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.     

Design and Implementation of an Accurately Regulated Multiple Output ZVS DC–DC Converter

An accurately regulated multiple-output zero-voltage switching (ZVS) DC-DC converter is proposed. The converter is composed of three outputs altogether. The first and second outputs are regulated through the duty cycle control of two asymmetrical half bridge converters, while the third output is regulated through the phase shift of the two asymmetrical half bridge converters. The characteristic of this multiple-output dc-dc converter is analyzed and design process is investigated. ZVS is realized for all the main switches. Therefore this multiple-output dc-dc converter can operate with higher efficiency at higher switching frequency. The operation stages, ZVS condition and control detail are also presented. A 400 V input, 48 V/10 A, 5 V/20 A, 12 V/5 A outputs prototype is built to verify the design. The efficiency at rated input voltage full load is 93.36%.     

Energy Management Power Converters in Hybrid Electric and Fuel Cell Vehicles

Using a bidirectional dc-dc converter along with low-voltage energy storage for the high-voltage dc bus and traction motor drives has been a prominent option for hybrid electric and fuel cell vehicles. This paper will describe the significance of energy management power converters and their circuit topology options for efficiency, size, and cost considerations. Whether isolated or nonisolated, soft switching techniques have been widely used in high-power bidirectional dc-dc converters. Through some design examples, the component selection and circuit design optimization are discussed, and their efficiency evaluation results are also given. Major difficulties of developing a high-power bidirectional dc-dc converter are found in lack of high-power passive components and lack of multiphase dc-dc controllers. More development work needs to be done in these areas     

The design and experimentation of the new cascaded DC-DC boost converter for renewable energy

After renewable energy generated, a direct current value is converted to a direct current value at another level for a power electronics and power system application that is often considered. In this article, the design and application of a new generation multi-time cascaded DC-DC converter are discussed. The dc-to-dc converter is three-levels, and the switches for each step have a working time and a non-working time. Mathematical models are established depending on the relationship between current and voltage according to the operating and non-operating states of the switches at each stage. After these mathematical models are creating, the new generation multi-timed DC-DC converter is run in Matlab Simulink and simulation results are validated in experimentation. The output voltage and inductor current are observed with a scope. Then, the results from the proposed converter are compared with the results of the traditional converters. The results show the effectiveness of the proposed dc-dc converter.     

Analysis and Design for a New ZVS DC–DC Converter With Active Clamping

A new zero voltage switching (ZVS) boost converter is presented in this paper. By using an auxiliary switch and a capacitor, ZVS for all switches is achieved with an auxiliary winding in one magnetic core. A small diode is added to eliminate the voltage ringing across the main rectifier diode. This clamping technique can also be utilized in other dc-dc converters, and a family of new ZVS dc-dc converter is derived. A prototype (500 W/193 kHz) is made to verify the theoretical analysis. The efficiency is higher than 94% at 90-V input at full load     

Small Signal Analysis of Energy Factor and Mathematical Modeling for Power DC–DC Converters

Mathematical modeling for power dc-dc converters is a historical problem accompanying dc-dc conversion technology since the 1940s. The traditional mathematical modeling is not available for complex structure converters since the differential equation order increases very high. We have to search for other ways to establish mathematical modeling for power dc-dc converters. We have defined energy factor (EF) and new mathematical modeling for power dc-dc converters that have attracted much attention in recent years. This paper describes the small signal analysis of EF and mathematical modeling for power dc-dc converters in continuous conduction mode and discontinuous conduction mode. EF and the subsequential parameters can illustrate the unit-step response and interference recovery. This investigation may be helpful for system design and dc-dc converters characteristics. Two dc-dc converters: Buck converter and super-lift Luo-converter as the samples, are analyzed in this paper to demonstrate the applications of EF, pumping energy, stored energy (SE), capacitor/inductor SE ratio, energy losses, time constant tau, and damping time constant tau_d     

Low cost high efficiency DC-DC converter for fuel cell powered auxiliary power unit of a heavy vehicle

In this paper, a new dc-dc converter for solid oxide fuel cell (SOFC) powered auxiliary power unit (APU) is proposed. The proposed converter does not consider the leakage inductance of the transformer as a parasite and uses it for energy transfer, thus avoiding problems of low efficiency and difficulty in control, caused by leakage inductance. The need for a separate filter inductor is also eliminated. Soft switching is done for some of the switches of the proposed converter, thereby further increasing the efficiency of the converter. Thus, the achieved low cost and high efficiency of the proposed converter make it suitable for SOFC powered APU applications. Simulation and experimental results are presented to verify the proposed dc-dc converter. The achieved cost and efficiency of the prototype are 50.8$/kW and 90%, respectively.     

A Novel ZVS Resonant Reset Dual Switch Forward DC–DC Converter

This paper presents a new topology named zero-voltage switching (ZVS) resonant reset dual switch forward dc-dc converter, which, compared with resonant reset single switch forward dc-dc converter, maintains the advantage that duty cycle can be more than 50%, at the same time disadvantages of high voltage stress for main switches and low efficiency are overcome. In addition, ZVS is achieved for all switches of the presented topology. Therefore, this proposed topology is very attractive for high voltage input, wide range, and high efficiency applications. In this paper, the operation principle and characteristic of this topology are analyzed in detail. Next, the design consideration is presented. Finally, the advantages mentioned above are verified by experimental results     

Dual-bridge DC-DC converter: a new topology characterized with no deadtime operation

Two new topologies characterized by no deadtime and small valued filter inductor, the Dual-Bridge dc-dc converter and the Dual-Bridge dc-dc converter with ZVS, are presented and analyzed. Compared to the conventional Full-Bridge converter, the dc-dc converters with the proposed topologies have lower input current ripple, less stress on power switching components and smaller output filter inductor. Simple self-driven synchronous rectification can be used in the new topologies for high efficiency implementation. Prototype dc-dc converters have been tested for the verification of the principles. Both simulations and experiments verify the feasibility and advantages of the new topologies. The advantages and disadvantages of the topologies are discussed.     

A new family of isolated converters that uses the magnetizinginductance of the transformer to achieve zero-voltage switching

A new family of isolated, zero voltage switched power converters which utilizes the magnetizing inductance of the transformer to achieve zero voltage turn-on of the primary switches is proposed. By employing saturable inductor(s) on the secondary side, soft turn-off of the output rectifier(s) is obtained with a minimum circulating energy flowing through the power converter. The proposed converters can operate either with a variable or a constant switching frequency. A complete DC analysis and design guidelines for the half-bridge topology are described, and the performance of a 100 W experimental power converter is presented     

A New Approach to Reducing Output Ripple in Switched-Capacitor-Based Step-Down DC–DC Converters

Rapidly dropping power supply voltages and tight voltage regulation requirements for integrated circuits challenges power supply designers. A novel interleaved discharging (ID) approach is presented to reduce the output ripple in step-down switched-capacitor (SC) dc-dc converters. Simulation and experimental results of a four-stage SC dc-dc converter show that the ID approach can reduce the output ripple by a factor of three. The proposed approach also improves the converter efficiency by 7%. The ID method provides flexibility in the design optimization of step-down SC dc-dc converters     

Low-voltage-swing monolithic dc-dc conversion

A low-voltage-swing MOSFET gate drive technique is proposed in this paper for enhancing the efficiency characteristics of high-frequency-switching dc-dc converters. The parasitic power dissipation of a dc-dc converter is reduced by lowering the voltage swing of the power transistor gate drivers. A comprehensive circuit model of the parasitic impedances of a monolithic buck converter is presented. Closed-form expressions for the total power dissipation of a low-swing buck converter are proposed. The effect of reducing the MOSFET gate voltage swings is explored with the proposed circuit model. A range of design parameters is evaluated, permitting the development of a design space for full integration of active and passive devices of a low-swing buck converter on the same die, for a target CMOS technology. The optimum gate voltage swing of a power MOSFET that maximizes efficiency is lower than a standard full voltage swing. An efficiency of 88% at a switching frequency of 102 MHz is achieved for a voltage conversion from 1.8 to 0.9 V with a low-swing dc-dc converter based on a 0.18-/spl mu/m CMOS technology. The power dissipation of a low-swing dc-dc converter is reduced by 27.9% as compared to a standard full-swing dc-dc converter.     

Sustained Slow-Scale Oscillation in Higher Order Current-Mode Controlled Converter

DC-DC converters under current-mode control have been known to exhibit slow-scale oscillation as a result of a Hopf-type bifurcation as one or more of the parameters of the outer voltage loop are varied. In the absence of the outer voltage loop (i.e., open loop), slow-scale oscillation was generally not observed in simple low-order dc-dc converters, i.e., buck, buck-boost, and boost converters. In this paper, slow-scale bifurcation in a higher order current-mode controlled converter is studied. It has been found experimentally that, even in the absence of a closed outer voltage loop, a current-mode controlled Cuk converter can exhibit a slow-scale Hopf-type bifurcation. The phenomenon was observed in a commercial low-ripple dc-dc converter which has been designed using the Cuk converter and the LM2611 controller. Such slow-scale oscillation of the inner current loop can also be observed in full-circuit SPICE simulations. An averaged model has been developed and implemented in SPICE to find the Hopf bifurcation boundaries. With this averaged model, the Hopf bifurcation can be explained conveniently using the traditional loop gain analysis. Specifically, the extra degrees of freedom in higher order dc-dc converters have opened up a new possible mode of instability which has not been found in simple low-order dc-dc converters.     

Dual-Current Pump Module for Transient Improvement of Step-Down DC–DC Converters

This paper presents a novel dual-current pump module (DCPM) to improve the transient response of dc-dc converters. The DCPM operates only during transient to provide two additional current injections for step-up load and current drains for step-down load. Due to the two current pump paths, the current stress on the switches of the DCPM is also reduced. The measurement results show that the DCPM can enhance the dynamic recovery time of the buck dc-dc converter by more than an order.     

Zero-Voltage Transition Current-Fed Full-Bridge PWM Converter

In this paper, a new zero-voltage transition current-fed full-bridge converter with a simple auxiliary circuit is introduced for high step-up applications. In this converter, for the main switches, zero-voltage switching condition is achieved at wide load range. Furthermore, all semiconductor devices of the employed simple auxiliary circuit are fully soft switched. The proposed converter is analyzed and a prototype is implemented. The experimental results presented confirm the validity of the theoretical analysis. Finally, the proposed auxiliary circuit is applied to other current-fed topologies such as current-fed push-pull and half-bridge converters to provide soft switching.     

Analysis, Design, and Implementation of a Parallel ZVS Converter

A soft-switching converter is presented in this paper to achieve a zero-voltage-switching (ZVS) turn on for all switches. Two half-bridge converters with asymmetric pulsewidth-modulation scheme are connected in parallel to control the output voltage at the desired value and achieve load-current sharing. Based on the output capacitance of power switches and the resonant inductance, including the external inductance and the transformer leakage inductance, the resonance can be achieved at the transition interval of power switches. Therefore, the ZVS turn on of power switches can be realized. The peak voltage of the power switches is limited to input dc voltage. The center-tapped rectifier is adopted at the transformer secondary side to achieve a full-wave rectification. Operation principles, steady-state analysis, and design equations of the proposed converter are discussed in detail. Finally, experimental results based on a 240-W prototype are provided to verify the performance and the feasibility of the proposed converter.     

A new ZVS bidirectional DC-DC converter for fuel cell and battery application

This paper presents a new zero-voltage-switching (ZVS) bidirectional dc-dc converter. Compared to the traditional full and half bridge bidirectional dc-dc converters for the similar applications, the new topology has the advantages of simple circuit topology with no total device rating (TDR) penalty, soft-switching implementation without additional devices, high efficiency and simple control. These advantages make the new converter promising for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required. The operating principle, theoretical analysis, and design guidelines are provided in this paper. The simulation and the experimental verifications are also presented.     

一种采用倍流同步整流的高效率AC/DC变换器

文章介绍了一种基于不对称半桥的改进型AC/DC变换器。为了提高低压大电流应用场合的变换器效率,变换器次级采用倍流同步整流技术,而初级开关管能自然实现零压开通。因而,变换器的次级整流损耗和初级功率开关管损耗被大大降低。文中详细分析说明了电路的具体工作过程和设计要求,最后,仿真结果验证了电路设计的合理性。     

A Bidirectional Isolated DC–DC Converter as a Core Circuit of the Next-Generation Medium-Voltage Power Conversion System

This paper describes a bidirectional isolated dc-dc converter considered as a core circuit of 3.3-kV/6.6-kV high-power-density power conversion systems in the next generation. The dc-dc converter is intended to use power switching devices based on silicon carbide (SiC) and/or gallium nitride, which will be available on the market in the near future. A 350-V, 10-kW and 20 kHz dc-dc converter is designed, constructed and tested. It consists of two single-phase full-bridge converters with the latest trench-gate insulated gate bipolar transistors and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive and control circuit losses from the whole loss. Moreover, loss analysis is carried out to estimate effectiveness in using SiC-based power switching devices. Loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc-dc converter. As a result, the overall efficiency may reach 99% or higher     

Output ripple analysis of switching DC-DC converters

State space averaging methods are used to derive time-invariant models that bound the envelope of trajectories of pulsewidth modulated (PWM) dc-dc converters. The results are compared to conventional averaging methods used in power electronics, and it is shown that, at times, designing a dc-dc converter based on the averaged output of a converter can be ineffective because peak output values sometimes significantly deviate from the averaged output. This paper attempts to quantify this deviation by using both small-signal transfer functions and nonlinear models to model the maximum and minimum values of outputs of PWM converters. Issues in simulation and control loop design are also mentioned.