Zero-voltage-switching half-bridge DC-DC converter with modified PWM control method

Asymmetric control scheme is an approach to achieve zero-voltage switching (ZVS) for half-bridge isolated dc-dc converters. However, it is not suited for wide range of input voltage due to the uneven voltage and current components stresses. This paper presents a novel "duty-cycle-shifted pulse-width modulated" (DCS PWM) control scheme for half-bridge isolated dc-dc converters to achieve ZVS operation for one of the two switches without causing the asymmetric penalties in the asymmetric control and without adding additional components. Based on the DCS PWM control scheme, an active-clamp branch comprising an auxiliary switch and a diode is added across the isolation transformer primary winding in the half-bridge converter to achieve ZVS for the other main switch by utilizing energy stored in the transformer leakage inductance. Moreover, the auxiliary switch also operates at ZVS and zero-current switching (ZCS) conditions. Furthermore, during the off-time period, the ringing resulted from the oscillation between the transformer leakage inductance and the junction capacitance of two switches is eliminated owing to the active-clamp branch and DCS PWM control scheme. Hence, switching losses and leakage-inductance-related losses are significantly reduced, which provides the converter with the potential to operate at higher efficiencies and higher switching frequencies. The principle of operation and key features of the proposed DCS PWM control scheme and two ZVS half-bridge topologies are illustrated and experimentally verified.     

Analysis and Optimal Design Considerations for an Improved Full Bridge ZVS DC–DC Converter With High Efficiency

This paper proposes an improved full bridge dc–dc converter, which can achieve zero-voltage-switching (ZVS) with wide input voltage range and load range. The operation principle of the converter and the optimal design considerations for high efficiency and ZVS range are analyzed. By adding two clamp diodes and two small coupled inductors at the primary side of the transformer, the voltage ringing across rectifier diodes is reduced. Therefore, Schottky diodes can be employed to reduce conduction loss, and high efficiency is achieved. A 1.2-kW/105-kHz prototype was made with an efficiency higher than 95% at full load to verify the theoretical analysis.     

A 1-MHz Zero-Voltage-Switching Asymmetrical Half-Bridge DC/DC Converter: Analysis and Design

The asymmetrical half-bridge (AHB) topology discussed in this paper is one of the complementary driven pulse-width modulated converter topologies, which presents an inherent zero-voltage switching (ZVS) capability. In the previous work, the ideal operation of the converter and the ZVS realization process have been analyzed. However, the influence of the circuit parasitics on the output voltage drop and the design constraints of the circuit parameters to ensure the ZVS operation have not been investigated. The minimum load needed to ensure the ZVS operation is also not readily available. This paper presents a detailed and practical design for a 1-MHz AHB converter. A revised voltage transfer ratio of the converter is derived considering the influence of circuit parasitics and the ZVS transition. Two circuit parameters responsible for maintaining the ZVS operation are the transformer leakage inductance and the interlock delay time between the gate signals of two switches. A design method of the two parameters is proposed, which can ensure the ZVS transition. The possible ZVS range of the load variation is also investigated. A 50-W AHB converter with 1-MHz switching frequency was constructed, and a maximum efficiency of 91% was achieved.     

Interleaved ZVS Converter With Ripple-Current Cancellation

In this paper, an interleaved soft-switching converter with ripple-current cancellation is presented to achieve zero- voltage-switching (ZVS) turn-on and load current sharing. In order to achieve ZVS turn-on, an active snubber is connected in parallel with the primary winding of the transformer. The energy stored in the transformer leakage inductance and magnetizing inductance can be recovered so that the peak voltage stress of switching devices is limited. The resonance at the transition interval is used to realize ZVS turn-on of all switches. In order to achieve three-level pulsewidth-modulation (PWM) scheme, an addition fast-recovery diode is used in the converter. Three-level PWM scheme can reduce the ac ripple current on the output inductor such that the output inductor can be reduced. The current-doubler rectifier is adopted in the secondary side of the transformer to reduce the transformer secondary-winding current and output voltage ripple by canceling the current ripple of two output inductors. The output voltage is controlled at the desired value using the interleaved PWM scheme. These features make the proposed converter suitable for the dc-dc converter with high output current. The operation principles, steady state analysis, and design equations of the proposed converter are provided in detail. Finally, experiments based on a 600-W (12 V/50 A) prototype are provided to verify the effectiveness and feasibility of the proposed converter.     

A current-tripler dc/dc converter

This paper proposes a novel zero-voltage-switching (ZVS) current-tripler dc/dc converter. Compared to the conventional phase-shifted ZVS full-bridge dc/dc converter with current-doubler rectifier, the proposed current-tripler dc/dc converter reduces the synchronous rectifier (SR) conduction loss as well as the transformer winding loss. Furthermore, the proposed transformer structure is very compact, and thus the power density of the converter could be greatly increased. Analysis and experimental results show that the proposed topology offers great advantages when the converter output current goes higher and the voltage goes lower, as demanded by future microprocessors and telecommunications systems. A 48-V/1.0-V, 100-A, 300-kHz prototype is implemented, and the experimental results show that it can achieve 87% efficiency at full load.     

A novel self-oscillating, boost-derived DC-DC converter with load regulation

This paper proposes a novel self-oscillating, boost-derived (SOBD) dc-dc converter with load regulation. This proposed topology utilizes saturable cores (SCs) to offer self-oscillating and output regulation capabilities. Conventionally, the self-oscillating dc transformer (SODT) type of scheme can be implemented in a very cost-effective manner. The ideal dc transformer provides both input and output currents as pure, ripple-free dc quantities. However, the structure of an SODT-type converter will not provide regulation, and its oscillating frequency will change in accordance with the load. The proposed converter with SCs will allow output-voltage regulation to be accomplished by varying only the control current between the transformers, as occurs in a pulse-width modulation (PWM) converter. A control network that combines PWM schemes with a regenerative function is used for this converter. The optimum duty cycle is implemented to achieve low levels of input- and output-current ripples, which are characteristic of an ideal dc transformer. The oscillating frequency will spontaneously be kept near-constant, regardless of the load, without adding any auxiliary or compensation circuits. The typical voltage waveforms of the transistors are found to be close to quasisquare. The switching surges are well suppressed, and the voltage stress of the component is well clamped. The turn-on/turn-off of the switch is zero-voltage switching (ZVS), and its resonant transition can occur over a wide range of load current levels. A prototype circuit of an SOBD converter shows 86% efficiency at 48-V input, with 12-V, 100-W output, and presents an operating frequency of 100 kHz.     

Analysis and Implementation of a ZVS-PWM Converter With Series-Connected Transformers

This brief presents the analysis, design, and implementation of zero-voltage switching (ZVS) active clamp converter with series-connected transformer. A family of isolated ZVS active clamp converters is introduced. The technique of the adopted ZVS commutation will not increase additional voltage stress of switching devices. In the adopted converter with series-connected transformer, each transformer can be operated as an inductor or a transformer. Therefore, no output inductor is needed. To reduce the voltage stress of the switching device in the conventional forward converter, the active clamp technique is used to recycle the energy stored in the transformer leakage back into the input dc source. Finally, experimental results are presented taken from a laboratory prototype with 100-W rated power, input voltage of 155 V, output voltage of 5 V, and operating at 150 kHz. [All rights reserved Elsevier].     

A novel ZVS DC/DC converter for high power applications

This paper presents a novel zero voltage switch (ZVS) pulse-width modulation (PWM) DC/DC converter for high power, high output voltage applications. By using two active switches in the secondary side of a transformer, the proposed converter achieves not only ZVS of the active switches in the entire load ranges but also soft commutation of the output rectifier diodes. The proposed topology has simple structure and control strategy. Simulation results and experimental results of a 2.8 kW 200 kHz DC/DC converter are presented.     

High-Efficiency Boost Half-Bridge Converter With Fast Boost Current Transferring ZVS Operation

A new boost half bridge (BHB) converter is presented. It is composed of additional switch, diode and coupled winding to boost inductor of BHB converter. Using the transferring of boost inductor current to coupled winding in a short period, the cancellation of zero voltage switching (ZVS) current, which always occurs in convention one, is prevented. Therefore, the ZVS operation is easily achieved by leakage inductor current of transformer. Furthermore, since negatively build-up leakage inductor current of boost winding helps the ZVS operation throughout full load range, the excellent ZVS operation and high efficiency is achieved.      

Improved voltage clamping scheme for ZVS PWM three-level converter

This paper proposes an improved zero-voltage-switching pulsewidth-modulation (ZVS PWM) three-level converter, which is improved from the original ZVS PWM three-level converter by merely exchanging the position of the resonant inductance and the transformer, such that the transformer is connected with the lagging switches. The improved converter has several advantages over the original, e.g., the clamping diodes conduct only once in a switching period, and the resonant inductance current is smaller in zero state, leading to a higher efficiency and reduced duty-cycle loss. A blocking capacitor is usually introduced to the primary side to prevent the transformer from saturating. This paper analyzes the effects of the blocking capacitor in different positions, and a best scheme is determined. A 2.5-kW prototype converter verifies the effectiveness of the improved converter and the best scheme for the blocking capacitor.     

An Analysis of the ZVS Two-Inductor Boost Converter under Variable Frequency Operation

The two-inductor boost converter has been previously presented in a zero-voltage switching (ZVS) form where the transformer leakage inductance and the MOSFET output capacitance can be utilized as part of the resonant elements. In many applications, such as maximum power point tracking (MPPT) in grid interactive photovoltaic systems, the resonant two-inductor boost converter is required to operate with variable input output voltage ratios. This paper studies the variable frequency operation of the ZVS two-inductor boost converter to secure an adjustable output voltage range while maintaining the resonant switching transitions. The design method of the resonant converter is thoroughly investigated and explicit control functions relating the circuit timing factors and the voltage gain for a 200-W converter are established. The converter has an input voltage of 20V and is able to produce a variable output voltage from 169V to 340V while retaining ZVS with a frequency variation of 1MHz to 407kHz. Five sets of theoretical, simulation and experimental waveforms are provided for the selected operating points over the variable load range at the end of the paper and they agree reasonably well. The converter has achieved part load efficiencies above 92% and an efficiency of 89.6% at the maximum power of 200W     

Active-clamp ZVS converter with step-up voltage conversion ratio

This article presents the circuit implementation and design considerations of a zero voltage switching (ZVS) converter with voltage step-up for battery-based applications. An active-clamp circuit including one auxiliary switch and one clamp capacitor is connected in parallel with the main switch to allow resonant behaviour by the output capacitances of switches and transformer leakage inductance during the transition interval. Thus, the ZVS turn-on of switches can be achieved. The switching losses and thermal stresses of the semiconductors are reduced. The circuit configuration, operation principle and design considerations of the converter are discussed in detail. Finally, experiments conducted on a laboratory prototype rated at 200 W are provided to verify the theoretical analysis and the effectiveness of the proposed converter.     

A leakage-inductance-based ZVS two-inductor boost converter with integrated magnetics

A two-inductor boost converter topology has conduction loss and transformer utilization advantages in converting low-voltage higher current inputs to high output voltages. In this letter, a new zero-voltage switching (ZVS) two-inductor boost converter with integrated magnetics is proposed. In the new topology, the two current source inductors, a resonant inductor and a two-winding transformer, are integrated into one single magnetic core with three windings. Two windings simultaneously perform the functions of the current source inductors and the transformer primary. The transformer leakage inductance forms the resonant inductance. This leads to a much more compact converter design with a significant reduction in the number of core and winding components. A theoretical analysis establishes the operating point of the ZVS converter. Both of the theoretical and experimental waveforms, including flux waveforms for the legs of the integrated core structure, are presented at the end of the letter.     

一种零电压开关Zeta变换器的设计

给出了一种零电压开关Zeta变换器,这种变换器可以提高效率和减小功率开关管的电压应力.当变换器工作在连续模式时,应用谐振电容和变压器的漏感实现功率开关管的零电压导通.详细分析了变换器的工作原理,并设计了相应的电路进行验证.仿真结果表明所设计的Zeta变换器效率达92.21%,输出电压纹波为125 mV.它可被用于等离子显示屏(PDP)电源系统.     

The Power Loss Optimization of a Current Fed ZVS Two-Inductor Boost Converter With a Resonant Transition Gate Drive

This paper develops a power loss optimization method in a current fed zero-voltage switching (ZVS) two-inductor boost converter, which is suitable for the module integrated converter applications in grid interactive photovoltaic systems. The paper conducts the numerical analysis of the variable power loss components and establishes a set of the circuit parameters for an optimized operating point with a minimized average power loss. The ZVS two-inductor boost cell is fed from a sinusoidally modulated two-phase synchronous buck converter with an interphase transformer and produces a rectified sinusoidal voltage, which can be applied to an unfolding stage to generate the grid compatible voltage. The boost cell is also equipped with a resonant transition gate drive circuit to reduce the power loss in the drive circuit under high frequency operations. The experimental results for a prototype 1-MHz 100-W ZVS two-inductor boost converter are presented at the end of the paper.     

Transformer secondary leakage inductance based ZVS dual bridge DC/DC converter

A novel zero voltage switching (ZVS) dual bridge dc/dc converter is presented. The proposed converter is composed of two dual-transistor-forward converter, coupled with a single high frequency transformer. ZVS is realized by introducing a proper leakage inductance to the secondary of the high frequency isolation transformer with a corporation of a designed pulse-width modulation control. Operation principle and ZVS condition of the proposed converter are analyzed. Experimental results obtained from a 3.2-kW prototype are given. Extensions of the proposed converter topologies and experimental results of one extension converter are presented.     

Utilization of an active-clamp circuit to achieve soft switching inflyback converters

Flyback derived power convertor topologies are attractive because of their relative simplicity when compared with other topologies used in low power applications. Incorporation of active-clamp circuitry into the flyback topology serves to recycle transformer leakage energy while minimizing switch voltage stress. The addition of the active-clamp circuit also provides a mechanism for achieving zero-voltage-switching (ZVS) of both the primary and auxiliary switches. ZVS also limits the turn-off di/dt of the output rectifier, reducing rectifier switching losses, and switching noise due to diode reverse recovery. This paper analyzes the behavior of the ZVS active-clamp flyback operating with unidirectional magnetizing current and presents design equations based on this analysis. Experimental results are then given for a 500 W prototype circuit illustrating the soft-switching characteristics and improved efficiency of the power converter. Results from the application of the active-clamp circuit as a low-loss turn-off snubber for IGBT switches is also presented     

Zero-Voltage Switching Two-Transformer Full-Bridge PWM Converter With Lossless Diode-Clamp Rectifier for PDP Sustain Power Module

This paper presents a zero-voltage switching (ZVS) two-transformer full-bridge (TTFB) pulsewidth modulation (PWM) converter with lossless diode-clamp rectifier for a plasma display panel sustaining power module (PSPM). The TTFB converter has series-connected two transformers which act as an output inductor as well as a main transformer. Although the naturally doubled leakage inductor due to the series-connected two transformers contributes to achieve the ZVS of the lagging leg, it creates a serious voltage ringing across the output rectifier diodes. This results in the heavy voltage stresses across the rectifier diodes. Thus the dissipative snubber circuits are required in spite of the severe power dissipation. To overcome these problems, a new lossless diode-clamp rectifier (LDCR) is employed as the output rectifier, which helps the voltage across rectifier diodes to be clamped at one half the output voltage ($V_o/$2) or a full output voltage$(V_o)$. Therefore, no dissipative snubber circuits for the rectifier diodes are needed and a high efficiency as well as a low noise output voltage can be realized. In addition, the clamping capacitors of the LDCR can help considerably to reduce the primary circulating current. The operations, analysis, and design consideration of proposed converter are presented. Also, a 425-W, 385-$V_ dc$input, 170-$V_ dc$output prototype is constructed and experimental results show the validity of the proposed converter.     

一种新颖有源箝位ZVS正激变换器的研究

介绍了一种中心抽头全波整流有源箝位ZVS正激变换器的工作原理及主要参数计算。有源箝位电路由一个箝位开关管和箝位电容组成。变压器磁芯实现无损复位,励磁能量和漏感能量全部传递到负栽.磁芯利用率高,功率开关管承受电压应力降低。通过变压器漏感与开关管输出电容的谐振,主开关管与箝位开关管都可以实现ZVS开通,提高了变换器工作效率。文章首先分析了变换器工作原理,然后给出了主要参数的计算方法,最后通过样机(48V输入5V/20A输出)实验验证了该拓扑的高效性能。     

A self core reset and zero voltage switching forward convertertopology

A self core reset and zero voltage switching (ZVS) forward converter topology is presented in this paper. By employing a simple auxiliary circuit, the proposed topology is able to achieve self reset of the power transformer without the use of the conventional tertiary reset winding, and its main switch can be turned on and turned off under ZVS independent of line and load conditions. This simplifies the power transformer, and the switching losses are substantially removed to improve the overall efficiency. Steady state analysis of the circuit is performed. Based on the analysis, a design procedure is presented, and the effects of the circuit parameters on the flux excursion of the power transformer are investigated to make sure self reset can be achieved without increasing the core losses. Simulation and experiment on a 5 V, 100 W prototype circuit operated at 200 kHz are carried out to verify the design, about 5% higher overall efficiency is obtained in the prototype converter than in its conventional counterpart