Research On Resonant Converters With Wide Voltage Range

Developing new energy resources has becoming an important solution for the energy crisis and environment pollution.New energy generation and new energy vehicles are important components of new energy resources.When dc-dc converters are applied in new energy generation and new energy vehicles,they are required to have a wide range voltage regulation ability and high efficiency.The LLC converter is widely used in medium-to-high power applications because the switches can realize natural ZVS and the rectifier diodes can achieve natural ZCS in a wide load range However,due to the disadvantage of the narrow voltage gain range of LLC resonant conveter,it is difficult for LLC resonant converter to be applied in applications which require wide voltage range regulation ability.In order to broaden the voltage gain range of LLC resonant converter,this paper focuses on the rectifier of LLC resonant converter,and the voltage gain range of LLC resonant converter is widened while retaining the characteristics of LLC resonant converter.Firstly,this paper analyzes the working principles of the traditional LLC resonant converter.Then the working charateristics of LLC resonant converter are analyzed in detail based on fundamental harmonic analysis(FHA).Moreover,the design method of LLC resonant converter is introduced.Secondly,the influence of the transformer turn ratio on the voltage gain characteristic is discussed in this paper.The relationship between the voltage gain and the turn ratio of the transformer under the same switching frequency and output power is deduced.According to the relationship,an improved LLC resonant converter with variable-rectifier is obtained.The operation principles of the converter are analyzed in detail.The converter has two modes,and a mode transition scheme is employed to achieve smooth and fast transition between two modes.A 500 W prototype is built and tested to verify the feasibility of the converte.Finally,this paper discusses a DC/DC converter for hold-up operation.Input voltage is relatively fixed when it works in normal state while during the hold-up time,the range of input voltage is wide.Therefore,an LLC converter for hold-up operation is proposed in this paper.The voltage gain is improved by changing the configuration of rectifier.Operation principles,characteristics of the proposed LLC resonant converter are analysed in detail.Experimental results are given to verify the effectiveness of the proposed converter.