Research On Wide Gain Resonant Bidirectional DC-DC Converter

With the change of energy structure,the DC microgrid based on distributed power supply and energy storage system develops rapidly.As the voltage of super-capacitor fluctuates over a wide range,a wide gain DC-DC converter is needed to connect it to the DC microgrid bus.In view of the problem that it is difficult for existing converters to achieve the goal of wide gain when the input voltage varies in a large range,and the port voltage fluctuation is limited by the realization of soft switching,this paper presents a variable-three-level resonant bidirectional DC-DC converter topology,and the voltage variation range and soft switching characteristics are studied in detail.The major works are organized as follows:1.The research status and key technologies of wide gain DC-DC converter at home and abroad are summarized.The technical points of topology proposed in this paper are expounded.The principle of three-level inverter bridge is analyzed.The concept of variable three-level duty cycle is proposed.The voltage gain and energy transfer characteristics of series resonator and multi-resonator are discussed.The application of phase shift control in three-level resonant converter and the realization of soft switch are described.Various modeling methods of resonant DC-DC converter are summarized.The steps of the first harmonic analysis are studied in detail,and it is determined to use different frequency components to model the converter.2.To solve the problem that series resonant DC-DC converter is difficult to achieve the wide gain target and the ZVS range is reduced under the condition of voltage fluctuation,a variable-three-level series resonant bidirectional DC-DC converter(VTL-SR-BDC)topology is proposed.When the input voltage changes,the three-level full bridge runs at different three-level duty cycle,so as to maintain the voltage stability of the output port.It makes the voltage ratio of the resonator constant to 1,ensuring the ZVS characteristic of the switch tube.By using the first harmonic analysis method,the system is modeled from the time domain and the phasor domain respectively.It analyzes the working characteristics and the soft switching implements condition of the converter.Finally,the system parameters are designed according to the soft switch range.At the same time,the simulation experiment verifies its positive and negative operation effect.3.A variable-three-level multi-resonant bidirectional DC-DC converter(VTL-MR-BDC)topology is proposed in this section,for the purpose to improve the transmission efficiency and turn-off current the series resonant converter.The resonant tank is composed of LCLC circuit,which can transmit fundamental frequency and triple frequency energy.Thus,it can confine the circulating energy and improve the efficiency of conversion.The resonant current is composed of fundamental frequency and triple frequency,which increases the zero crossing slope of the resonant current.This increases the turn-off current and further broadens the scope of ZVS implementation.On the basis of Fourier decomposition,the fundamental frequency component and triple frequency component are considered for modeling.It analyzes the operating characteristics and soft switching conditions.Finally,the parameter design method of VTL-MR-BDC is presented systematically.At the same time,the proposed topology structure is verified by the simulation system.And the operation effect of this structure is compared with the VTL-SR-BDC.