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Quasi-ZVS Active Auxiliary Commutation Circuit for Two Switches Forward Converter
#1

Quasi-ZVS Active Auxiliary Commutation Circuit for Two Switches Forward Converter


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Abstract:

This paper presents a family of single-ended
converters that adequately designed and commanded can
perform ZVS turn-off and turn-on with a value near to zero
namely Quasi-ZVS (QZVS) at main switches. The auxiliary
circuit presents low reactive energy and is composed of one
inductor, one diode and one switch, which operate with ZCS. To
demonstrate the feasibility of the proposed technique, it is
applied to a two switches forward converter. It is not necessary
the use 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
converters. Complete analysis of the operation stages, as well as
the design procedures for the correct operation of the converter
are presented.

INTRODUCTION

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
process.

THE QUASI-ZVS SINGLE-ENDED FAMILY

In this section is presented the QZVS single-ended family
of non-isolated (boost, buck, buck-boost, SEPIC, zeta and
cúk) 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.

DESIGN CONSIDERATIONS

Regarding the switches selection, majority carrier type
such as MOSFETs are indicated to be used as main switches,
since their commutations are with ZVS (and Quasi-ZVS). On
the other hand, the auxiliary switch Sa1 operates with ZCS,
and it is recommended the use of the minority carrier type
switches, like IGBT.
A special care must be taken to design the resonant
inductor Lr. In stage 8, when the resonance among capacitors
C1 and C2 and inductors Lr and Ld occurs, the voltages across
both capacitors must reach a value near to zero. This is the
feature of the Quasi-ZVS.
When the voltage across the transformer reaches zero
(vAB=0), the load current flows through diode D4, and Ld
inductor energy starts a resonance, as it can be seen in the
equivalent circuit illustrated in Fig. 8. The magnetizing
inductance Lm is neglected in this analysis, because Lr is
much smaller than Lm (Lr << Lm).
In circuit presented in Fig. 8, the capacitors C1 and C2
resonate with inductors Lr and Ld. In this resonance, a value
near to zero is adopted (VQZVS), at which main switches must
turn-on. In this way, the resonant inductor value can be
calculated by (1).

CONCLUSIONS

In this paper, a family of converter with ZVS at turn-off
and with Quasi-ZVS at turn-on is presented.
The auxiliary circuit is composed of few elements that
present low rms and average current values. These features
result in small volume and low cost auxiliary circuit. In
addition, this circuit presents low commutation losses
because it operates with ZCS.
Reply
#2

The auxiliary circuit has low reactive energy and is composed of an inductor, a diode and a switch, which work with ZCS. To demonstrate the feasibility of the proposed technique, it is applied to a two-switch converter. It is not necessary to use a third winding on the transformer or auxiliary voltage sources to achieve smooth switching. Implementation is possible due to the use of an appropriate command, different from that conventionally used in two forward switching converters. A complete analysis of the operation stages is presented, as well as the design procedures for the correct operation of the inverter. Experimental results from a prototype of 250W / 48V @ 100kHz demonstrate the feasibility of this active auxiliary switching circuit (AACC) applied to two forward switching converters. In addition, a new switching concept is introduced, where the main switches switch with QZVS.
Reply

Marked Categories : auxiliary commutation, auxiliary commutation circuit diagram, zvs with inductor commutation circuit daigram, zvs resonant forward pdf, operation of auxiliary commutation, image of zvs of forward converter, zvs of forward converter ppt, zcs circuit microcontroller based, download seminar presentation on zvs of forward converter,

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