Date of Award


Publication Type

Master Thesis

Degree Name



Electrical and Computer Engineering


Battery capacity, Battery impedance, Battery management system, Coulomb counting, Measurement errors, State of charge


Balakumar Balasingam




Accurate state of charge (SOC) estimation in rechargeable batteries is always a challenge since many parameters can affect the SOC of the battery. Amongst all the developed methods for SOC estimation, Coulomb counting has been one of the most common and traditional methods. Nevertheless, the accuracy of this method is debatable. It was assumed that Coulomb counting can accurately estimate SOC by assuming the battery capacity and initial SOC. In this thesis, we analyze the Coulomb counting method thoroughly and we showed that this method is susceptible uncertainties. The sources of uncertainties that affect Coulomb counting accuracy are: (i) current measurement error; (ii) current integration approximation error; (iii) battery capacity uncertainty; and the (iv) timing oscillator error/drift. The SOC error due to all these uncertainties can be categorized into two forms; time-cumulative and SOC-proportional. The time-cumulative error increases over time and can invalidate SOC estimation by Coulomb counting. The SOC-proportional error increase with the accumulated SOC and it can affect SOC accuracy within one cycle of charge/discharge. A simulation analysis is presented to demonstrate and verify the effect of these uncertainties under several realistic scenarios. We also have discussed the approaches to reduce these uncertainties.