The state estimate of a battery includes the estimate of state of charge (SOC) and state of energy(SOE). SOC in electric vehicles serves a similar function to that of the petrol gauge in the traditional oil-fueled automotive. For hybrid vehicles, an accurate estimate of SOC is the precondition for the optimization of the vehicle control. Effectively estimating SOC and involving it in the vehicle control play an important role in collecting the battery information, optimizing the vehicle operation and driving experience, enhancing the utilization rate of battery capacity and energy, preventing the battery from over-charging and over-discharging, and ensuring the safety and service life during its use. SOE analyzes the remaining capacity from the viewpoint of energy, and, in terms of usage, it can build a simple (linear) relation between the remaining capacity and the time of use or running distance of an electric vehicle. In actual use, the main function of the battery is to store and release energy. The running distance and endurance time of the electric vehicle are directly related to the quantity of energy released by the battery. Hence, describing the SOC and the state of the battery from the viewpoint of energy is of more practical significance.
3.1 Definition of SOC
3.1.1 The Maximum Available Capacity
The discharging capacity is closely related to the current, ambient temperature, and the running conditions. In different running conditions, the difference ...