Abstract
In this paper, high-efficiency bidirectional LLC resonant converters with primary auxiliary windings in transformers of resonant circuits are proposed. Even though resonant capacitors are used on the primary and secondary sides, the proposed converter can operate, regardless of the direction of the power flow, with the high gain characteristics of the LLC resonant converter without the mutual coupling of resonant capacitors. The operation principles and gain characteristics of the proposed bidirectional DC–DC converters are described in detail. A 3.3 kW prototyped bidirectional LLC resonant converter for interfacing 750 VDC buses was built and tested to verify the effectiveness and applicability of this proposed converter.
Highlights
Voltage source-isolated or current source-isolated bidirectional DC–DC converters using a high-frequency transformer are generally used in energy storage systems for renewable energy sources and future electric vehicles [1,2,3]
In heavy load conditions and frequency regions lower than the resonant frequency, the slope of the CLLC gain characteristics decreases, which means that zero voltage switching (ZVS) cannot be achieved
4 the voltage resonant circuit, the current flows through the primary common connection line on when thecharged currentin is the flowing in their anti-parallel diodes, Q2 and Qthe operated with ZVS
Summary
Voltage source-isolated or current source-isolated bidirectional DC–DC converters using a high-frequency transformer are generally used in energy storage systems for renewable energy sources and future electric vehicles [1,2,3]. In heavy load conditions and frequency regions lower than the resonant frequency, the slope of the CLLC gain characteristics decreases, which means that zero voltage switching (ZVS) cannot be achieved. To operate with the wide range of voltages in the bidirectional power transfer, a two-stage DC–DC converter (as shown in Figure 1a) composed of a hard-switched buck/boost converter for output voltage control and an unregulated LLC converter for electrical isolation has been used in various applications [7]. Bidirectional LLC resonant converters with a wide input and output voltage range are proposed, as shown in Figure 2 [8].
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