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Research On State Of Charge Estimation Of Nimh Battery Used In Electric Vehicles

Posted on:2011-03-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:G L WuFull Text:PDF
GTID:1102330338989389Subject:Motor and electrical appliances
Abstract/Summary:PDF Full Text Request
Researchers pay attention to NiMH battery in the new energy source and the clean energy source because of its many virtues, such as little pollution, high energy density, high power density and long life. Not only NiMH battery applies in electric vehicles as the sole energy source, but also in hybrid vehicles as the auxiliary energy source. The precision of NiMH battery state of charge (SOC) estimation is a key factor for electric vehicles and battery. NiMH battery SOC estimation has been a key technique to improve the performance of electric vehicles system. This thesis analyzed and discussed the problems of dynamic hysteretic characteristic, model parameters choice of extended kalman filter (EKF) and low temperature, which affect the precision of SOC estimation.The dynamic hysteretic characteristic of open circuit for NiMH is obvious, and it causes the difficulty of SOC correction quickly when electric vehicle parks for a short time. To deal with the problem, experiments were undertaken and experimental formulas were established among SOC, open circuit voltage and idle time after charge/discharge. Based on the two experimental formulas, an improved open circuit voltage method with NiMH dynamic hysteretic characteristic was proposed, which corrects SOC quickly and accurately when electric vehicle parks for a short time.In general, most of researchers only apply EKF with discharge model parameters to estimate SOC, which decreases the estimation precision. To solve the problem, variable current charge profile and variable current discharge profile were designed to compare the precisions of EKF with charge model and discharge model parameters respectively. Based on the results talked above, the reason of decreasing the precision was found. Therefore, a model parameter self-adjusting EKF based on average current sign was proposed, which was verified by experiment and improves the precision of SOC estimation and makes up the shortcoming of EKF with only discharge model parameters.In order to import Peukert equation to symbol NiMH battery available capacity,discharge experiments at different rate were undertaken at low and room temperature. From the experiment result, we found that the applicability of Peukert equation is related with current and temperature. Furthermore, a Peukert equation used in NiMH battery under low temperature was proposed. Based on the Peukert equation under low temperature, a SOC loss model was proposed.Temperature affects the precision SOC estimation of Ampere-hour method. To solve the problem, coulomb efficiency experiments were undertaken at low and room temperature. Combined with SOC loss model, an Ampere-hour SOC estimation model with coulomb efficiency coefficient at low temperature had been set. The proposed method was verified by experiment and it improves the precision of SOC estimation at low temperature.Finally, in order to improve the precision in the whole SOC estimation process, a mixed SOC estimation method was proposed in the thesis, which combines the virtues of the achievements of the thesis. The initial SOC is estimated by the improved open circuit voltage method. The process SOC is estimated by a model parameter self-adjusting EKF based on average current sign. Based on the above achievements, a NiMH battery management system (BMS) has been developed. Apply the BMS to NiMH battery module and group, the experiment results show that the mixed SOC estimation method improves the precision of SOC estimation greatly.
Keywords/Search Tags:Electric Vehicles, Nickel Metal Hydride Battery, State of Charge, Open Circuit Voltage, Model Parameters, Temperature
PDF Full Text Request
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