High Step-down Conversion Ratio Research Articles

A Low Voltage Stress PFC Rectifier Based on Nonoverlapping Strategy Using Resonant Switched-Capacitor Converter

In order to break limited step-down ratio range and poor regulation capacity in the conventional resonant switched-capacitor converters for rectifier application, a single-stage ac/dc rectifier based on the dual-resonance switched-capacitor converter is proposed in this article. Through utilizing a dual-resonant structure and nonoverlapping strategy to realize wide continuous voltage gain of the proposed converter, high power factor (PF) and low total harmonic distortion (THD) based on the narrow dead zone are guaranteed by operating at high step-down conversion ratio in this converter topology. Moreover, the voltage gain is concentrated between resonant frequency and double resonant frequency to achieve a narrow switching frequency range for rectifier application. Furthermore, operating at flat voltage stress curves to obtain low voltage stress character. Comprehensive mode analysis, input PF and THD, and stress analysis are given, and analysis results indicate that the proposed power factor correction converter can work with soft turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and zero-current turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ; high efficiency is realized. Finally, an experimental prototype with 85–130 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> input and 47 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> /44 W output is built and tested for verifying the operation modes and PFC performance, and the comparison between different rectifiers and the proposed one is provided.

Asymmetrical PWM Scheme to Widen the Operating Range of the Three-Phase Series-Capacitor Buck Converter

The three-phase series-capacitor (3P-SC) buck converter is analyzed extensively in this study for high-voltage step-down applications with a wide input voltage range. This structure is attractive due to its high step-down conversion ratio and inherent current balancing. However, the inductor currents of the 3P-SC converter become unbalanced when the duty cycle exceeds 1/3. This results in significant stress and reduces the utilization of switching devices. This article proposes an asymmetrical pulsewidth modulation (PWM) scheme for the 3P-SC converter to overcome the limitations of the conventional PWM scheme. By using the proposed switching scheme, the duty cycle can be increased to one while retaining the high conversion ratio and current balancing functionality. Thereafter, the proposed asymmetrical PWM strategy is generalized for multiphase series-capacitor (nP-SC) converters. Finally, to validate the performance of the proposed PWM strategy, a 1.2-kW prototype 3P-SC converter is fabricated and tested.

Performance of a coupled inductor for interleaved buck converter with improved step‐down conversion ratio

This paper proposes a dual-winding coupled inductor (DWCI) based interleaved buck converter (IBC) with improved step-down conversion ratio to improve the ripple in inductor currents and to achieve lower value of the output filter capacitor. The proposed IBC achieves a high step-down conversion ratio by using a switch-capacitor cell. In the continuous conduction mode (CCM), the systematic analysis of ripple current in the windings of DWCI shows the improvement of ripple in inductor current compared to the existing IBCs. Further, the coupling factor of the DWCI reduces the requirement of the minimum value of the output filter capacitor. The operation principle and boundary load condition of the proposed IBC with DWCI are analysed. Furthermore, the small-signal modelling of the proposed IBC with DWCI is investigated. In the voltage-mode control framework, a PI-controller is designed to investigate the sensitivity to the load parameter variation and the performance of the reference output voltage. The proposed converter with DWCI is implemented and experimental results are provided.

Dual PWM Control for High Step-Down DC-DC Converters

The conventional step-down dc–dc converters under the single pulsewidth modulation (PWM) control scheme may not provide enough step-down voltage conversion capabilities with considering the minimum on -time and the switching frequency of the power switch. In order to overcome this difficulty, a dual PWM control scheme for designing the high step-down dc–dc converter is proposed in this article. Both high-frequency and low-frequency PWM waveform generators are utilized in synthesizing the dual PWM control of buck converters. The resulting PWM waveform will lead to various switching cycles, and five operating modes of the buck converter, which can be defined accordingly. The operation principle of the proposed converter and its small-signal switched model are presented in detail. One salient feature of the proposed design is that if the duty cycle of the high-frequency PWM is exactly equal to that of the low-frequency PWM, by exploring the volt–second balance condition, the voltage gain can be expressed as the quadratic formula of the duty cycle of the PWM signal when power switches are operated under the continuous conduction mode. Thus, a high step-down conversion ratio and significant reductions of the inductor current ripple can be ensured simultaneously. Since no modifications of the conventional circuit topology are made, the proposed scheme is very cost-effective. Simulation studies and hardware prototype circuit implementations are conducted to validate the proposed design with satisfactory performance.

Two‐phase high efficiency interleaved buck converter with improved step‐down conversion ratio and low voltage stress

A two-phase interleaved buck converter (IBC) providing a high step-down conversion ratio is proposed in this study. The proposed IBC uses a switch-capacitor cell to achieve a high step-down conversion ratio compared to the conventional IBC. The cell consists of two parallel switches and two crossly placed identical capacitors. These identical capacitors are charged in series and discharged in parallel by producing a lower output voltage compared to the conventional IBC at the same duty ratio. The proposed converter provides less voltage and current stresses. The operation principle, the ripple and the average current through the inductors are described in continuous conduction mode. The boundary load condition is also determined. By describing the charging and discharging of the two identical capacitors of the cell, the capacitance value is determined. The losses and efficiency are analysed, and 96.33% efficiency is achieved. Finally, the proposed converter is implemented and experimental results are provided.

Nonisolated High Step-Down Converter With ZVS and Low Current Ripples

In this paper, a nonisolated high step-down converter is proposed. Energy transfer capacitor and built-in transformer are employed to achieve a very high step-down conversion ratio. Due to the interleaved technique, small values of output inductance can be used, leading to a fast transient response. Furthermore, the use of a coupled inductor reduces inductor current ripples, which implies lower losses. Two main switches and two synchronous rectifiers are used in the converter and all can achieve zero-voltage-switching. As no floating switches are employed, grounded gate drivers and boost strap drivers can be used, avoiding the use of complex isolated gate drivers. In addition, if the switches are shorted, the high input voltage does not appear at the output; thus, the load is protected. A 48 V/1 V 30 A prototype was built, and experimental results are provided to verify the performance of the converter.

High-Efficiency Nonisolated Converter With Very High Step-Down Conversion Ratio

This paper introduces a new nonisolated converter topology with very high step-down conversion ratio and high efficiency for high current low voltage point-of-load voltage regulator modules. Compared to a conventional two-phase buck converter, the new converter triples the effective duty-ratio and lowers the voltage stress of the transistors, significantly reducing the overall volume of the converter while maintaining high efficiency. The new converter is capable of delivering high current to the output by two interleaved phases and further features an inherent current sharing to balance the load between the phases. The use of lower voltage stress transistors allows operation at high switching frequencies that translates into fast dynamic response to load perturbations. The operation of the topology is verified on a 30 W, 48 V-to-1 V prototype, demonstrating peak efficiency of 91.5% and above 88% for most of the load range.

PID, 2-DOF PID and Mixed Sensitivity Loop-Shaping Based Robust Voltage Control of Quadratic Buck DC-DC Converter

DC-DC Quadratic Buck Converter (QBC) is largely used in applications where the high step-down conversion ratio is required. In the practical implementation, QBC is subject to uncertainties, disturbance, and sensor noise. To address the QBC control problems, a two-degree of freedom PID (2-DOF PID) is designed in the robust control framework. Further, for comparison purpose, a one-degree of freedom PID (1-DOF PID) and mixed sensitivity loop-shaping (MS-LS) controller are also proposed. Considering QBC parasitic components, the QBC small-signal transfer function is derived based on a practical approach. Sensitivity functions are used to specify the desired design requirements, and non-smooth optimization is used to tune both PID's parameters. The three control structures are implemented and tested in the Matlab/Simulink environment. As attested by simulation results, the 2-DOF PID exhibits a better regulation accuracy with enhanced robust stability and robust performance for a wide range of supply voltage/load variation and sensor noise effect.

A Novel Transformer-less Interleaved Four-Phase Step-Down DC Converter With Low Switch Voltage Stress and Automatic Uniform Current-Sharing Characteristics

In this paper, we propose a novel transformer-less direct current (dc) converter that features low switch voltage stress and automatic uniform current sharing. An interleaved four-phase voltage divider operating from a 400 V dc bus is used to achieve a high step-down conversion ratio with a moderate duty ratio. Based on the capacitive voltage division, the proposed converter achieves two major objectives, i.e., increased voltage conversion ratio, due to energy storage in the blocking capacitors, and reduced voltage stress of active switches and diodes. As a result, the proposed converter permits the use of lower voltage rating MOSFETs to reduce both switching and conduction losses, thereby improving the overall efficiency. In addition, due to the charge balance of the capacitors, the proposed converter enables automatic uniform current sharing of the interleaved phases without adding extra circuitry or complex control methods. The operation principles and performance analyses of the proposed converter are presented, and its effectiveness is verified by a 500 W output power prototype circuit that converts 400 V input voltage into 24 V output voltage.

High step‐down interleaved buck converter with low voltage stress

This study presents a four-phase interleaved buck converter with low voltage stress and high step-down conversion ratio. The proposed converter provides an extended duty cycle and low voltage stress for switches and diodes, in high step-down applications. This makes it possible to use switches with lower voltage rating and thus reduce both switching and conduction losses to improve the overall efficiency. Extremely low output current ripple and continuous input current are two other advantages of the proposed converter. Also, the output current can be shared between interleaved modules without using additional current sharing control technique due to charge balance of input and blocking capacitors. All these benefits are obtained without adding any active auxiliary component or using transformers. The experimental results from a prototype of the proposed converter designed for 400–24 V, operating at 0.5 kW, verify the theoretical analysis.

English

English

A Novel Transformerless Interleaved High Step-Down Conversion Ratio DC–DC Converter With Low Switch Voltage Stress

In this paper, a novel transformerless interleaved high step-down conversion ratio dc-dc converter with low switch voltage stress is proposed. In the proposed converter, two input capacitors are series-charged by the input voltage and parallel-discharged by a new two-phase interleaved buck converter for providing a much higher step-down conversion ratio without adopting an extreme short duty cycle. Based on the capacitive voltage division, the main objectives of the new voltage-divider circuit in the converter are for both storing energy in the blocking capacitors for increasing the step-down conversion ratio and reducing voltage stresses of active switches. As a result, the proposed converter topology possesses the low switch voltage stress characteristic. This will allow one to choose lower voltage rating MOSFETs to reduce both switching and conduction losses, and the overall efficiency is consequently improved. Moreover, due to the charge balance of the blocking capacitor, the converter features automatic uniform current sharing characteristic of the interleaved phases without adding extra circuitry or complex control methods. The operation principles and relevant analysis of the proposed converter are presented in this paper. Finally, a 400-V input voltage, 25-V output voltage, and 400-W output power prototype circuit is implemented in the laboratory to verify the performance.

Transformerless Three-Level DC-DC Buck Converter with a High Step-Down Conversion Ratio

For high power high step-down dc-dc conversion applications, conventional three-level dc-dc converters are subject to extreme duty cycles or increased volume and cost due to the use of transformers. In this paper, a transformerless three-level dc-dc buck converter with a high step-down conversion ratio is proposed. The converter comprises two asymmetrical half bridges, which are of the neutral point clamped structures. Therefore, the output pulse voltage of the converter can be obtained in terms of the voltage difference between the two half bridges. In order to realize harmonious switching of the converter, a modulation strategy with capacitor voltages self balance is presented. According to the deduced output dc voltage function, transformerless operation without extreme duty cycles can be implemented. Experimental results from a 1kW prototype verify the validity of the proposed converter. It is suitable for ship electric power distribution systems.

Design and MATLAB Simulation of a Fuel Cell Based Interleaved Buck Converter with Low Switching Losses and Improved Conversion Ratio

The Interleaved Buck Converter (IBC) having low switching losses and improved step-down conversion ratio is suitable for the applications where the input voltage is high and the operating duty is below 50%. It is similar to the conventional IBC, but two active switches are connected in series and a coupling capacitor is employed in the power path. This IBC shows that since the voltage stress across all the active switches is half of the input voltage before turn-on or after turn-off when the operating duty is below 50%, the capacitive discharging and switching losses can be reduced considerably. This allows the IBC to have higher efficiency and operate with higher switching frequency. In addition, it has a higher step-down conversion ratio and a smaller output current ripple compared with a conventional IBC. Closed loop control using PI controller has been done to improve the system performances. By replacing the conventional voltage source by a renewable one will enhance its reliability and is more economical. So here the dynamics of a polymer electrolyte membrane fuel cell (PEM Fuel cell) is modelled, simulated and presented. MATLAB -SIMULINK is used for the modelling and simulation of the fuel cell stack. Design and analysis of the converter is done for a DC input of 200V and duty ratio D<0.5. The expected output DC voltage is 24V/10A. Simulation of both conventional and new IBC is done using MATLAB/SIMULINK and their outputs are compared.

Interleaved Buck Converter Having Low Switching Losses and Improved Step-Down Conversion Ratio

This paper proposes a new interleaved buck converter (IBC) having low switching losses and improved step-down conversion ratio, which is suitable for the applications where the input voltage is high and the operating duty is below 50%. It is similar to the conventional IBC, but two active switches are connected in series and a coupling capacitor is employed in the power path, such as Cuk, Sepic, and Zeta converters. The proposed IBC shows that since the voltage stress across all the active switches is half of the input voltage before turn-on or after turn-off when the operating duty is below 50%, the capacitive discharging and switching losses can be reduced considerably. This allows the proposed IBC to have higher efficiency and operate with higher switching frequency. In addition, the proposed IBC has a higher step-down conversion ratio and a smaller output current ripple compared with a conventional IBC. The features, operation principles, and relevant analysis results of the proposed IBC are presented in this paper. The validity of this study is confirmed by the experimental results of prototype converters with 150-200 V input, 24 V/10 A output.

5 kW DC/DC converter for hydrogen generation from photovoltaic sources

This paper covers the design of a DC–DC power converter aimed for hydrogen production from photovoltaic sources. Power conditioning for such application is usually driven by different constraints: high step-down conversion ratio is required if the input voltage of such equipment has to be compatible with photovoltaic sources that are connected to grid-connected inverters; galvanic isolation; high efficiency and low mass. Taking into account those factors, this work proposes a push–pull DC/DC converter for power levels up to 5 kW. The operation and features of the converter are presented and analyzed. Design guidelines are suggested and experimental validation is also given.