This paper proposes a bidirectional three-level LLC resonant converter with a new pulse width and amplitude modulation (PWAM) control method. With different control signals, it has three different operation modes with different voltage gains. Therefore, it can achieve wide voltage gain range by switching among these three modes, which is attractive for energy storage system applications needing wide voltage variation. The proposed topology operates with constant switching frequency, which is easy to implement with digital control. And it can achieve soft switching for all the switches and diodes in the circuit as conventional LLC resonant converter. The performance of the proposed converter is validated by the experimental results from a 1kW prototype with 20A maximum output current.
This paper proposes a new LLC resonant DC-DC topology with bidirectional power flow capability. All the switches in the proposed topology can achieve zero voltage switching (ZVS) at turn on, and zero current switching (ZCS) is achieved for the output side switches at turn off. Compared with the traditional bidirectional dual active bridge (DAB) converter, the turn off current is greatly reduced, and the frequency modulation control scheme can almost eliminate the large circulating energy. Therefore, the conversion efficiency can be much improved, which makes it quite attractive in energy storage applications. The output characteristic of the proposed LLC converter is different from the conventional unidirectional LLC resonant converter. A new analytical model is also proposed in this paper. The detailed operating principle and performance of the proposed topology are analyzed. And a 1 kW prototype is built to verify the theoretical analysis. Over 98% efficiency is achieved base on the prototype.
A novel three-port LLC resonant converter is proposed in this paper, which interfaces the clean energy resources like photovoltaic generation, wind power and fuel cell system with the energy storage system like battery. The switching frequency of the proposed topology is constant and equal to the resonant frequency, so zero voltage switching (ZVS) is achieved in the transformer primary side and zero current switching (ZCS) is achieved in the secondary side, which contributes to high conversion efficiency. The battery port of the converter is bidirectional operated to balance the load requirements and energy supplied by the source. The direction of charging/discharging current flowing through the battery in a switching cycle doesn't change, so the current ripple of battery is relatively low, which helps to extend the lifetime of the battery.
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