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.

State-of-Charge Monitoring and Electrolyte Rebalancing Methods for the Vanadium Redox Flow Battery

Abstract: A major issue with all flow batteries is the control of the imbalance between the two half-cell electrolytes that arises as a result of the differential transfer of ions across the membrane and the inevitable gassing side reactions that can occur during charging. While a number of methods are available to rebalance electrolyte state of charge and restore capacity, reliable methods are needed to monitor the state-of-charge of each individual half-cell solution in order to determine the appropriate action to be taken by the battery control system. In this study different methods of state-of-charge monitoring have been considered for application in the All-Vanadium Redox Flow Battery (VRB). Half-cell potentials and electrolyte conductivities were calibrated as a function of state-of-charge and evaluated for state-of-charge monitoring of individual half-cell electrolytes for the purpose of capacity restoration and control. An empirical model based on experimental conductivity data has been shown to provide accurate predictions, with an average error of 0.77%, of the conductivity of the positive half-cell electrolyte as a potential state-of-charge detection tool. Separate monitoring of the two half-cell electrolyte potentials has also been used to determine the state-of-charge of each half-cell solution in order to detect system imbalance. This was used in small laboratory cell tests to determine necessary actions to restore capacity by either remixing the two solutions, or by using chemical rebalancing methods, depending on the cause of the solution imbalance.

VRB Modelling for the Study of Output Terminal Voltages, Internal Losses and Performance

Abstract: There is a growing interest in using large scale energy storage in wind systems for power smoothing and energy redistribution. Vanadium-redox batteries are well suited for this type of application because of their high efficiency, high scalability, fast response, long life and low maintenance requirements. This paper looks into determining an appropriate electrical vanadium-redox battery (VRB) model for this type of application. In particular, model details including stack voltage, series resistance, state of charge (SOC) and transients modeling are examined. The model is used to obtain results on the energy content, and terminal voltage profile of the battery. The battery performance is also assessed, including VI transfer characteristic, transient response and efficiency.

Battery Energy Storage Systems in Energy and Reserve Markets

Abstract: Recent Federal Energy Regulatory Commission (FERC) Order 841 requires that Independent System Operators (ISOs) facilitate the participation of energy storage systems (ESSs) in energy, ancillary services, and capacity markets, by including ESS bidding parameters that represent the physical and operational characteristics. However, in the existing market frameworks that allow Battery Energy Storage Systems (BESSs) to participate, the bids and offers do not explicitly represent the physical and operational characteristics such as the state of charge (SOC), discharge rate, degradation, etc. This paper proposes a novel BESS operational cost model considering degradation cost, based on depth of discharge and discharge rate. The model is developed considering Lithium-ion batteries, and the approach can be applied to other conventional electrochemical batteries, but not flow batteries. A detailed bid/offer structure based on the proposed BESS operational cost functions is formulated. Thereafter, a new framework and mathematical model for BESS participation in an LMP based, co-optimized, energy and spinning reserve market, are developed. Three case studies are presented to investigate the impact of BESS participation on system operation and market settlement. The proposed model is validated on the IEEE Reliability Test System (RTS) to demonstrate its functionalities.

Temperature-Compensated Model for Lithium-Ion Polymer Batteries With Extended Kalman Filter State-of-Charge Estimation for an Implantable Charger

Abstract: As implantable devices become more sophisticated and their extended functionalities impact their energy requirements, they not only rely on charging for the extra energy but also become ever more sensitive to battery deep discharge or overcharge. Accurate state-of-charge (SOC) estimation plays a fundamental role in ensuring the operation safety of implantable medical devices. Temperature variation can impact the battery model parameters and directly affect the accuracy of SOC estimation. This study investigates a temperature-compensated model for lithium-ion polymer batteries that incorporates an extended Kalman filter method to estimate the state of the dynamic nonlinear system and its parameters, from 37 °C to 40 °C at intervals of 1 °C. Both simulation and experimental results indicate that the estimation error can be effectively limited to within ±3%. Through the accurate SOC estimation, the conventional constant current to constant voltage charging strategy is guided in order to reduce the charging time and increase the charging capacity.