Research On Hybrid Modulation Method Of Hybrid Switching Bidirectional AC/DC Converter

With the continuous development of renewable energy,a large number of distributed power generation and energy storage devices are connected to the grid,and bidirectional AC/DC converters with bidirectional energy flow property have become an important interface for energy exchange between the grid and distributed energy systems.It can not only supply electric energy to DC power equipment,but also be connected in parallel with the power grid to adjust the harmonic index of the power grid current,which is of great significance to the safe and stable operation of the power grid.However,more and more complex application conditions put forward strict requirements on the conversion efficiency and reliability of bidirectional AC/DC converters,and it is difficult to meet the requirements of high efficiency and low cost by simply using Si-IGBT or SiC-MOSFET.Therefore,it is of great significance to investigate new high-performance switching structures and modulation methods to improve the overall performance cost ratio of bidirectional AC/DC converters.Combining the advantages of Si-IGBT and SiC-MOSFET,this paper adopts a hybrid switch composed of Si-IGBT with large current capacity and SiC-MOSFET with small current capacity in parallel as the switching device of bidirectional AC/DC converter,and investigate a new hybrid modulation method to achieve lower device junction temperature,higher conversion efficiency and greater output power capacity.The main research content of the paper is as follows:Introduced the common drive mode of hybrid switch with Si-IGBT and SiC-MOSFET in parallel,designed a new type of gate drive circuit for the common drive mode,gave the working principle and mathematical analysis,designed the prototype of the drive circuit,and experiments verify the feasibility of the drive circuit.At the same time,for the two driving modes applicable to the hybrid switch bidirectional AC/DC converter,the loss models of the converter in the rectification and inversion modes are respectively established,and the influence of the hybrid switching delay time on the power loss is clarified.Aiming at the problem of unbalanced temperature distribution of switching devices in bidirectional AC/DC converters working in rectification mode,a hybrid modulation method is proposed to balance the heat distribution of the switching tube and improve system reliability.A thermal model of the hybrid switch is established,and a calculation method for the junction temperature of the hybrid switch in the hybrid modulation mode is deduced.In order to obtain the thermal resistance value of the hybrid switch under actual working conditions,a hybrid switch thermal resistance test platform was built in this paper,and thermal simulation was carried out.The simulation results proved the superiority of the hybrid modulation method.The control strategy of hybrid switch bidirectional AC/DC converter was designed,and its theoretical and simulation analysis was carried out.An experimental platform for a hybrid switch bidirectional AC/DC converter was built.The experimental results showed that the converter can operate stably in both rectification and inversion modes,which verified the effectiveness of the control system and modulation method.