5116 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 10, OCTOBER 2014 Letters A Modified Dual-Output Interleaved PFC Converter Using Single Negative Rail Current Sense for Server Power Systems Serkan Dusmez, Shamim Choudhury, Manish Bhardwaj, and Bilal Akin Abstract—The interleaved PFC topologies have been widely used since they allow for smaller components, improved thermal perfor- mance, better transients, and reduced current ripple. In this letter, conventional two-phase interleaved universal input PFC topology is modified to obtain dual independent outputs for server applica- tions, which minimizes the transient effects of interleaving legs on each other through two split dc buses. A new digital control method using only one current sensor located on the negative dc rail is proposed to control the dual-output interleaved PFC converter. Double-loop digital control of two interleaving stages is imple- mented using a single low-cost microcontroller (TMS320F28027- PiccoloA). In the proposed control technique, the control circuitry, input voltage, and current sensing circuits are shared between two PFC power stages, which minimize the size and the cost of the design significantly. Index Terms—AC–DC conversion, digital control, interleaved converter, power factor correction (PFC), server power supply. I. INTRODUCTION T HE boost-type power factor correction (PFC) circuit, con- sisting of a diode bridge followed by a dc–dc boost converter [1]–[3], is the widely preferred state-of-art converter topology used in the front-end PFC stage in server power sup- plies. For dual-output server power supplies, two independent PFC converters followed by step-down converters can be uti- lized; however, this would result in high cost and size. Instead, both the PFC stage and the second stage dc/dc converter can be split into multiphases, by which the phases can be interleaved for better system performance [4]–[11]. This technique brings several advantages for high-power systems. Since the power is processed by multiple converters, and the current of each con- verter is halved, the conduction losses for each MOSFET, given by I 2 R, are reduced by a factor of four. In addition, the am- plitude of the overshoots during the transients can be reduced, and better transient response can be achieved. However, if the Manuscript received November 2, 2013; revised February 3, 2014 and March 13, 2014; accepted April 11, 2014. Date of current version May 30, 2014. Recommended for publication by Associate Editor J. Biela. S. Dusmez and B. Akin are with the Department of Electrical Engi- neering, University of Texas—Dallas, Richardson, TX 75080 USA (e-mail: serkan.dusmez@utdallas.edu; bilal.akin@utdallas.edu). S. Choudhury and M. Bhardwaj are with the Texas Instruments Inc., Houston, TX 77251 USA (e-mail: sach@ti.com; mbhardwaj@ti.com). 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.2014.2319734 Fig. 1. Modified dual-output interleaved PFC converter. second stage dc–dc converters are connected in parallel to the same dc link, the transients of the first converter affect the op- eration of the second converter or vice versa as they share the same dc bus [12]–[14]. In order to alleviate the mutual interfer- ence during transients, the traditional interleaved PFC stage is modified to have two independent dc links as shown in Fig. 1. With the advent of low-cost, high-performance microcon- trollers (MCUs), new approaches to power converter control are possible [15]–[18]. MCU-based digital control eliminates con- trol complexities and difficulties in realization of the control for interleaved PFC circuits, while providing power supply design- ers a tool for flexible control design, high-frequency operation, improved performance, and increased system integration [18]. The extended computation capability of such MCUs allows im- plementation of sophisticated nonlinear control algorithms, in- tegrate multiple converter control into the same processor, and optimize the total system cost. The advantages of a digitally con- trolled interleaved dual output topology over the conventional topology controlled by two analog PFC controllers operated without phase shift can be summarized as follows: 1) lower input current ripple due to ripple cancellation effect even if two output voltages are different, 2) two smaller inductors in comparison to one bulky inductor for a given input current ripple criteria, 3) reduced zero crossing distortions as digital implementation is more flexible in implementing advanced techniques such as in- troducing an offset signal to the current feedback signal, 4) less number of feedbacks and associated analog signal conditioning circuits, and 5) autotuning of controller coefficients with respect to load and line voltage. The digital control of the PFC boost converter as well as the interleaved converter has been explored in [9] and [10]. Following similar digital control approach for the modified dual- output PFC stage would require two inductor current sensors. This paper proposes a cost-effective method to control two- phase interleaved PFC stages with dual independent outputs by only sensing the negative rail current through a current sense 0885-8993 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.