The co-phase power supply system enables the interconnection of power supply sections within the coverage area of a single traction substation. This system ensures continuous train operation, enhances the direct utilization of regenerative braking energy, and increases the flexibility of integrating photovoltaic and energy storage into the traction network. This paper examines the operation characteristics of photovoltaic and energy storage systems in co-phase traction networks and provides a theoretical foundation for their integration strategies. First, this paper describes how photovoltaic and energy storage systems can be connected to the in-phase TPSS through traction substations or the traction network. Second, a power flow calculation model for the TPSS based on the unified chain circuit model is developed, followed by creating a sensitivity model for the voltage of the catenary and the injected current of photovoltaic and energy storage. Finally, the voltage-current sensitivity model developed in this paper is compared with the power flow model’s results to verify its accuracy. The impact of changes in the position of photovoltaic and energy storage is analyzed based on the voltage sensitivity model.