Voltage and current stress reduction in single-stage power factorcorrection AC/DC converters with bulk capacitor voltage feedback

Single-stage power factor correction (PFC) AC/DC converters integrate a boost-derived input current shaper (ICS) with a flyback or forward DC/DC converter in one single stage. The ICS can be operated in either discontinuous current mode (DCM) or continuous current mode (CCM), while the flyback or forward DC/DC converter is operated in CCM. Almost all single-stage PFC AC/DC converters suffer from high bulk capacitor voltage stress and extra switch current stress. The bulk capacitor voltage feedback with a coupled winding structure is widely used to reduce both the voltage and current stresses in practical single-stage PFC AC/DC converters. This paper presents a detailed analysis of the bulk capacitor voltage feedback, including the relationship between bulk capacitor voltage, input current harmonics, voltage feedback ratio, and load condition. The maximum bulk capacitor voltage appears when the DC/DC converter operates at the boundary between CCM and DCM. This paper also reveals that only the voltage feedback ratio determines the input current harmonics under DCM ICS and CCM DC/DC operation. The theoretical prediction of the bulk capacitor voltage as well as the predicted input harmonic contents is verified experimentally on a 60 W AC/DC converter with universal-line input     

开关电容boost—buck功率因数校正组合开关变换器

文章提出了一种基于开关电容网络的boost-buck组合开关变换器,当其输入环节工作在不连续导电模式（DCM）时,具有功率因数校正（PFC）功能,详细分析了这类变换器的工作原理、临界条件、输入输出电压变比以及各器件的应力。实验结果与理论分析相符。     

Analysis and Design of a Novel Three-Phase AC–DC Buck-Boost Converter

This paper proposes a novel three-phase ac-dc buck-boost converter. The proposed converter uses four active switches, which are driven by only one control signal. This converter is operated in discontinuous conduction mode (DCM) by using the pulsewidth modulation (PWM) technique, and the control scheme very easily and simply achieves purely sinusoidal input current, high power factor, low total harmonic distortion of the input current and step-up/down output voltage. Also, the proposed converter provides a constant average current to the output capacitor and load in each switching period. Thus, the ripple component of sixth times line frequency will not appear in the output voltage. Therefore, a smaller output capacitor can be used in the proposed converter. Moreover, the steady-state analysis of voltage gain and boundary operating condition are presented. Also, the selections of inductor, output capacitor and input filter are depicted. Finally, a prototype circuit with simple control logic is implemented to illustrate the theoretical analysis.     

A new modulation strategy for a buck-boost input AC/DC converter

This paper presents a novel modulation strategy for a power factor corrected (PFC), isolated AC/DC converter derived from the integration of a nonisolated, two switch buck-boost AC/DC converter with an isolated dual active bridge DC/DC converter (2SBBDAB). This strategy, termed discontinuous leading/trailing edge (DLTE) modulation, serves to maximize the duty cycle of the input switch while keeping the current in the buck-boost inductor discontinuous. Hence, the crest factors of the currents in the switching devices are minimized, the input switch is turned on at zero current and the zero-voltage switching ranges of the bridge switches are unaffected by the integration. A conventional isolated, PFC AC/DC converter typically consists of a boost converter cascaded with a forward converter. The ratings required of the power switching devices of the 2SBBDAB employing the DLTE modulation strategy are similar to those required of the conventional design for wide line voltage operation. However, the 2SBBDAB converter has higher line voltage surge immunity than that of the conventional design and, unlike the conventional design, it has inherent inrush current limiting. The DLTE modulation strategy may be applied to the family of converters composed of the two switch buck-boost integrated with half and full-bridge forward converters     

Single-stage three-phase buck-boost type AC-DC converter with highpower factor

A new control process for single-stage three-phase buck-boost type AC-DC power converters with high power factor, sinusoidal input currents and adjustable output voltage is proposed. This converter allows variable power factor operation, but this work focus on achieving unity power factor. The proposed control method includes a fast and robust input current controller based on a vectorial sliding mode approach. The active nonlinear control strategy applied to this power converter, allows high quality input currents. Given the comparatively slow dynamics of the DC output voltage, a proportional integral (PI) controller is adopted to regulate the converter output voltage. The voltage controller modulates the amplitudes of the current references, which are sinusoidal and synchronous with the input source voltages. Experimental results from a laboratory prototype show the high power factor and the low harmonic distortion characteristics of the circuit     

Buck–Boost-Type Unity Power Factor Rectifier With Extended Voltage Conversion Ratio

A buck-boost-type unity power factor rectifier is proposed in this paper. The main advantage of the proposed rectifier over the conventional buck-boost type is that it can perform input power factor correction (PFC) over a wider voltage conversion range. With a single switch, a fast well-regulated output voltage is achieved with a zero-current switch at turn-on. Moreover, the switch voltage stress is independent of converter load variation. The proposed converter is well suited for universal offline PFC applications for a low power range (<150 W ). The feasibility of the converter is confirmed with results obtained from a computer simulation and from an experimental prototype.     

一种车用恒流/恒压模式的四开关Buck-Boost变换器控制策略研究

对一种车用恒流/恒压模式的四开关Buck-Boost变换器的控制策略进行了研究。在输入输出电压接近时引入Buck-Boost模式,从而在不同输入输出电压大小关系下,通过检测功率管占空比大小,实现Buck模式、Boost模式和Buck-Boost模式之间的平滑切换,提高了系统的稳定性。通过设计最大值选择电路,使变换器在充电应用中自动从恒流模式切换到恒压模式,模式切换平滑稳定。仿真结果表明,在24 V输出电压下,变换器从Buck模式切换到Buck-Boost模式时,输出电压下冲为9.2 mV,变换器从Boost模式切换到Buck-Boost模式时,输出电压下冲为92 mV。变换器在Buck模式与Boost模式下均能实现恒流/恒压模式的自动平滑切换。     

A digitally controlled PWM/PSM dual-mode DC/DC converter

A digitally controlled pulse width modulation/pulse skip modulation(PWM/PSM) dual-mode buck DC/DC converter is proposed.Its operation mode can be automatically chosen as continuous conduction mode (CCM) or discontinuous conduction mode(DCM).The converter works in PSM at DCM and in 2 MHz PWM at CCM.Switching loss is reduced at a light load by skipping cycles.Thus high conversion efficiency is realized in a wide load current.The implementations of PWM control blocks,such as the ADC,the digital pulse width modulator(DPWM) and the loop compensator,and PSM control blocks are described in detail.The parameters of the loop compensator can be programmed for different external component values and switching frequencies, which is much more flexible than its analog rivals.The chip is manufactured in 0.13μm CMOS technology and the chip area is 1.21 mm~2.Experimental results show that the conversion efficiency is high,being 90%at 200 mA and 67%at 20 mA.Meanwhile,the measured load step response shows that the proposed dual-mode converter has good stability.     

New single-stage PFC regulator using the Sheppard-Taylor topology

This paper describes a new usage of the DC/DC converter developed by D.I. Sheppard and B.E. Taylor in 1983 for achieving high power factor and output regulation. This converter may be viewed as a cascade of a modified boost stage and a buck stage, with the two stages sharing the same active switch. Two possible operation regimes are described. In the first regime, the converter's input part, which is a modified boost converter, operates in discontinuous mode, and the output part, which is a buck converter, operates in continuous mode. In this regime, high power factor is naturally achieved, and the output voltage is regulated by duty-cycle modulation via a simple output feedback. In the second regime, the input part operates in continuous mode, and the output part operates in discontinuous mode, with duty-cycle modulation maintaining a high power factor and frequency modulation regulating the output. Some comparisons between the Sheppard-Taylor converter and conventional boost and buck cascade are given in the paper     

Practical switch based state-space modeling of DC-DC converterswith all parasitics

All parasitics such as switch conduction voltages, conduction resistances, switching times, and ESRs of capacitors are counted in a proposed DC-DC power convertor state-space modeling based method on nonideal switching functions. An equivalent simplified model is derived from the complex circuit with parasitics. The modeling procedure is shown for the buck-boost converter as the general converter among the buck, boost, and buck-boost converters. The pole frequency, DC voltage gain, and efficiency are analyzed and verified by experiments that show good agreement with theory. The procedures for determining the gain margin of the controller, the turn ratio of an isolation transformer, the optimum duty factor, and the switching frequency are given for an example flyback converter     

ZVZCS single-stage PFC AC-to-DC half-bridge converter

A zero-voltage- and zero-current-switched single-stage AC-to-DC half-bridge converter with high power factor is presented to reduce the switching losses and to achieve sinusoidal, unity power factor input currents. The single-stage approach, which combines a boost converter used as power-factor correction with a half-bridge converter used as DC-to-DC conversion into one power stage, has a simple structure and low cost. At the same time, the switching losses could be considerably reduced, because the switches of the proposed converter are designed to be turned on at zero voltage and off at zero current. Detailed analysis and experimental results are presented on the proposed converter, which is operated at constant switching frequency and in discontinuous conduction mode     

Spectral characteristics of randomly switched PWM DC/DC convertersoperating in discontinuous conduction mode

This paper addresses a comparative study of the spectral characteristics of four random-switching schemes that apply to the basic pulsewidth-modulation (PWM) DC/DC converters operating in discontinuous conduction mode (DCM). They include randomized pulse position modulation, randomized pulsewidth modulation, and randomized carrier frequency modulation with fixed duty cycle and with fixed duty time, respectively. Mathematical models that characterize the input current and output voltage of the three basic PWM converters operating in DCM are derived. In particular, the effectiveness of spreading the dominant switching harmonics in the input current that normally exist in the standard PWM scheme and the introduction of low-frequency harmonics in the output voltage with respect to the randomness level are investigated. The validity of the models and analyses are confirmed experimentally by using a DC/DC buck converter     

Synthesis and analysis for a novel single-stage isolated high power factor correction converter

A novel single-stage isolated high power factor correction (HPFC) converter operating in the discontinuous conduction mode is proposed in this paper. It is an integration of a buck-boost converter with a flyback converter by means of components placement and synchronous switching technology. It can achieve HPFC, tight output voltage regulation and lower voltage stress of the bulk capacitor, which is independent of the loads. The small-signal mathematical model for the proposed converter is derived separately by the averaging method and the current injected equivalent circuit approach. The IsSpice simulations and experimental results successfully verify the dynamics and performances of the proposed converter.     

A new topology for unipolar brushless DC motor drive with high power factor

A new converter topology is proposed for driving a permanent magnet brushless DC (BLDC) motor with unipolar currents. It is based on a front-end single-ended primary inductance converter (SEPIC) and a switch in series with each phase. All the switches are ground-referenced, which simplifies their gate drives. The available input voltage can be boosted for better current regulation, which is an advantage for low voltage applications. For operation with an AC supply, the SEPIC converter is designed to operate in the discontinuous conduction mode. In this operation mode, it approximates a voltage follower and the line current follows the line voltage waveform to a certain extent. The reduction in low-order harmonics and improved power factor is achieved without the use of any voltage or current sensors. The simplicity and reduced parts count of the proposed topology make it an attractive low-cost choice for many variable speed drive applications.     

A feedback loop regulated bootstrap driver circuit with improved drive capability for high voltage buck DC–DC converter

A novel bootstrap driver circuit applied to high voltage buck DC–DC converter is proposed. The gate driver voltage of the high side switch is regulated by a feedback loop to obtain accurate and stable bootstrapped voltage. The charging current of bootstrap capacitor is provided by the input power of the DC–DC converter directly instead of internal low voltage power source, so larger driver capability of the proposed circuit can be achieved. The bootstrap driver circuit starts to charge the bootstrap capacitor before the switch node SW drop to zero voltage at high-side switch off-time. Thus inadequate bootstrap voltage is avoided. The proposed circuit has been implemented in a high voltage buck DC–DC converter with 0.6 µm 40 V CDMOS process. The experimental results show that the bootstrap driver circuit provides 5 V stable bootstrap voltage with higher drive capability to drive high side switch. The proposed circuit is suitable for high voltage, large current buck DC–DC converter.     

基于伏秒平衡原理的Buck-Boost变换器分析

针对现有"电力电子技术"教材中普遍存在的对Buck-Boost变换器的分析不完整等问题,本文基于伏秒平衡原理对Buck-Boost变换器进行了全面分析,推导出变换器全范围的输入输出电压关系,电流连续模式(CCM)和断续模式(DCM)的临界工作条件以及电路各参数对电流纹波和电压纹波的影响等。本文一方面有助于更全面深入地理解Buck-Boost变换器的工作原理及特性,另一方面有助于DC-DC变换器分析方法的统一,具有一定的教学指导意义。     

一种新型交错并联同相降压升压DC/DC转换器

为了有效降低电流纹波和提高转换器效率,提出一种新型交错并联同相降压升压DC/DC转换器。提出的结构通过采用输入/输出（I/O）磁耦合交错并联和阻尼网络技术,降低了开关的电压应力、内部电压振荡和I/O电流纹波,并提升了转换器的效率。采用状态空间平均法,在连续导通模式下分析了提出转换器的稳态运行,从理论上证明了其优势。样机的功率设置为360W,输出电压为36 V,模拟结果以及实验结果显示,当输出电流为6A时,转换效率最高达到96%,最大输入电流纹波百分比仅为9.4%,相较于其他类似转换器,提出的转换器具有效率较高和I/O电流纹波较低的优势。     

Integrated ZCS quasi-resonant power factor correction converterbased on flyback topology

An integrated zero current switching (ZCS) quasiresonant converter (QRC) for the power factor correction with a single switch is presented in this paper. The power factor correction can be achieved by the discontinuous conduction mode (DCM) operation of an input current. The proposed converter offers good power factor, low level line current harmonics, and tight output regulation. The design equations are suggested and a prototype converter has been designed based on these equations and experimentally investigated. The input current waveform of the prototype shows less than 15% of total harmonic distortion. Also, the efficiency and power factor of about 84% and 0.977, respectively, can be obtained under the rated condition     

A single-stage power factor correction AC/DC converter based on zero voltage switching full bridge topology with two series-connected transformers

A single-stage power factor correction ac/dc converter based on zero voltage switching (ZVS) full bridge topology with two series-connected transformers is proposed in this paper. The proposed converter offers a very wide ZVS range due to the configuration of two series-connected transformers. It features a high efficiency over wide load ranges. Furthermore, it shows the low voltage stress on a dc link capacitor. The proposed converter also gives the high power factor and low input current harmonics complied with IEC 61000-3-2 Class D requirements by integrating a boost stage operated in a discontinuous current mode. The ZVS conditions, large signal modeling, and design procedure are discussed in detail. Experimental results are presented to show the validity of the proposed converter.     

Characterization of single-stage three-phasepower-factor-correction circuit using modular single-phase PWM DC-to-DCconverters

The complete DC characteristics of three-phase modular power-factor-correction (PFC) converters using single-phase pulsewidth modulation (PWM) DC-to-DC converter modules for high-power applications are studied. Using circuit averaging, the converter input and output quantities are determined numerically. Both the continuous and discontinuous output current modes of operation (CCM and DCM) are studied in detail. Near-unity power factor can be achieved with the converter modules operating in the DCM. An averaged model was used to study and determine the boundaries between DCM and CCM over the full period of the three-phase input voltage. It is found that high power factor is inherent in the converter system provided that the converters are operated in the DCM and the voltage conversion ratio is selected properly. The criteria for obtaining high power factor are analyzed and the optimal circuit parameters are determined to obtain the best achievable power factor. Both simulations and experimental results from a 1.5-kW prototype using full-bridge converter modules have confirmed the analysis