Research And Implementation On Model-Based Design Of Active Equalization For Lithium Ion Power Battery Pack

With increasingly developed new energy automotive technology and related vehicle models gradually launched, lithium ion battery has been widely used. So how to efficiently and safely managing and using of lithium batteries has become the focus of researches. It is learnt from practice that a large number of single battery will produce a series of consistency of imbalances in tandem use, which will directly reduce the driving range of electric vehicles, shorten the battery life, eventually increase the using cost of electric vehicles indirectly, and hinder the application and promotion of electric vehicles.The paper analyzes the causes and forms of monomer cell consistency imbalances and makes comparison analysis on the common topologies of usual equilibrium circuit. The author adopts the improved centralized multi-level topological as the equilibrium solution and designs the variables determination solution, correction algorithm solution and the model of self-regulating execution balanced strategy which is based on the characteristics of hardware.In hardware design, a two-way forward type isolation transformer type of DC/DC as the energy shift module is selected and synchronous rectification is applied in order to improve the conversion efficiency. Selecting the MOSFET featuring lower voltage and lower resistance as the monomer selection switch, not only reduces the cost and size, but also extends the operating life of the circuit, compared with relay solution. A stackable system level equilibrium solution can be directly compatible with BMS system by adding CAN protocol matrix.In this paper, software design is based on model development by using the Matlab Simulink/Stateflow tools to build complete hierarchical model algorithm of software structures. Meanwhile various object control models are built, including abstract model of balanced board, hardware abstraction model, the charging and discharging equipment model, battery pack consistency model. And on this basis, MIL(model in the loop) will achieve simulation. The simulation verifies both the effect of the control algorithm implementation and the improved effectiveness of using active balancing on the cell. Finally, in the RTW environment model, the writing of the software target system architecture is completed and some driver module is built, realizing one key to generate a complete project code and successfully downloading to the target MCU in the end.In order to show the real balance effect of power battery pack of equilibrium system, the research has built a simple physical experimental platform, written the data monitoring and drawing software on PC, and experimented the active balancing of real lithium ion battery. Experimental results indicate that equilibrium system designed in this research achieves the effect of stablizing and balacing the 3A bidirectional current on any cell within the group of 12; moreover, the energy transfer efficiency maintains above 82%; the equilibrium has achieved the intended effect.