes a multilevel dc–dc converter topology for fast charging of electric and plug-in hybrid electric vehicles (EVs and PHEVs). The proposed dc–dc converter topology converts the front end ac–dc converter output and provides regulated supply to the EV propulsion battery. The proposed topology consists of full-bridge converter at the primary, while the secondary side consists of voltage doubler rectifier units and combination of diodes and <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> for reconfiguration of the voltage doubler rectifiers to generate the multilevel voltage. The multilevel voltage at the output helps in reducing the output filter size and increases the power density of the converter. The topology utilizes the resonance between leakage inductor of high frequency transformer, parasitic output capacitors of full-bridge <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s and voltage doubler capacitors to achieve soft switching (ZVS turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> ) for all the full-bridge devices and soft turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> for the rectifier diodes. The load limited ZVS turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> capability of conventional full-bridge topologies is mitigated through the use of resonance between magnetizing inductance of transformer and <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> output capacitors. The converter is designed for 650 V dc bus input and 200–400 V EV battery output at 100 kW rated charging power. The analysis of the proposed converter in continuous and discontinuous modes of operation, soft switching operation, and the component design guidelines are presented in this article. The proposed converter is validated through detailed PLECS simulation results for 100 kW charging power. Experimental results from laboratory prototype of 500 W power are also presented to validate the design methodology and converter performance.

Electrochemical production of extremely high concentrations of hydrogen peroxide in discontinuous processes

This work reports the development and application of a gas diffusion electrode based on Printex L6 carbon for the production of high concentrations of hydrogen peroxide (H2O2) using a flow-by electrochemical reactor in discontinuous operation mode. With the application of current densities ranging between 75 and 200 mA cm−2, the use of Printex L6 carbon-based GDE generated H2O2 concentrations in the range of 4,000–5,000 mg/L, despite the formation of scavengers. The proposed technique also promoted the production of ozone and persulfate species though at low concentrations. The application of the Printex L6 carbon-based GDE led to a roughly 3.4–3.9-fold increase in H2O2 concentrations ​​compared to Vulcan XC-72R carbon-based GDE which was used for comparison purposes (Vulcan XC-72R carbon is currently-one of the most widely employed carbon materials in electrochemical processes). In addition, the Printex L6 carbon-based GDE exhibited high stability with a lifetime of 36 Ah (7,5 days) of uninterrupted use at 200 mA cm−2. The improvements observed in the Printex L6 carbon-based GDE can be attributed to the presence of higher amounts of carboxyl oxygenated functional groups in the material and its greater electrochemically active surface area compared to the Vulcan XC-72R-based GDE.

Design of Modified Luo Converter for Electric Vehicle Battery Charger

Higher energy and battery efficiency are now major concerns for Electric Vehicle (EV) manufacturers and consumers. The main component of the two-stage EV on-board charger is the DC-DC converter. The phase displacement of full-bridge to operate the switch at either zero voltage or zero current in a power switch DC-DC converter, currently has issues such as voltage variation on the consequent side, which is secondary of the transformer, and it implies poor performances. Power Factor Correction (PFC) converters used in modern EV chargers achieve high performance and adequacy throughout charging. A modified luo converter is designed to achieve high efficiency in EV charging. A luo converter is a type of PFC that is commonly used as a converter of DC to DC with improved voltage regulation in the presence of rapidly changing line voltages. In this aimed work, a reformed separate Luo converter-based electric vehicle charger is developed. To suppress voltage oscillations, two devices which means switches and two clipping diodes are connected at the elementary side in the detachment of High Frequency Transformer (HFT). The Luo converter handles Discontinuous Conduction Mode (DCM) of operation, decreases control complexity, and keeps converter's output constant. In the feedback system, the Constant Current and Constant Voltage (CC-CV) mode technique is used in conjunction with the PI controller to improve competence and reduce transmission leakage. The proposed system's performance is evaluated by applying in MATLAB/SIMULINK software, and the outcomes are promising.

Low Frequency Operation and dsPIC Micro-controller Implementation for Multilevel Quasi Z Source Inverter in Photovoltaic Application

In this paper implementation of a micro-controller based pulse width modulation for multilevel quasi Z source inverter (qZSI) is presented. First implementation of component design of qZSI is taken into consideration with continuous and discontinuous operation mode. In this paper operation of multilevel qZSI with low switching frequency is presented. After this detailed modelling for qZSI is established for implementing of PIC microcontroller (PIC 16F877A) to generate the switching signals. Development ofa five-level quasi z-source inverter prototype is done and by proper adjustment of the shoot through (ST) switching state and non-shoot through (NST) switching state the control signal to the gate drivers is applied. Effective implementation of the proposed scheme is shown by the hardware result.

Prediction of long-term extreme response of two-rotor floating wind turbine concept using the modified environmental contour method

The modified environmental contour method (MECM) is assessed for the prediction of 50-year extreme response of a two-rotor floating wind turbine concept (2WT) deployed in two offshore sites in the northern North Sea (Norway 5) and the North Atlantic Ocean (Buoy Cabo Silleiro). The sites considered are in areas known for their floating wind development potential. The environmental contour method (ECM) is used to reduce the computational effort of full long-term analysis (FLTA) by only considering environmental conditions associated with a given return period. MECM is a modification of the ECM where additional environmental contours are included to account for discontinuous operation modes of dynamic structures. The results obtained in MECM are benchmarked against FLTA results and compared to ECM results. ECM leads to large underpredictions of responses governed by wind loads if compared to FLTA, as it is not capable of taking into account important operational modes of the 2WT. It is found that MECM, which includes the wind turbines cut-off contour, is able to reduce most response underpredictions within 15% difference compared to FLTA results. MECM may thus be considered as a sufficiently accurate and computationally efficient method for the long-term extreme analysis of 2WT concepts.

Smart Efficiency Tracking for Novel Switch—LLC Converter for Battery Charging Applications

In this study, a novel smart efficiency tracking (SET) algorithm for GaN-based LLC resonant converter for quick battery charging of light electric vehicles is proposed. Conventional frequency modulation (FM) method, single pulse width modulation method (S-PWM) and discontinuous operation mode method (DOM) are used to track the converter efficiency which varies for different loading conditions during the battery charging process. First, the charging modes are explained to define the efficiency variation clearly. Then, the theoretical background of GaN-based LLC resonant converter is presented and the details of design study are given. Third, the principles of three different switching control strategies, the modeling study and the simulation results are put forward. Finally, the details of the implementation of three different switching strategies are presented for the validation of the study. Furthermore, the implementation of the design and its impact on battery charging are discussed. The proposed efficiency tracking method is validated with a 20% efficiency increase for the low loading conditions of GaN-based LLC converter.

Design of New High Step-Up DC-DC Converter Topology for Solar PV Applications

A new topology for high step-up nonisolated DC-DC converter for solar PV applications is presented in this paper. The proposed high-voltage gain converter topology has many advantages like low-voltage stress on the switches, high gain with low duty ratio, and a continuous input current. The analytical waveforms of the proposed converter are presented in continuous and discontinuous modes of operation. Voltage stress analysis is conducted. The voltage gain and efficiency of the converter in presence of parasitic elements are also derived. Performance comparison of the proposed high-gain converter topology with the recently reported high-gain converter topologies is presented. Validation of theoretical analysis is done through the test results obtained from the simulation of the proposed converter. For the maximum duty ratio of 80%, the output voltage of 670 V is observed, and the voltage gain obtained is 14. Comparison of theoretical and simulation results is presented which validates the performance of the proposed converter.

High Bandwidth Inductor Current Estimator for Digitally Controlled DC–DC Converters for Light Load Applications

This article presents a digital current estimator designed for switching converters operating under light load conditions. The proposed technique can estimate the inductor current for continuous and discontinuous conduction modes of operation with independent gain control for average and ripple components. The impact of inductor parameter tolerance, MOSFET ON-state resistance, and diode forward voltage drop on the estimation are analyzed. The theory of estimation and its implementation on field programmable gate array is detailed. The proposed theory is validated experimentally on a buck converter prototype with an accuracy of 5% on average and 1% on the ripple component. The applicability of the estimation method is verified on a digital current hysteresis-controlled buck converter and unity power factor boost rectifier.

SEPIC converter in discontinuous conduction mode: Small signal modeling and analysis

AbstractIn this article, a new approach is applied to solve the small signal state space average (SSA) model for pulse width modulated (PWM) single ended primary inductor converter (SEPIC) under discontinuous conduction mode (DCM) of operation. Authors proposed a novel approach to get duty ratio constrains that is based on variation of current in inductor. The approach used a unique correction matrix (M) in the modeling process and obtained better results for DCM. To demonstrate the whole technique, the SEPIC‐based power supply of 75 W is designed and system loop gain is derived with the help of this new technique. The frequency response of the proposed system is captured with the help of linearization technique using MATLAB Simulink platform. The frequency plot from the proposed techniques is much closer to simulation results as compared to conventional method. This claims high predictions for dc–dc converter operating in DCM with wide range of input supply. The proposed model is analyzed with previous SSA small signal modeling for comparative results on the basis of frequency analysis and stability. The experiment results of designed power supply have shown good power quality performance at 220‐V AC mains for light‐emitting diode (LED) lighting application.