IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 44, NO. 5, OCTOBER 1997 597 An Integrated Battery Charger/Discharger with Power-Factor Correction Carlos Aguilar, Student Member, IEEE, Francisco Canales, Member, IEEE, Jaime Arau, Senior Member, IEEE, Javier Sebasti´ an, Member, IEEE, and Javier Uceda, Senior Member, IEEE Abstract—Distributed power-supply systems are an attractive solution to meeting the requirements (redundancy, modularity, battery backup, etc.) for the next generation of power-supply systems. In addition, the normalization regarding power fac- tor and total harmonic distortion (THD) makes it necessary to include the power-factor correction in the input stage in those architectures. This paper presents a novel approach of an integrated battery charger/discharger which offers power-factor correction and battery galvanic isolation in a simple structure. Placing the battery in the primary side overcomes the need of galvanic isolation integration in each one of the dc/dc on-board converters when this topology is used as part of a distributed power-supply system. Index Terms—AC–DC power conversion, batteries, communi- cation system power supplies, dc power systems, reactive power correction, switched-mode power supplies, pulsewidth-modulated power converters. I. INTRODUCTION N OWADAYS, it is not enough to increase the power density, which implies use of high-frequency conversion strategies, elaborate mounting techniques, etc., to meet the requirements of modularity, redundancy, and battery backing, all of which appear to be necessary for the next generation of power supplies. Distributed architecture in power-supply systems solves part of the problem, introduces new challenges and opens very attractive research areas. The most interesting challenge in the primary stage of a power supply is probably power-factor correction (PFC) [1]. However, an important disadvantage of distributed power systems (DPS’s) is that they need to incorporate galvanic isolation in each one of the dc/dc on-board converters. One possible solution to this problem is to incorporate the battery into the primary side at the front-end converter [2], [3]. One drawback, however, is that PFC is not incorporated. This paper presents a new approach in order to incorporate battery galvanic isolation by placing the battery into the primary side and the PFC features in a single-stage topology, to be used as a front-end converter in a DPS. Manuscript received March 16, 1996; revised January 29, 1997. C. Aguilar, F. Canales, and J. Arau are with the Centro Nacional de Investigaci´ on y Desarrollo Tecnol´ ogico (CENIDET), Cuernavaca, Morelos, M´ exico. J. Sebasti´ an is with the Universidad de Oviedo, Campus Universidad de Viesques, E-33204 Gij´ on, Spain. J. Uceda is with the Universidad Polit´ ecnica de Madrid, 28006 Madrid, Spain. Publisher Item Identifier S 0278-0046(97)06520-9. II. PROPOSED CIRCUIT The circuit of the proposed topology is shown in Fig. 1(a) [4]. The topology operates as a preregulator with PFC capacity, with the battery integrated into the primary side. The converter in its normal operation is capable of carrying out the battery charging. The function of the energy backup is carried out by means of a winding and an extra switch . The switch selects the operation mode and protects the battery from higher charging current levels than those specified by the battery manufacturer. The converter has normal, backup, and charging operation modes, which will be described in the following sections. A. Normal Mode of Operation When the main power input is functioning properly, the MOSFET is turned off and the transistor is turned on. The equivalent circuit of the proposed converter for this operation mode is shown in Fig. 1(b). In this condition, the equivalent circuit is a discontinuous-conduction-mode (DCM) flyback converter; the power flow from to the load is controlled by the duty cycle of MOSFET with a pulsewidth modulated (PWM) pattern. The current in the secondary side is given by the following equation [5]: (1) where duty cycle of ; switching period of ; magnetizing inductance referred to the secondary; secondary voltage. If the secondary voltage is (2) then (3) The average input current of the converter is (4) (5) 0278–0046/97$10.00  1997 IEEE