Nonisolation Soft-Switching Buck Converter With Tapped-Inductor for Wide-Input Extreme Step-Down Applications

In this paper, a new zero-voltage switching (ZVS) buck converter with a tapped inductor (TI) is proposed. This converter improves the conventional tapped inductor critical conduction mode buck converters that have the ZVS operation range determined by the TI turn ratios. It includes another soft switching range extension method, the current injection method, which gives an additional design freedom for the selection of the turn-ratios and enables the optimal design of the winding ratio of the TI so that the efficiency may be maximized. This soft-switching buck converter is suitable for wide input range step-down applications. The principle of the proposed scheme, analysis of the operation, and design guidelines are included. Experimental results of the 100-W prototype dc-dc converter are given for hardware verification also. Finally, based on the proposed soft-switching technique, a new soft-switching topology family is derived.     

Novel zero-current-switching (ZCS) PWM switch cell minimizingadditional conduction loss

This paper proposes a new zero-current-switching (ZCS) pulsewidth modulation (PWM) switch cell that has no additional conduction loss of the main switch. In this cell, the main switch and the auxiliary switch turn on and turn off under zero-current condition. The diodes commutate softly and the reverse-recovery problems are alleviated. The conduction loss and the current stress of the main switch are minimized, since the resonating current for the soft switching does not flow through the main switch. Based on the proposed ZCS PWM switch cell, a new family of DC-to-DC PWM converters is derived. The new family of ZCS PWM converters is suitable for the high-power applications employing insulated gate bipolar transistors. Among the new family of DC-to-DC PWM converters, a boost converter was taken as an example and has been analyzed. Design guidelines with a design example are described and verified by experimental results from the 2.5 kW prototype boost converter operating at 40 kHz     

Analysis, design, and implementation of an active clamp forward converter with synchronous rectifier

The system analysis, circuit design, and implementation of active clamp based forward converter with synchronous rectifier are presented in this paper. To release the energy stored in the leakage inductor and to minimize the spike voltage at the transformer primary side, active clamp circuit included one clamp switch and one clamp capacitor is adopted in the circuit. Based on the partial resonance with the output capacitor of switch and the leakage inductor of transformer, the main switch is turned on at zero voltage switching (ZVS). The clamp switch is also operated at ZVS operation based on the resonance of leakage inductor and clamp capacitor. The synchronous switches are used at the secondary side to further reduce the conduction losses. The experimental results based on the laboratory prototypes are presented to verify the circuit performance.     

A new ZVT-PWM DC-DC converter

In this paper, a new active snubber cell that overcomes most of the drawbacks of the normal "zero voltage transition-pulse width modulation" (ZVT-PWM) converter is proposed to contrive a new family of ZVT-PWM converters. A converter with the proposed snubber cell can also operate at light load conditions. All of the semiconductor devices in this converter are turned on and off under exact or near zero voltage switching (ZVS) and/or zero current switching (ZCS). No additional voltage and current stresses on the main switch and main diode occur. Also, the auxiliary switch and auxiliary diodes are subjected to voltage and current values at allowable levels. Moreover, the converter has a simple structure, low cost, and ease of control. A ZVT-PWM boost converter equipped with the proposed snubber cell is analyzed in detail. The predicted operation principles and theoretical analysis of the presented converter are verified with a prototype of a 2 kW and 50 kHz PWM boost converter with insulated gate bipolar transistor (IGBT). In this study, a design procedure of the proposed active snubber cell is also presented. Additionally, at full output power in the proposed soft switching converter, the main switch loss is about 27% and the total circuit loss is about 36% of that in its counterpart hard switching converter, and so the overall efficiency, which is about 91% in the hard switching case, increases to about 97%     

一种应用于48V-1V系统的隔离型混合模式降压变换器

提出了一种应用于48 V-1 V系统的隔离型混合模式降压变换器,利用飞电容和变压器实现高转换比应用下的高转换效率。混合变换器结合了开关电容变换器和开关电感变换器,其中飞电容承担了部分电压降,实现了功率开关管电压应力的降低。由于开关节点处的电压摆幅较小,开关损耗随之减小;通过使用更低压的功率开关管,实现功率开关管导通损耗减小。在此基础上,隔离型混合模式降压变换器通过时序控制可以实现软开关,进而实现功率开关管开关损耗减小,使得整体效率提升。在隔离型混合模式降压变换器中,飞电容还具有隔直电容的作用,可以防止变压器偏磁。在典型应用下,即在48 V输入电压、1 V输出电压、500 kHz开关频率下,峰值效率为94.84%。     

An improved boost PWM soft-single-switched converter with lowvoltage and current stresses

This paper presents an improved regenerative soft turn-on and turn-off snubber applied to a boost pulsewidth-modulated (PWM) converter. The boost soft-single-switched converter proposed, which has only a single active switch, is able to operate with soft switching in a PWM way without high voltage and current stresses. This is achieved by using an auxiliary inductor, which is magnetically coupled with the main inductor of the converter. In order to illustrate the operating principle of this new converter, a detailed study, including simulations as well as experimental results, is carried out. The validity of this new converter is guaranteed by the obtained results     

A Digital Current-Mode Control Technique for DC–DC Converters

The objective of this paper is to propose a simple digital current mode control technique for dc-dc converters. In the proposed current-mode control method, the inductor current is sampled only once in a switching period. A compensating ramp is used in the modulator to determine the switching instant. The slope of the compensating ramp is determined analytically from the steady-state stability condition. The proposed digital current-mode control is not predictive, therefore the trajectory of the inductor current during the switching period is not estimated in this method, and as a result the computational burden on the digital controller is significantly reduced. It therefore effectively increases the maximum switching frequency of the converter when a particular digital signal processor is used to implement the control algorithm. It is shown that the proposed digital method is versatile enough to implement any one of the average, peak, and valley current mode controls by adjustment of the sampling instant of the inductor current with respect to the turn-on instant of the switch. The proposed digital current-mode control algorithm is tested on a 12-V input and 1.5-V, 7-A output buck converter switched at 100kHz and experimental results are presented     

ZVT-PWM AC-DC boost converter with ZCS auxiliary circuit

A low conduction loss, low-cost zero-voltage-transition-pulsewidth modulation (ZVT-PWM) boost converter with a zero current switching (ZCS) auxiliary circuit is developed to achieve high-conversion-efficiency operation. The unique locations of the resonant capacitor and inductor ensure that low switching stress and commutation losses are obtained in this converter. It is very suitable for high power-factor-correction pre-regulators     

A 0.9-V Input Discontinuous-Conduction-Mode Boost Converter With CMOS-Control Rectifier

A 0.9-V input discontinuous-conduction-mode (DCM) boost converter delivering 2.5-V and 100-mA output is presented. A novel low-voltage pulse-width modulator is proposed. The modulator can be directly powered from the 0.9-V input instead of using the 2.5-V output as in general modulator designs. Sophisticated low-voltage analog blocks, which normally consume a large amount of power and chip area, are not required in the modulator. The impact of output-voltage ripple and transient-induced output-voltage perturbation on the operation of analog blocks inside the modulator is eliminated. Boost converter start-up sequence is also greatly simplified. A CMOS-control rectifier (CCR) is also proposed to improve converter power efficiency. The CCR is used to replace the conventional rectifying switch to provide adaptive dead-time, which helps to minimize charge-sharing loss and body-diode conduction loss. Corresponding thermal stress on the rectifying switch is hence minimized. The CCR also enables the use of small off-chip inductor and capacitor at sub-MHz switching frequency to improve light-load efficiency. This converter has been implemented in a 0.35- $mu$m CMOS process. It is designed to operate at ${sim}$ 667 kHz with a 1 $mu$ H inductor and 4.7 $mu$ F output capacitor to reduce both switching loss and form factor. Experimental results prove that the converter can be directly powered from 0.9-V input with ${sim}$ 85% efficiency at 100-mA output.      

Watkins-Johnson converter completes tapped inductor converter matrix

The Watkins-Johnson converter has been identified as belonging to the tapped inductor converter families extending once more the matrix of DC-DC converter topologies. This converter is analysed in terms of the tap position and the switch duty cycle and its operation as a rail-to-tap buck converter is verified.     

Fault diagnosis algorithm based on switching function for boost converters

A fault diagnosis algorithm, which is necessary for constructing a reliable power conversion system, should detect fault occurrences as soon as possible to protect the entire system from fatal damages resulting from system malfunction. In this paper, a fault diagnosis algorithm is proposed to detect open- and short-circuit faults that occur in a boost converter switch. The inductor voltage is abnormally kept at a positive DC value during a short-circuit fault in the switch or at a negative DC value during an open-circuit fault condition until the inductor current becomes zero. By employing these abnormal properties during faulty conditions, the inductor voltage is compared with the switching function to detect each fault type by generating fault alarms when a fault occurs. As a result, from the fault alarm, a decision is made in response to the fault occurrence and the fault type in less than two switching time periods using the proposed algorithm constructed in analogue circuits. In addition, the proposed algorithm has good resistivity to discontinuous current-mode operation. As a result, this algorithm features the advantages of low cost and simplicity because of its simple analogue circuit configuration.     

Design and Application for PV Generation System Using a Soft-Switching Boost Converter With SARC

In order to improve the efficiency of energy conversion for a photovoltaic (PV) system, a soft-switching boost converter using a simple auxiliary resonant circuit, which is composed of an auxiliary switch, a diode, a resonant inductor, and a resonant capacitor, is adopted in this paper. The conventional boost converter decreases the efficiency because of hard switching, which generates losses when the switches are turned on/off. During this interval, all switches in the adopted circuit perform zero-current switching by the resonant inductor at turn-on, and zero-voltage switching by the resonant capacitor at turn-off. This switching pattern can reduce the switching losses, voltage and current stress of the switching device. Moreover, it is very easy to control. In this paper, we have analyzed the operational principles of the adopted soft-switching boost converter, and it is designed for PV generation system. Simulation and experimental results are presented to confirm the theoretical analysis.      

A magnetically coupled regenerative turn-on and turn-off snubberconfiguration

This paper presents a magnetically coupled regenerative turn-on and turn-off snubber configuration applied to a boost converter, which operates in continuous conduction mode (CCM). In addition to reducing the stresses in the switch, providing soft transitions in its turn-off voltage and turn-on current, it transfers the energy stored in the snubber capacitor to the load. This is achieved by using a coupled inductor mounted on the main inductor of the converter, which resets the capacitor voltage at each switching period. Design equations, as well as experimental results are presented, showing the high performance of the boost converter using the proposed snubber     

High-Power Density Design of a Soft-Switching High-Power Bidirectional dc–dc Converter

A bidirectional dc-dc converter typically consists of a buck and a boost converters. In order to have high-power density, the converter can be designed to operate in discontinuous conducting mode (DCM) such that the passive inductor can be minimized. The DCM operation associated current ripple can be alleviated by interleaving multiphase currents. However, DCM operation tends to increase turnoff loss because of a high peak current and its associated parasitic ringing due to the oscillation between the inductor and the device output capacitance. Thus, the efficiency is suffered with the conventional DCM operation. Although to reduce the turnoff loss a lossless capacitor snubber can be added across the switch, the energy stored in the capacitor needs to be discharged before device is turned on. This paper adopts a gate signal complimentary control scheme to turn on the nonactive switch and to divert the current into the antiparalleled diode of the active switch so that the main switch can be turned on under zero-voltage condition. This diverted current also eliminates the parasitic ringing in inductor current. For capacitor value selection, there is a tradeoff between turnon and turnoff losses. This paper suggests the optimization of capacitance selection through a series of hardware experiments to ensure the overall power loss minimization under complimentary DCM operating condition. According to the suggested design optimization, a 100-kW hardware prototype is constructed and tested. The experimental results are provided to verify the proposed design approach.     

Boost Converter With Coupled Inductors and Buck–Boost Type of Active Clamp

This paper proposes a boost converter with coupled inductors and a buck-boost type of active clamp. In the converter, the active-clamp circuit is used to eliminate the voltage spike that is induced by the trapped energy in the leakage inductor of the coupled inductors. The active switch in the converter can still sustain a proper duty ratio even under high step-up applications, reducing voltage and current stresses significantly. Moreover, since both main and auxiliary switches can be turned on with zero-voltage switching, switching loss can be reduced, and conversion efficiency therefore can be improved significantly. A 200 W prototype of the proposed boost converter was built, from which experiment results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively. It is relatively feasible for low-input-voltage applications, such as fuel cell and battery power conversion.     

Integrated ZVS DC–DC converter with continuous input current and high voltage gain

An integrated zero-voltage-switching (ZVS) DC–DC converter with continuous input current and high voltage gain is proposed. The proposed converter can operate with soft switching, a continuous inductor current and fixed switching frequency. The voltage stress of the power switches is relatively low compared to the output voltage. Moreover, soft-switching characteristic of the proposed converter reduces switching loss of active power switches and raise the conversion efficiency. The reverse-recovery problem of output rectifiers is also alleviated by controlling the current changing rates of diodes with the use of the leakage inductance of a coupled inductor. The operation and performance of the proposed DC–DC converter were verified on an 115?W experimental prototype operating at 100?kHz.     

A novel single-phase soft-switched rectifier with unity power factor and minimal component count

A novel, single-phase soft-switched boost AC-DC rectifier that operates with power-factor correction is proposed in this paper. The rectifier is a modified boost voltage-doubler converter well suited for low-line-input applications. It operates with fewer conduction losses and half the switch voltage stresses found in a standard boost converter. Soft switching in the converter is achieved using a zero-current-switching quasi-resonant technique. In the paper, the converter and its modes of operation are discussed and analyzed. The method of control is explained, and a design procedure is derived and then demonstrated with an example. The feasibility of the converter is shown with experimental results obtained from a prototype.     

Optimized design of a fully soft-switched boost-converter suitable for power factor correction

A fully soft-switched boost-converter using a one auxiliary switch is presented here. It uses the minimum number of components in the auxiliary circuit with minimum current stress of the main switch. Since the resonant capacitor charges only through an inductor and a diode, the circuit conduction losses are minimized. The main and auxiliary insulated gate bipolar transistor (IGBT) switches share a common emitter connection, facilitating direct drive to them. Various operating modes of the converter are presented in detail and analysed. The choice of the resonating capacitor and inductor has been done through an optimization process based on the guiding equations working under different modes. In this optimization process, emphasis has been given on minimum voltage stress on the auxiliary switch for a wide duty cycle range of operation. Based on the design, the principle of operation has been verified with computer simulation. Experimental results from a laboratory prototype with active power factor correction confirms the operation of this converter.     

A zero-voltage-switched PWM boost converter with an energyfeedforward auxiliary circuit

A zero-voltage-switched (ZVS) pulsewidth-modulated (PWM) boost converter with an energy feedforward auxiliary circuit is proposed in this paper. The auxiliary circuit, which is a resonant circuit consisting of a switch and passive components, ensures that the converter's main switch and boost diode operate with soft switching. This converter can function with PWM control because the auxiliary resonant circuit operates for a small fraction of the switching cycle. Since the auxiliary circuit is a resonant circuit, the auxiliary switch itself has both a soft turn on and turn off, resulting in reduced switching losses and electromagnetic interference (EMI). This is unlike other proposed ZVS boost converters with auxiliary circuits where the auxiliary switch has a hard turn off. Peak switch stresses are only slightly higher than those found in a conventional PWM boost converter because part of the energy that would otherwise circulate in the auxiliary circuit and drastically increase peak switch stresses is fed to the load. In this paper, the operation of the converter is explained and analyzed, design guidelines are given, and experimental results obtained from a prototype are presented. The proposed converter is found to be about 2%-3% more efficient than the conventional PWM boost converter     

一种提高单电感双输出升/降压型转换器轻载效率的设计策略

为了提高单电感双输出升/降压型直流-直流转换器在轻载下的效率,设计实现了适用于不同转换条件的非连续导通模式(DCM)功能和脉冲频率调制(PFM)控制。前者降低了电感电流的均方根值,减少了导通损耗;后者降低了开关频率,减少了开关损耗。详细分析了在PFM控制下转换器的驱动能力、电感电流纹波和输出电压纹波之间相互制约的关系,并采取了一种可以由两路任意升/降压输出灵活复用的自适应导通时间控制方法。经0.25μm 2P4M CMOS混合信号工艺流片验证,测试结果显示DCM和PFM时序与设计方案吻合,各种转换条件下输出电压纹波在40~70 mV。通过比较发现,对轻载效率的提升可以达到30%以上。