Research On Control Strategy Of LLC Resonant Converter With Wide Input Range

At present,the world is in a state of energy shortage,Energy is increasingly becoming a key factor in determining the overall competitiveness of a country.New energy power generation technology because of its clean and efficient advantages such as the national development priorities in the future,However,new energy power generation units are easily affected by climate and weather,resulting in large fluctuations in output voltage.In order to provide a stable DC link voltage to the downstream converter,a wide input range DC/DC converter is required between the power generation unit and the downstream converter.LLC resonant converter because of its high efficiency and high power density and other advantages of the most appropriate,However,the LLC resonant converter is susceptible to voltage fluctuations.Therefore,this article focuses on the wide input range LLC resonant converter topology and control strategy.Aiming at the advantages and disadvantages of variable frequency control and fixed frequency control of two-level full-bridge LLC resonant converter,this paper combines two control methods.When the input voltage is lower when using frequency control strategy,when the input voltage is higher frequency control strategy,This combination of fixed frequency control and variable frequency control can effectively improve the input voltage range of the converter;When the LLC converter output current larger secondary switch loss will increase,In order to reduce the switching loss,This paper presents a new type of synchronous rectification technique.This kind of synchronous rectification method does not need to add extra auxiliary circuit,not only improves the efficiency of LLC resonant converter,but does not increase the extra cost;BUCK-LLC two-stage DC/DC converter,the first-stage converter can stabilize the voltage fluctuation of the power generation unit,the post-stage LLC resonant converter can improve the efficiency of the converter,and is more suitable for the new energy power generation system with wide output range.This paper analyzes the BUCK-LLC two-stage converter topology,and small signal modeling.For BUCK-LLC two-stage converter This paper presents a double loop fixed frequency control strategy,making the converter for a wide range of input voltage.In order to verify the topology and control strategy of the LLC resonant converter,a 300W prototype was built in the laboratory.Experimental results show that the control strategy adopted in this paper can widen the input voltage range of LLC resonant converter and is suitable for working in new energy power generation system.