Research Of Half-Bridge Three-Level Bidirectional LLC Resonant Converter

With the deterioration of the environmental climate,clean energy technologies are increasingly valued and developed by the international community.As an important carrier of clean energy,electricity is crucial for the conversion,transmission and storage of electricity.The bidirectional DC/DC converter can not only realize the voltage level conversion,but also realize the bidirectional transmission of energy,which is suitable for new energy power generation,photovoltaic energy storage systems,uninterruptible power supplies and the like.The bidirectional L-LLC resonant topology can maintain the excellent characteristics of the traditional unidirectional LLC converter in both forward and reverse operation,and has the characteristics of zero voltage turn-on,high power density,and high conversion efficiency in the full load range.The half-bridge three-level structure switching tube voltage stress is only half of the DC bus voltage,suitable for medium and high voltage applications.Therefore,this thesis takes the half-bridge three-level bidirectional LLC resonant converter based on L-LLC resonant structure as the research object,and studies it in detail.Firstly,the working principle and commutation process of the half-bridge three-level bidirectional LLC resonant converter are analyzed.The equivalent circuit of the bidirectional LLC resonant converter is modeled by fundamental analysis method.The output voltage gain function is derived.Then the influence of resonance parameters on gain characteristics and soft switching characteristics is analyzed.Secondly,based on the working principle and characteristic analysis,the resonant parameters of the half-bridge three-level bidirectional LLC resonant converter are optimized.Then the design of the magnetic component,the voltage dividing capacitor and the selection of the power switch tube were completed.Thirdly,the unidirectional output control strategy and the bidirectional switching control strategy of the converter are studied.Firstly,for the light load output problem,the equivalent circuit of the converter considering the parasitic parameters is modeled,and the influence of the parasitic parameters on the light load output characteristics is analyzed.A continuous variable frequency burst control method is proposed to realize the light load and Control of no-load output voltage.Then,for the wide-range voltage output problem,a three-stage hybrid control strategy is proposed,which combines the high-efficiency characteristics of the three control methods of “frequency conversion,phase shifting and variable frequency burst” in different gain regions to achieve high efficiency and wide range voltage.Output.Aiming at the two-way switching control method,this paper studies a commutation control method based on voltage-current hybrid judgment to realize energy bidirectional transmission switching control.Finally,the design of the hardware circuit and software system of the half-bridge three-level bidirectional LLC resonant converter is completed.The 12 kw experimental platform prototype was built to verify the correctness and feasibility of the theoretical analysis and control strategy of the half-bridge three-level LLC resonant converter proposed in this paper.