Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

High-brightness LEDs are considered remarkable lighting devices due to their high reliability, chromatic variety, and increasing efficiency. As a result, a high number of solutions for supplying LED strings are emerging. One-stage solutions are cost-effective, but their efficiency is low because they have to fulfill several purposes with only one converter: power factor correction (PFC), galvanic isolation (in some cases), and current regulation. Two-stage and three-stage solutions have higher efficiency because each stage is optimized for only one or two tasks and they are the preferred options when supplying several strings at the same time. In this paper, a two-stage solution is proposed. The first stage is the well-known PFC boost converter. The second stage, on which this paper is focused, is the asymmetrical half bridge (AHB). Its design has been optimized based on the needs and characteristics of LED-based street lighting applications. The proposed transformer design (with asymmetrical secondary windings) minimizes the conduction losses while the model of the converter during the dead times optimizes their duration, reducing switching losses in the MOSFETs and diodes. Experimental results obtained with a 40-W prototype show an efficiency as high as 94.5% for this second stage and validate the proposed design procedure and model.

Design of a Soft-Switching Asymmetrical Half-Bridge Converter as Second Stage of an LED Driver for Street Lighting Application

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.

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

Due to their high reliability and luminous efficacy, high-brightness light-emitting diodes are being widely used in lighting applications, and therefore, their power supplies are required to have also high reliability and efficiency. A very common approach for achieving this in ac-dc applications is using a two-stage topology. The power factor corrector boost converter operating in the boundary conduction mode is a very common converter used as first stage. It is normally designed without electrolytic capacitors, improving reliability but also increasing the low-frequency ripple of the output voltage. The asymmetrical half-bridge (AHB) is a perfect option for the second stage as it has very high efficiency, it operates at constant switching frequency, and its output filter is small (i.e., it can be also easily implemented without electrolytic capacitors). Moreover, the AHB is an excellent candidate for self-driven synchronous rectification (SD-SR) as its transformer does not have dead times. However, the standard configuration of the SD-SR must be modified in this case in order to deal with the transformer voltage variations due to the input voltage ripple and, more important, due to the LED dimming state. This modification is presented in this paper. Another important issue regarding the AHB is that its closed-loop controller cannot be very fast and it cannot easily cancel the previously mentioned low-frequency ripple. In this paper, a feed-forward technique, specifically designed to overcome this problem, is also presented. The experimental results obtained with a 60-W topology show that efficiency of the AHB may be very high (94.5%), while the inherent control problems related to the AHB can be overcome by the proposed feed-forward technique.

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High-Efficiency Asymmetrical Half-Bridge Converter Without Electrolytic Capacitor for Low-Output-Voltage AC–DC LED Drivers

High-Brightness Light Emitting Diodes (HB-LEDs) are considered the future trend in lighting not only due to their high efficiency and high reliability, but also due to their other outstanding chara...

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An Overview of the AC-DC and DC-DC Converters for LED Lighting Applications

A small-signal model of soft-switched asymmetrical half-bridge DC/DC converter operating in a continuous inductor conduction mode is proposed. The analysis of this model is applicable to converters with any type of output rectifier (full-wave or half-wave). Based on the proposed model, the feedback compensation network for a prototype converter was designed. An open loop frequency response and voltage ripple attenuation of the converter with closed feedback loop were calculated. The experimental results validated all theoretical predictions. >

Small-signal modeling of soft-switched asymmetrical half-bridge DC/DC converter

A modification is proposed for the asymmetrical zero-voltage-switched (ZVS) half-bridge DC-DC converter topology that substantially changes the static transfer function and the voltage stress distribution within the converter power mesh. This modification allows the converter circuit to be optimised for higher efficiency and power density. It is also postulated that the modification with its corresponding benefits can be utilised in other complementary driven topologies. Although the asymmetrical H-B converter is inherently capable of ZVS switching, only the proper choice of parameters can insure ZVS in all modes of operation. The DC circuit analysis and design procedure for the power stage components are presented. Experimental results, in good agreement with the analysis, are presented for a 300 W converter operating at 500 kHz, with 5 VDC/60 Amp output, and 84% efficiency at 75 W/in/sup 3/.

Modified asymmetrical ZVS half-bridge DC-DC converter

Abstvact An analysis of the Softswitched Asymmetrical Half-bridge DC-DC converter operation is presented. Both, the switching processes analysis as well as the steady state analysis are presented in general terms which makes them applicable for different topological configurations of the converter. The steady state analysis provides expressions for calculating mean, peak and rms currents and voltages across the power mesh components. The switching process analysis demonstrates the multiplicity of switching modes possible and associated switching state sequences. It is shown that only some of them are desirable for attainment of zero voltage switching (ZVS). The proper choice of circuit parameters and determination of ZVS boundaries is established. AU switching modes are simulated on PSpice.

Soft-Switched Asymmetrical Half-bridge DC/DC Converter: Steady-State Analysis. An Analysis Of Switching Processes.

A new AC/DC power converter with high power factor is presented. This power converter has the advantages over both standard two-stage power factor corrected AC/DC power converters and single stage PFC power converters. These advantages are the overall simplicity of the power train, an optimised steady DC voltage maintained across the DC cell, constant operating frequency, inherent inrush current limiting capability, high efficiency due to the chosen topology's inherent ZVT capability and simple and inexpensive control circuits. The principle of operation is discussed and the design procedure for the power mesh is proposed. The small-signal model of the PFC cell is included.

V. Meleshin

Papers

Small-signal modeling of soft-switched asymmetrical half-bridge DC/DC converter

Modified asymmetrical ZVS half-bridge DC-DC converter

Soft-Switched Asymmetrical Half-bridge DC/DC Converter: Steady-State Analysis. An Analysis Of Switching Processes.

Integrated AC/DC converter with high power factor