For providing a reliable power supply in an islanded AC microgrid, it is crucial to ensure that the operating states meet the safety constraints. However, conventional distributed secondary control methods often struggle to handle voltage and frequency constraints, limiting their practical applicability. To address these limitations, this paper proposes a novel prescribed performance control (PPC) based distributed secondary coordination method for islanded AC microgrids. The proposed method introduces a systematic framework that integrates bijective transformation with distributed secondary control. In this framework, the constrained distributed voltage and frequency control problems can be transformed into unconstrained ones, enabling strict adherence to predefined performance boundaries. Additionally, Lyapunov-Krasovskii functional analysis is employed in this paper to ensure asymptotic stability and calculate the stable boundaries in the transformed error space under time-delay conditions. The effectiveness of stability recovery and prescribed performance is tested in both MATLAB/Simulink and RTLab-based hardware-in-the-loop (HIL) experimental environments.