State of charge

About: State of charge is a research topic. Over the lifetime, 12013 publications have been published within this topic receiving 201419 citations. The topic is also known as: SoC & SOC.

An Energy Management Strategy for a Concept Battery/Ultracapacitor Electric Vehicle With Improved Battery Life

Abstract: Using multi-input converters (MICs) in hybrid energy storage systems (HESSs) presents several advantages, such as low component count, control simplicity, and fully control of source energies. The power levels of sources in these systems need to be determined wisely by an energy management strategy (EMS). This paper presents an EMS for a battery/ultracapacitor (UC) HESS including a bidirectional MIC for electric vehicles (EVs). Thanks to the fact that energy flow between battery and UC is free in this MIC, the proposed EMS not only regulates the state-of-charge of UC but also smooths the battery power profile by using a fuzzy logic controller and a rate limiter. Therefore, it results in a sustainable HESS with longer battery life. Through a simulation study and an experimental setup including a real EV, the performance of the proposed system is evaluated comprehensively. Then, based on experimental results, battery cycle-life improvement due to the battery/UC hybridization is explored.

Energy gauge for lead-acid batteries in electric vehicles

Abstract: This article proposes a new coulometric approach to calculate the state of charge of a lead-acid battery in electric vehicles. The main existing state of charge algorithms have two major defects: a state of charge definition not adapted to electric vehicle applications and the nonoptimal use of static performance of the accumulator to estimate its state under dynamic stresses. In order to improve these two weaknesses, we propose a new coulometric algorithm linked to the performance of the electric vehicle and where the ampere-hours virtually discharged are obtained by applying statistical equivalence coefficients to the real current profile. The evaluation of this new algorithm on real discharges reveals a significant improvement with less than 5% errors in all cases studied.

Method of charge control for vehicle hybrid drive batteries

Abstract: A method for controlling the charging of fast discharge and recharge type propulsion battery components of engine-electric hybrid drive systems for road vehicles, wherein the control objectives are to, minimize discharge of gas through battery cell vents, minimize fuel use, allow employment of a small battery, and provide for long discharge-recharge cycle life, and the control method consists in the steps of, 1--providing so that, if not earlier terminated as a result of operator termination of braking, or a drop in vehicle speed, termination of regenerative braking will be initiated at a point in time determined by a control system generated indication of state of charge just prior to initiation of braking, and the subsequent history of cell current, 2--providing so that, following a partial battery discharge, when and as motor speed allows, supplementary engine implemented battery charging will take place prior to the next advent of regenerative braking, with charge termination made responsive to attainment of a battery voltage per series connected cell that is determined by a control system generated indication of state of charge following discharge, 3--providing to temporarily revert to non-hybrid, engine implemented drive, when cell voltage on battery deep discharge falls below a value that depends in a predetermined way on cell current, 4--when and as service use conditions so warrant, providing to effect increase in battery temperature with use of heat supplied by the engine exhaust, and providing, additionally, to temporarily revert to non-hybrid, engine implemented drive, when, and for so long a period as battery cell internal temperature holds below a predetermined value.

Fast Model Predictive Control for Redistributive Lithium-Ion Battery Balancing

Abstract: Energy storage systems with Lithium-ion batteries require balancing due to individual cells having manufacturing inconsistencies, different self-discharge rates, internal resistances, and temperature variations. Nondissipative redistributive balancing further improves on the pack capacity and efficiency over a dissipative approach where energy is consumed across shunt resistors. This paper presents a high-level fast model predictive control (MPC) in continuous time. The optimization problem uses performance metrics to balance the state of charge (SoC) in the battery pack. It is shown in simulation that MPC achieves a single point convergence of the SoC when compared against a common rule-based algorithm. This improves the efficiency of the power electronics and prolongs the life of each battery cell since frequent switching between charging and discharging of intermediate cells is avoided. Experimental results are presented to show a redistributive battery balancing system that achieves a balanced state in the minimum amount of time by coupling the fast MPC with microcontrollers available on todays market.

Two electrical models of the lead-acid battery used in a dynamic voltage restorer

Abstract: Two electrical models of a lead-acid battery, a short-term discharge model and a long-term integrated model, were used to investigate the system performance of a battery-supported dynamic voltage restorer (DVR). The short-term model provides a simple but effective description when the DVR compensates voltage sags over a short period. The integrated model can predict accurately the terminal voltage, state of charge, battery capacity and gassing current. It gives a good description of the battery response during both discharge and charge. Parameters of both models can be determined easily from measured battery output voltages obtained from load-step tests. Both models were successfully implemented in EMTDC/PSCAD and interfaced with the digital model of a 10 kVA DVR physical prototype. They gave a very close agreement between extensive experimental data and simulation results. Application issues such as current harmonics and microcycles during charge/discharge are discussed with respect to their impact on loss of capacity and reduced lifetime of the lead-acid battery.