软开关双管正激电源设计方案

Quasi-ZVS Active Auxiliary Commutation Circuitfor Two Switches Forward ConverterJ.E. Baggio, L. Schuch, H.L. Hey, H.A. Gründling, H. Pinheiro, J.R. Pinheiro Federal University of Santa MariaCT / NUPEDEE / GEPOC97105-900 - Santa Maria - RS - Brazil e-mail: josebaggio@, renes@ctlab.ufsm.br Abstract: This paper presents a family ofsingle-endedprocess.converters that adequately designed and commanded can The effects associated to these three factors are minimizedperform ZVS turn-off and turn-on with a value near to zeroby the use of zero voltage switching. However, some circuitsnamely Quasi-ZVS (QZVS) at main switches. The auxiliarydo not operate with ZVS in all operation conditions. Even ifcircuit presents low reactive energy and is composed of onethe voltage across the switch do not reaches zero, aninductor, one diode and one switch, which operate with ZCS. Toimprovement of the converter performance can be obtained,demonstrate the feasibility of the proposed technique, it isby using auxiliary circuits that reduce the voltage to valuesapplied to a two switches forward converter. It is not necessaryuse of a third winding in the transformer neither auxiliary Voltage sources to achieve soft switching. The implementation is possible due to the use of an appropriate command, different than it is used conventionally in two switches forward near to zero. This is the basic principle of Quasi-ZVS (QZVS): to reduce the voltage across the switch to a value as near to zero as possible.The QZVS occurs when there is not enough energyplete analysis of the operation stages, as well asavailable to reset the snubbers capacitors. The use ofthe design procedures for the correct operation of the converterauxiliary circuits with low cost and low reactive energy is theare presented. Experimental results obtained from a prototypemain feature of QZVS.of 250W/48V@100kHz demonstrate the feasibility of this Active Auxiliary Commutation Circuit (AACC) applied to two switches forward converter. Furthermore, a new concept of switching is introduced, where the main switches commutate with QZVS.A great number of researchers have concentrated efforts to obtain converters with low commutation losses. As a result, converters operating with zero voltage and/or current switching have been exhaustively studied to reduce the drawbacks of hard commutation.Hard commutation losses are mainly linked to three factors: the reverse recovery current of diodes; the discharge of the energy stored in capacitors parallel to the switch (specially in MOSFETs); the simultaneous occurrence of voltage and current on the switch during the commutation II. T HE Q UASI-ZVS S INGLE-ENDED F AMILYIn this section is presented the QZVS single-ended familyof non-isolated (boost, buck, buck-boost, SEPIC, zeta andI. I NTRODUCTIONcúk) and isolated(flyback, forward and two switches forward) converters. The basic converters of this family are presented in Fig. 1, and the state planes of these converters are presented in Fig. 3. A family with characteristics similar to the presented one was introduced in [7] with ZVS operation. However, under certain operating conditions, ZVS is not obtained. Anyway, with an appropriate design, the commutations can occur with QZVS. The presented converters allow QZVS in continuous conduction mode (CCM), discontinuous conduction mode (CCM) and critical conduction mode (CM). This can be seen C1 Lr Sa1 S1C1 Lr Sa1 Da1Da1 Da1 D1E C R0L LS1 LR0 LrED1 E C1C C R0S1 Sa1D1(a) (b) (c)D1Lr D1 D3 LC1 D2T(n1) T(n2) C R0 R0Lr T(n3) L S1D2 R0 D4 CE T(n1) T(n2) Lr Da1 Sa1 T(n2)E C EDa1 D3Da1Sa1 C1 T(n1) C2Sa1 C1S1 S1 D1 S2(d) (e) (f)Fig. 1 - Quasi-ZVS family: (a) Buck; (b) Boost; (c) Buck-Boost; (d) Flyback; (e) Forward; (f) Two switches Forward.in the state plane of the buck converter depicted in Fig. 2. When operating in CCM, the auxiliary circuit presents the highest reactive energy. On the other hand, in DCM the is obtained at auxiliary switch while main switches turn-off with ZVS and turn-on with Quasi-ZVS.TABLE I: LIMITS BETWEEN ZVS AND QZVS.auxiliary circuit presents less reactive energy, but theConverter Z VS Q ZVScommutation occurs with higher voltage level (see Fig. 2).Buck V o ≥ E/2 V o < E/2Operating in CM the switches commutate as near of zero asBoost V o ≥ 2.E V o < 2.Epossible with less reactive energy than in CCM. As a result ofBuck-Boost V o≥ E V o < Ethese features, the CM is the most adequate operation mode,Flyback n.Vo ≥ 2.E n.Vo < 2.E in the point of view of the auxiliary switches.Forward n.Vo ≥ E/2 n.Vo < E/2 Z.ILrRTwo Switches Forward Not possible Possible III. T HE QZVS T WO S WITCHES F ORWARD C ONVERTER Fig.4 presents the two switches forward converter with theE-Vo E V cAACC. This converter is composed of two main switches (S1,(a)S2), two main diodes (D1, D2), one transformer (T1(N1:N2)),Z.ILr Z.ILr。