High-gain Isolated Push-pull Bidirectional DC/DC Converter For Energy Storage

With the continuous improvement of renewable energy penetration rate and the rapid development of smart grid,electric power routers have received great attention from experts and scholars at home and abroad in recent years.The energy storage system is an important part of the power router.The isolated bidirectional DC/DC converter serves as an interface for energy exchange between two different voltage levels,balances the power relationship in the power router,and directly affects the function and performance of the power router.Therefore,this topic is to develop a new type of high-gain isolated push-pull bidirectional DC/DC converter for the energy storage system of electric energy routers.The main work includes the following aspects:Firstly,the details of the working principle of Boost isolated push-pull bidirectional DC/DC converter in the matching mode of transmission inductance voltage are analysised.According to the relationship between duty cycle and shift,the working process is divided into forward and reverse working modes,and the static gain of the converter is derived.The power transmission characteristics under the full working mode of the system and the relationship between the effective value of the transmission inductor current and the shift comparison are derived,which lays the foundation for the modeling of the converter.The PSIM software is used to simulate and verify each working mode of the system.Secondly,the modal average hierarchical modeling method is proposed for the problem that the average value of one switching period of the transmission inductor current is zero and cannot be directly described by the state space model.The low-order non-coupling small-signal mathematical model of the system is established to realize the decoupling of the circuit before and after.Based on the previous mathematical model of the converter,a dual closed-loop control model of the current inner loop and the voltage outer loop with the goal of controlling the clamping capacitor voltage is established.Based on the mathematical model of the latter stage of the converter,a phase-shifted single-voltage loop phase-shift control model aimed at controlling the output voltage is established.The regulator parameters are optimized to improve the dynamic and static performance of the system.Then,on the basis of analyzing the soft switching characteristics under ideal conditions,the process of charging and discharging the parasitic capacitance of the switch tube is considered.The soft switching characteristics of the primary and secondary switch tubes are analyzed separately in this paper.The soft switching conditions of each switch tube under the six working modes of positive and negative are deduced,so as to obtain the soft switching constraints under the full working mode of the system.Taking into account the requirements of the system power transmission characteristics,current ripple coefficient index and soft switching conditions,the value of the inductance in the system is optimized to improve system performance.The effect of the magnetizing inductance on the soft switching characteristics is analyzed to further ensure the realization of soft switching.Finally,based on theoretical analysis and simulation verification,the system hardware design and software design are completed.A bidirectional DC/DC converter experimental platform is built.The 96 V voltage input,700 V voltage output and 1kW forward power transmission are realized,and the basic working mode and soft switching characteristics of the system are verified.