A Dual IGBT Soft Switched Active Power Factor Corrector Sam Ben- Yaakov*, Gregory Ivensky, Vladimir Tantser, and Oleg Friedman Tel: +972- 7-6461561; Fax: +972- 7-6472949; Email: sby@bguee.bgu.ac.il Power Elecb"onics Laboratory Department of Electrical and Computer Engineering Ben-Gurion University of the Negev P. 0. Box 653, Beer-Sheva 84105, ISRAEL Factor Corrector (APFC) based on a boost topology that differs from previously described ones [5] in the fact that a DSSS, optimized for IGBTs, is applied (Fig. I). The paper presents a theoretical analysis of operation of the DSSS, performance of the DSSS, design of a APFC stage with DSSS and experimental results of APFC with the DSSS. Abstract -A novel topology of an Active Power Factor Corrector (APFC) based on a boost converter was studied theoretically and experimentally. The new design differs from previously described ones in the fact that it applies a Dual Switch Soft Switcher (DSSS) optimized for IGBTs. The main advantage of the DSSS is zero current switching of the main IGBT and auxiliary IGBT during both turn on and turn off while all other power devices are also soft switched. The experimental 1 kW ac/dc APFC was run at a switching frequency of 66kHz. Theoretical and experimental results were found to be in good agreement. THD was estimated to be about 3%, the efficiency was measured to be about 96% . II. THE DUAL SWITCH TOPOLOGY AND ANAL YSIS OF ITS OPERA TION I. INTRODUcrlON The recently introduced fast and ultra fast IGBTs [I] are considered to be a cost effective choice in medium to high power applications. However, the relatively long turn-off time of these devices limit the switching frequency to about 25KHz. This limitation is especially noticeable in the single-switch active power factor correction circuit, in which the use of an IGBT as the main switch could be highly beneficial. Consequently, the switching frequency limitation hampers the wide use of IGBTs in this class of applications which are presently of great commercial interest. This shortcoming could be corrected by a soft switching strategy that reduces the switching losses of the IGBT, permitting thereby efficient operation at high switching frequencies. The ideal arrangement for an IGBT soft switcher is Zero Current Switching (ZCS) or Zero Voltage Switching (ZVS) at turn on, but ZCS at turn off [2,3]. ZCS at turn off is highly desirable since it can help remove the stored charge which otherwise might cause a long current tail. The recently introduced Dual Switch Soft Switcher (DSSS) [4] meets these demands: it ensuressoft switching during turn on and ZCS during turn off of the IGBTs while maintaining soft switching of all other power devi~s. The objective of this study was to'nvestigate the operation of a novel topology of an Active Power The Dual Switch Soft Switcher (DSSS) optimal for IGBTs is used in the boost converter (Fig. I). This switcher [4] includes two branches connected in parallel. The main switch Ql. shunted by an antiparallel diode Dl and connected in series with a resonant inductor Lr. forms the first branch. The second branch comprises the auxiliary switch Q2 in series with a diode DS. shunted by another antiparallel diode D2 and connected in series with a resonant capacitor Cr- The common point of Lr. Ql and Dl is clamped to the output of the converter through an auxiliary circuit which includes a Zener diode Dz and an ordinary diode D3. The common point of Cr. D2 and DS is clamped to the output of the converter through a diode D4. The operation of DSSS is explained briefly as follows. The auxiliary switch Q2 is turned on just prior to the instant that the main switch Ql is due to be turned off. This creates a sinusoidal current in the series resonance network (Lr.Cr) which forces a negative current through the branch of the main switch (Ql.Dl). Consequently. Ql current reduces smoothly to zero whereupon the resonant current is channeled through the reverse diode Dl. When this diode is conducting. the gate drive of the main switch Ql can be removed under zero current conditions achieving thereby true ZCS. During 'turn on' of the main switch QI. the resonant inductor Lr ensures ZCS by limiting the rate of the current rise. The analysis of the DSSS was carried out under the following assumptions: 1. The converter elements are ideal. * Corresponding author.