14-10-2010, 04:28 PM
Abstract—
This paper proposes a new soft-switched continuousconduction- mode (CCM) boost converter suitable for high-power applications such as power factor correction, hybrid electric vehicles, and fuel cell power conversion systems. The proposed converter achieves zero-voltage-switched (ZVS) turn-on of active switches in CCM and zero-current-switched turn-off of diodes leading to negligible reverse-recovery loss. The components’ voltage ratings and energy volumes of passive components of the proposed converter are greatly reduced compared to the conventional zero-voltage-transition converter. Voltage conversion ratio is almost doubled compared to the conventional boost converter. Extension of the proposed concept to realize multiphase dc–dc converters is discussed. Experimental results froma 1.5-kW prototype are provided to validate the proposed concept.
Introduction
Continuous- conduction-mode (CCM) boost converters have been widely used as the front-end converter for active input current shaping . In recent years, CCM boost converters are increasingly needed in high-power applications such as hybrid electric vehicles and fuel cell power conversion systems. High power density and high efficiency are major concerns in high-power CCM boost converters. The hard-switched CCM boost converter suffers from severe diode reverse-recovery problem in high-current high-power applications.
That is, when the main switch is turned on, a shootthrough of the output capacitor to ground due to the diode reverse recovery causes a large current spike through the diode and main switch. This not only incurs significant turn-off loss of the diode and turn-on loss of the main switch, but also causes severe electromagnetic interference (EMI) emission.
The effect of the reverse-recovery-related problems become more significant for high switching frequency at high power level. Therefore, the hard-switched CCM boost converter is not capable to achieve high efficiency and high power density at high power level.
Many soft-switching techniques on CCM boost converters have been proposed . The zero-voltageswitched (ZVS) quasiresonant converter (QRC) achieves soft switching of the main switch with ZVS and the diode with zero current switched (ZCS), but both main switch and diode suffer from an excessive voltage stress due to resonant operation.
The ZVS quasisquare-wave converter (QSW) technique offers ZVS turn-on for both main switch and diode without increasing their voltage stresses. However, both main switch and diode suffer from a high current stress resulting in significant conduction losses. Furthermore, turn-off loss of the main switch is considerable. Since both ZVS-QRC and ZVS-QSW techniques achieve soft switching only at the expense of increased conduction losses due to voltage or current stresses of the components, they are not suitable for high-power applications.
The zero-voltage-transition (ZVT) pulsewidth modulation (PWM) converter achieves soft switching of the main switch and diode without increasing their voltage or current stresses, since ZVS is achieved by partial resonance of the shunt branch across the main switch. Furthermore, the reverserecovery- related problem is alleviated by controlling diode current decrease rate di/dt during its turn off. However, severe undesired resonance may occur in the shunt branch. Adding a rectifier and saturable inductor can mitigate the resonance, but this causes circuit complexity and additional cost. Also, the auxiliary switch in the shunt branch is hard switched, and the duty ratio of the auxiliary switch limits the effective duty ratio of the main switch, leading to decreased voltage conversion ratio of the converter.
