2888 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 6, JUNE 2012 A New Single-Phase Single-Stage Three-Level Power Factor Correction AC–DC Converter Mehdi Narimani, Student Member, IEEE, and Gerry Moschopoulos, Senior Member, IEEE Abstract—In this paper, a new three-level single-stage power- factor-corrected ac/dc converter is presented. The proposed circuit integrates the operation of a boost power factor correction con- verter and a three-level dc/dc converter into one converter. It does not have the problem of high component stress due to high ris- ing intermediate bus voltages at light load conditions that other single-stage converters have because of its three-level structure. It can operate over a wider load range with significantly less out- put inductor current ripple; moreover, its input current has little distortion. In the paper, the operation of the new converter is ex- plained in detail and analyzed, its steady-state characteristics are determined, and its design is discussed. Experimental results ob- tained from a prototype are presented to confirm the feasibility of the new converter. Index Terms—AC–DC power conversion, single-stage power fac- tor correction (SSPFC), three level converters. I. INTRODUCTION P OWER factor correction (PFC) is necessary nowadays for an ac-dc power supply to comply with harmonic standards such as IEC 1000-3-2 [1]. Although it is possible to satisfy these standards by adding passive filter elements to the traditional passive diode rectifier/LC filter input combination, the resulting converter would be very bulky and heavy due to the size of the low-frequency inductors and capacitors [2] [Fig. 1(a)]. For conventional two-stage ac–dc converters with output isolation where an ac–dc conversion (rectifying) stage and an isolated dc– dc conversion stage are used, an ac-dc boost converter is used in the rectifying stage for most applications. The boost converter shapes the input line current so that it is almost sinusoidal, with a harmonic content compliant with agency standards, but the cost and complexity of the overall two-stage converter are increased because an additional switching converter must be implemented [2]. This has led to the emergence of single-stage power-factor-corrected (SSPFC) converters. There have been numerous publications about SSPFC con- verters, particularly for low-power ac–dc flyback and forward converters [1]–[16]. These cheaper and simpler converters are widely used in industry and their properties and characteristics have been well established. Research on the topic of higher power ac–dc single-stage full-bridge converters, however, has Manuscript received June 15, 2011; revised September 4, 2011; accepted October 19, 2011. Date of current version March 16, 2012. Recommended for publication by Associate Editor D. Xu. The authors are with the University of Western Ontario, London, Ontario, Canada. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPEL.2011.2174256 proved to be more challenging, and, thus there have been much fewer publications [17]–[19]. Previously proposed single-stage ac–dc full-bridge converters have the following drawbacks [Fig. 1(b)–(f)]: 1) Some are current-fed converters with a boost inductor connected to the input of the full-bridge circuit. Although they can achieve a near-unity input power factor, they lack an energy-storage capacitor across the primary-side dc bus, which can result in the appearance of high voltage overshoots and ringing across the dc bus. It also causes the output voltage to have a large low-frequency 120-Hz ripple that limits their applications. 2) Some are resonant converters [17], [20], [21] that must be controlled using varying switching-frequency control, which makes it difficult to optimize their design (espe- cially their magnetic components) as they must be able to operate over a wide range of switching frequency. 3) Some converters have two converters stages [22] that allow for a portion of the power that is transferred from the input to the output to be processed only once. It is for this reason that they are considered by some to be single-stage converter, but the fact is they have two converter stages and thus have the cost and complexity associated with two-stage converters. 4) Most are voltage-fed, single-stage, pulse-width modula- tion (PWM) converters with a large energy-storage ca- pacitor connected across their primary-side dc bus. These converters do not have the drawbacks of resonant and current-fed SSPFC converters. They operate with fixed switching frequency, and the bus capacitor prevents volt- age overshoots and ringing from appearing across the dc bus and the 120-Hz ac component from appearing at the output. Voltage-fed converters, however, have the follow- ing drawbacks: a) The primary-side dc bus voltage of the converter may become excessive under high-input-line and low-output-load conditions. This is because SSPFC converters are implemented with just a single con- troller to control the output voltage, and the dc bus voltage left unregulated; it is dependent on the converter’s input line and output load operating conditions and component values. The high dc bus voltage results in the need for higher voltage rated devices and very large bulk capacitors for the dc bus. For example, the converter in [19] has a dc bus voltage of 600 V [2], [17]–[19], [21]. b) The input power factor of a single-stage voltage- fed converter is not as high as that of current-fed 0885-8993/$26.00 © 2011 IEEE