With the development of power grid business and the increase in electronic devices

the wiring system is susceptible to lightning transients

which may lead to equipment damage. Therefore

an effective transient evaluation method is urgently needed. Existing research mainly focuses on transmission line models and direct lightning strike analysis

but there is a lack of systematic research on the induced transient behavior of closed-loop structures under indirect lightning strikes. In this paper

the partial element equivalent circuit (PEEC) method is employed

and the external incident field is calculated in combination with the engineering model of the lightning channel. A full-wave PEEC formula suitable for closed-loop structures is established. The research reveals that there is a numerical instability problem when calculating the induced lightning transient current. This paper conducts an in-depth analysis of the causes of this instability and proposes an algorithm with high numerical stability. After comparison and verification with the Finite-Difference Time-Domain (FDTD) method

this algorithm demonstrates good accuracy and stability. Additionally

the research also explores the instability problem when calculating the external voltage source based on the Uman formula. Finally

the proposed PEEC algorithm is applied to the analysis of the induced transients in the direct current circuit of photovoltaic (PV) panels under indirect lightning strikes

verifying the engineering applicability of the method and providing a theoretical basis and practical tool for the lightning protection design of complex cable systems.