Research On Isolated DC/DC Converter With Wide Range Output

The world is facing the challenges of environmental degradation and resource shortage,and the environment-friendly and efficient energy system has become research hotspot.Electric vehicle(EV)batteries and supercapacitors have advantages in terms of environmental protection and energy utilization,but they require wide charging range and high efficiency.To solve this problem,two kinds of multi-resonant converters and a hybrid full bridge converter are proposed.First of all,two kinds of LCLCL and LLC-LC multi-resonant converters are introduced.They have different structures but similar working principles.Compared with LLC converter,LCLCL and LLC-LC converters not only have better soft switching characteristics,but also have more advantages in gain.The output voltage is less affected by load,which solves the problem of light-load or no-load voltage regulation of LLC converter.LCLCL and LLC-LC converters can use third harmonic to transmit the active power,and the loss caused by the reactive power cycle of the converter and the effective value of the loop current are reduced,which improve the efficiency.At the same time,LCLCL and LLC-LC converters have better inherent soft startup capability and over-current protection function.In order to verify the working principle and superiority of LCLCL and LLC-LC converters,two 2.5kW experimental prototypes were designed respectively.Through comparative analysis,LCLCL multi-resonant converter has more advantages in resonant element stress and efficiency.Secondly,a dual LC parallel multi-resonant converter with notch function is proposed.The converter is similar to LCLCL and LLC-LC multi-resonant converters in working principle and gain characteristics.It not only has all their advantages,but also has higher efficiency and lower voltage and current stress of resonant elements.The multi-resonance converter has more resonance parameters,which increases the difficulty of parameter design.From the perspective of gain and efficiency,the influence of resonance parameters on the converter is analyzed in detail and a complete parameter design scheme is given.Finally,the correctness of the theoretical analysis and the rationality of the parameter design are proved by a 3.3 kW experimental prototype.The converter has high efficiency under constant current(CC)charging and constant voltage(CV)charging modes,and its peak efficiency reaches 97.72%.Finally,a hybrid full-bridge converter composed of a phase shift control active rectification full-bridge(PSCAR-FB)converter and a full-bridge LLC converter(FB-LLC)is proposed.A time-sharing phase-shift control strategy is proposed for the hybrid full-bridge converter: the secondary-side phase shift control mode(SPSCM)and the primary-side phase shift control mode(PPSCM).The output voltage can be independently adjusted by this control scheme.The soft switching range of primary side switches is wide through the shared bridge arms,and the series inductance of the phase-shifting full-bridge converter does not need to be specially designed to help realize zero-voltage switching(ZVS).The output side of the hybrid full-bridge converter is connected in series,which reduces the voltage stress on the secondary power devices.The converter's working principle and steady state characteristics were experimentally verified by a 3kW prototype.Experimental results show that the converter maintains high efficiency over the entire output voltage range,and the peak efficiency is 97.43%.