The transmission of renewable energy via flexible DC systems has become an inevitable development trend for large-scale renewable energy grid integration. The associated two-terminal weak feed (TTWF) AC systems are often composed of 100% power electronic equipment. Traditional fault control strategies adopted by the converters at both ends of the line after a fault lead to limited fault currents, thereby reducing the effectiveness of conventional differential protection. Based on the challenges in current differential protection in TTWF AC systems under conventional control strategies, a current differential protection scheme based on negative-sequence control coordination strategy is proposed. First, the fault characteristics of TTWF AC systems are theoretically derived, and a boundary function is presented to quantitatively assess the performance of current differential protection actions. Secondly, the action boundary and sensitivity of current differential protection with the improved fault control coordination strategy are analyzed. Finally, combining the action boundary, sensitivity and adaptive function, an improved current differential protection scheme based on adaptive function is proposed. Simulation results show that the proposed protection scheme can reliably identify faults even under conditions of a 300 fault resistance and 25 dB noise interference. It is well-suited for the protection requirements of TTWF AC systems under various scenarios and demonstrates higher sensitivity.