Research On Bidirectional Full-bridge DC-DC Converter Based On High Frequency Isolation

In the case where energy needs to flow in bi-directions,such as DC uninterruptible power supply(DC-UPS)system,aerospace power system and other traditional fields,bidirectional DC-DC converters have been widely used,and the technology is relatively mature.With the development of power industry technology,especially the advancement of power electronics technology,in the field of V2 G and new energy,the performance requirements of bidirectional converters are getting higher and higher.Aiming at the application requirements of current medium and large power DC-DC converters,this paper focuses on high-frequency isolated bidirectional full-bridge DC-DC converters and studies its key technologies.For the two working modes of the bidirectional DC-DC converter,the working mode process is analyzed in detail,and the inherent defects of the full-bridge converter are summarized.Lagging bridge arm is difficult to realize its soft voltage switching(ZVS),and there is the duty ratio loss phenomenon of the secondary side.On this basis,the parameters of the main circuit of the 5k W bidirectional DC-DC full-bridge converter are designed.The selection of transformers and key components are completed.The establishment of the smallsignal model is the key to the controller designing.Based on the non-isolated forward Buck and reverse Boost small-signal models,the small-signal model of the bidirectional fullbridge DC-DC converter is established by using the method of state space averaging.The control method is studied,and the voltage loop,current loop and power loop control converter are used to realize constant voltage,constant current and constant power output respectively.In order to adapt to different applications,the converter is required to output any voltage value within the rated output voltage range.In the case that the dead time can not be ignored,this paper analyzes the problem that the phase shift voltage regulation method can not reliably output zero voltage,and proposes that the regulation mode is switched to PWM duty cycle control during low-voltage output;The parallel capacitor of switchs completing its charge and discharge in dead time is is a necessary condition for realizing ZVS.For different load conditions,the required dead time range is obtained,and the process of dynamically adjusting the dead time is given.The experimental platform of 5k W bidirectional full-bridge DC-DC converter based on DSP digital control is built,and the system composition is analyzed.The design of some hardware circuits and the digital PID controller is completed.The experimental results show that the converter can achieve the desired goal and achieve the required functionality.The research results can play an important role in applications such as new energy grid-connected system,electric vehicles and other fields where energy needs to flow in bi-directions.