Online Battery Impedance Spectroscopy Using Pseudo-Random Binary Sequence
Authors
Olsen, Anton Hviid ; Altuna Aristizabal, Lierni ; Khatiwada, Bhupal
Term
3. term
Education
Publication year
2025
Submitted on
2025-12-19
Pages
52
Abstract
As electric vehicles become more common, there is a growing need to assess how their batteries age and how much usable capacity remains. This thesis explores a low-cost way to estimate a battery’s Nyquist plot— a graph of impedance versus frequency that reflects battery health—while the battery is powering a Permanent Magnet Synchronous Machine (PMSM) through an inverter. The approach injects a small Pseudo‑Random Binary Sequence (PRBS) into the d‑axis current reference of a Field‑Oriented Control (FOC) drive, minimizing speed disturbance. PRBS excites a broad, flat set of frequencies, similar to Electrochemical Impedance Spectroscopy (EIS), but uses the existing drivetrain instead of specialized lab hardware. In simulations, the method was feasible but sensitive to disturbances. Experiments with both 4‑bit and 11‑bit PRBS confirmed its practicality. The PRBS was applied at standstill and during operation; during operation it achieved similar Nyquist accuracy despite the influence of the q‑axis current. Because of the inherent PRBS frequency content, only part of the Nyquist plot could be recovered, limiting the frequency range. Overall, PRBS‑based excitation can be used to obtain a battery’s Nyquist plot during normal motor operation, but it is noise‑sensitive and provides only partial frequency coverage.
Elbiler bliver mere udbredte, og derfor er der behov for bedre metoder til at vurdere batteriers forringelse og restkapacitet. Denne afhandling undersøger en lavomkostningsmetode til at udlede et Nyquist-diagram – en graf over batteriets impedans på tværs af frekvenser, som kan sige noget om tilstand og kapacitet – mens batteriet driver en permanentmagnet-synkronmaskine (PMSM) via en inverter. Ideen er at injicere et svagt pseudo-random binærsekvens (PRBS) signal i d-akse strømreferencen i en feltaorienteret regulering (FOC), så motorhastigheden påvirkes minimalt. PRBS dækker mange frekvenser med samme amplitude, lidt som elektrokemisk impedansspektroskopi (EIS), men uden behov for ekstra dyrt laboratorieudstyr. I simuleringer viste metoden sig mulig, men følsom over for forstyrrelser. Eksperimenter med både 4-bit og 11-bit PRBS bekræftede anvendeligheden. Metoden blev brugt både i stilstand og under drift; under drift gav den en tilsvarende nøjagtighed i Nyquist-diagrammet, selvom q-akse strømmen påvirkede systemet. På grund af PRBS’ frekvensindhold kunne kun en del af Nyquist-diagrammet estimeres, hvilket begrænser dækningsområdet. Samlet set kan PRBS anvendes til at opnå batteriets Nyquist-diagram under normal motordrift, men metoden er støjfølsom og giver kun delvis frekvensdækning.
[This apstract has been rewritten with the help of AI based on the project's original abstract]