With the degree of electrification in rural areas greatly improved, the establishment of photovoltaic, energy storage integration of “optical storage straight soft” system in rural areas can be used as a pilot target to achieve zero carbon. The three-port converter is the core of the “optical storage straight soft”. It not only has the characteristics of flexible buck-boost of bidirectional Buck-Boost circuit and bidirectional power flow of dual active bridge circuit, but also has simple structure and high integration. However, due to the integration with dual active bridge (DAB), backflow power (BP) is generated during operation. The existence of backflow power (BP) will increase the switching loss and reduce the conversion efficiency. In order to further improve the conversion efficiency, this paper proposes a parameter optimization method with zero backflow power in a certain working range for the problem of backflow power (BP) in the three-port converter under PWM plus double phase shift control.