Due to weak-feed characteristics of converter-interfaced renewable energy sources

fault characteristics in new type distribution systems are significantly weakened

rendering traditional relay protection techniques increasingly inapplicable. Active signal injection-based protection enhances fault characteristics by actively modulating converter output behavior during faults

thereby overcoming the limitations imposed by weakened characteristics and emerging as a key development direction for protection technologies in new type distribution systems. Focusing on typical fault types

research progress on protection in new type distribution systems is reviewed

highlighting the limitations of traditional passive protection methods and the necessity of developing active signal injection-based protection strategies. On this basis

the key technologies such as the generation and selection of injected signals are analyzed

common issues in existing studies are summarized

and typical application scenarios are discussed. Finally

future research directions are outlined

aiming to provide references for further in-depth studies on active signal injection-based protection technologies for new type distribution systems.