Yu Yue, Lin Cong, and Zhang Heng, researchers from the School of Electronics and Information Engineering of Guangdong Ocean University, wrote an article in the 8th issue of "Electrical Technology" in 2019 (the title of the paper is "Active balance control system for lithium-ion batteries based on state of charge "Research and implementation"), in order to solve the problem of energy imbalance of the power battery pack, this paper designs a lithium-ion battery active balance control system. The system is composed of main control chip TMS320F28335, detection circuit, DC/DC circuit, equalization circuit, driving circuit and so on.
The system uses the unscented Kalman filter algorithm to estimate the state of charge of the lithium-ion battery pack in real time, designs an energy storage inductive equalization circuit based on battery characteristics, and uses a fuzzy-PI control algorithm to modulate the PWM signal to achieve active energy balance of the battery pack. The hardware experiment platform of the balanced control system is built, and the experimental results have reached the expected goal.
In order to ensure sufficient output voltage and output power, the power battery pack is usually composed of many single cells connected in series or in parallel. Due to the limitations of the current manufacturing process, there are great differences in the relevant parameters of each single battery, and with the increase in the number of times the battery pack is used, this difference becomes more prominent, which directly leads to the inconsistency of the capacity of each single battery, making the working capacity Larger single cells are undercharged and under-discharged, and small-capacity single cells are overcharged and over-discharged, resulting in energy waste, accelerating battery aging, shortening battery life, and even causing safety accidents such as explosions.
Using the balance control technology to make the state of charge (SOC) of each single battery in the battery pack tend to be consistent, which can improve the energy utilization rate of the power battery pack, reduce the consumption of the battery pack, and ensure the operation of the entire electrical equipment Safety.
At present, there are many studies on the balance control of battery packs, each with its own advantages and disadvantages.
In summary, this paper designs an active balance control system for lithium-ion batteries based on SOC. filter, UKF) algorithm real-time estimation of the SOC of the lithium-ion battery pack is used as the balance criterion, and the fuzzy-PI algorithm is used to modulate the PWM signal to modulate the balance current, so as to realize the active balance of battery pack energy. And built an experimental prototype of the active balance control system with four lithium iron phosphate batteries connected in series to verify the effect.
  Summarize
Aiming at the energy imbalance problem of lithium-ion battery packs, this paper designs an active equalization control system, which realizes the detection of voltage and current, and the UKF algorithm estimates the SOC of each lithium-ion battery and the balance control of the battery pack. The system uses SOC as the balance criterion, and when the difference between the SOC of any battery and the average SOC of the battery pack is greater than 2%, the balance control is started.
The equalization effect of the system was tested by building the hardware platform of the battery pack active equalization control system with four lithium iron phosphate batteries connected in series, and the energy recovery rate reached 69.2%. Since the inductive energy storage circuit cannot be interrupted, the stability of the system needs to be further optimized.