DCM Mode Research Articles

A Novel Switched Hybrid-Voltage Doubler High Gain DC-DC Converter for Renewable Energy Applications

Background: In renewable energy system applications, the power converter is essential for transferring energy into the load centre. The AC network voltage is much higher than the renewable energy source voltage; therefore, a transformer is commonly used to step up the voltage. However, the size and cost of the system are larger due to the presence of a bulky transformer, and also the efficiency is deteriorated due to PWM voltage being applied to the transformer. Objective: To eliminate the requirement of the transformer, DC link voltage is boosted up to a higher level using a high-gain converter. Various DC-DC converters have been proposed in recent studies; however, the involvement of the active switches is high to produce higher voltage gain, which reduces efficiency. In order to overcome this limitation, this particular paper proposes a novel switched hybrid-voltage doubler high gain DC-DC converter, which helps to achieve higher gain with a minimum number of components count compared to other reported converters. It also reduces the device's stress, thereby increasing its efficiency. Method: This paper describes the detailed operational studies along with CCM and DCM modes. The mathematical analysis under each operating state is reported in this paper. A detailed comparative study on the performance merits of the proposed converter, along with other recently reported converters, is presented. Results: Finally, the simulation results are presented to validate the operation of the proposed converter. Furthermore, a 500 W laboratory setup is developed to verify the operation details and practical feasibility of the converter through experimental results and presented in this paper. Conclusion: From the measured results, it is concluded that the proposed converter can play the most promising role in the transmission phase in renewable energy system implementations since it boosts the voltage to the adequate point as required by the system.

Single Phase AC to DC Isolated ZETA Power Factor Correction Converter fed LED drives

This paper deals with PFC-isolated Zeta converter fed LED drive to overcome the power factor problems. The proposed circuit topology consists of diode bridge rectifier and isolated Zeta converter with high frequency transformer. A single –phase supply is used to feed a DBR followed by a filter to avoid any switching ripple in DBR and the supply system. An isolated Zeta converter is operated to work under DCM mode. This combination of DBR and PFC converter is used to feed a LED drive. This converter is simulated in MATLAB platform. This converter provides better results such as unity power factor and less current harmonic distortion.

New Digital Control Method for Improving Dynamic Response of Synchronous Rectified PSR Flyback Converter With CCM and DCM Modes

In order to improve the dynamic response of synchronous rectified primary-side regulation (PSR) flyback converter with CCM and DCM modes, a novel digital control method is proposed. In a dynamic process, when output voltage is detected to fluctuate greatly, two special working modes called light-to-heavy mode and heavy-to-light mode are introduced. The output capacitor will be quickly charged and discharged by an optimized control scheme to make the output voltage's dynamic fluctuation smaller. On the other hand, during the dynamic process control, for eliminating overshoot and oscillation when the output voltage returns to the reference voltage, the load is detected by the output voltage slope to determine the appropriate operating mode. With the proposed control method, the dynamic performance can be greatly improved. An field programmable gate array (FPGA)-controlled 20-V/5-A synchronous rectified PSR flyback converter is established to verify the proposed control scheme. In the prototype test, compared to the traditional multimode control, the undershoot voltage and overshoot voltage of the proposed control scheme are improved from 5.02 to 1.63 V and 3.15 to 1.73 V, respectively. The undershoot and overshoot recovery times are reduced from 83.43 to 1.79 ms and 40.32 to 1.85 ms, respectively.

Analysis and design of novel non-isolated quadratic boost DC-DC converter

This column elucidates analysis and design of novel single switch non-isolated quadratic boost converter. The operating principle is discussed both in CCM and DCM mode. Analysis includes closed loop average current mode control. The proposed converter exhibits stable operation under input voltage and load change. Linear control theory is applied for the loop compensator design. The suitability of the proposed scheme is well visualised and validated through simulation results procured using PSIM 9.1.1 and experimental results obtained from a practical 75 watt converter. The converter is designed for 75 watts with 89%-90% measured efficiency, where voltage and current ripple is 2% of output voltage and 1% of rated inductor current, respectively.

Design a Single Stage AC to DC Converter for LED Driver With Power Factor Improvement

This paper shows the design of a single switch LED driver circuit which is based on the operation of boost converter and flyback converter with power factor correction. In the proposed driver circuit, the boost converter is made to operate in DCM mode for achieving a high power factor and the flyback converter is used for isolating the input-output in order to provide safety. In addition to this, a snubber circuit is also designed for clamping the peak voltage of the main switch into low voltage and also to recycle the leakage inductor energy. A capacitor of low-voltage rating is made to function as the DC bus capacitor due to reason that some amount of the input power is conducted directly towards the output side; the amount of power remaining is then stored in the DC bus capacitor. In this way, the proposed LED driver circuit provides a power factor of greater value, i.e., above 0.95 PF and also a high value of power conversion efficiency, i.e., above 90%.

Incorporation of Harmonic Injection in an Interleaved Flyback Inverter for the Implementation of an Active Anti-Islanding Technique

Over recent years, the output power of micro-inverters [module-incorporated inverter (MIC)] is progressively pushed to higher levels, following the current photovoltaic (PV) modules market trends. The interleaved Flyback inverter—under discontinuous conduction mode of operation (DCM)—is an appealing solution for PV applications which are based on MIC technology. This topology provides increased power level for distributed PV generation exploitation with simple control configuration, high efficiency, and reduced filter size. In this paper, the harmonic injection capability is incorporated into the interleaved Flyback inverter for the implementation of an active anti-islanding scheme. A suitable technical solution is proposed that bypasses the unfolding H-bridge, without affecting the active power generation of the inverter and without requiring any hardware modification. In addition, a mathematical model based on the instantaneous power balance theory is presented, being a powerful analysis tool for inverters operating under complete magnetic discharge such as the Flyback inverter (either conventional or interleaved) under DCM or boundary conduction mode of operation. The proposed model predicts accurately the steady-state operational behavior of the Flyback inverter under current harmonic injection, either in grid-tied or islanding operation. The proposed technical implementation method and mathematical model are verified through simulation and experimental results. Finally, an anti-islanding set-up based on the proposed harmonic injection technique is presented and implemented into the Flyback micro-inverter. The proposed set-up is verified through experimental results on various quality factor values, as well as for weak grid conditions.

Accurate Modeling of Nonideal Low-Power PWM DC-DC Converters Operating in CCM and DCM using Enhanced Circuit-Averaging Techniques

The development of enhanced modeling techniques for the simulation of switched-mode Pulse Width Modulated (PWM) DC-DC power converters using circuit averaging is the main focus of this article. The circuit-averaging technique has traditionally been used to model the behavior of PWM DC-DC converters without considering important nonideal characteristics of the switching devices. As a result, most of these existing approaches present simplified models that are ideal or linearized, and do not accurately account for the performance characteristics of the converter. This is especially problematic for low-power applications. In this article, we present an enhanced nonideal behavioral circuit-averaged model that makes the simulation of DC-DC converters both computationally efficient and accurate, thereby presenting an important tool for circuit designers. Experimentally, we show that our Verilog-A-based new model allows for accurate simulation of both Buck- and Boost-type PWM converters operating in either CCM or DCM modes while providing more than one order of magnitude speedup over the transistor-level simulation.

Small-signal transmittances of DC-DC step-down PWM converter in various operation modes

Abstract Small-signal transmittances: input-to-output and control-to-output of BUCK converter power stage working in CCM or DCM mode are discussed. Ideal converter case and converter with parasitic resistances are considered separately. Derivations of small-signal transmittances, based on different approaches to finding the converter averaged models, are presented and the results are compared. Apart from theoretical considerations, some results of numerical calculations are presented.

Steady state and averaged state space modelling of non-ideal boost converter

Switched mode power converters are the most important circuits for battery powered applications such as hybrid electric vehicles, lighting systems as well as integrated circuits. These converters are usually studied in its ideal form. However, practical converters behave differently due to associated parasites and thus affect both steady state and stability. So, this paper analyses steady state and state space modelling of non-ideal boost converter. A converter is operated in both CCM and DCM modes. Models are derived by considering capacitance effects of diode and switch in addition to other parasites. The models derived are detailed and care has been taken to avoid assumptions and approximations though the models are very complex. The methodology adopted can be easily extended for other converters. Effect of every parasite and switching frequency on performance of the converter are clearly evaluated by plotting time domain and frequency domain plots in MATLAB. Simulation results show that there is a considerable deviation in performance of practical converters from its ideal case and the deviation is just not due to the inclusion of parasites but also due to the shift in operating point (duty cycle).

DESIGN & ANALYSIS OF FLY BACK CONVERTER FOR GRID & FILAMENT POWER SUPPLIES OF TRAVELLING WAVE TUBE

In High Power Pulsed Radar Transmitters the gridded TWT are used and consists of floating deck modulator unit which houses the Grid and Filament power supplies. The Grid Control includes the Grid Positive & Grid Negative Power Supplies. The Positive voltage is used to turn on the TWT & Negative voltage is used to operate the TWT in off state. The Filament power supply heats the cathode to required temperature to emit electrons. The aim of the project is to design the Grid power supplies and Filament Power supply based on the Fly back Converter topology which is operated at 100 KHz in DCM mode and CCM mode respectively. The Pulse width modulation technique is used to maintain the voltage at desired value using an IC UC1526.The switching device is protected ag

Current Sensorless Control of Front-end Bidirectional AC/DC Converter Based on Half-bridge Topology

Abstract Electrical grid modernization concept promotes the use of DC subgrids in order to improve efficiency, minimizing energy conversion count in the source-to-load chain. The present paper discusses an average current sensorless control algorithm for proposed bidirectional AC/DC converter, which is based on a dual half-bridge topology with common neutral wire that is not commutating during converter operation. The proposed current sensorless control algorithm has been obtained analytically for rectification, grid-tied and stand-alone inverter modes. The average value of inductor current tracks the reference current signal with constant switching frequency. Two control functions for inductor’s discontinuous and continuous current modes have been defined for each of the operation modes, and a sensorless transition between DCM and CCM modes has been stated. The proposed sensorless control algorithm has been also adapted for use with LCL input filter. The results of simulation in the PSIM software approved the analytical model, keeping the average inductor current to follow the reference value in inductor discontinuous and continuous conduction modes. Experimental investigation of the proposed current control algorithm provided similar results confirming the discussed theory.

Equivalent circuits for averaged description of DC-DC switch-mode power converters based on separation of variables approach

Abstract Large-signal and small-signal averaged models of basic switch-mode DC-DC power converters: BUCK (step-down) and BOOST (step-up) are presented. Models are derived with the separation of variables approach and have the form of equivalent circuits, suitable for a circuit simulation. Apart from equivalent circuits, small-signal transmittances of converters for CCM and DCM modes are discussed. Parasitic resistances of all components of converters are taken into account. A few examples of simulations and measurement results of selected converter characteristics are also presented. It is shown, that neglecting parasitic resistances (often met in works of other authors) may lead to serious errors in an averaged description of converters.

소프트 스위칭 기법을 이용한 1단 PFC-flyback 컨버터

The flyback converter has been applied widely in isolated DC/DC power converters because this converters employ a single MOSFET switch. The leakage inductance should be minimized for high efficiency of flyback converter. but in reality, it is very difficult. Namely, The Snubber circuit is essential to recover the leakage inductance stored energy when the switch is turn off. Flyback Converter typically operates in DCM mode and when switch is turn off in hard switching, this hard switching action results in a high power losses and switching stresses. In order to overcome these problems, a novel soft switching flyback converter using resonant snubber circuit is proposed in this paper. The resonant snubber circuit is composed of the transformer leakage inductance and a capacitor. To verify and confirm the proposed resonant snubber circuit, PSIM simulation and hardware prototype are implemented. Simulation and Experimental results indicate that the proposed resonant snubber circuit is effective.

Averaged models of pulse-modulated DC-DC power converters. Part I. Discussion of standard methods

Abstract The averaged models of switch-mode DC-DC power converters are discussed. Two methods of averaged model derivation are considered - the first, based on statespace averaging and the second, on the switch averaging approach. The simplest converters: BUCK, BOOST and BUCK-BOOST working in CCM (continuous conduction mode) or DCM are taken as examples in detailed considerations. Apart from the ideal converters, the more realistic case of converters with parasitic resistances is analyzed. The switch averaging approach is used more frequently than the other and is believed to be more convenient in practical applications. It is shown however, that in the deriving the averaged models based on the switch-averaging approach, some informalities have been made, which may be the source of errors in the case of converters with parasitic resistances, or working in DCM mode.

Averaged models of pulse-modulated DC-DC power converters. Part II. Models based on the separation of variables

Abstract The separation of variables approach to formulate the averaged models of DC-DC switch-mode power converters is presented in the paper. The proposed method is applied to basic converters such as BUCK, BOOST and BUCK-BOOST. The ideal converters or converters with parasitic resistances, working in CCM and in DCM mode are considered. The models are presented in the form of equation systems for large signal, steady-state and small-signal case. It is shown, that the models obtained by separation of variables approach differ in some situations from standard models based on switch averaging method.

Emergence of steady and oscillatory localized structures in a phytoplankton–nutrient model

Co-limitation of marine phytoplankton growth by light and nutrient, both of which are essential for phytoplankton, leads to complex dynamic behaviour and a wide array of coherent patterns. The building blocks of this array can be considered to be deep chlorophyll maxima, or DCMs, which are structures localized in a finite depth interior to the water column. From an ecological point of view, DCMs are evocative of a balance between the inflow of light from the water surface and of nutrients from the sediment. From a (linear) bifurcational point of view, they appear through a transcritical bifurcation in which the trivial, no-plankton steady state is destabilized. This paper is devoted to the analytic investigation of the weakly nonlinear dynamics of these DCM patterns, and it has two overarching themes. The first of these concerns the fate of the destabilizing stationary DCM mode beyond the centre manifold regime. Exploiting the natural singularly perturbed nature of the model, we derive an explicit reduced model of asymptotically high dimension which fully captures these dynamics. Our subsequent and fully detailed study of this model—which involves a subtle asymptotic analysis necessarily transgressing the boundaries of a local centre manifold reduction—establishes that a stable DCM pattern indeed appears from a transcritical bifurcation. However, we also deduce that asymptotically close to the original destabilization, the DCM loses its stability in a secondary bifurcation of Hopf type. This is in agreement with indications from numerical simulations available in the literature. Employing the same methods, we also identify a much larger DCM pattern. The development of the method underpinning this work—which, we expect, shall prove useful for a larger class of models—forms the second theme of this paper.

Evaluation of two different metabolic hypotheses for dichloromethane toxicity using physiologically based pharmacokinetic modeling for in vivo inhalation gas uptake data exposure in female B6C3F1 mice

Dichloromethane (DCM, methylene chloride) is a lipophilic volatile compound readily absorbed and then metabolized to several metabolites that may lead to chronic toxicity in different target organs. Physiologically based pharmacokinetic (PBPK) models are useful tools for calculation of internal and target organ doses of parent compound and metabolites. PBPK models, coupled with in vivo inhalation gas-uptake data, can be useful to estimate total metabolism. Previously, such an approach was used to make predictions regarding the metabolism and to make subsequent inferences of DCM's mode of action for toxicity. However, current evidence warrants re-examination of this approach. The goal of this work was to examine two different hypotheses for DCM metabolism in mice. One hypothesis describes two metabolic pathways: one involving cytochrome P450 2E1 (CYP2E1) and a second glutathione (GSH). The second metabolic hypothesis describes only one pathway mediated by CYP2E1 that includes multiple binding sites. The results of our analysis show that the in vivo gas-uptake data fit both hypotheses well and the traditional analysis of the chamber concentration data is not sufficient to distinguish between them. Gas-uptake data were re-analyzed by construction of a velocity plot as a function of increasing DCM initial concentration. The velocity (slope) analysis revealed that there are two substantially different phases in velocity, one rate for lower exposures and a different rate for higher exposures. The concept of a “metabolic switch,” namely that due to conformational changes in the enzyme after one site is occupied – a different metabolic rate is seen – is also consistent with the experimental data. Our analyses raise questions concerning the importance of GSH metabolism for DCM. Recent research results also question the importance of this pathway in the toxicity of DCM. GSH-related DNA adducts were not formed after in vivo DCM exposure in mice and DCM-induced DNA damage has been detected in human lung cultures without GSH metabolism. In summary, a revised/updated metabolic hypothesis for DCM has been examined using in vivo inhalation data in mice combined with PBPK modeling that is consistent with up-to-date models of the active site for CYP2E1 and suggests that this pathway is the major metabolizing pathway for DCM metabolism.