Research And Control Of Three-level Current Push-pull Bidirectional DC/DC Converter

With the development of new energy distributed power generation and the country’s deployment of smart grids,power routers have become a research hotspot in recent years.Isolated bidirectional converters,as the main part of the power routers to achieve flexible control of electrical energy,not only serve as the gap between different voltage levels.The bridge for energy flow also achieves electrical isolation.Aiming at the problem of battery energy storage in regional power routers,this thesis proposes a three-level current type push-pull bidirectional DC/DC converter.The main research contents are as follows:According to the different states of the transmission inductor voltage,the working range of the three-level current-type push-pull bidirectional DC/DC converter is divided into four forward modes(battery discharge)and four reverse modes(battery charging).The working principle and control method of the converter in some modes are analyzed in detail,and the gain formula of the converter is deduced.On this basis,the power expression of each working mode and the effective value expression of the transmission inductor current are deduced to provide a theoretical basis for the actual working mode selection.Aiming at the problem that the average value in the transmission inductor current cycle is zero and the traditional average state space model cannot be established,this thesis adopts a time-weighted state average model modeling method to establish a low-order small-signal mathematical model of the converter.The Bode diagram is used to tune the parameters of each regulator in the control loop,and the design scheme is analyzed theoretically and verified by simulation.The condition of the switch tube to realize soft switching is studied,the transient switch equivalent circuit of the switch tube is established,and the relationship between the realization of soft switching and the parallel capacitance of the switch tube and the magnetizing inductance of the push-pull transformer is derived,and the realization of soft switching needs to be satisfied Conditions,and carry out simulation verification and experimental verification.On the basis of theoretical analysis and simulation,this thesis designs a three-level current-type push-pull bidirectional DC/DC converter prototype,and obtains the typical working waveform of the circuit on the prototype.Through experiments,it is obtained that the switch tube has different parallel capacitances and different parallel capacitances.The switching waveform under the magnetizing inductance verifies the accuracy of the theoretical analysis in this thesis and the effectiveness of the control strategy.