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Study On The SOC Estimation Method Of Nickel-Metal Hydride Battery For HEV

Posted on:2011-01-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:F GaoFull Text:PDF
GTID:1222360305483209Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Human are obliged to change energy usage in response to the coming era of high oil price and the alarm of global warming. As a big consumer of fuel and a major source of green house gases, automobile exerts a critical influence on energy and environment issues. Hybrid Electric Vehicle (HEV) has leading the change trends of automotive industry due to its higher fuel-efficiency, lower emissions and compatibility with the existing traffic system. China has been the biggest automobile manufacturer and market in the world, developing HEV technology would not only do good to energy and enviroment issues, but also help Chinese automobile industry to catch up with the world’s latest level.Although the traditional automobile becomes mature through more than 100 years’ development, new problems arise when battery joins the power system of automobile as auxiliary power. Until now, the bottlenecks of the development of HEV are battery performance and battery management. The former involves rate capacity, specific power, service life, temperature adaptability; and the key point of the latter is the estimation and measurement of battery state of charge (SOC).Having the characteristics of high charge/discharge acceptance, good safety, and long lifetime, Ni-MH battery dominants the HEV battery marketplace. This dissertation mainly focuses on battery management and SOC estimation based on commercial power type Ni-MH battery. In this work, the impact factors of SOC estimation are analyzed firstly, then the necessary special experiments are designed, and a logic programs for limiting SOC control is put forward. Furthermore, some regularities of the composition of the internal resistance and its variations are studied in detail, which is the key to determine the voltage changes in different working conditions. In order to understand the relationship between battery’s outward manifestation and internal structure and construction, single-particle technology is used to investigate the electrochemical performance of electrode active material. The results show that the experimental system is significant for further study of electrode materials and battery management. The main work of this dissertation includes:(1) A screening parameter system is established to ensure the cells’ consistency, which are selected for the studies. The parameters include capacity, high power performance, temperature adaptability, and self-discharge rate. All the qualified cells for the studies are selected according to these parameters from available commercial Ni-MH battery.(2) Basing on the working condition of HEV battery, a modified concept of SOC is defined. According to this definition, a plenty of exploratory experiments relevant to SOC are proceeded, such as the relationship between stable Open Circuit Voltage (OCV) with SOC, the polarization influence on battery voltage, the temperature influence on battery charge/discharge curve, the deterioration and self-discharge influence on battery performance. The results show the complexity of SOC prediction on one hand, and provide basic data and theoretical basis on the other hand.(3) In chapter 3, on the bases of the interrelated experiments with SOC, a limiting SOC control program is proposed. According to the characteristics of HEV,20% SOC and 80% SOC are defined as the battery’s lower and upper limits of the SOC in order to keep battery working in a safe and efficient status. A number of experiments, which are relevant to limited SOC, are conducted to verify the experimental program. Under severe condition control, destination voltage data of limiting SOC that are corresponding to different temperatures and different current pulse are acquired and the validity of the data is further verified. A linear relationship between pulse current and destination voltage is obtained, and it reveals the key role of internal resistance in voltage appearance. The effects of former current polarization on the voltage of the pulse under investigation are studied as well.(4) In accordance with the actual working conditions of the battery, the study of the internal resistance of the battery is emphasized in the chapter 4. (a) a resistance definition which is more adequate to power battery characterization is proposed, and this has made the mass-transfer polarization being included in this parameter, which is usually ignored; (b) the internal resistance is divided into charging internal resistance and discharging internal resistance, and this has made power battery’s charge characteristics be fully displayed; (c) the total internal resistance is measured through multi-step pulse method, a further division of the total internal resistance into apparent ohmic internal resistance and mass-transfer one is made to satisfy the individual analysis of the component on the internal resistance. Based on this, a lot of valuable laws upon the resistance experiments are found; (d) the internal resistance of positive and negative electrodes of the battery are analyzed separately by using two testing channels on one self-made three-electrode cell; (e) the variation of the internal resistance before and after battery’s deterioration is also investigated.(5) A new concept called "rest internal resistance" is proposed in this work to indicate the resistance that prevent the OCV from returning to a balanced state, and the various disciplines during the rest time of Ni-MH battery are studied. Were these disciplines combined with traditional OCV method, maybe it would provide valuable help for SOC estimation.(6) To reveal the nature of the battery’s external performance, single particle method is used to the study of the active material with an improved apparatus. Taking activation process of the hydrogen storage alloy as an example, the changes in morphology and electrochemical characteristics are shown in good quality, and a new parameter, which is relevant to HEV, is proposed to characterize the power output performance.
Keywords/Search Tags:Nickel-metal hydride secondary battery, Ni-MH battery, Hybrid electric vehicle, HEV, State of charge, SOC, Internal resistance, Single particle, Battery management
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