Digital power-factor correction for a capacitor-charging power supply

The design and construction of a low-power low-cost power supply capable of charging an energy storage capacitor from a 120-V AC source and capable of power-factor correction (PFC) is presented. The load that is generally connected to a capacitor-charging power supply (CCPS) is a pulsed power load (i.e., laser, cardiac defibrillator, or flash lamp). A flyback converter was incorporated into the CCPS because it is capable of charging a capacitor while maintaining a high power factor. The control system of the CCPS uses peak current control to achieve PFC and is implemented using standard "off-the-shelf" digital logic components. A 300-V prototype has been constructed and tested. The experimental results show that a high power factor is obtained by the CCPS utilizing a flyback converter and the digital logic control system.     

A single-stage quasi-resonant flyback converter using a synchronous rectifier

A single-stage quasi-resonant flyback converter using the synchronous rectifier (SR) is proposed for improving power factor and system efficiency. This converter operates at the critical conduction mode with the variable frequency (VF) control to reduce the switching loss of the primary switch. The bulk capacitor voltage can be independent of the output load and kept within a practical range for the universal line input. Therefore, the problem of high-voltage stress across the bulk capacitor is reduced. The proposed converter features relatively low bulk capacitor voltage in the universal line voltage and also complies with the Standard IEC 61000-3-2 Class D limits. Moreover, since it uses the voltage-driven SR, it achieves a high efficiency. The operational principle and theoretical analysis are presented. Experimental results for a 100?W (19?V/5.3?A) adapter at the VF were obtained to show the performance of the proposed converter.     

Single-Stage AC/DC Converter With Input-Current Dead-Zone Control for Wide Input Voltage Ranges

A single-phase single-stage ac/dc converter with input-current dead-zone control is proposed. It is based on flyback topology operating in discontinuous conduction mode (DCM). The current charging into the link capacitor is controlled according to line changes by adjusting the input-current blocking angle to alleviate an excessive increase of the link voltage. The reduced voltage stress can maintain an almost-constant voltage irrespective of load conditions by operating in dc/dc stage in DCM. Experimental results of a 60-W (5-V 12-A output) prototype converter show that the link voltage is limited within 384 V and that the measured power factor is more than 0.91 under universal voltage inputs and entire load conditions. In addition, the maximum efficiency is measured to be about 81% at the rated condition     

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     

Analysis and design of a single-stage single-switch bi-flyback ac/dc converter

An analysis and design of single-stage, single-switch bi-flyback ac/dc converter is presented. The main flyback stage controls the output power from the link capacitor voltage with Discontinuous Conduction Mode (DCM) or Continuous Conduction Mode (CCM) operation, while an auxiliary flyback stage supplies the power to the output directly from ac line input with DCM operation.

This scheme can effectively reduce the voltage stress on the link capacitor and can achieve the power factor correction (PFC) without a dead band at line zero-crossings, which reduces the harmonic distortion in ac line current. Theoretical analysis of the converter is presented and design guidelines to select circuit components are given. The experimental results on a 60?W (15?V, 4?A), 100?kHz ac/dc converter show that maximum link voltage and maximum efficiency are around 415?V and 82%, respectively. The power factor is above 0.96 under universal line input and load conditions.     

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.     

Integrated Buck-Flyback Converter as a High-Power-Factor Off-Line Power Supply

This paper investigates the integrated buck-flyback converter (IBFC) as a good solution for implementing low-cost high-power-factor ac-dc converters with fast output regulation. It will be shown that, when both buck and flyback semistages are operated in discontinuous conduction mode, the voltage across the bulk capacitor, which is used to store energy at low frequency, is independent of the output power. This makes it possible to maintain the bulk capacitor voltage at a low value within the whole line voltage range. The off-line operating modes of the IBFC are also investigated to demonstrate that the control switch of the proposed converter handles lower root-mean-square currents than those in similar integrated converters. The off-line operation of the IBFC is analyzed to obtain the design characteristics of the bulk capacitor voltage. Finally, the design and experimental results of a universal input 48 V-output 100 W ac-dc converter operating at 100 kHz is presented. Experiments show that the IEC-61000-3-2 input current harmonic limits are well satisfied and efficiency can be as high as 82%.     

Flexible and low cost design for a flyback AC/DC converter with harmonic current correction

This study presents a new simple flyback ac/dc converter with harmonic current correction and fast output voltage regulation. In the proposed ac/dc converter, an extra winding wound in the transformer provides two key advantages. The size of the bulk inductor used in the conventional boost-based power factor correction cell can be significantly reduced in the proposed converter. The voltage across bulk capacitor can be held under 450V by tuning the transformer winding ratio even though the converter operates in a wide range of input voltages (90 V/spl sim/265V/ac). This new converter complies with IEC 61000-3-2 under the load range of 200 W, and can achieve fast output voltage regulation.     

Integrated high-quality rectifier-regulators

A new family of AC-DC converters is derived which integrate the functions of low-harmonic rectification, low-frequency energy storage, and wide-bandwidth output voltage control into a single converter containing one, two, or four active switches. These converters utilize a discontinuous conduction mode input inductor, an internal energy storage capacitor, and transformer secondary circuits which resemble the bridge, forward, flyback, or Cuk DC-DC converters. A large-signal equivalent circuit model for this family is presented, which uses the “loss-free resistor” concept. Design strategies and experimental results are given. High-performance regulation with satisfactory line-current harmonics is demonstrated with conventional duty-ratio control. Further improvements in line current are possible by simultaneous duty-ratio and switching-frequency control     

Single-switch parallel power factor correction AC-DC converters with inherent load current feedback

Single-stage power factor correction (PFC) ac-dc converters usually suffer from high bulk capacitor voltage stress and extra switch current stress. Bulk capacitor voltage feedback with a coupled-winding structure can dramatically alleviate the stresses. However, this type of feedback is indirect because the feedback only occurs after the bulk capacitor voltage increases. This paper presents a family of single-switch single-stage parallel PFC ac-dc converters with inherent load current feedback. Unlike the bulk capacitor voltage feedback, which utilizes the decreased duty ratio and the increased bulk capacitor voltage to reduce the input power at light load, the load current feedback can reduce the input power automatically at light load while maintaining an unchanged duty ratio. The proposed converters combine the advantages of simple topology, low bulk capacitor voltage, and no extra current stress across the switch. The concept is verified using an ac-dc converter with universal-line input and 5-V, 60-W output power. The input current harmonics meet IEC1000-3-2 Class D requirements.     

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.     

Control algorithms and circuit designs for optimal flyback-chargingof an energy-storage capacitor (e.g., for flash lamp or defibrillator)

A flyback-type of a transformer-coupled DC/DC power converter supplies a train of current pulses to charge an energy-storage capacitor to a desired high voltage, converting input DC power obtained from a lower voltage DC source. The energy-storage capacitor is charged to a specified voltage within a specified time with minimum peak and RMS currents in the transistor, the rectifier diode, the transformer windings and the DC power source, minimizing the i²R losses. This is done by generating: (1) energy-storage current pulses in the power transistor and the transformer primary winding in which the current increment from the beginning to the end of a pulse is only a small fraction of the final (peak) value; and (2) energy-delivery flyback current pulses in the capacitor and the transformer secondary winding in which the current decrement from the beginning to the end of a pulse is only a small fraction of the initial (peak) value. Recommended methods are: (1) hysteretic current-mode control with current sensing in both transformer windings; (2) peak-current-commanding current-mode control with switching frequency or transistor-nonconducting time varying in a prescribed way during the charging; or (3) valley-current-commanding current-mode control with switching frequency or transistor-conducting time varying in a prescribed way during the charging. Compared with one nonoptimal method, peak currents are reduced by a factor of about 2 and i²R power losses are reduced by a factor of about 1.33     

基于双向半桥DC-DC的超级电容器储能系统仿真研究

引入了双向半桥DC—DC变换器对超级电容器进行充放电的换流方式;阐述了超级电容器在双向半桥DC—DC变换器工作原理;分析了单端稳压和稳压快速充电两种控制策略,并给出了双闭环控制的原理框图;最后搭建了以直流电机为负载的上述两种控制策略下的仿真系统,通过设定电机运行多种工况,完整地考察了超级电容与位能负载间的多种换流情况。仿真结果验证了该变换电路不仅能够实现馈能的完全吸收,还具有较’陕速的放电过程动态响应,且电路简单,易于工程实现,满足了位能型负载下超级电容器储能系统的变换要求。     

Adaptive off-time control for variable-frequency, soft-switchedflyback converter at light loads

The soft switching of a flyback converter can be achieved by operating the circuit in the critical conduction mode. However, the critical-mode operation at light loads cannot be maintained due to a very high switching frequency and the loss of the output voltage regulation. A control which regulates the output down to the zero load and maintains soft switching at light loads is proposed. The proposed control scheme was implemented in the 380 V/19 V, 65 W flyback DC/DC converter     

A Very Simple Control Strategy for Power Factor Correctors Driving High-Brightness LEDs

This paper presents a new control strategy for power factor correctors (PFCs) that are used to drive high-brightness LEDs. This control strategy is extremely simple and is based on the use of a conventional peak-current-mode controller with a suitable selection of the compensation ramp waveform. Neither an analog multiplier nor an input voltage sensor is needed to achieve quasi-sinusoidal line waveforms at nominal conditions and full load. If the converter belongs to the flyback family (flyback, buck–boost, SEPIC, Cuk and Zeta), the line waveform appears notably distorted if the compensation function is a linear ramp, but becomes almost sinusoidal if the linear ramp is substituted by a properly chosen exponential function. The line waveform is slightly distorted when the load varies or when the converter works under either overvoltage or undervoltage conditions. However, the waveform maintains a very high power factor (PF) even under these conditions. Moreover, the line current is cycle-by-cycle-controlled due to the peak-current-mode control, and hence, the input-current feedback loop is extremely fast, thereby allowing this type of control to be used with high-frequency lines (above 400 Hz).      

基于UPC1909的有源箝位软开关变换器

在常规的硬开关电路中,由于变压器漏感及寄生电容的影响,常常在开关转换瞬间会产生很高的电压尖峰。本文采用有源箝位反激式变换器电路,实现了零电压零电流(ZVZCS)软开关变换,使电压尖峰得到了抑制。该电路成功地应用了UPCI909控制芯片,简化了传统的驱动电路。实验结果表明,主开关管两端电压被箝位在一定数值,实现了零电压零电流开关,效率达到90％。     

基于电荷控制反激变换器的设计与研究

对比传统的峰值电流控制反激变换器,提出一种新的电荷控制方式。利用PSIM仿真软件分别设计了两种控制方式连续工作模式下的时域电路模型;利用状态空间平均法建立其统一的交流小信号模型,并通过仿真软件SIMPLIS、MathCAD验证频域分析和数学模型的准确性。最后,设计了两台实验样机进行对比。实验表明,电荷控制方式下反激变换器具有更快的瞬态响应、更高的稳流精度、更小的输出电压纹波以及更宽的稳定范围,验证了理论分析的正确性。     

一种新型单级功率因数校正AC/DC变换器的研究

文章研究了一种新型单级单开关PFC反激变换器。该变换器负载变轻时其储能电容电压不会飘升,应用于宽范围交流输入电压,储能电容电压低于450V。变换器用其变压器中的一个附加绕组实现了升压功能。由于省去了大电感,减小了变换器的体积和重量,在中小功率应用场合下,变换器符合IEC61000-3-2class D谐波标准,并且具有输出电压快速调节能力。     

离线反激式LED恒流源的设计

LED是未来电光源的发展方向,民用普及化需要高效率低成本的恒流源驱动器。本文采用不连续导通模式(DCM)的工作原理,在正常工作时保持恒流输出,在负载断开时输出电压稳定在某个预设的最大输出电压上,从而保护了次级输出电路,实现了一款价廉、高效、安全的离线反激式恒流源驱动器。