Digital Balance Control System Of Lithium-Iron Phosphate Power Battery

Lithium-ion battery has gradually become a research hotspot with itsadvantages of high energy density, high reliability and no pollution. Lithium-ionbattery pack is composed by a large number of single cells by series and parallel.However, the diversity of manufacturing process, battery material, resistance andalso environment temperature can cause voltage imbalance internal the batterypack in its production process. This imbalance is bound to lead to the shorteningof its life and even causes damage in the process of using the battery pack.Therefore, the significance of equilibrium control research to the battery pack isself-evident.Most of the existing balance control methods use switched capacitor, shuntresistor, converter directly to the single cells of battery pack for balance control,and they have the advantages of simple structure and low cost. However, thesemethods also have the obvious deficiencies. Because the battery pack iscomposed by a large number of single cells by series and parallel, its internalelectrical characteristics are extremely complex, which makes the balancingprocess have the characteristics of time variation, nonlinearity and uncertainty. Itis difficult to establish a mathematical model because of these electriccharacteristics of the internal complexity. Even if a mathematical model may becreated, the external environmental factors can also lead to the change ofmathematical model due to the working condition. Thus, traditional controlalgorithm is difficult in balancing control for the battery pack, also difficult toachieve a good balanced performance.Basing on the above analysis, this paper build a lithium-ion battery balancecontrol circuit with multi-tap output transformer winding structure based on half-bridge circuit topology which uses MOSFET as power switch. To achieveClosed-Loop control to the balanced controller with digital control based on C8051F020, and then developed the balanced algorithm. This paper reduces thelithium-ion battery’s complex problem of balance control into two-input single-output control problem. In addition, this paper proposes a new fuzzy controlstrategy and designs a battery equalization controller based on energy closed-loop model. Simulation experiments will be carried out about static equilibriumwithout load and about dynamic equilibrium with load.Simulation results show that the proposed control algorithm can solve thestrong coupling problem between the internal error voltage and the external loadcurrent, and can determine the control output in real time for any input errorvoltage signal value or the load current value, and can stabilize the system in theshort time. This control strategy has a great practical significance for optimizingthe performance of balance control.