Abstract: The transformation of converter technology has led to the weakening or even cancellation of passive components at the line boundary, making it difficult to achieve fault identification across the full line length based solely on the single-end electrical characteristics. In response to this issue, this paper fully utilizes the high controllability of the converter, actively constructs specific response characteristics of the converter to internal and external faults, establishes active boundaries that cooperate with single-end quantity protection, and thus achieves fault identification across the full line length at a single end. On this basis, further discussion is conducted on the additional control strategies for active boundary characteristics and the selection criteria for key parameters. The propagation law of active boundary response in fault circuits is analyzed, and a single-end full-line high speed protection criterion is designed to match it. The simulation verification results show that the proposed method can still reliably identify high-resistance faults, improving the reliability and sensitivity of traditional single-end protection.