20-03-2012, 01:20 PM
digital simulation of ZVS DC to DC converter using simulink
simulation.pdf (Size: 378.16 KB / Downloads: 98)
Introduction
Several new techniques for high frequency DC-DC conversion have been proposed to reduce
component stresses and switching losses while achieving high power density and improved
performance [1]-[11]. Among them, the phase-shifted zero-voltage-switching (ZVS) full bridge [1]-[3]
is one of the most attractive techniques since it allows all switches to operate at ZVS by utilizing
transformer leakage inductance and metal oxide semiconductor field effect transistors (MOSFETs)
junction capacitance without adding an auxiliary switch. However, the complexity of the full-bridge is
almost highest among the conventional topologies due to its large switch count and complicated
control and driving. Active-clamp forward topology [4]-[6] is another typical example to successfully
realize ZVS for the switches by utilizing the leakage inductance, magnetizing inductance and junction
capacitance. However, the topology of the converter is asymmetric and the energy-delivery is
unidirectional. In other words, voltage and current stresses being higher compared to symmetric halfbridge
and full-bridge converters. This disadvantage limits power level of the active-clamp forward
topology applications. In addition, dc bias of magnetizing current may exits in the transformer [5].
DCS PWM Control Scheme
the half-bridge dc-dc converter with current double rectifier. The ideal waveforms for
the symmetric PWM control is sketched in Figure 2(a), where Lk, is the leakage inductance; ip,im, are
the transformer primary-side input and magnetizing currents, respectively; and iD1 is the forward
current through rectifier diode D1. Besides the hard switching, conventional symmetric PWM control
has transformer-leakage-inductance related disadvantages. During the off-time period when both
switches are off, the energy stored in the transformer leakage inductance may be recycled to primary dc
bus through body diodes of MOSFETs. However, because of reverse recovery current of body diodes,
the oscillation between the transformer leakage inductance and the MOSFETs junction capacitance is
significant on the primary side. To suppress the ringing, usually, snubber circuits are necessarily added,
but losses dissipated in the snubber become dramatically large, especially at high input current and
high switching frequencies.
Proposed DCS PWM Control Scheme
Figure 2(b) shows the key waveforms of the half-bridge converter with the proposed DCS PWM
control. Based on symmetric PWM control, S2 driving signal Vgs2 is shifted left such that the Vgs2
rising edge is close to the falling edge of S1 driving signal Vgs1. When S1 is turned off, the
transformer primary current charges the junction capacitance of switch S2. After the voltage across
drain-to-source of S2 drops to zero, the body diode of S2 conducts to carry the current. During the
body diode conduction period, S2 may be turned on at zero-voltage switching. No ringing occurs
during the transition period.