Electric-propulsion systems for ships, also known as electric propulsion devices, represent the current direction of development for maritime power. Issues concerning the environment and fuel economy have compelled the maritime transport sector to seek solutions that reduce emissions and improve fuel efficiency. In this process, power electronics technology plays a significant role in the propulsion systems of ships. Selecting an efficient battery system is of great importance for enhancing the cruising range of yachts and minimizing environmental impact. The battery model is crucial for revealing the working principles of batteries, and it is extremely critical for the application and development of battery technology. The Battery Management System (BMS) serves a crucial regulatory function, optimizing both the safety and performance of battery cells. Central to its operation is the precise estimation of the battery's State of Charge (SOC), a process dependent on an exacting battery model. This system not only enhances longevity and reliability but also ensures that energy storage solutions meet high standards of efficacy. This study focused on testing the impedance characteristics of lithium-sulfur batteries (LSB) at various SOC points and establishing first- and second-order RC equivalent circuit models. The model parameters were identified through experimental data. Subsequently, a simulation platform was constructed using MATLAB/Simulink to simulate the behavior of LSB under a constant current discharge condition. The simulation results showed that the second-order RC model had significantly lower errors than the first-order model, demonstrating higher accuracy. These achievements can provide technical support for the research of energy storage systems in the green aviation and maritime industries.

1. Introduction
2. EIS and Basic Theory of Equivalent Elements
    2.1 Basic Theory of EIS
    2.2 Basic Theory of Equivalent Elements
3. Establishing Equivalent Circuit Models for LSB
    3.1 EIS Experiment
    3.2 Establishing an Equivalent Circuit Model
4. Parameter Identification for LSB Model
    4.1 Open-Circuit Voltage Parameter Identification
    4.2 Parameter Identification for First-Order RC Model
    4.3 Parameter Identification of the Second-Order RCModel
5. Model Simulation Platform Construction
    5.1 Construction of the First-Order RC ModelSimulation Platform
    5.2 Construction of the Second-Order RC ModelSimulation Platform
6. Model Simulation Verification
    6.1 First-Order RC Model Simulation Verification
    6.2 Second-Order RC Model Simulation Verification
7. Conclusions
Acknowledgment
References

• Zhengrui Zhang(International Maritime Academy, Hainan Tropical Ocean University, Sanya, China)
• Mingyu Wang(International Maritime Academy, Hainan Tropical Ocean University, Sanya, China) Corresponding author
• Qianyong Zhang(International Maritime Academy, Hainan Tropical Ocean University, Sanya, China, Maritime College, Shandong Jiaotong University, Weihai, Shandong, China)
• Zhe Gao(International Maritime Academy, Hainan Tropical Ocean University, Sanya, China)