Boundary Conduction Mode Research Articles

Analysis of A Transformerless Single Switch High Gain DC–DC Converter for Renewable Energy Systems

A new transformerless single switch high gain dc–dc converter for renewable energy systems is proposed in this paper. The proposed converter solves two main problems: the low voltage produced by Photovoltaic (PV) solar panels and the discontinuous input current caused by the switching power supplies by stepping up the voltage of the PV panel and providing a continuous input current, respectively. The proposed converter is derived by adding a switched capacitor/inductor cell and a voltage multiplier stage to the traditional boost converter. The advantages of the converter are: high voltage conversion ratio, reduced voltage stress on the active switch and diodes, reduced gate driver requirements due to using only one switch and continuous input current to increase the life time of the solar PV panel. A detailed analysis of the operating principal in the continuous conduction mode, boundary conduction mode, discontinuous conduction mode, design consideration, nonideality of the converter is discussed. A laboratory prototype is built to verify the performance of the converter. The prototype is tested with different output powers (50–150 W) with an input voltage of 20 V and a duty cycle of 50%. The proposed converter succeeds in stepping the 20 V up to 200 V while providing a continuous input current at a 96% efficiency when the output load draws 100 W.

A GaN BCM AC–DC Converter for Sub-1 V Electromagnetic Energy Harvesting With Enhanced Output Power

A gallium nitride (GaN) boundary conduction mode (BCM) dual-boost ac-dc converter for low-voltage electromagnetic energy harvesting (EH) is presented in this article. The μW-to-mW EH system is very susceptible to any tiny losses from power converters, interconnections, and system parasitic. To have better utilizations of harvested energy, an output power enhanced power conversion design is proposed. First, impedance matching is satisfied between electromagnetic generator and ac-dc converter to achieve maximum delivered power. The ac-dc converter is designed under BCM for constant input impedance. EH's winding inductance is employed as the boost inductor in the ac-dc converter. A codesign principle for converter on-time with electromagnetic generator's winding characteristics is revealed. Second, power transistors in EH low-voltage conversion are optimized to realize high efficiency. Power transistors' low-voltage switching characteristics are significantly different from high-voltage situation with no or little miller plateau region. Low-voltage power transistors are compared from both device characteristics and calculated power loss to provide device selection guidance. A GaN-based dual-boost ac-dc converter under BCM operation with constant on-time controller is designed in this article to provide 3.3 V output for a 500-Ω load resistor. It achieves peak efficiency of 82.4% for open-loop operation at 0.6 V/100 Hz input and peak efficiency of 72.3% for close-loop operation at 0.75 V/100 Hz.

Backpack energy harvester managed by a modified fly-back converter

A backpack energy harvester (EH) managed by a modified fly-back converter is proposed. This modified fly-back converter is controlled by a constant-on time control (COT) algorithm, The COT is one of pulse frequency modulation schemes, which switches in boundary conduction mode. Due to the structure of the modified fly-back converter and the alternator, the energy delivery to battery is proportional to the voltage of coupled capacitor. As opposed to the conventional fly-back, the proposed modified fly-back has the metal–oxide–semiconductor field-effect transistor and the capacitor exchanged in roles to achieve input rectified voltage sensing. Moreover, the proposed modified fly-back converter utilizes the internal winding inductance of the alternator utilized as part of the fly-back converter, to save the size of the converter circuitry and lower the cost. With the COT control strategy, the output power is estimated by measuring the capacitor voltage, which is converted to digitals by a 10-bit analog-to-digital converter and a time-to-digital converter. The results show clearly the fair linearity between the rotational speed of alternator, capacitor voltage and output power. Finally, the control algorithm of boundary conduction mode (BCM) is utilized for tackling well the intermittent input power generated by the EH. The average output powers of 1.166 W for striding and 1.766 W for jogging are successfully achieved.

Integrated Modeling Framework for Investigating Multiscale Microstructural Impacts on the Ionic Conductivity of Garnet Solid Electrolytes

Although recent years have seen the emergence of several solid electrolyte candidates with intrinsically high ionic conductivities for all-solid-state batteries, practical processing and synthesis routes often generate grain boundaries and other interfaces that can perturb primary conduction channels. In this talk, we will present our development of a multiscale modeling framework for predicting the effective ionic conductivity through a solid electrolyte with a complex polycrystalline microstructure, which allows us to address challenges associated with directly probing these effects. We first demonstrate an efficient mesoscopic computational method for predicting the effective ionic conductivity through a solid electrolyte with a complex polycrystalline microstructure. By considering the interplay between concurrent grain boundary and bulk conduction modes, this method surpasses simplified circuit descriptions to account for realistic, nontrivial networks of conduction channels. Using the Li7-x La3Zr2O12 (LLZO) garnet solid electrolyte as a technologically relevant model system, we then parameterize our simulation framework using a multiscale approach that connects synthetic microstructures from phase-field simulations with diffusivity tensors from molecular dynamics simulations of ordered and disordered systems. Systematically designed simulations of the effective ionic conductivity of polycrystalline LLZO are applied to elucidate the relationship between relevant microstructural features and overall ionic transport properties, with a focus on topological features of grains and grain boundary networks. In particular, we will discuss atomistic and mesoscopic tunability of grain boundary and microstructure, respectively, controlling mass transport in LLZO. We identify specific instances in which competition between conduction modes results in a high sensitivity to microstructural features, highlighting the need to account for the detailed microstructural information when assessing mass transport in LLZO and related solid electrolyte materials, while simultaneously offering design guidance for achieving desired ionic transport properties in processed polycrystalline LLZO.This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

A New Variable Frequency Zero Voltage Switching Control Method for Boost Converter Operating in Boundary Conduction Mode

This paper proposes a new variable frequency zero voltage switching (ZVS) control method for boost converter operating in boundary conduction mode (BCM). The intended method keeps the converter in BCM despide of the load and input voltage variations. This is done by changing switching frequency in a certain specified range. The proposed method can guarantee circuit performance in BCM via zero-crossing detection of the inductor current and changing the switching frequency. In addition, with a slight modification in control structure, it is possible to achieve a fully ZVS in all cases. This converter control is carried out in analog form without using microprocessors which, compared with the digital one, has less noise, cost and processing challenges in high frequency applications. Simulation results obtained from applying the proposed method on a GaN-based synchronous boost converter in two different switching frequency ranges (100KHz and 1MHz) are indicative of the proposed strategy advantages.

A high-current 1.5-stage LED driver with current-mode BCM PFC and low-voltage film capacitors

In this paper, current-mode boundary conduction mode (BCM) of a high-efficiency LED driver with high power factor, utilizing low-voltage film capacitors, is presented, and its theoretical design and considerations are discussed. The 1.5-stage driver consists of a forward-flyback and buck converter. Higher efficiency was reached using the reduced redundant power processing approach. Most of the processed energy is transferred to the output through flyback, while the rest removes the low harmonic ripple in the output current through the forward-buck path. An acceptable amount of odd harmonics is injected into the input current by using current-mode BCM control method, further reducing bus capacitance. To validate these principles, a laboratory prototype has been built and experimental results of a high-current 85 W (29.5 V/2.9 A) lamp with 50 Hz, 185–255 V power supply are provided. The results show that output current ripple is low, and the input current harmonics are within the standard regulations.

Dual range flyback topology for high efficiency at dual voltage mains

This study introduces a dual range flyback converter, which overcomes low efficiency of the conventional flyback converter for universal mains voltages, i.e. 220 and 110 V AC mains. The topology comprises of reconfigurable primary power loops enabled by additional state switches. This combination allows the converter to run in parallel or series modes, enhancing the performance at 220 V AC high line or 110 V AC low line mains. It reduces the voltage rating of devices, supports two working points that operate in boundary conduction mode under fixed frequency and improves the utilisation of the devices. A 100 kHz, 60 W, 110 V AC or 220 V AC to 13 V DC converter has been designed and tested. The experimental results of the proposed converter have been compared against a conventional flyback converter. The results show a small improvement of performance at low voltage (110 V AC) and considerable performance improvement at high voltage (230 V AC): 0.6 and 2.3% efficiency improvement at full load, respectively.

A Novel High Voltage Gain SEPIC Converter Based on Hybrid Split-Inductor for Renewable Application

ABSTRACT The modified single-ended primary inductor converter (SEPIC) reported in the literature has limitations namely, low static gain and high input current ripples. This resulted in poor efficiency with high switching losses and switching stress. Hence, in order to overcome the above-said limitations, this paper proposes a high static gain SEPIC converter with reduced input current ripple. The proposed converter resembles a split-inductor design consisting of three diodes and two inductors. The static gain of the converter is significantly improved while input current ripple gets reduced by using a split-inductor. Additionally, the low value of input current ripple causes minimal switching stress and switching losses. Hence, the efficiency of the proposed converter improves significantly. The working principle and theoretical analysis of the proposed converter is studied in detail for continuous, discontinuous and boundary conduction modes. Moreover, a small signal/transient analysis is also discussed to validate the feasibility as well as the stability of the proposed system using the transfer function approach. In order to validate the effectiveness of the proposed converter, a MATLAB/Simulink model has been designed. Further, a laboratory prototype has been developed and the experimental results obtained are in agreement with the simulated results.

Soft-Switching Techniques for Single-Inductor Multiple-Output LED Drivers

Although a plethora of prior-art single-inductor multiple-output (SIMO) light-emitting diode (LED) drivers have been reported, they remain inadequate for resource-constraint drone applications due to compromised power efficiency and weight. This article proposes a monolithic SIMO red–green–blue–white LED driver that features high power efficiency and light weight. The former is obtained by employing our proposed soft-switched cross-current-eliminated controller and proposed on-chip bidirectional current sensor. The latter is achieved by means of employing a tiny inductor attributed to boundary conduction mode and high switching frequency. To the best of authors’ knowledge, the proposed SIMO LED driver is the first-ever design that features soft switching for all power switches and innate elimination of current cross-regulation. In comparison with the state-of-the-art designs listed in the benchmark table, the proposed design features the highest power efficiency of 96.2%, smallest output inductor of 820 nH, shortest LED current settling time of 900 ns, and the highest switching frequency of 2 MHz.

Sensorless Ripple Current Mode Control to Achieve Inductor-Deviation-Tolerant BCM Operation for Boost Converter

For switched mode power converters, boundary conduction mode (BCM) operation is an attractive alternative to improve the bandwidth, overall size, and efficiency. In this article, a sensorless ripple current mode (SRCM) controller is proposed to achieve inductor-deviation-tolerant BCM operation for boost converter. Compared to conventional approaches with current sensing or ZCD, the proposed controller relies on a digital algorithm to ensure consistent BCM operation. The algorithm calculates on / off durations of the main switch so that the inductor current valley value converges to zero. The convergence process is proved by a damped current model with considerations of parasitics and output voltage ripple. Since the convergence is not related to the inductor value, the SRCM controller achieves inductor-deviation-tolerant BCM operation. Furthermore, to improve the power efficiency, an optimal transition condition and a compensation time are adopted to achieve valley switching (VS). Finally, both consistent BCM operation and VS are achieved by the proposed control strategy. Simulations and experimental results prove that the controller effectively improves the closed-loop stability, the robustness to inductor deviation, and the power efficiency.

A Hybrid Boundary Conduction Modulation for a Single-Phase H-bridge Inverter to Alleviate Zero-Crossing Distortion and Enable Reactive Power Capability

Boundary conduction mode (BCM) featuring zero-voltage switching has caught researchers’ eyes recently. In single-phase full-bridge inverter with one leg operating in high switching frequency and one leg in line frequency, it is easy to achieve high conversion efficiency for low-power applications. However, severe distortion will be introduced during zero-voltage crossing area due to too low switching frequency around this area, and reactive power generation is not allowed under this modulation scheme due to zero-voltage crossing issue. This article proposes a hybrid BCM strategy for a single-phase full-bridge inverter to both alleviate voltage zero-crossing distortion and enable reactive power generation by reshaping the triangular waveform of inductor current into quadrangle waveform through rearranging the driving signals during voltage zero-crossing area. This alleviates zero-crossing distortion by avoiding too low switching frequency and enables reactive power generation by employing the hybrid BCM around voltage zero-crossing area. High efficiency can be maintained by combining the proposed hybrid BCM employed only for a small portion of zero-crossing area and the conventional BCM for the rest. The principle of operation, theoretical analysis, and simulation results are presented in this article. A 300-W microinverter prototype was built to verify the feasibility and effectiveness of the proposed hybrid BCM scheme.

A single-stage soft-switching LED driver based on CLCL resonant converter and BCM circuit for lighting application

This paper proposes a single-stage LED driver based on the CLCL resonant circuit and boundary conduction mode (BCM) boost circuit. The input voltage of an LED driver is categorized into two capacitors, which will reduce the input peak voltage by making a single-stage LED driver to work under maximum input voltage modes. The proposed CLCL resonant circuit contains a soft-switching feature where the major and minor area works under zero voltage and zero current phases, respectively. Moreover, this approach has reduced very small turn-off loss, turn-off current of a switch, which in turn proves the system efficiency. In this paper, the proposed BCM circuit, as well as CLCL resonant converter circuit, has been explained with five operational phases, and experimentation and analysis were made for proposed and existing methodologies. For validation of the proposed system, a 100 W investigational prototype is used, and experimental results were analyzed with the theoretical result.

Inherently Non-Pulsating Input Current DC-DC Converter for Battery Storage Systems

With an ever-growing number of batteries being integrated into the electric grid, bidirectional converters with non-pulsating dc input current are required to replace the existing bidirectional converters so as to extend the lifetime of such dc power suppliers. Bidirectional DC-DC converters are increasingly used in a variety of applications including uninterruptable power supplies, electric vehicles and renewable energy systems. In this study, we propose a new topology of bidirectional dc-dc converter with inherently non-pulsating input current (NPIC), which is intended to be used for battery energy storage systems. With simple modifications from the conventional converters, the proposed NPIC converter has no inherent pulsating input current in the step-down (buck) mode under both continuous and boundary conduction modes (CCM and BCM), whereas in the step-up (boost) mode, the proposed NPIC converter retains the desired voltage gain. Underpinning theories, operating principles and steady-state performances are analyzed and presented in detail, which are then corroborated by simulation and experimentation. The proposed converter topology, with simple design principle and ease for implementation, is likely to have wide-ranging applicability in interfacing electrochemically functioned dc sources to modern power systems.

Realising ZVS and ZCS in a continuous conduction boost converter with boundary mode control

Boost regulators working in the continuous conduction mode (CCM) are very popular in switch-mode power conversion. This configuration is widely adapted for power factor correction (PFC) in switch mode AC to DC converters. For lower power levels of up to 200 watts, boundary conduction mode (BCM) PFC is adapted, and for power requirements beyond about 200 W, CCM boost with average current control scheme is favoured. A novel technique is proposed in this paper to achieve complete soft-switching viz. Zero voltage switching and zero current switching for the main boost switch in CCM mode. The uniqueness of the scheme lies in not adding any auxiliary MOSFET switch and/or control algorithm. All the switching elements exhibit soft-switching, thus improving efficiency and reducing the EMI considerably. Most of the reported techniques for soft switching in CCM boost utilise additional active switches. A working model is fabricated to demonstrate and validate the scheme. The test results and the waveforms are presented and analysed. An 800 watts PFC converter exhibiting complete soft switching is built using the proposed technique and is evaluated for its performance.

Optimal Zero-Voltage-Switching Method and Variable ON-Time Control for Predictive Boundary Conduction Mode Boost PFC Converter

This article presents a fully zero-voltage-switching (ZVS) method and an optimal variable on -time (VOT) control for the predictive boundary conduction mode (BCM) boost power factor correction (PFC) converter. The operation analysis of the BCM boost PFC converter, which considers the parasitic capacitances, is performed. Based on the analysis, a novel Taylor approximation method to derive the equations of switching off -time for achieving fully ZVS is proposed. Then, an inductor current approximation method is applied to derive the VOT equation in order to reduce the input current total harmonic distortion (THD). A calculation method for selecting the accurate parasitic capacitance is proposed. Most importantly, the derived equations for achieving ZVS and VOT control are simple and take short calculation time in a DSP controller, and, thus, they can be applied to the predictive control. Experimental results demonstrate that the fully ZVS operation can be achieved by the proposed ZVS method. The input current THD is indeed improved by the optimal VOT control.

Nonisolated Symmetrical Interleaved Multilevel Boost Converter With Reduction in Voltage Rating of Capacitors for High-Voltage Microgrid Applications

This article proposed a nonisolated symmetrical interleaved multilevel boost converter for high-voltage microgrid applications. The proposed converter configuration is derived from the integration of a voltage multiplier (VM) circuit with the front-end structure of the classical two-phase interleaved converter. Moreover, equal voltage rating capacitors and diodes are suitable to design multiple stages of the proposed converter. The proposed converter can feed from two independent sources or single source in the interleaved approach. The continuous input current, high-voltage gain, reduced voltage rating of capacitor (that causes reduction in cost), reduced components, and flexibility in number of sources make the proposed converter more attractive for renewable dc-microgrid applications such as, photovoltaic (PV) system, fuel cell (FC) system, and hybrid PV-FC system. Furthermore, the voltage gain of the converter can be increased by just adding similar stages of VM without preferring the high-voltage rating capacitors and without disturbing the front-end structure of the converter. Nonidealities are considered to analyze the proposed converter in a more practical way. The characteristics and operation of the proposed converter are discussed in this article with the continuous conduction mode and Discontinuous Conduction Mode boundary conditions. The design of the reactive components and selection of semiconductor devices are discussed. Additionally, the proposed converter is compared with recently proposed dc-dc multilevel converters. To support the proposed work, simulation and experimental results are provided which shows a good agreement with the analytical approach.

A Soft-Switched Modulation for a Single-Phase Quasi-Z-Source-Integrated Charger in Electric Vehicle Application

A modulation for a single-phase quasi-Z-source-integrated electric vehicle charger (qZSC) system is proposed, which can achieve multiple zero-voltage-switching and zero-current-switching (ZCS) transitions without any auxiliary circuit. Though the modulation has a couple of hard-switching turn-off transitions, they occur at low current values. The switch of a quasi-Z-source network also can be turned on with ZCS. The inductor currents of the quasi-Z-source network operate in boundary conduction mode or discontinuous conduction mode to achieve all freewheeling diodes turned off naturally. Besides, there is no additional voltage stress and current stress on all switches in comparison with hard switching. Therefore, it is observed that the efficiency of the qZSC system using the novel modulation increases significantly. The details of operation principles for this soft-switching qZSC are analyzed. A simulation model is built and a 1.3-kW prototype is established to verify the proposed theory.

Multimode Modulation With ZVS for a Single-Phase Single-Stage Inverter

This article presents a modulation with zero-voltage switching (ZVS) for a single-phase, single-stage inverter intended for photovoltaic applications. In single-stage inverters, the dc-ac conversion stage is merged with the active power pulsation buffer stage. The proposed architecture uses a flying capacitor to handle the difference between the instantaneous input and output power, instead of the traditional bulky input capacitor. In this single-stage inverter, both the input current and the output voltage are controlled by the current of a single inductor. The inductor is operated in variable frequency boundary conduction mode. Multiple operation modes are used along the line cycle, all of them with ZVS in all transitions. The operation mode and control times are determined by the target input current, target inductor current, input voltage, output voltage, and flying capacitor voltage through equations that model the inductor waveform. These equations are solved with a fixed-point iteration method in a field-programmable gate array (FPGA). The modulation and control are validated in a 1 kVA prototype with 400 V input and 240 Vrms, 60 Hz output.

Adaptive Boundary Control Using Natural Switching Surfaces for Flyback Converters Operating in the Boundary Conduction Mode with Parameter Uncertainties

The derivation and implementation of the natural switching surfaces (NSS) considering certain parametric uncertainties for a flyback converter operating in the boundary conduction mode is the main focus of this paper. The NSS with nominal parameters presents many benefits for the control of nonlinear systems; for example, fast transient response under load-changing conditions. However, the performance worsens considerably when the converter actual parameters are different from the ones used in the design process. Therefore, a novel control strategy for NSS considering the effects of parameter uncertainties is proposed. This control law can estimate and adapt the control trajectories in a minimum number of switching cycles to obtain excellent performances even under extreme parameter uncertainties. The analytical derivation of the proposed adaptive switching surfaces is presented together with simulations and experimental results showing adequate performance under different tests, including comparisons with a standard PI controller.

Unified model of Sepic converter in continuous and discontinuous conduction modes

Aiming at the problems of the modelling methods for Sepic converter, they were described as in inexact, large amount of calculation and complicated expressions. A suitable hybrid switching model for both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) is proposed. Firstly, according to the working process of the Sepic converter, the switching conditions of Sepic converter between different working conditions are formulated. Secondly, by introducing the logic proposition and the equivalent translation principle, the switching conditions of the converter in different modes can be transformed into mixed logical inequalities, moreover then, a unified model of Sepic converter in CCM and DCM modes is obtained. Finally, the simulation experiment of Sepic converter operating in CCM, BCM (boundary conduction mode) and DCM modes were conducted, and compared with the state space averaging method, the validity of effectiveness of the proposed approach was shown.