Discontinuous Mode Operation Research Articles

Design and control strategies for a modular hydroKinetic smart grid

This paper sets out to explore and promote the use of a hydrokinetic microturbine module designed to obtain energy from water streams. It is made up of a hydrokinetic rotor, a permanent magnet generator, power electronic stages and a microcontroller to regulate power production. It is further complemented by a control strategy focused on maximizing the electrical power produced when varying different water velocities. This method is based on three operating zones defined by the electrical frequency produced by the generator, and where different values of direct current set points are defined. It is set in motion in a boost converter power stage, using a maximum current control, with constant off time in the power switch, and continuous or discontinuous mode of operation depending on the current value required. The control strategy has been validated though the use of dynamic simulations.The microturbine modules are suitable for alignment in rows to increase the power produced. The modules connected in smart grids define the hydrokinetic smart grid concept. A global control strategy for hydrokinetic smart grids has also been proposed and tested.

Hysteresis Switching Control of the Ćuk Converter Operating in Discontinuous Conduction Modes

In this brief, the behaviors of the Cuk converter operating in discontinuous conduction modes (DCMs) under a hysteresis controlled switching are studied. The hysteresis switching is defined in terms of values of a common quadratic Lyapunov function and Lyapunov stability conditions are established for all possible switchings, which represent a DCM of operation. A set of simulation results are provided to illustrate the converter’s behaviors when the hysteresis switching control results in discontinuous modes of operation.

Low-Frequency Impedance Monitoring and Corresponding Failure Criteria for Aluminum Electrolytic Capacitors

Condition monitoring of aluminum electrolytic capacitors (AECs) is essential for predictive maintenance of power electronic converters. The AEC is considered at the end of its life when its capacitance or equivalent series resistance (ESR) reaches corresponding critical values. In the literature, it is found that either of these parameters may reach its critical limit depending on the operating conditions and applications. However, most of the existing health monitoring techniques of the AEC in dc–dc converters are based on the estimation of ESR. To address the aforementioned issue, this paper proposes to estimate the low-frequency impedance of the AEC, which is dominated by its capacitance value, thereby allowing health monitoring based on the capacitance value. The technique is based on injection of a low-frequency current ripple into the AEC using duty ratio control of the dc–dc converter. The parameters of new and aged capacitors are experimentally obtained at various temperatures and are used to establish the failure criteria. Furthermore, the proposed method is applicable for both the continuous conduction mode and the discontinuous conduction mode (DCM) of operation. For DCM operation, a sampling instant to recover a low-frequency waveform is suggested based on mathematical analysis. Detailed simulation studies are performed and results are included in this paper. Experimentation is carried out on a dc–dc boost converter integrating solar photovoltaic with the dc system. Experimental results are found to be in agreement with simulation results.

Evaluation of the Potential Use of Laminar Extrudates on Stabilizing Micronized Coumarin Particles by Supercritical Fluids (RESS)—Study of Different RESS Processing Variables and Mode of Operation

The study evaluates the ability of extrudates to deliver coumarin particles micronized by the rapid expansion of supercritical solutions (RESS). The RESS parameters were drug load (2-50g), pressure (15-42MPa) and temperature (40-60°C) in the extraction and pressure in the expansion (0.1-5MPa) chambers in batch or continuous and CO2 flow rate in the continuous mode of operation. Particles were characterized for size (laser diffractometry, optical and electronic microscopies-19-61μm), surface area (BET-0.282-0.423m2/g), density (pycnometry-1.273-1.358g/cm3) and yield (2-70%). Extrudates were characterized for the force of extrusion (4kN), release of coumarin (100%/24h) and mechanical properties (bending strength and stiffness increased, whereas elasticity decreased in storage) and X-ray diffractometry (micronized particles and extrudates have shown identical patterns) and calorimetry (DSC, enthalpies increased on storage). In the discontinuous mode of operation, increased loads in the extraction or increased pressure in the expansion chambers led to larger particles, whereas increased temperature and pressure in the extraction chamber led to smaller particles. In the continuous mode of operation, a decrease on the expansion pressure, load and CO2 flow rate led to increased yields. An increase on the flow rate led to a decrease on the particles' diameter, but an increase on coumarin load in the extraction chamber led to an increase in diameter. The study has identified the key parameters in RESS continuous and discontinuous modes of operation affecting the properties of the micronized coumarin particles and has proved the ability of extrudates with a laminar shape on delivering micronized particles.

A Novel Nonisolated Ultra-High-Voltage-Gain DC–DC Converter With Low Voltage Stress

Regarding the inherent structure of some nonpolluting resources such as fuel cell (FC) stacks and photovoltaic (PV) panels, the output exhibits a low voltage, which cannot be employed in the common conventional utilizations. Accordingly, an interference dc–dc converter is extremely required. This paper demonstrates the feasibility of using an ultra-high-voltage-gain dc–dc converter in either the FC or the PV applications. While keeping the high voltage gain, the proposed topology illustrates low switches’ voltage stress resulted in high efficiency. The continuous and discontinuous conduction operation modes, as well as efficiency analysis, are investigated. The prototype setup of 250 W and 400 V output voltage is implemented. The proposed dc–dc converter merits involving ultra-high-voltage ratio, low switches’ voltage stress, and high efficiency are verified via experimental results.

High Step-Down Dual Output Light Emitting Diode Driver

A conventional power factor correction (PFC) based light emitting diode (LED) drivers composed of two-stage DC-DC conversions has several drawbacks such as; increased system size due to more component count, less efficiency and complex control etc. The grid powered LED lighting demand for high step-down conversion because the required voltage level of LED light is very less. Thus, this work proposes a one-switch dual-output (OSDO) coupled inductor buck (CIB) LED driver with current auto balancing. OSDO-CIB converter can eliminate most of the drawbacks of conventional counterparts. The proposed OSDO-CIB converter can provide various benefits such as; compact size, high efficiency, less total harmonic distortion (THD), simple control, and significant reduction in device voltage/current rating due to coupled inductors. The converter is designed with discontinuous conduction mode (DCM) of operation in order to achieve in-phase current and voltage, high power factor (PF) and a low THD. This paper mainly emphasized on detailed operating modes and steady-state analysis of proposed converter. Further, proto-type of the converter is built and experimental validations are presented.

Limitations of Bifurcation Diagrams in Boost Converter Steady-State Response Identification

Steady-state responses of the boost converter operating in discontinuous conduction mode of operation are identified by using bifurcation diagrams as a typical simulation tool for identification of steady-state responses. The structure of simulated bifurcation diagrams is dependent on the initial period of sampling and the initial instant of sampling. The influence of these parameters on calculation of bifurcation diagrams was studied. Some possible issues, pitfalls and misinterpretations are commented as well as some recommendations about steady-state response identification are given

Operation of Current Source Inverters in Discontinuous Conduction Mode

This paper identifies the characteristics of a current source inverter operating in discontinuous conduction mode, and proposes a new multiobjective pulse-width modulation (PWM) method to mitigate voltage boosting and harmonic distortion effects. The method takes into account load impedance effects. Controls are also developed to enable transition between the multiobjective PWM method and conventional PWM as the current source inverter operates in discontinuous and continuous modes of operation. The concept is verified experimentally on a 3 kW test bed.

Online Monitoring Technique for Aluminum Electrolytic Capacitor in Solar PV-Based DC System

To interconnect low-voltage solar photovoltaics (PV) with dc system, a dc–dc boost converter is required. To minimize the switching frequency oscillations in solar PV voltage, aluminum electrolytic capacitors (AECs) are connected between solar PV and the converter. Operational life of AECs depends on electrical and environmental parameters and is less than that of solar PV panels. Equivalent series resistance (ESR) of AEC increases with life, thereby increasing the voltage ripple across PV terminals. This results in less power extraction from solar PV. This paper proposes a method for health monitoring of AEC using the parameters measured for maximum power point tracking (MPPT) (PV voltage and current). The proposed technique is applicable for both continuous conduction mode and discontinuous conduction mode of operation of the converter. Effect of temperature on ESR is incorporated for accurate determination of the health of capacitor. Key advantage is that no additional current or voltage sensor is required to implement this technique, thereby offering a low-cost solution. Further, the proposed technique does not require significant processing capabilities and is implemented in the same digital controller used for MPPT. Detailed simulation studies are carried out and results are included in this paper. A laboratory prototype of dc–dc boost converter is developed for experimentation. Results are in agreement with that obtained from simulation studies.

Improved Power Quality Switched-Mode Power Supply Using Buck–Boost Converter

The analysis, design, modeling and development of a switched mode power supply (SMPS) for computers is presented here for improved power quality. The proposed SMPS is capable to mitigate existing problems in a conventional SMPS. It is designed to attain close to unity input power factor (PF) and low harmonic distortion at the input ac mains with regulated multiple dc output voltages. A non-isolated front end power factor corrected converter is designed in discontinuous conduction mode (DCM) of operation and control. Simulated performance of proposed power supply is presented to validate the design and to demonstrate the performance with near unity PF operation. Experimental validation of the proposed SMPS is also carried on a prototype built in the laboratory and the test results are compared with the simulation results to validate the design and modeling. An improved power quality is achieved with almost unity power factor in wide range of input ac voltages and loads.

Simulation Based Studies of Energy Saving Measures in the Aluminum Tool and Die Casting Industry

This study, which focuses on analyzing aluminum melting and die casting procedures is part of the Smart Melting project in the research network Green Factory Bavaria (GFB). The aim of the present research project is to investigate these procedures and to suggest measures to increase the overall energy efficiency. The analysis starts with the capture of the operating structure, the relations between supply and consumption of liquid aluminum and an evaluation of aluminum furnaces themselves. The study concentrates on shaft furnaces whose specific energy consumption is 25 % higher than stated by the manufacturers. At the same time the melting capacity of the furnaces ranges at the lower end according to the manufacturer's data. The reason for this deviation is a discontinuous operation mode due to demand fluctuations. Consequently the flue gas has still a high temperature which means a high waste of energy. Based on these facts the furnace charge and operation mode have to be optimized and the high temperature flue gas can be used to preheat the pig aluminum.A numerical model of aluminum furnaces is applied to investigate this optimization potential. This model can simulate either a single aluminum furnace (case 1) or a furnace integrated in the entire manufacturing plant (case 2). The advantage of case 1 is the furnace's operation on its most efficient point because there is no influence of the die casting process. In case 1 an improvement of the furnace charge leads to a higher capacity utilization and therefore to a reduction of 30 % specific energy consumption and a 50 % increase of melting capacity. Whereas in case 2 the simulation of the entire manufacturing plant results in a rise of 25 % melting capacity and a 16 % decrease of specific energy consumption. The simulation proved increasing energy efficiency due to preheating the pig aluminum in both cases.

Arsenic removal by discontinuous ZVI two steps system for drinking water production at household scale

Different countries in Europe still suffer of elevated arsenic (As) concentration in groundwaters used for human consumption. In the case of households not connected to the distribution system, decentralized water supply systems, such as Point of Use (POU) and Point of Entry (POE), offer a direct benefit for the consumers. Field scale ex-situ treatment systems based on metallic iron (ZVI) are already available for the production of reduced volumes of drinking water in remote areas (village scale). To address drinking water needs at larger scale, we designed a pilot unit able to produce an elevated daily volume of water for human consumption. We tested the long-term As removal efficiency of a two steps ZVI treatment unit for the production of 400 L/day clean water based on the combination of ZVI corrosion process with sedimentation and retention of freshly formed Fe precipitates. The system treated 100 μg/L As(V)-contaminated oxic groundwater in a discontinuous operation mode at a flow rate of 1 L/min for 31 days. Final removal was 77–96% and the most performing step was aeration/sedimentation (A/S) tank with a 60–94% efficiency. Arsenic in the outflow slightly exceeded the drinking water limit of 10 μg/L only after 6000 L treated and Fe concentration was always below 0.2 mg/L. Under proposed operating conditions ZVI passivation readily occurred and, as a consequence, Fe production sharply decreased. Arsenic mobility attached to particulate was 13–60% after ZVI column and 37–100% after A/S tank. Uniform amorphous cluster of Fe nanoparticles (100 nm) formed during aeration drove As removal process with an adsorption capacity corresponding to 20.5 mgAs/gFe. Research studies often focus only on chemico-physical aspects disregarding the importance of biological processes that may co-occur and interfere with ZVI corrosion, As removal and safe water production. We explored the microbial transport dynamics by flow cytometry, proved as a suitable tool to monitor the fate of both single cells and bioactive particles along the treatment train of the pilot unit. A net release of bioactive particles, representing on average 26.5% of flow cytometric events, was promoted by the ZVI filter, with densities 10 times higher than those found in the inflow. In conclusion, the proposed system was efficient to treat large daily volumes of As contaminated groundwater. However, filter design and operating conditions should be carefully adapted to specific situation, since several key factors affect As removal efficiency. An effort in the optimization of ZVI filter design should be made to reduce fast observed ZVI passivation and low As adsorption capacity of the whole filter. More attention to biomass retention and bioactive particles travelling within the unit should be given in order to elucidate bacteria influences on As removal efficiency and related sanitary risks on long term basis.

Mathematical Modeling of Hybrid Electrical Engineering Systems

A large class of systems that have found application in various industries and households, electrified transportation facilities and energy sector has been classified as electrical engineering systems. Their characteristic feature is a combination of continuous and discontinuous modes of operation, which is reflected in the appearance of a relatively new term “hybrid systems”. A wide class of hybrid systems is pulsed DC converters operating in a pulse width modulation, which are non-linear systems with variable structure. Using various methods for linearization it is possible to obtain linear mathematical models that rather accurately simulate behavior of such systems. However, the presence in the mathematical models of exponential nonlinearities creates considerable difficulties in the implementation of digital hardware. The solution can be found while using an approximation of exponential functions by polynomials of the first order, that, however, violates the rigor accordance of the analytical model with characteristics of a real object. There are two practical approaches to synthesize algorithms for control of hybrid systems. The first approach is based on the representation of the whole system by a discrete model which is described by difference equations that makes it possible to synthesize discrete algorithms. The second approach is based on description of the system by differential equations. The equations describe synthesis of continuous algorithms and their further implementation in a digital computer included in the control loop system. The paper considers modeling of a hybrid electrical engineering system using differential equations. Neglecting the pulse duration, it has been proposed to describe behavior of vector components in phase coordinates of the hybrid system by stochastic differential equations containing generally non-linear differentiable random functions. A stochastic vector-matrix equation describing dynamics of the processes has been obtained in the paper. The equation contains both continuous and discrete components, which characterize an amplitude signal modulation. An equation for probability density of phase coordinate distribution in the system has been developed on the basis of a mathematical model for a hybrid system.

CONDUCTIVE-DIAMOND ELECTROCHEMICAL OXIDATION OF A PHARMACEUTICAL EFFLUENT WITH HIGH CHEMICAL OXYGEN DEMAND (COD). KINETICS AND OPTIMIZATION OF THE PROCESS BY RESPONSE SURFACE METHODOLOGY (RSM)

Conductive-diamond electrochemical oxidation processes are promising technologies for treating biorefractory industrial wastes with organic loads below 20000 mg L-1. In this work, electrochemical oxidation of a real industrial pharmaceutical wastewater with conductive-diamond anodes has been studied. The electrolyses were carried out in discontinuous operation mode under galvanostatic conditions, using a bench-scale plant equipped with a single compartment electrochemical flow cell. For optimizing the process and studying the interaction between the operating conditions, different experiments were performed by modifying the current density (from 25 to 180 mA cm-2) and recirculation flow rate (from 105 to 565 ml min-1) with residence times between 0 and 570 minutes. The corresponding contribution of these two operative parameters on COD removal and its evolution versus residence time was studied. A time of 98 minutes was obtained in order to evaluate the highest influence of operative parameters. For this time, the current density was found to have a considerable positive effect, while the flow rate proved to be a statistically insignificant variable. ANOVA test reported significance for three of the five involved variables and Response Surface Methodology technique was used to optimize COD removal.

The Boost Converter – Revisited

The dc-to-dc boost converter is a single-switch, single-inductor, switching circuit used to efficiently transform energy from one dc voltage level to a greater voltage level of the same relative polarity. For a specific resistive load range, as the duty cycle decreases, the boost converter inductor enters a discontinuous current mode of operation - the output load current having decreased to a definable level. This paper analyses the fact that a further reduction of load current, as the duty cycle decreases towards zero, will always result in the re-emergence of a continuous inductor current condition. Further, at the other load extreme, high-current, progressively for increasing load current, starting at low duty cycle conditions, the minimum inductor current always increases from a fixed normalised current level, for a specific load range. These and other hitherto unexplored boost converter properties are analysed and verified mathematically and with PSpice simulations.

Computationally efficient models for simulation of non-ideal DC–DC converters operating in continuous and discontinuous conduction modes

This paper discusses dynamic modeling of non-isolated DC–DC converters (buck, boost and buck–boost) under continuous and discontinuous modes of operation. Three types of models are presented for each converter, namely, switching model, average model and harmonic model. These models include significant non-idealities of the converters. The switching model gives the instantaneous currents and voltages of the converter. The average model provides the ripple-free currents and voltages, averaged over a switching cycle. The harmonic model gives the peak to peak values of ripple in currents and voltages. The validity of all these models is established by comparing the simulation results with the experimental results from laboratory prototypes, at different steady state and transient conditions. Simulation based on a combination of average and harmonic models is shown to provide all relevant information as obtained from the switching model, while consuming less computation time than the latter.

Distributed PV Power Extraction Based on a Modified Interleaved SEPIC for Nonuniform Irradiation Conditions

Nonuniform irradiation of a photovoltaic (PV) source, consisting of series-connected modules with bypass diodes, results in multiple peaks in the power–voltage characteristics. This makes the maximum power point tracking (MPPT) difficult because the conventional MPPT algorithms can only deal with single power peak characteristics. This paper proposes a novel distributed MPPT (DMPPT) scheme based on an interleaved single-ended primary inductor converter (SEPIC) converter configuration for compensating the mismatch in characteristics of series-connected PV modules. The proposed scheme obviates the need for bypass diodes across the modules, resulting in single-peak power–voltage characteristics. The proposed DMPPT circuit is derived from an interleaved SEPIC converter that works on the “return energy” concept. The proposed configuration equalizes the voltages across PV modules of the string, resulting in their operating close to its maximum power point. Discontinuous conduction mode of operation is implemented, obviating the voltage-sensing requirements across modules, eliminating the reverse recovery loss of diodes and the turn-on loss of the main switch. The proposed DMPPT scheme uses a simple circuit with reduced control complexity and needs only a few passive elements and only one switching device, compared with the existing DMPPT schemes. The theoretical claims are validated with simulations and extensive hardware experiments.

Hyper‐plane sliding mode control of the DC–DC buck/boost converter in continuous and discontinuous conduction modes of operation

In this study, a new proportional–integral-type hyper-plane sliding mode controller has been designed for output voltage control of the DC–DC buck/boost converter for its continuous and discontinuous conduction modes of operating conditions. The proposed controller is robust and stable against parameters uncertainties, load disturbance and variations of the converter input voltage. In addition, it is capable of cancelling the non-minimum phase nature effect of the converter so that the designed controller does not need to know the inductor reference current. Moreover, the coefficients of the controller have been designed so that the steady-state error of the converter asymptotically converges to zero. The controller is designed based on fixed-frequency equivalent control approach. Using MATLAB/SIMULINK toolbox and digital signal processor (TMS320F2810) from Texas Instruments, some simulation and practical results are presented to verify the capability and effectiveness of the proposed control approach.

Analysis of Variable Speed PFC Chopper Fed BLDC Motor Drive

<p>This paper provides the detailed analysis of the DC-DC chopper fed Brushless DC motor drive used for low-power applications. The various methods used to improve the power quality at the ac mains with lesser number of components are discussed. The most effective method of power quality improvement is also simulated using MATLAB Simulink. Improved method of speed control by controlling the dc link voltage of Voltage Source Inverter is also discussed with reduced switching losses. The continuous and discontinuous modes of operation of the converters are also discussed based on the improvement in power quality. The performance of the most effective solution is simulated in MATLAB Simulink environment and the obtained results are presented.</p>

Current Source Rectifiers in Discontinuous Conduction Modes of Operation

Although the operation of a three-phase current source rectifier (CSR) for ac-to-dc conversion using phase control or low-frequency pulse control is well established in a wide variety of applications, CSR realization using high-frequency pulsewidth-modulation control has been recently studied as a potentially competitive alternative to a voltage source rectifier. In the CSR, reverse blocking gate turn-off switches are realized using series-connected diodes, which prevent any reversal of the dc-link current. A significant consequence of this limitation occurs at light load conditions. The dc-link inductor current enters the discontinuous mode of operation and leads to the loss of the control of the output voltage and a highly distorted input current, which compromise the potential advantages of the approach. This paper characterizes the CSR while operating in the discontinuous conduction mode and proposes a modulation strategy that restores the control of the output voltage and ensures a nearly sinusoidal current at light loads. Simulation and hardware results are provided for a 3-kW laboratory-scale prototype system.