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In this article, a new soft-switching auxiliary circuit structure for the synchronous rectification noninverting buck–boost converter (NIBBC) is proposed. This new auxiliary circuit, which contains a fully coupled inductor (or a transformer), a snubber inductor, a capacitor, and a power diode, will provide zero voltage switching (ZVS) turn-ON conditions for all power transistors of the proposed NIBBC. In addition, waveform ripples in the auxiliary circuit of the output side are reduced, and then the output current ripple is also reduced. Meanwhile, the current across the main inductor is not affected by the auxiliary circuit. In order to analyze the proposed NIBBC, operating principles, soft-switching implementation conditions, and main characteristics of the proposed NIBBC are presented in this article. Finally through building a 400-W experimental prototype, key waveforms and measuring efficiency curves are obtained. Experiment result shows that all transistors of the new NIBBC operate under ZVS conditions. The efficiency of the proposed NIBBC is improved by comparing to the triangular current mode soft-switching NIBBC. [ABSTRACT FROM AUTHOR]

In this paper, several new coupled-inductor-based soft-switching dc–dc converters are proposed. These converters are obtained by changing the coupled branch of several existing dc–dc converters. Meanwhile they have similar characteristics to these existing converters, and provide more choices for the practical application. Then by applying an existing efficiency improvement method, which is used in the buck-type soft-switching converter, to all abovementioned converters, several new converters with efficiency improvement characteristics are obtained. This efficiency improvement method utilizes the low conduction performance of the transistor to reduce the loss. In addition, this method has the same control complexity to original topologies, because the auxiliary transistor has the same control timing to one of main transistors. The characteristic of new converters and efficiency improvement method are presented by analyzing two new topologies (boost-type converters). Finally simulation and experimental results are given and analyzed by designing a prototype. Based on these results, soft-switching conditions and efficiency improvement capability are verified. [ABSTRACT FROM AUTHOR]

In this paper, a soft switching DC–DC converter is presented for a hybrid energy storage system (HESS) in an electric vehicle (EV), using fixed boundary layer sliding mode control (FBLSMC) and variable switching frequency modulation. This strategy is aimed at improvement of the transient performance, energy transfer efficiency and system robustness for the HESS which is composed of a battery, an ultracapacitor (UC) and a bidirectional DC–DC converter. The state-space model of such DC–DC converter is firstly established involving all operating modes and system uncertainties. The FBLSMC scheme is proposed for the satisfactory voltage/current tracking despite system uncertainties. It can guarantee the system robustness and avoid the chattering existing in conventional sliding mode control (CSMC). In order to ensure the soft switching under transient load variations, a variable switching frequency modulation method is introduced into the controller. Finally, experimental results confirm that (1) within the full-load range the efficiency of the DC–DC converter with variable switching frequency is ∼96% in contrast to 90% efficiency at hard switching, and (2) the energy delivered by the UC follows the reference closely for EVs. [ABSTRACT FROM AUTHOR]

This paper presents a novel topology for a nonisolated bidirectional dc–dc converter with soft-switching capabilities, which usually operates at a zero-voltage-switching (ZVS) condition. A nonisolated dc–dc converter combines a buck converter and a backward boost converter into one circuit, which consists of a half-bridge power switch, an inductor, and capacitors. In order to realize ZVS conditions, the proposed converter utilizes a coupled inductor, a small independent inductor, and auxiliary switches and diodes. Due to ZVS, switching stress on switch components is reduced, and the reverse recovery problem of MOSFET antiparallel body diodes is also eliminated. Moreover, the operating modes of the proposed converter can be switched between a ZVS mode and a conventional hard-switching mode on the basis of load conditions. The soft-switching mode is for heavy loads, and the hard-switching mode is for light-load conditions. Therefore, the highest efficiency can be obtained at almost all load ranges. The detailed theoretical analyses in each mode are presented, and a 1-kW prototype is also built to verify the principle of the circuit and the theoretical analysis. [ABSTRACT FROM PUBLISHER]