Research On Dual Active Full-bridge DC-DC Converters

Over-exploitation of natural resources is adverse to sustainable development.The rise of new energy generation has solved many problems,such as shortage of non-renewable energy and environmental pollution,etc.It further promotes the formation and development of Energy Interconnection that can intelligently manage the deployment of power grids.Among them,the isolation performance of the power electronics' interface technology determines its safety,and it is also very important to the managing and dispatching ability of power grid.Double active full-bridge dc-dc converter with high frequency transformer in the middle has symmetrical active Bridges on both sides.It is well popular both domestic and overseas,because it has the advantages of good transmission performance,strong boost capacity,fast dynamic response.And it is also easy to implement soft switching technology.In order to improve the booster ability and efficiency of DAB converter,quasi Z impedance network is added on both sides of the original bridge,which combined into a new dc converter.We used PWM shoot-through control,which is also different from the previous phase-shifting control.Under this control method,the boost capacity is improved,and we don't need to set dead-band time.The waveform distortion rate is small,which improves the efficiency of dc converter.It also can output high energy quality.Firstly,this paper introduces the background and research status of quasi-z-source DAB converter,and analyzes its topological structure and working principle.For traditional phase-shifting control,dead-band time and complicated control method is inevitable,so the control strategy is studied further.The full-bridge circuit and quasi Z impedance network circuit are modeled by the state-space average method.Combining them can set up the whole mathematical model.In this paper,the quasi-z source module is studied in depth,and the boost factor of network is derived by the equation of the equivalent circuit of straight state and non-straight state.Then,the quasi-Z impedance network and high-frequency transformer are designed.Aiming at the problems of poor output performances and easy to be disturbed in the open-loop state of the converter,type II loop compensation controller and PID controller are designed.And the rationality of the design is verified by simulation.The MPPT quick charging method based on muss charging curve is divided into three stages to charge the battery,with high efficiency and good effect.the working process of gradual charge,rapid charge and floating charge are also analyzed and simulated respectively.Finally,the Saber simulation model is established and the performances of the converterunder open-loop control,type II loop compensation control and PID control are compared and analyzed by the simulation results.Set up experimental prototype to verify its output characteristics and efficiency.