Showing papers on "State of charge published in 2007"

Optimizing a Battery Energy Storage System for Primary Frequency Control

Abstract: This paper presents a method for the dimensioning of a battery energy storage system (BESS) to provide a primary frequency reserve. Numerical simulations based on historic frequency measurements are used to determine the minimum possible capacity, i.e., the lowest possible cost, which fulfills the technical requirements of the grid code. We implement a novel control algorithm with adjustable state of charge limits and the application of emergency resistors. At current European market prices, an optimized lead-acid BESS can be a profitable utility solution for the primary frequency control.

State-of-Charge Determination From EMF Voltage Estimation: Using Impedance, Terminal Voltage, and Current for Lead-Acid and Lithium-Ion Batteries

Abstract: State-of-charge (SOC) determination is an increasingly important issue in battery technology. In addition to the immediate display of the remaining battery capacity to the user, precise knowledge of SOC exerts additional control over the charging/discharging process, which can be employed to increase battery life. This reduces the risk of overvoltage and gassing, which degrade the chemical composition of the electrolyte and plates. The proposed model in this paper determines the SOC by incorporating the changes occurring due to terminal voltage, current load, and internal resistance, which mitigate the disadvantages of using impedance only. Electromotive force (EMF) voltage is predicted while the battery is under load conditions; from the estimated EMF voltage, the SOC is then determined. The method divides the battery voltage curve into two regions: 1) the linear region for full to partial SOC and 2) the hyperbolic region from partial to low SOC. Algorithms are developed to correspond to the different characteristic changes occurring within each region. In the hyperbolic region, the rate of change in impedance and terminal voltage is greater than that in the linear region. The magnitude of current discharge causes varying rates of change to the terminal voltage and impedance. Experimental tests and results are presented to validate the new models.

Application of Z-Source Inverter for Traction Drive of Fuel Cell—Battery Hybrid Electric Vehicles

Abstract: This paper presents a Z-source inverter control strategy used to control power from the fuel cell, power to the motor, and state of charge (SOC) of the battery for fuel cell (FC)-battery hybrid electric vehicles (FCHEV). Traditional pulsewidth modulation inverter always requires an extra dc/dc converter to interface the battery in FCHEVs. The Z-source inverter utilizes an exclusive Z-source (LC) network to link the main inverter circuit to the FC (or any dc power source). By substituting one of the capacitors in the Z-source with a battery and controlling the shoot through duty ratio and modulation index independently, one is able to control the FC power, output power, and SOC of the battery at the same time. These facts make the Z-source inverter highly desirable for use in FCHEVs, as the cost and complexity is greatly reduced when compared to traditional inverters. These new concepts will be demonstrated by simulation and experimental results

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.

Method and system for charging multi-cell lithium-based batteries

Abstract: A method and system for charging multi-cell lithium-based batteries. In some aspects, a battery charger includes a housing, at least one terminal to electrically connect to a battery pack supported by the housing, and a controller operable to provide a charging current to the battery pack through the at least one terminal. The battery pack includes a plurality of lithium-based battery cells, with each battery cell of the plurality of battery cells having an individual state of charge. The controller is operable to control the charging current being supplied to the battery pack at least in part based on the individual state of charge of at least one battery cell.

A Unique Ultracapacitor Direct Integration Scheme in Multilevel Motor Drives for Large Vehicle Propulsion

Abstract: This paper introduces a new set of methods to directly integrate ultracapacitor banks into cascaded multilevel inverters that are used for large vehicle propulsion. The idea is to replace the regular dc-link capacitors with ultracapacitors in order to combine the energy storage unit and motor drive. This approach eliminates the need for an interfacing dc-dc converter and considerably improves the efficiency of regenerative braking energy restoration in large vehicles using multilevel converters. Utilizing the proposed modulation control set, the two cascaded inverters can have their dc voltage levels maintained at any ratio (even a noninteger ratio) or dynamically varied over a wide range without disrupting the normal operation of the electric motor. As an advantage, ultracapacitor voltage or state of charge can be freely controlled for braking and/or acceleration power management. A regenerative energy management scheme is also proposed based on the vehicle's speed range considerations. Detailed simulation and experimental results verified the proposed methods.

Optimal power management of plug-in HEV with intelligent transportation system

Abstract: Hybrid electric vehicles (HEV) have demonstrated their capability of improving the fuel economy and emission. The plug-in HEV (PHEV), utilizing more battery power, has become a more attractive upgrade of HEV. The charge-depletion mode is more appropriate for the power management of PHEV, i.e. the state of charge (SOC) is expected to drop to a low threshold when the vehicle reaches the destination of the trip. In the past, the trip information has been considered as future information for vehicle operation and thus unavailable a priori. This situation can be changed by the current advancement of intelligent transportation systems (ITS) based on the use of on-board geographical information systems (GIS), global positioning systems (GPS) and advanced traffic flow modeling techniques. In this paper, a new approach of optimal power management of PHEV in the charge-depletion mode is proposed with driving cycle modeling based on the historic traffic information. A dynamic programming (DP) algorithm is applied to reinforce the charge-depletion control such that the SOC drops to a specific terminal value at the final time of the cycle. The vehicle model was based on a hybrid SUV. Only fuel consumption is considered for the current stage of study. Simulation results showed significant improvement in fuel economy compared with rule-based power management. Furthermore, simulations on several driving cycles using the proposed method showed much better consistency in fuel economy compared to the rule-based control.

Method of operating a plug-in hybrid electric vehicle

Abstract: A method of operating a plug-in hybrid electric vehicle is provided including the steps of: A) determining whether the plug-in hybrid electric vehicle is receiving power from an external power source; B) disabling the operation of the plug-in hybrid electric vehicle and executing a thermal program if the plug-in hybrid electric vehicle is receiving power from the external power source, wherein the thermal program includes charging a high voltage battery and monitoring the state of charge of the high voltage battery; C) determining if the plug-in hybrid electric vehicle continues to receive power from the external power source; and D) enabling operation of the plug-in hybrid electric vehicle if the plug-in hybrid electric vehicle is no longer receiving power from the external power source.

State of charge control method and systems for vehicles

Abstract: State of charge control for electric and hybrid vehicles. In one embodiment, a battery may be electrically connected to an electric motor to propel a vehicle. In such an embodiment, during vehicle operation a state of charge of the battery may fluctuate within a given state of charge range and may be regulated to a target state of charge. Such target state of charge may be set below the midpoint of the state of charge range. As the vehicle operates various devices may be controlled to regulate the state of charge to the target. In particular, an electric motor may be employed to lower the state of charge and an internal combustion engine may be employed to raise the state of charge. In other embodiments, regenerative braking, solar power or the like may be employed to raise the state of charge from at or below the target state of charge to the upper state of charge limit.

The State and Parameter Estimation of an Li-Ion Battery Using a New OCV-SOC Concept

Abstract: The open circuit voltage (OCV) is widely used to estimate the state of charge (SOC) in many SOC estimation algorithms. But the relationship between the OCV and SOC can not be exactly same for all batteries. Because the conventional OCV-SOC differs between batteries, there is a problem in that the OCV-SOC data should be measured to accurately estimate the SOC in different batteries. Therefore, the conventional OCV- SOC should be modified. In this paper, a new OCV-SOC that is independent of the battery conditions is proposed. Thus, problems resulting from the defects of the EKF can be avoided by preventing the OCV-SOC data from varying. In this paper, the SOC and battery capacity are estimated using the dual EKF with the proposed OCV-SOC.

Dynamically adaptive method for determining the state of charge of a battery

Abstract: A method for determining the state of charge (SOC) of a lithium ion battery is provided. The method leverages a circuit model of the lithium ion battery, and generates four battery parameters from which the SOC is derived.

State-of-Charge Estimation for Electric Scooters by Using Learning Mechanisms

Abstract: Because of its nonlinear discharge characteristics, the residual electric energy of a battery remains an open problem. As a result, the reliability of electric scooters or electric vehicles is lacking. To alleviate this problem and enhance the capabilities of present electric scooters or vehicles, we propose a state-of-charge learning system that can provide more accurate information about the state-of-charge or residual capacity when a battery discharges under dynamic conditions. The proposed system is implemented by learning controllers, fuzzy neural networks, and cerebellar-model-articulation-controller networks, which can estimate and predict nonlinear characteristics of the energy consumption of a battery. With this learning system, not only could it give an estimate of how much residual battery power is available, but it also could provide users with more useful information such as an estimated traveling distance at a given speed and the maximum allowable speed to guarantee safe arrival at the destination

Trip Based Power Management of Plug-in Hybrid Electric Vehicle with Two-Scale Dynamic Programming

Abstract: The plug-in HEV (PHEV), utilizing more battery power, has become the next-generation HEV with great promise of higher fuel economy. The charge-depletion mode is more appropriate for the power management of PHEV, i.e. the state of charge (SOC) is expected to drop to a low threshold when the vehicle reaches the destination of the trip. Globally optimized charge-depletion power management would be desirable. However, this has so far been hampered due to the a priori nature of the trip information and the prohibitive computational cost of global optimization techniques such as dynamic programming (DP). This situation can be changed by the current advancement of intelligent transportation systems (ITS) based on the use of on-board GPS, GIS, real-time and historical traffic flow data and advanced traffic flow modeling techniques. In this paper, charge-depletion control of PHEV is nearly globally optimized with a two-scale dynamic programming approach based on trip modeling with real-time and historical traffic data. For DP based charge-depletion control of PHEV, the SOC is desired to drop to a specific terminal value at the end of the trip. By specifying the origin and destination of a trip, the trip model, i.e. the driving cycle, is first obtained with the average of the historic traffic data, and the globally optimized SOC profile can be obtained by solving the overall or the macro-scale DP problem. The actual power management can be adapted during real-time vehicle operation with a micro-scale DP framework. The whole trip is divided into a number of segments, and for each segment, a smaller DP will be solved using the on-line traffic data transmitted to the vehicle from the traffic flow sensors within the segment. The SOC obtained in the macro-scale DP solution at the terminal location is reinforced to be the final value. Simulation study has been performed on a hybrid SUV model from ADVISOR, and a defined trip in the greater Milwaukee area. The simulation results demonstrated significant improvement in fuel economy using DP based charge-depletion control compared to rule based control, and also the benefit of adaptation using the two-scale DP method.

A new direct current internal resistance and state of charge relationship for the Li-ion battery pulse power estimation

Abstract: The conventional test to obtain the direct current internal resistance (DCIR) has only experimented with a duration time of 5 seconds in the discharge region[3]~[5]. To obtain the DCIR, the duration time, Deltat and the region condition are important for the hybrid electric vehicle (HEV). In this paper, a new measurement method to obtain a direct current internal resistance (DCIR) is proposed. The proposed approach is performed during 10 seconds in the charge and discharge regions in order to obtain the new relationship between the DCIR and the state of charge (SOC). Thus, this obtained data can be used to estimate the battery pulse power using the previous SOC algorithm, extended Kalman filter (EKF)[6], which includes the DCIR-SOC relationship. The experiments are achieved using a fresh 1.3 Ah 18650 type Li-ion battery at 25degC.

Holding a Hybrid Electric Vehicle on an Inclined Surface

Abstract: In a powertrain that includes wheels supporting a vehicle, an engine, a first machine able to operate alternately as an electric motor and electric generator, a second machine electric able to operate as an electric motor, and an electric storage battery having a variable state of charge, a method for holding the vehicle stationary on an incline including determining a magnitude of torque at the wheels required to hold the vehicle on the incline, determining whether the state of charge is low or high relative to a reference state of charge, determining whether a temperature of the first machine is low or high relative to a first reference temperature, and whether a temperature of the second machine is low or high relative to a second reference temperature, using the engine and the machines in various combinations to produce the required torque at the wheels.

Battery Management System (BMS) and driving method thereof

Abstract: A Battery Management System (BMS) and a battery management method include a sensing unit to measure a battery terminal voltage, current, and temperature, and a Main Control Unit (MCU) to compare the measured battery terminal voltage, current, and temperature to a State of Charge (SOC) reset condition and to reset a battery estimate SOC according to the comparison result. The MCU resets the battery estimate SOC to a first reset SOC when the SOC reset condition corresponds to a first SOC and reset the battery estimate SOC at a second reset SOC when the SOC reset condition corresponds to a second SOC.

Apparatus and method for determination of the state-of-charge of a battery when the battery is not in equilibrium

Abstract: The invention relates to a method and an apparatus, like a charger for determining the state-of-charge of a battery which has been charged or discharged and which has not reached its equilibrium state, the method comprising the steps of determining the EMF of the battery by extrapolation of the battery voltage sampled during relaxation after the charge or the discharge process, wherein the extrapolation is based on a model using only variables sampled during the relaxation process and deriving the state-of-charge from the EMF of the battery by using a predetermined relation between the EMF and the state-of- charge. This method is a voltage-prediction method without the need to store parameters beforehand. Instead, the voltage relaxation end value is determined based on the measured first part of a voltage relaxation curve and mathematical optimisation/fitting of a function to this measured part of the relaxation curve.