DFT 기반 배터리 EIS 고속 측정에 관한 연구 = A Study on Rapid Battery EIS Measurement Based on DFT

다국어 초록 (Multilingual Abstract)

A Study on Rapid Battery EIS Measurement Based on DFT CHANHO LEE Advisor : Prof. Lim Sangkil, Ph.D. Department of Electronic Engineering Graduate School of Chosun University As EV(Electric Vehicles) and ESS(Energy Storage Systems) expand, rapid and accurate on-site battery diagnostics for state of charge and state of health are essential. Existing BMS(Battery Management Systems) and traditional methods like DCIR(Direct Current Internal Resistance), ACIR(Alter Current Internal Resistance), and sweep-based EIS(Electrochemical Impedance Spectroscopy) face significant limitations, including insufficient data, excessive measurement times, and reliance on bulky, high-cost equipment for high-voltage environments. To address these issues, this paper proposes a high-speed, multi-frequency EIS topology and control algorithm using square wave injection and a synchronous DFT(Discrete Fourier Transform). A current-controlled single-phase full-bridge inverter with a large-capacity series capacitor completely cancels the battery's DC offset, enabling safe, low-cost implementation in multi-cell high-voltage conditions. Using a DFT based synchronous reference frame transformation, the system simultaneously extracts multiple odd harmonics from a single square wave to instantaneously reconstruct broadband complex impedance. System precision was verified through PSIM and MATLAB/Simulink co-simulations alongside hardware experiments on single 18650 cells and 4-series configurations across various State of Charge levels. Nyquist plots from the proposed board closely matched a high-end commercial EIS analyzer (HIOKI IM3590). Real resistance aligned almost perfectly, and the imaginary part showed a negligible 0.001Ω error, accurately capturing complex non-linear electrochemical behaviors. This technique reduces measurement time by replacing sequential frequency sweeps with a single-cycle injection. Furthermore, it enables the cost-effective measurement of high-voltage battery packs, which conventionally requires prohibitively expensive diagnostic hardware. This makes it a highly practical, scalable on-site solution for evaluating battery degradation and assessing second-life reusability.

목차 (Table of Contents)

• 제1장 서론 1
• 1.1 연구 배경 1
• 1.2 논문 구성 2
• 1.3 기존 연구와의 차별성 3
• 제2장 배터리 등가회로와 기존 임피던스 측정법 5
• 2.1 리튬 이온 배터리의 특성 및 Randles 회로 5
• 2.2 기존 임피던스 측정 8
• 2.2.1 DCIR 8
• 2.2.2 ACIR 10
• 2.2.3 EIS 12
• 제3장 고속 배터리 EIS 측정 토폴로지 및 제어 기법 · 14
• 3.1 DFT 기반 구형파의 고조파 및 임피던스 측정 알고리즘 14
• 3.1.1 전류 제어 풀 브리지 인버터를 이용한 구형파 14
• 3.1.2 푸리에 급수, 변환과 이산 푸리에 변환 22
• 3.2 직렬 커패시터를 활용한 배터리 전압 제거 토폴로지 28
• 제4장 시뮬레이션 및 실험 결과 34
• 4.1. EIS 장비와 시뮬레이션 EIS 분석 34
• 4.1.1 HIOKI 사의 IM3590 장비 EIS 측정 34
• 4.1.2 PSIM과 MATLAB/Simulink 기반 시뮬레이션 37
• 4.2. 제안하는 방식의 고속 EIS 측정 51
• 4.2.1 실험 환경 구성 51
• 4.2.2 실험 파형 54
• 제5장 결론 63
• 참 고 문 헌 64