Research On LLC Resonant Converter For Batteries Equalization

With the rapid development of new energy vehicle, Series of Li-ion battery pack has been the power source of electric vehicle. Even Li-ion battery has the outstanding features such as light、high energy density with small size、no memory effect、fast charge ability and long life cycle, but there is a inequality between batteries which may cause the over charge or over discharge and even worse reduce the life and safety if without correct. This paper on the basis of the existing equalization circuit topologies proposes a multi-winding resonant convert topology for batteries equalization.Firstly, the paper illustrates the meaning and purpose of battery equalization, study the working principle of Li-ion battery and it’s stricture and charging methods, summarize the existing equalization circuit topologies and equalization strategies. Then give the equalization topology based on the LLC resonant converter and equalization strategy, and illustrate working principle of equalizing system.Secondly, the working principle and features of LLC resonant converter is introduced here. Design the circuit parameters based on the battery. Use the Extend describing function method modeled the LLC resonant converter battery equalizer. And use the Matlab tool depicts the system open loop transfer function from control to output. Design the Digital compensator for system based on the classical control theory. And simulate circuit with the parameters designed before and finished close loop simulation with the digital compensator.Digital control has been the heated control method for recent years. In this paper use the TMS320F28335 as microprocessor to realize the digital control and frequency modulation control. At the same time use the DSP detections 12 batteries voltage and send dates through SCI and SPI. So the voltage dates can be seen on the computer.Finally on the basis of hardware and soft programming design and finish the experimental verification. The experiment realizes the 12 batteries equalization and ZVS function.