Discontinuous Mode Operation Research Articles

Analysis, Design, and Implementation of a Single-Phase Power-Factor Corrected AC-DC Zeta Converter with High Frequency Isolation

This paper deals with the analysis, design, and implementation of a single phase AC-DC Zeta converter with high frequency transformer isolation and power factor correction(PFC) in two modes of operation, discontinuous current mode of operation(DCM), and continuous current mode of operation(CCM). A Digital Signal Processor(DSP) based implementation is carried out for validation of the Zeta converter developed design in discontinuous mode of operation. A comparison of both modes of operation is presented for a 1kW power rating from the point of view of steady state and dynamic behavior, power quality, simplicity, control technique, device rating, and converter size. The experimental results of a developed prototype of Zeta converter are presented for validation of the developed design. It is observed that CCM is most suitable for higher power applications where it requires some complex control and sensing of the additional variables.

A Hybrid Control Algorithm for Voltage Regulation in DC–DC Boost Converter

A new switching control algorithm based on state trajectory approximation is proposed to regulate the output voltage of a representative second-order DC-DC converter - the boost converter. The essence of the proposed algorithm is to trap the system into a stable limit cycle while ensuring the required voltage regulation. Unlike some of the earlier algorithms, the concept is applicable to both continuous and discontinuous current modes of operation, making it viable over a wide operating range under various load and line disturbances. A hybrid-automaton representation of the converter is used to perform the analysis, and the control problem is simplified to a guard-selection problem. Guard conditions, governing the transition of the converter operation from one discrete state to the other in a hybrid-automaton representation, are derived. The hybrid-automaton-based control system is implemented by using the state flow chart feature of MATLAB, and extensive simulations are carried out to check the suitability of the algorithm. The hybrid control law is also validated in real time by using a laboratory prototype. The experimental and simulation results prove the effectiveness of the proposed control law under varying line and load conditions.

A Photocatalytic Active Adsorbent for Gas Cleaning in a Fixed Bed Reactor

Efficient photocatalysis for gas cleaning purposes requires a large accessible, illuminated active surface in a simple and compact reactor. Conventional concepts use powdered catalysts, which are nontransparent. Hence a uniform distribution of light is difficult to be attained. Our approach is based on a coarse granular, UV-A light transparent, and highly porous adsorbent that can be used in a simple fixed bed reactor. A novel sol-gel process with rapid micro mixing is used to coat a porous silica substrate withTiO2-based nanoparticles. The resulting material posses a high adsorption capacity and a photocatalytic activity under UV-A illumination (PCAA = photocatalytic active adsorbent). Its photocatalytic performance was studied on the oxidation of trichloroethylene (TCE) in a fixed bed reactor setup in continuous and discontinuous operation modes. Continuous operation resulted in a higher conversion rate due to less slip while discontinuous operation is superior for a total oxidation toCO2due to a user-defined longer residence time.

Contribution of pH dependent osmotic pressure to amino acid transport through nanofiltration membranes

A concept is presented to determine the osmotic pressure of amino acid solutions by altering the stoichiometric coefficient of the van’t Hoff law corresponding to the dissociation state of the amino acids. The osmotic pressure is greatly affected by the feed pH, which significance has been overseen in membrane permeation studies. Nanofiltration experiments were carried out in order to investigate the effect of osmotic pressure on the permeation of amino acids through polymeric membrane. l-Alanine aqueous solutions of various feed pH (6.0, 9.7 and 11.1) were concentrated in discontinuous operation mode with complete retentate recycle. It has been stated by many authors, that polymeric nanofiltration membranes possess higher rejection for amino acids in negatively charged form than for zwitterions. In our study we demonstrate that this tendency can be reversed in higher concentration range.

Numerical analysis and experimental validation of heat transfer in ground heat exchangers in alternative operation modes

A finite element numerical model has been developed for the simulation of the ground heat exchangers (GHEs) in alternative operation modes over a short time period for ground-coupled heat pump applications. Comparisons between the numerical and analytical results show that the finite line-source model is not capable of modeling the GHEs within a few hours because of the line-source assumption. On the other hand, the experiments with respect to the alternative cooling and heating modes have been undertaken during a short-time period. The comparisons show a reasonable agreement between the numerical and the measured data. The results illustrate that the finite element numerical model can be used to simulate the heat transfer behavior of the GHEs in short time scales instead of the typical finite line-source model. Finally, the variation of the U-tube pipe wall temperatures demonstrates that the discontinuous operation mode and the alternative cooling/heating modes can effectively alleviate the heat buildup in the surrounding soil.

Ultra-low-power components for an RFID Tag with physical and chemical sensors

In this work the development and optimization of the main components for a multisensing flexible Tag with RFID communication capabilities and integrated physical and chemical sensors for logistic datalogging applications will be reported. For this specific scenario, several constraints must be considered: power consumption must be limited for long-term operation, reliable ISO compliant RFID communication must be implemented, and special encapsulation issues must be faced for reliable sensor integration. In this work, the developments on application specific electronic interfaces and on ultra-low-power Metal OXdide semiconductor (MOX) gas sensors will be reported. The electronics for sensor control and readout as well as for RFID communication are based on an ultra-low-power MSP430 microcontroller from Texas Instruments together with a custom RFID front-end based on analog circuitry and a CPLD digital device, and are designed to guarantee a passive ISO15693 compliant RFID communication in a range up to 6 cm. A thin film battery for sensor operation is included, thus data acquisition and storage can be accomplished when no reader field is present. This design allows the user to access both the traceability and sensor information even when the on-board battery is exhausted. The physical sensors for light, temperature and humidity are commercially available devices, while for chemical gas sensing innovative MOX sensors are developed, based on ultra-low-power micromachined hotplate arrays specifically designed for flexible Tag integration purposes. A single MOX sensor requires only 8.9 mW for continuous operation, while temperature modulation and discontinuous sensor operation modes are implemented to further reduce the overall power consumption. The development of the custom control and RFID front-end electronics, together with innovative ultra-low-power MOX sensor arrays with flexible circuit encapsulation techniques will be described.

Incompleteness of bifurcation diagram in predicting the behaviour of Ćuk converter in discontinuous conduction mode

AbstractThe bifurcation phenomena have been studied in current mode‐controlled Ćuk converter considering continuous conduction as well as discontinuous conduction mode of operation. Some peculiarities have been observed in discontinuous conduction mode, which indicate some incompleteness of the bifurcation diagrams in providing details of the system behaviour. Copyright © 2007 John Wiley & Sons, Ltd.

AC-DC Cuk Converter for Power Quality Improvement of Vector Controlled PMSM Drive

This paper deals with the analysis, design and digital signal processor (DSP) based hardware implementation of a high frequency isolated AC-DC Cuk converter in discontinuous current mode (DCM) of operation used for power quality improvement at AC mains in vector controlled permanent magnet synchronous motor (PMSM) drive. The design of the Cuk converter is presented to feed the voltage source inverter (VSI) of a vector controlled PMSM drive system. Modeling and simulation is carried out in a standard PSIM software environment. Test results are obtained on DSP based hardware implemented AC-DC Cuk converter fed PMSM drive to demonstrate the improvement in the power quality at AC mains.

Comparison of the Aluminum Speciation in Chemical and Electrochemical Dosing Processes

The aim of this work is to study the differences between the hydrolyzing aluminum species formed in an aqueous solution when the aluminum is added by aluminum salt solution dosing and when it is supplied by electrodissolution. The dosing of aluminum is the first step in the coagulation processes, and it marks the more important differences between the coagulation and the electrocoagulation processes. It has been found that the speciation of aluminum in an aqueous solution does not depend directly on the dosing technology, but on the total concentration of aluminum and pH. This latter parameter changes in different ways for the solution dosing and the electrochemical dosing technologies, and this can be the main difference between both technologies: the pH value increases during the electrochemical process and decreases during the solution dosing process. In continuously operated processes, and feeding the solution dosing and the electrochemical dosing processes with solutions at different pHs (with the aim to obtain the same pH at the steady state), the results obtained in the speciation were nearly the same. More significant differences have been obtained in the comparison of the dosing processes for the discontinuous operation mode as it is impossible to maintain both the aluminum concentration and the pH at the same value. In the acidic range of pHs, the predominant species are the monomeric cationic hydroxoaluminum species. Increases in the pH lead to the coexistence of these monomeric species with increasing amounts of polymeric cations and precipitates. Under pHs close to neutrality, the predominant species are the aluminum hydroxide precipitates, and increases in the pH lead to the dissolution of the precipitates to form monomeric anionic hydroxoaluminum, which is the predominant species at alkaline pHs. The formation of precipitates is promoted in solutions containing sulfates. The ζ potential has been found to give important information and to depend mainly on the pH: pHs below 8 lead to positive values of the ζ potential, while higher values of pH cause negative ζ potentials. This behavior has been explained in terms of the formation of particles of aluminum hydroxide precipitate and of the adsorption of ionic species on their surface.

Break-up of oil-in-water emulsions by electrochemical techniques

Electrochemically-assisted technologies can be successfully applied to the treatment of oil-in-water (O/W) emulsions. In this work, it is studied the influence of the main parameters (electrical charge passed, pH, electrolyte, oil content and operation mode) in the efficiency of these processes, when aluminium electrodes are used. The pH was found to be the most significant parameter, and good removal efficiencies were only obtained for pHs in the range 5–9. The electrical charge passed was observed to be directly related to the aluminium supplied to the waste. For a given oil concentration it is required that a minimum electrical charge is passed to break-up the emulsion. Further increases in the electrical charge lead to increase in the COD removal. The influence of the oil concentration is related to that of the electrical charge passed: for a given dose of aluminium, the higher the oil content the lower the COD-removal efficiency. Likewise, to produce the break-up of the emulsion it is required a minimum dose of aluminium (electrical charge passed), lower doses do not attain the rupture of the emulsion. The type of electrolyte and its concentration were also found to influence the process efficiency. Better efficiencies were obtained in the treatment of chloride-containing wastes and for low concentration of electrolyte. The destabilization of the O/W emulsion was found to be favoured in the discontinuous operation mode. Bridging flocculation is a primary destabilization mechanism that can explain the experimental results obtained in this work.

β-Galactosidase from Talaromyces thermophilus immobilized on to Eupergit C for production of galacto-oligosaccharides during lactose hydrolysis in batch and packed-bed reactor

The b-galactosidase from Talaromyces thermophilus CBS 236.58 immobilized onto Eupergit C produced galacto-oligosaccharides (GalOS) in batch- wise and continuous packed-bed mode of operation. A maximum yield of GalOS of 12, 39 and 80 g l -1 was obtained for initial lactose concentrations of 50, 100 and 200 g l -1 , respectively, for batch conversion experiments. The immobilized enzyme could be re-used for several cycles for lactose hydrolysis and transformation. The maximum GalOS concentration of approximately 50 g l -1 was obtained with the dilution rate of 0.375 h -1 in a packed-bed reactor, when using an initial lactose concentration of 200 g l -1 . Continuous conversion of lactose in the packed-bed reactor resulted in the formation of relatively more trisaccha- rides than when employing the immobilized enzyme in discontinuous mode of operation.

Electrochemical treatment of the effluent of a fine chemical manufacturing plant

In this work, the electrochemical oxidation of an actual industrial wastewater with conductive-diamond anodes has been studied. The wastewater is the effluent of a fine chemicals plant. This effluent consists of an aqueous solution of solvents (ketones and alcohols) with a high concentration of aromatic compounds coming from the raw materials, intermediates and products of the different processes of the plant and its COD is around 6000 mg dm −3. The electrolyses were carried out in a discontinuous operation mode under galvanostatic conditions, using a bench-scale plant equipped with a single compartment electrochemical flow cell. The conductive-diamond electrochemical oxidation (CDEO) allowed achieving the complete mineralization of the waste with high current efficiencies. These efficiencies seem to strongly depend on the concentration, pH and temperature but not on the current density (in the range studied). This confirms that besides the hydroxyl radicals mediated oxidation, CDEO combines other important oxidation processes such as the direct electrooxidation on the diamond surface and the oxidation mediated by other electrochemically formed compounds generated on this electrode. Other two advanced oxidation processes (ozonation and Fenton oxidation) have been also studied in this work for comparison purposes. Both technologies were able to treat the wastes, but they obtained very different results in terms of efficiency and mineralization. The efficiency of ozonation and electrochemical oxidation were very similar (especially during the first stages), although the energy consumption required by the electrochemical process to remove at fixed percentage of COD or TOC was significantly smaller than that of ozonation. The possible accumulation of carboxylic acid as final products excludes the use of Fenton oxidation as a sole treatment technology.

Unified average and small-signal modeling of direct-on-time control

A unified and consistent method for the average and small-signal modeling of switched-mode converters under direct-on-time (DOT) or voltage mode (VM) control applicable to fixed- and variable-frequency operation in discontinuous (DCM) and continuous (CCM) modes of operation is proposed. The method is based on the direct estimation of the state-variable derivatives using their physical and circuit theoretical dependence on the corresponding circuit elements. This has been the first time that it has been explicitly recognized that the time-varying local average value of the inductor current is the state variable instead of the instantaneous current being also continuous within a cycle regardless of the operation mode. The method provides a common basis for the average modeling of VM control and leads eventually to the well-recognized results obtained using state-space averaging (SSA) in CCM or its modified version in DCM under fixed-frequency operation as well as accurate full-order models also in the variable-frequency operation. In addition, the method known as unterminated modeling is introduced, providing a useful tool for the dynamic analysis of switched-mode converters.

Analysis and design of single-phase power factor-corrected AC DC Cuk converter with high-frequency isolation

In this paper, an analysis and design of a high-frequency transformer isolated single-phase buck-boost AC–DC Cuk converter is presented for both discontinuous and continuous conduction modes (DCM and CCM) of operation. Both modes of operation are considered for the design of 2.6-kW rating with high-level steady-state and dynamic performance. A comparative analysis of Cuk converter is also presented in both modes of operation of DCM and CCM from point of view of steady-state and dynamic behaviour, power quality, simplicity, control technique, device rating and converter size. It is observed that CCM is most suitable for higher power applications in which it requires a little complex control and sensing the additional variables.

05/02800 Isolation and determination of cultural characteristics of a new highly CO 2 tolerant fresh water microalgae

This paper studies the synthesis of structured triacylglycerols (STAGs), rich in polyunsaturated fatty acids (PUFAs) by a two-step enzymatic process: (i) alcoholysis of fish oils (cod liver and tuna oils) with ethanol to obtain 2-monoacylglycerols (2-MAGs), catalyzed by 1,3 specific lipases and (ii) esterification of these 2-MAGs with caprylic acid (CA, 8:0), also catalyzed by a 1,3 specific lipase, to produce STAGs of structure CA–PUFA–CA. As regards the alcoholysis reaction, three factors have been studied: the influence of the type of lipase used (lipase D from Rhizopus oryzae, immobilized on Accurel MP1000, and Novozym 435 from Candida antarctica), the operational mode of a stirred tank reactor (STR operating in discontinuous and continuous mode) and the intensity of treatment (IOT = lipase amount × reaction time/oil amount). Although higher 2-MAG yields were obtained with lipase D, Novozym 435 was selected due to its greater stability in the operational conditions. The highest 2-MAG yield (63%) was attained in the STR operating in discontinuous mode at an IOT of 1 g lipase × h g oil−1 (at higher IOT the 2-MAGs were degraded to glycerol). This system was scaled up to 100 times the initial volume, achieving a similar yield (65%) at the same IOT. The 2-MAGs in the final alcoholysis reaction mixture were separated from ethyl esters by solvent extraction using solvents of low toxicity (ethanol and hexane); the 2-MAG recovery yield was over 90% and the purity was approximately 87–90%. Regarding the esterification of the 2-MAGs, the following factors were studied: the influence of the lipase type used, the presence or absence of solvent (hexane) and the reaction time or intensity of treatment (IOT = lipase amount × reaction time/2-MAG amount). Of the five lipases tested, the highest STAG percentages (over 90%) were attained with lipases D and DF, immobilized on Accurel MP1000. These STAGs contain 64% CA, of which 98% is at positions 1 and 3. Position 2 contains 5% CA and 45% PUFAs, which means that all the PUFAs that were located at position 2 in the original oil remain in that position in the final STAGs. The lipase D immobilized on Accurel MP1000 is stable in the operational conditions used in the esterification reaction. Finally the purification of STAGs was carried out by neutralization of free fatty acids with hydroethanolic solution of KOH and extraction of STAGs with hexane. By this method purity was over 95% and separation yields were about 80%.

Bioslurry phase degradation of di-ethyl phthalate (DEP) contaminated soil in periodic discontinuous mode operation: Influence of bioaugmentation and substrate partition

The degradation of DEP contaminated soil was studied in the soil slurry phase sequencing batch reactor (SS-SBR). Experiments were conducted for studying the degradation of DEP using four different reactors. Effect of bioaugmentation using ETP microflora on the degradation of DEP was also investigated and found an enhanced degradation. The reactors were operated with a total cycle period of 48 h, comprising one and half hours of fill 45 h of react and one and half hours of decant phases. The metabolites for the DEP degradation in slurry phase have been identified. During the operation of bioaugmented reactor, the substrate partition data showed higher desorption of DEP from soil phase to aqueous phase compared to other reactors studied. The degradation of DEP in the slurry phase confirmed to zero order kinetic equation in bioaugmented reactor. The half life period of DEP degradation in the soil phase of bioaugmented reactor was 19 days. Process performance during the investigation was monitored by determining dissolved oxygen (DO), pH, oxygen consumption rate (OCR) and substrate concentration by high performance liquid chromatography (HPLC).

Variable-Frequency Predictive Digital Current Mode Control

A variable-frequency predictive digital control method for the inductor current in switched-mode converters is introduced in this letter. This method is predictive in nature because the transistor off-time required for achieving the target current is calculated ahead of time. The transistor on-time is kept constant, which results in variable switching frequency. The control laws for continuous and discontinuous modes of operation of the three basic converters are derived. Stability and robustness criteria are presented. The variable-frequency predictive control obviates the need for current-loop compensation and has the advantages of single-cycle response and relatively simple implementation. The control method is demonstrated in a digital signal processor (DSP) for a boost power factor corrector (PFC), which shows excellent current tracking and a very low harmonic distortion of the line current.

Production of structured lipids by acidolysis of an EPA-enriched fish oil and caprylic acid in a packed bed reactor: analysis of three different operation modes.

Structured triacylglycerols (ST) enriched in eicosapentaenoic acid (EPA) in position 2 of the triacylglycerol (TAG) backbone were synthesized by acidolysis of a commercially available EPA-rich oil (EPAX4510, 40% EPA) and caprylic acid (CA), catalyzed by the 1,3-specific immobilized lipase Lipozyme IM. The reaction was carried out in a packed bed reactor (PBR) operating in two ways: (1) by recirculating the reaction mixture from the exit of the bed to the substrate reservoir (discontinuous mode) and (2) in continuous mode, directing the product mixture leaving the PBR to a product reservoir. By operating in these two ways and using a simple kinetic model, representative values for the apparent kinetic constants (kX) for each fatty acid (native, Li or odd, M) were obtained. The kinetic model assumes that the rate of incorporation of a fatty acid into TAG per amount of enzyme, rX (mole/(h g lipase)) is proportional to the extent of the deviation from the equilibrium for each fatty acid (i.e., the difference of concentration between the fatty acid in the triacylglycerol and the concentration of the same fatty acid in the triacylglycerol once the equilibrium of the acidolysis reaction is reached). The model allows comparing the two operating modes through the processing intensity, defined as mLt/(V[TG]0) and mL/(q[TG]0), for the discontinuous and continuous operation modes, respectively. In discontinuous mode, ST with 59.5% CA and 9.6% EPA were obtained. In contrast, a ST with 51% CA and 19.6% EPA were obtained when using the continuous operation mode. To enhance the CA incorporation when operating in continuous mode, a two-step acidolysis reaction was performed (third operation mode). This continuous two-step process yields a ST with a 64% CA and a 15% EPA. Finally, after purifying the above ST in a preparative silica gel column, impregnated with boric acid, a ST with 66.9% CA and 19.6% EPA was obtained. The analysis by reverse phase and Ag+ liquid chromatography of the EPA-enriched ST demonstrated that the CA was placed in positions 1 and 3 and the EPA was occupying position 2 of the final ST.

The Double Discontinuous Mode Operation of a Converter: A Method for Soft Switching

This paper describes a way of ensuring soft switching in a converter without using additional components. This method is called double discontinuous mode (DDM). In particular, it permits any free wheeling diode to switch off at zero current, and for transistors to switch on at zero current and to switch off at zero voltage. The method illustrated here refers to a buck, but this concept may be applied to any type of converter, with or without transformer. Various mathematical models of this method are developed, and its characteristics and fields of application highlighted in this paper.

A single-reset-integrator-based implementation of line-current-shaping controller for high-power-factor operation of flyback rectifier

The objective of this paper is to present a simple yet accurate implementation of a resistor-emulator-type line-current-shaping controller for high-power-factor operation of a flyback rectifier. The important feature is that input voltage sensing is not required. In the circuit realization of the controller, no multiplier is used. Current shaping is performed directly on the input filter inductor current. The modulator uses only one reset integrator for the generation of duty ratio. The analysis presented in this paper shows the effect of input filter capacitance on discontinuous conduction mode of operation of the flyback inductor. Design equations for selection of the input filter components are derived. A low-frequency small-signal model of the rectifier is developed and verified by measurement up to 1 kHz. The performance of the controller is first tested by the SABER circuit simulator package. Then, a 100-W 110-V AC input 50-V DC output single-phase flyback rectifier prototype is built for experimental verification.