Research On Equalization Control Technology For Super-capacitors Of Strong Mixing Hybrid Electric Car

Recently, some severe environmental issues have been presented to all the governments due to concerns about conservation of energy and declining the emissions of vehicles. Aimed at reducing automobile fuel consumption and improving the air quality, more and more strong-mixing HEV appear as the excellent representative of new energy vehicles and have attracted the wide attention. As a new storage component of HEV, the super-capacitor has very important impact on security, economy and power of vehicles. Therefore, the proposed research on the balance control technology of super-capacitor is significant for prolonging the service life of capacitor, boosting the power property and ensuring the safety of automobile.Because of the limitation of the voltage and capacity of one super-capacitor, a number of single capacitors should be connected in series to satisfy the power requirement of HEV. Due to factors like the existence of manufacturing error, some parameters such as inner resistance, capacity and voltage of capacitors are different. Meanwhile, the differences in operating temperature between capacitors lead to the variation of capacitor conversion efficiency and the over-charge or over-discharge instance. It aggravates the unbalance of capacitor packs.Based on the principle and physical structure of super-capacitors, the reasons and harm of differences are analyzed. In order to ensure the consistency of capacitor pack before use, they are packed by parameters of voltage, capacity and inner resistance; In addition, the working principle, feature and application area of all kinds of equilibrium control technology for super-capacitor are summarized.To ensure the consistency of the capacitors’ working temperature, the thermal management scheme has been discussed. The influence results of temperature on capacitors’ performance are obtained through the high-low temperature test, the finite volume method is also applied to the thermodynamic equation. The temperature field of capacitor packs is calculated on the basis of establishment of internal fluid mechanics and the heat-transfer control equation. The cooling air duct is designed and temperature calculation model is set by using software Star CCM+. The simulation results demonstrate that the maximum variation of temperature is less than 4℃ and the temperature consistency can be regulated furthest among single capacitor.Even though a deliberate per-match of the capacitor package and minimize the difference in temperature through thermal management scheme, still can not fundamentally solve the problem of inconsistency among the capacitors. So the feasible subsystem with it "low charge, high discharge" system architecture has designed in order to solve the actual capacitor imbalances phenomenon. The method of capacity compensated equalization is designed. And using the fuzzy logic control strategy realized in microcontroller, the capacitors’ capacities are compensated by the equalization subsystem. For the sake of satisfying HEV power batteries relevant tests requirements, the high power batteries test bench is built, the result of experiment shows that the equalization subsystem does not only compensate the differences of capacitors, but also make each cell exert its better performance.