Baek-Haeng Lee

Study on 1.5 kW battery chargers for neighborhood electric vehicles

In this study, a 1.5 [kW] on-board battery charger for neighborhood electric vehicles was developed. The developed charger has a built-in power factor correction circuit and a resonant phase shift full-bridge (PSFB) for power conversion. Although an additional snubber is not used, the switching noise generated in the switch and the diode is reduced, owing to the built-in resonant-type PSFB converter, and the desired improvement in noise reduction and efficiency of input/output is achieved. The power conversion controller was controlled using a dedicated integrated circuit.

Experimental study on the effects of pre-heating a battery in a low-temperature environment

The performance of a plug-in hybrid electric vehicle (PHEV) or an electric vehicle (EV) is closely related to the performance of its high-voltage battery pack. This is why, among the various means of maintaining a batterys peak performance, the importance of thermal management is emphasized. Since the early stages of the development of Li-ion batteries, much emphasis has been placed on battery cooling in order to secure stability, while less attention has been given to battery heating. However, in a low-temperature environment, using a battery without heating it severely undermines the batterys performance and life expectancy. A PHEV or an EV operates with energy that is stored by charging the battery, which can then be heated by an external source in a low-temperature environment prior to driving. In this study, a battery HILS and an environment simulation system are used to verify that pre-heating a battery in a low-temperature environment, using an external source, such as a charging stand, improves the batterys performance as compared to circumstances in which this is neglected.

Analytical study on low-frequency ripple effect of battery charging

With the recent interest in environment-friendly vehicles such as electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs), various topologies are being proposed for the on-board charger (OBC) required to charge the lithium battery that serves as the energy storage system. If a specific topology is selected and used, the output current of the charger is bound to contain low-frequency ripple that is twice the input power supply frequency. In this study, to analyze the effects of the low-frequency ripple on the lithium battery, a number of charging/discharging cycles are performed to apply low-frequency ripple current and constant current to PHEV lithium battery cells with similar properties. In addition, we conducted capacity test for each specific cycle to compare their performances to analyze the effects of OBCs low-frequency ripple on the battery.

Dynamic SOC Compensation of an Ultracapacitor Module for a Hybrid Energy Storage System

The ultracapacitor module has recently been recast for use in hybrid energy storage systems (HESSs). As a result, accurate state-of-charge (SOC) estimation for an ultracapacitor module is as important as that of primary sources in order to be utilized efficiently in an energy storage system (ESS). However, while SOC estimation via the open-circuit voltage (OCV) method is generally used due to its linear characteristics compared with other ESSs, this method results in many errors in cases of highcurrent charging/discharging within a short time period. Accordingly, this paper introduces a dynamic SOC estimation algorithm that is capable of SOC compensation of an ultracapacitor module even when there is a current input and output. A cycle profile that simulates the operating conditions of a mild-HEV was applied to a vehicle simulator to verify the effectiveness of the proposed algorithm.

The Dynamic Control of Hybrid Energy Storage Sysem for Mild HEV

To improve the cycle life and efficiency of an energy storage system for HEV, a dynamic control system consisted of a switch between battery and ultracapacitor module and a controller is proposed, which is appropriate for mild hybrid vehicle with 42 V power net. The switch can be controlled based on the status of the battery and the ultracapacitor module, and a control algorithm that could largely decrease the number of high charging current peak is also implemented. Therefore the cycle life of the battery can be improved such that it is suitable for a mild hybrid vehicle with frequent engine start-stop and regenerative-braking. Also, by maximizing the use of the ultracapacitor, the system efficiency during high current charging and discharging operation is improved. Finally, this system has the effects that improves the efficiency of energy storage system and reduces the fuel consumption of a vehicle. To verify the validity of the proposed system, this paper presented cycles test results of different energy storage systems: a simple VRLA battery, hybrid energy pack (HEP, a VRLA battery in parallel with Ultracapacitor) and a HEP with a switch that controlled by energy management system (EMS). From the experimental result, it was proved the effectiveness of the algorithm.

Modeling of the Lithium Battery Cell for Plug-In Hybrid Electric Vehicle Using Electrochemical Impedance Spectroscopy

Online simulations are utilized to reduce time and cost in developing and optimizing the performance of plug-in hybrid electric vehicle (PHEV) and electric vehicles (EV) systems. One of the most important factors in an online simulation is the accuracy of the model. In particular, a model of a battery should accurately reflect the properties of the actual battery. However, precise dynamic modelling of a high-capacity battery system, which significantly affects the performance of a PHEV, is difficult because of its nonlinear electrochemical characteristics. In this study, a dynamic model of a high-capacity battery cell for a PHEV is developed by the extraction of the equivalent impedance parameters using electrochemical impedance spectroscopy (EIS). Based on the extracted parameters, a battery cell model is implemented using MATLAB/Simulink, and charging/discharging profiles are executed for comparative verification.

Development of the Integrated Power Converter for the Environmentally Friendly Vehicle and Validation of the LDC using Battery HILS

For OBC (On-Board Charger) and LDC (Low DC-DC Converter) used as essential power conversion systems of PHEV (Plug-in Hybrid Electric Vehicle), system performance is required as well as reliability, which is need to protect the vehicle and driver from various faults. While current development processor is sufficient for embodying functions and verifying performance in normal state during development of prototypes for OBC and LDC, there is no clear method of verification for various fault situations that occur in abnormal state and for securing stability of vehicle base, unless verification is performed by mounting on an actual vehicle. In this paper, a CCM (Charger Converter Module) was developed as an integrated structure of OBC and LDC. In addition, diverse fault situations that can occur in vehicles are simulated by a simulator to artificially inject into power conversion system and to test whether it operates properly. Also, HILS (Hardware-in-the-Loop Simulation) is carried out to verify whether LDC is operated properly under power environment of an actual vehicle.

A Study on Battery Model Verification Using Battery HILS

The development of technology for environmentally friendly cars such as plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs) has increasingly progressed according to the conversion of vehicle development paradigms to energy issues, environmental regulations, the government’s “New Deal” policies, and so on. As a result, the importance of the battery system that is the main power source for environmentally friendly cars has grown. The most effective way of the development of PHEVs and EVs is using battery hardware-in-the-loop simulation (HILS) to significantly reduce development costs and time in vehicle-level environments for the development and evaluation of battery systems, including a battery management system (BMS). Therefore, in the present study, a battery HILS was developed and tested. It was noted through the test that the developed battery HILS could be used as a method to assess the accuracy of battery modeling in real time by applying it to developed battery system models using the electrochemical impedance spectroscopy (EIS) method.

A study on the temperature stabilization time during temperature environmental test of the battery system for green cars

The latest paradigm in the global automobile market is shifting toward environment-friendly vehicles (such as HEVs, PHEVs, and EVs), and high-efficiency, large-capacity lithium rechargeable batteries are being used to increase vehicles fuel efficiency and extend the driving distance. However, there have been safety concerns, including batteries in recently sold environment-friendly vehicle catching fire. In order to address these issues and to secure safety, manufacturers of rechargeable batteries and environment-friendly vehicles are performing reliability tests prior to installing batteries in the vehicles. Most standards for temperature-related environmental tests for battery systems are in the works, and the ones that have been established adhere to the specifications for electrical systems installed in conventional automobiles. Therefore, this study analyzes the results of comparative experiments to assess whether the temperature environmental evaluation test guidelines for electrical systems in conventional vehicles can be applied to battery systems for environment-friendly automobiles.

PHEV battery module modeling based on statistical averaging method

Regarding modeling of battery system, if the properties of unit cells comprising the system are different, overall battery system model based on a specific cell may cause an error due to the differences in cell properties. In this paper, the statistical method to minimize the error according to the deviation of properties of unit cells comprising the battery module is proposed. The simulation result of battery module model based on statistical method is compared to the experiment result of PHEV battery module. Through this, the usefulness of proposed statistical averaging method is verified.