This paper deals with the estimation of core temperature (Tc) of a Lithium (Li) ion battery using measured ambient and surface temperatures. The temperatures were measured using thermocouples placed at appropriate locations. A second order thermal model was considered for the core temperature (Tc) estimation. A set of coupled linear ordinary differential equations (ODEs) were obtained by applying Kirchhoff’s current and voltage laws to the thermal model. The coupled ODEs were redefined in the discrete state space representation. The thermal model did not account for small changes in surface temperature (Ts). MATLAB/Simulink were used for modelling a Kalman filter with appropriate process and measurement noise levels. It was found that the temperatures closely followed the current patterns. For high currents, Tc dominated the surface temperature by about 3 K. Tc estimation plays a very important role in designing an effective thermal management and maintaining the state of health (SOH) during fast discharges under limits. Most of the battery management system (BMS) applications required Ts as the input to the controller. Hence, an inverse calculation for estimating Ts from known Tc was carried out and found to be reasonably accurate. It was found that the thermal parameter Cs played a major role in the accuracy of Ts prediction and must have low values to minimize errors.

Electric Vehicles (EV) and Hybrid EV (HEV) use Lithium (Li) ion battery packs to drive them. These battery packs possess high specific density and low discharge rates. However, some of the limitations of such Li ion batteries are sensitivity to high temperature and health degradation over long usage. The Battery Management System (BMS) protects the battery against overvoltage, overcurrent etc., and monitors the State of Charge (SOC) and the State of Health (SOH). SOH is a complex phenomenon dealing with the effects related to aging of the battery such as the increase in the internal resistance and decrease in the capacity due to unwanted side reactions. The battery life can be extended by estimating the SOH accurately. In this paper, an extensive review on the effects of aging of the battery on the electrodes, effects of Solid Electrolyte Interface (SEI) deposition layer on the battery and the various techniques used for estimation of SOH are presented. This would enable prospective researchers to address the estimation of SOH with greater accuracy and reliability.

Core temperature (Tc) estimation plays an important in role in establishing an effective thermal management system of a battery. In the present work, Tc of a lead acid (Pb) battery was estimated using a Kalman filter, based on a thermal model of the battery using convection resistances and capacitances. The governing equations based on measured surface temperature (Ts) and ambient temperature (Tamb) were derived. Since Tc cannot be measured directly, estimation technique was used to predict the same using measured Ts and Tamb. Five test cases for which the profiles of Tc versus time were available were analyzed. It was found that the errors in the predictions varied from 0.25 °C to 3.5 °C., depending on the nature of Tc profiles, with minimum errors when Tc has slow variations with time.

Design of DC-DC converters like Cuk and SEPIC, which are fourth-order converters, play a vital role in the design of electric vehicle (EV) charging systems and drivers for LED. These converters possess a unique feature of input current being continuous due to the presence of an inductor in series with the supply voltage. In the present work, a generalized approach for obtaining the frequency response of the transfer function of the duty cycle to output voltage (Gvd) for converters operating in continuous conduction mode (CCM) having two switches is proposed. A practical Cuk converter and SEPIC operating in CCM were selected and their analyses in open loop were studied using the LTSpice simulation tool. The behavior of the output voltage and inductor currents under variable ESR’s (equivalent series resistance) of inductors was studied. It was observed that Gvd of these converters was unstable. Hence, an appropriate controller to stabilize the system and achieve a proper gain margin and phase margin in closed-loop operation is required.

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