Investigation Of The Power Battery Pack Preheating System With Passive Balancing System

Under low temperature,the lithium-ion battery needs to be heated to the appropriate temperature and then recharged.In order to make full use of the battery capacity in the battery pack,it is necessary to set up a balancing system for the battery pack.To meet with the demand of both battery preheating and balancing,use the heater both as the heating resistor of the preheating system and the balancing resistor of the passive balancing system.Researches have been made in this paper about battery preheating technology and battery passive balancing technology,and a power battery pack preheating system with passive balancing system has been designed.A schematic layout was discussed on how to arrange the heating unit in the battery pack and how the balancing resistance distributed in the heating unit.A low-temperature charging experiment of the single cell was conducted,then the heating power of the preheating system was discussed.The temperature of the battery group gradually decreased after stopping heating,which means it was necessary to adjust the target temperature according to the required charging time,to ensure an appropriate temperature of the battery pack throughout the whole charging process.Considering this,and based on the experiment,calculation the charging time based on the SOC of battery pack,and a new target temperature calculating algorithm based on the heat transfer regularity.According to the battery pack capacity scatter plot,to make full use of the minimum capacity of single cell in the battery pack,it is necessary to ensure that the minimum remaining discharge battery is the minimum remaining charge battery at the same time.So an on-line balancing algorithm of the battery pack witch combined with single point SOC consistent was proposed,and a balancing control bandwidth of different SOCnew states was developed.For 72V/100Ah battery pack,considering the balance demand and the cause of temperature rise when balancing,the resistance of the balancing system was set to 4? and the balancing current to about 1A.On the basis of the proposed balancing algorithm,the method for SOH estimate was put forward.Based on the above research results,the connection mode of the heating unit and the topological structure of the system was designed respectively according to the parameters of off-board charger and traditional passive balancing system.Then the temperature rise experiment and the low temperature charging preheating experiment was carried out on a 72V/100Ah battery pack.Experiments showed that the balancing system kept the temperature rise within 7? in the battery pack at 20? ambient temperature.The system achieve a temperature rise of 16? at-20? ambient temperature and keep the temperature above 0? in 4h.Experiments proved the effectiveness of the system.