Research On Parameter Matching And Control Strategy Of Hybrid Energy Storage System For HEV

Batteries have been used as main energy storage devices in hybrid electric vehicles (HEVs) for many years. However due to their lower specific power, the ability to capture and provide bursts of high power during acceleration, hill-climbing and regenerative braking is limited. Hence the hybrid energy storage system (HESS) which combines both merits of batteries and ultracapacitors is becoming a promising option for short-term high-power applications. The use of ultracapacitors in combination with batteries allows the primary HEV energy storage unit to be optimized for both energy and power. As a new type of transportation with multi-energy sources for HEV itself, not only the energy flows become more complex, but also new challenge is brought to its parameters matching and control strategy after introducing ultracapacitors. While as an important means to improve HEV dynamic performance as well as economic performance, the design of parameters matching and control strategy for HESS is the core technology of HEV. Therefore thorough and further study is necessary. In this paper, the working features of HEV and HESS are investigated deeply, based on which the theories and application issues involving the modeling method, the parameters matching and control strategies for HEV system and HESS have been studied.HEV equipped with HESS is a complex system which related to battery, ultracapacitor, fuel and other energy sources. In order to describe the energy flows in HEV more clearly and provide a reference to develop the control strategy of HESS, Energetic Macroscopic Representation (EMR) is introduced to analyze and build modeling for HEV in view of energy flows and power chains. Moreover a control strategy is obtained by specific inversion rules. The battery modeling method based on experiments is put more attention. The energy flows of the model with EMR become much clearer, intuitive, and it establishes a foundation for the study of parameters matching as well as the development of control strategies.The problems for the power and energy sharing in HESS are studied. First of all, the influences on power and energy requirements for the whole vehicle by the design goals, performances of HEV as well as specific driving cycles are analyzed. In view of the power and energy, the parameters matching for HESS are investigated. Moreover, according to different optimization objectives, the initial results of parameters matching are optimized. On this basis, a method of HESS parameters matching which takes vehicle fuel economy, accelerating performance and vehicle using costs into account is provided. The optimization results of parameters matching for three HEVs with different hybridization factors are presented. The hybridization ratios of HESS are also concluded.A reasonable and effective control strategy for HEV with HESS can improve the system efficiency and battery service life. On the basis of analyzing the energy flow modes of HEV, a control strategy namely nonlinear proportion factor dynamic coordination is proposed. Based on the analysis of the above control strategy, a dynamic programming-based global optimal control strategy which fully considered the efficiency of each component in HEV is presented. To compare with the nonlinear proportion factor dynamic coordination strategy, the fuel consumption is not increased. The cycle numbers of battery are further decreased which benefits its cycle life improvement. Take shanghai drive cycle as example, the regenerative energy callback ratio improves 3%.Based on EMR control algorithm, the experiment platform is also established. Finally, experiments for HESS consisting of Ni-MH battery pack, ultracapacitor stack and DC/DC converter are conducted under basic modes and specific city drive cycles to verify the correctness and effectiveness of established simulation model as well as the proposed control strategy.The paper aims to explore proper energy storage technology for HEV. The research results provide some guidance for the parameter matching and control of the hybrid energy storage sources. It creates basic conditions to break through the bottleneck of the HEV energy sources in future.