Buck Mode Research Articles

A high performance adaptive on-time controlled valley-current-mode DC–DC buck converter

This paper presents an AOT-controlled (adaptive-on-time, AOT) valley-current-mode buck converter for portable application. The buck converter with synchronous rectifier not only uses valley-current-mode control but also possesses hybrid-mode control functions at the same time. Due to the presence of the zero-current detection circuit, the converter can switch freely between the two operating modes without the need for an external mode selection circuit, which further reduces the design difficulty and chip area. The converter for the application of high power efficiency and wide current range is used to generate the voltage of 0.6–3.0 V with a battery source of 3.3–5.0 V, while the load current range is 0.05–2 A. The circuit can work in continuous conduction mode with constant frequency in high load current range. In addition, a stable output voltage can be obtained with small voltage ripple. In pace with the load current decreases to a critical value, the converter transforms into the discontinuous conduction mode smoothly. As the switching period increases, the switching loss decreases, which can significantly improve the conversion efficiency. The proposed AOT controlled valley current mode buck converter is integrated with standard 0.18 μm process and the simulation results show that the converter provides well-loaded regulations with power efficiency over 95%. When the circuit switches between the two conduction modes drastically, the response time can be controlled within 30 μs. The undershoot voltage is controlled within 25 mV under a large current hopping range.

Magnetics-Based Efficiency Optimization for Low Power Cascaded-Buck-Boost Converter

This paper presents various techniques to achieve high efficiency for the bidirectional Cascaded-Buck-Boost converter. This converter has the features of low voltage across the switches and positive output voltage. The objective of this paper is to optimize the magnetics design to reduce the total losses in a low power non-isolated DC-DC circuit. A rigorous loss model with component nonlinearities is developed to determine the power loss distribution. It is validated by simulations and experiments. Based on the results of the power loss analysis and due to the low inductor profile and high efficiency target, nanocrystalline material will be the best candidate. Therefore, a new small volume low profile planar-nanocrystalline inductor is designed. Various deep de sign aspects for core and copper are discussed. The Finite-Element-Analysis (FEA) method is used to examine and visualize the inductor design. By implementing the planar-nanocrystalline inductor, a California Energy Commission (CEC) weighted efficiency of 99.05% for the buck mode and 98.98% for the boost mode are achieved with a peak efficiency of 99.24% and 99.21%, respectively.

Extend output voltage range of AC/AC converters using a reversible indirect matrix converter

AbstractThis paper proposes a reversible indirect matrix converter that expands the output voltage range. The proposed circuit has two operation modes. A buck mode that supplies an output voltage lower than the input voltage, and a boost mode that supplies an output voltage higher than the input voltage. In the boost mode, the proposed circuit has the characteristics of the current type inverter therefore, it is possible to obtain an output voltage with less harmonics. The proposed system is validated with a 2 kW prototype. The proposed circuit shows that the input/output voltage ratio of AC/AC direct conversion obtained is 0 to 1.2 or more. Moreover, the conversion efficiency of the proposed circuit is 92.8%.

A new nonisolated soft switched DC-DC bidirectional converter with high conversion ratio

ABSTRACT In this paper, a new soft switching bidirectional DC-DC converter with high conversion ratio is proposed. In the proposed converter, soft switching condition is provided with only one auxiliary switch for both directions, which simplifies the structure of the converter. The switching in boost mode is under ZCS condition and in buck mode is under ZVS condition. In the proposed converter, all diodes turn off under ZCS condition; therefore, losses related to diodes reverse recovery are eliminated. The control of the auxiliary switch is complementary to the main switch; thus, complex control circuit is not required. The voltage stress of the switch in boost mode is reduced extremely due to high voltage gain. The proposed converter is analysed, and to confirm the theoretical analysis, a 200-W prototype is implemented and the results are presented. Consequently, the efficiency of the proposed converter at full load is 97.5%.

Zero-Voltage Transition Nonisolated Bidirectional Buck–Boost DC–DC Converter With Coupled Inductors

This article presents a new zero-voltage transition (ZVT) pulsewidth-modulated (PWM) bidirectional dc–dc buck–boost converter. The main features of the suggested converter are simple control, simple structure, and the reduction of stresses on the power switches. In this converter, only two auxiliary switches, two snubber capacitors, one diode, and one coupled inductor are used to create zero voltage switching (ZVS) condition for all switching components in both power flow directions. The limited number of elements and the ZVS condition make a high-efficient converter that can be applied in many industrial applications. The proposed converter has the efficiency around 97% at full load in both boost and buck modes. Hence, the suggested soft-switching cell is in such a way that it can be applied in other basic nonisolated bidirectional converters such as cascade buck–boost, buck–boost/buck–boost, single-ended primary-inductor converter (SEPIC)/Zeta, and Cuk/Cuk. The confirmation of the theoretical waveforms and analysis of the suggested topology is done by the experiments carried out on a hardware prototype of a 100-W converter.

Soft Switching of Full-Bridge DC-DC Buck Converter

The conventional Bidirectional Full-bridge dc -dc converter is inefficient and may not be practical for the low power applications. This paper specifies an efficient DC-DC Converter that avoids power losses by using soft switching techniques like Zero Voltage Switching and Zero Current switching. The soft switching of Bidirectional Full-bridge DC-DC Converter operates as a buck converter when the power is positive and as a boost converter when the power flow is negative. Applications of soft switching Bidirectional Full-bridge DC-DC Converter are uninterrupted power supplies (UPS), distribution Systems, battery charger circuits, telecom power supplies, computer power systems. Detailed analysis of the converter is carried out in buck mode to obtain relations between the power circuit parameters. Based on the analysis, control schemes are described to operate the converter. The proposed full bridge DC-DC converter is simulated in Buck mode using MATLAB /SIMULINK.

Modulation strategy for improving the voltage gain of the dual‐active‐bridge converter

A novel modulation strategy for improving the voltage gain of a dual-active-bridge converter is proposed herein. Under the strategy, the converter performs a high-voltage gain under a low transformer turns ratio, thereby improving the transmission efficiency of the transformer because the large turns ratio typically results in large parasitic parameters, such as leakage inductance or distributed capacitance. In addition, voltage spikes can be avoided as the energy caused by leakage inductance is recycled to the output side. The operating principle of the proposed modulation strategy is discussed in detail herein. Moreover, the zero-voltage switching conditions in both buck and boost modes are analysed and derived. Finally, a prototype with a 350 V high voltage, 48 V low voltage, and 1 kW output power is established, and the conversion efficiencies of 94.2% in buck mode and 93.2% in boost mode are obtained. Experimental results verify the validity of the proposed modulation strategy.

A High Conversion Ratio and High-Efficiency Bidirectional DC–DC Converter With Reduced Voltage Stress

A dc-dc converter is proposed to achieve a high voltage conversion ratio for bidirectional power flow applications. The nonisolated topology is optimally designed to integrate both the switched capacitor and coupled inductor techniques for high efficiency. The windings of the coupled inductor are stacked at the low voltage source, which transfers any leakage energy of the coupled inductor directly into the output port and simplifies the clamping circuit. The optimal design keeps the voltage stress on the main switches low for the entire duty cycle operation. Thus, the converter demonstrates the advantage of wide-voltage gain based on common ground and low and steady voltage stress in both buck and boost modes of its operation. Furthermore, the converter can realize zero-voltage switching through the synchronous rectifiers without requiring extra hardware circuitry to enhance conversion efficiency. The operation principle, including the steady-state analysis, dynamic modeling, controller design, efficiency analysis, and optimization, are discussed in detail and verified by the experimental test. The prototype substantiates the theoretical analysis and soft-switching operation. The converter exhibits the capability for load and line regulation and demonstrates a peak efficiency of 96.38% in the boost mode and 95.61% in the buck mode of operation.

Small-Signal Modeling and Closed-Loop Control of Bidirectional Buck-Boost Current-Fed Isolated DC–DC Converter

The bidirectional buck-boost current-fed isolated dc–dc converter (B3CFIdc) has the advantages of low current stress, high efficiency, and wide power/voltage conversion range. The linear models of buck mode and boost mode of B3CFIdc are originally derived using state-space averaging method. The dual-closed-loop control configuration with the inductor current and output voltage is designed. In order to ensure the stability of both operation modes at the same time, the parameters of the controllers are designed using the method of Hurwitz criterion plus frequency response. The asymptotic stability of the operating conditions with periodic switching between the two modes caused by the periodic fluctuation of input voltage is verified using the linear switching theory. The detailed experimental results verify the correctness of the built small-signal models and the feasibility of the designed closed-loop control configuration and the design rule of the controller parameters.

Improved bidirectional DC/DC converter configuration with ZVS for energy storage system: analysis and implementation

This study proposes a novel design of soft-switching based bidirectional converter for the applications in energy storage systems. By implementing an additional auxiliary circuit to the conventional non-isolated converter, the proposed converter inherits better efficiency with minimised turn-on losses. Moreover, auxiliary switching devices are also soft-switched. This converter can be operated at high power outputs through ZVS turn-on operation. The operation principle, design analysis and experimental results are reported to validate its main features in the study. Furthermore, the performance of this converter is analysed on a 1 kW laboratory prototype for both boost and buck modes.

Time-sharing power supply full-bridge buck mode dual-input DC-DC converter

Time-sharing power supply full-bridge buck mode dual-input DC-DC converter

Disturbance observer based robust voltage control of photovoltaic generator interfaced by current mode buck converter

In this paper, a new control method for photovoltaic generator is presented. The novel method is implemented on photovoltaic generator charging a battery storage system thru buck converter. The controller tasks are re-shaping the buck plant converter, and cancel its right half-pole while keeping tight reference tracking and disturbance rejection. Moreover, the integrated system of generator-converter-load possesses nonlinear behavior due to the varying environmental conditions and the boundaries of photovoltaic generator versus battery state of charge, as revealed from an analysis of small-signal equations for possible unstable condition. It was shown that system constrains consequence in a complicated control task where standard controller of an inverse plant is insufficient to stabilize the system. Then a proportional integral controller is implemented. However, it is shown that varying closed-loop performance from over-damped to under-damped, depending on the operating point. Eventually utilizing a robust disturbance observer controller reveals that closed-loop performance remains nearly nominal throughout the entire operation range.

Single-Inductor Dual-Input Dual-Output Battery-PV Hybrid System With 2-D Adaptive On-Time Control for Internet of Things

In this article, we present a single-inductor dual-input dual-output power converter with two-dimensional adaptive-on-time (2-D AOT) control for Internet of things (IoT) applications. The proposed system combines energy from a 0.55-0.7 V photovoltaic (PV) module with a non-rechargeable 1.4-V zinc-air battery to extend the battery life. The proposed converter employs the buck-boost mode and the buck mode for the PV module and the battery, respectively, to produce two output voltages for different loading currents. The proposed 2-D AOT technique not only reduces the output voltage ripple but also improves the dual-source conversion efficiency over a wide input voltage range. Moreover, the response time of the self-tracking zero-current detector can also be improved by the proposed 2-D AOT. We fabricated the test chip using 0.18-μm technology in an area of 1.9 × 2.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measurement results demonstrated a peak efficiency of 92.5% with an input voltage range of 0.55-1.4 V. The output voltage ripple was less than 2.3% VOUT under different input voltage ranges.

A Buck-Boost Transformerless DC–DC Converter Based on IGBT Modules for Fast Charge of Electric Vehicles

A transformer-less Buck-Boost direct current–direct current (DC–DC) converter in use for the fast charge of electric vehicles, based on powerful high-voltage isolated gate bipolar transistor (IGBT) modules is analyzed, designed and experimentally verified. The main advantages of this topology are: simple structure on the converter’s power stage; a wide range of the output voltage, capable of supporting contemporary vehicles’ on-board battery packs; efficiency; and power density accepted to be high enough for such a class of hard-switched converters. A precise estimation of the loss, dissipated in the converter’s basic modes of operation Buck, Boost, and Buck-Boost is presented. The analysis shows an approach of loss minimization, based on switching frequency reduction during the Buck-Boost operation mode. Such a technique guarantees stable thermal characteristics during the entire operation, i.e., battery charge cycle. As the Buck-Boost mode takes place when Buck and Boost modes cannot support the output voltage, operating as a combination of them, it can be considered as critically dependent on the characteristics of the semiconductors. With this, the necessary duty cycle and voltage range, determined with respect to the input-output voltages and power losses, require an additional study to be conducted. Additionally, the tolerance of the applied switching frequencies for the most versatile silicon-based powerful IGBT modules is analyzed and experimentally verified. Finally, several important characteristics, such as transients during switch-on and switch-off, IGBTs’ voltage tails, critical duty cycles, etc., are depicted experimentally with oscillograms, obtained by an experimental model.

High efficiency wide input extreme output (WIEO) tapped inductor buck–boost converter for high power LED lighting

A power factor corrected single switch tapped-inductor buck–boost converter is proposed to achieve improved efficiency in extreme step-up and step-down conditions. This new and modified topology is having diode-tapped and switch-tapped configurations for step-down and step-up modes of operation, respectively. The proposed modified buck–boost converter is designed to operate in critical conduction mode (CrCM) to achieve quasi-resonant operation. Both the buck and boost functionalities of the buck–boost converter are analysed using state space analysis with closed loop stability under varying input and output conditions. Several advantages and necessity of tapped versions are discussed and implemented under wide input and extreme output (WIEO) conditions. Two different prototypes are developed at extreme buck and boost levels to establish the benefits of the proposed arrangements. The efficiency improvement of the proposed converter is compared with the conventional buck–boost converter. The achieved efficiency of diode-tapped buck mode and switch-tapped boost mode is found 95% and total harmonic distortion is observed only 4% at 230 V AC mains for a prototype of 150 W, which is much improved results as compared to the previous research work on the tapped-inductor converter.

A Hybrid String-Inverter/Rectifier Soft-Switched Bidirectional DC/DC Converter

In this article, a new bidirectional dc/dc converter topology based on a hybrid string-inverter/rectifier structure with an isolated CLLC resonant circuit is presented for energy storage applications. In this topology, a novel inverter/rectifier leg is presented that enables this circuit to operate in rectifying mode with much lower voltage ripple compared to the standard four-switch string rectifier circuit with the same capacitive filter. Compared to the dual-active-bridge circuit structure, the proposed inverter/rectifier leg is able to reduce the number of high-voltage switches required. A CLLC resonant circuit is employed to step-up/down the dc voltage levels. The operating principles of the proposed converter are discussed in this article. Silicon Carbide switches are used in both legs of the proposed converter, with zero-voltage switching turn- on and zero-current switching (ZCS) turn- off realized for all switches, whereas ZCS turn- on and off are achieved for all diodes. Simulation and experimental results are provided on a 1-kW, 100-kHz, 400-V/700-V converter system to highlight the merits of the proposed converter. Experimental results demonstrated that an efficiency of close to 97% is achieved in the proposed converter in both boost mode and buck mode at the full-load condition.

A Dual-Transformer-Based Bidirectional DC–DC Converter of Using Blocking Capacitor for Wide ZVS Range

In order to improve the efficiency of battery charging and discharging in a wide conversion gain, a dual-transformer-based full bridge converter using a block capacitor was proposed. By adding the blocking capacitor in the primary side of one transformer, an extended zero voltage switching (ZVS) range is obtained in a wide output voltage range, which is achieved by regulating the secondary voltage of the transformers to match the output voltage according to the voltage-second balance in both boost and buck modes. Besides, a mirror-symmetrical modulation is introduced in reverse power flow to avoid a limited ZVS range of the traditional dual-transformer converter. The power characteristics and ZVS range are analyzed in detailed. The analysis results and transformer current are compared with the published dual-transformer converter and the conventional dual active bridge (DAB) converter to demonstrate the advantages. Finally, a 300W prototype was built and tested to verify the effectiveness of the proposed converter.

Design and Development of Standalone Solar Photovoltaic Battery System with Adaptive Sliding Mode Controller

In this paper, a solar photovoltaic-battery located standalone system is proposed. The configuration of bidirectional buck-boost converter has been proposed for charging (buck) and discharging (boost) the battery storage system. Due to solar energy sources irregular nature and variations in load demand, DC micro grids mostly depend on control methods to overcome with DC link voltage variations and power stability. Adaptive sliding mode controller with washout filter is applied due to its good strength for unexpected change of energy resources and loads. This system includes a solar photovoltaic array basis on maximum power tracking from PV, boost converter to maximize power from the PV. A bidirectional DC-DC buck-boost converter is proposed being charging battery in buck mode and discharging battery in boost mode. Incremental conductance implemented to obtain maximum power from photovoltaic array. In this paper, study of comparison between proportional-plus integral method and sliding mode control method with washout filter has been also simulated in the MATLAB using Simulink and the Sim Power System toolbox.

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.

Uncertainty Estimator based Sliding Mode Control Schemes for Multimode Noninverting Buck-Boost DC-DC Converter

A noninverting buck-boost dc-dc converter can be operated in buck, boost and buck-boost mode depending on an input voltage and desired output voltage. An input voltage must be known to operate the converter in these operating modes. In this paper, two methods are proposed to estimate uncertainties in input voltage and load resistance. First, state observer based adaptive law is designed to estimate the uncertainties. Based on the estimates, a pulsewidth modulation based sliding mode control is proposed to control the output voltage of the converter. Another uncertainty estimator scheme, namely, disturbance observer is proposed to estimate the uncertainties and then a pulsewidth modulation based sliding mode control technique is proposed. Both the proposed schemes are compared and their robustness to the uncertainties is proved by simulation in MATLAB/Simulink.