What are the requirements for batteries in electric vehicles?

Main content:

  • 1.Pure electric field vehicle
  • 2.Pure electric road vehicles
  • 3.Hybrid Vehicles

    1.Pure electric field vehicle

    Pure electric field vehicle

    The road operating conditions of pure electric field vehicles are usually known in advance. Taking an electric forklift for handling goods as an example, the distance of its own movement and handling of goods during working hours is basically determined. Therefore, under this application condition, the energy required by the vehicle to perform a specific task can be accurately calculated. The vehicle manufacturer can determine the energy required by the battery when the vehicle completes specific tasks such as carrying goods based on the data provided by the customer.

    These data include
    ①The mileage traveled on the flat road;
    ② the slope of any slope;
    ③The weight of the goods and the height of the lift.

    In terms of power demand, item ① includes resistances F and F, while item ② takes into account the resistance F, the remaining one resistance F can be ignored due to the low running speed of the field vehicle. When carrying out lifting operations, additional power is also required, the magnitude of which is proportional to the total mass of the lifted object. In a specific working cycle, the total energy required by the battery that meets the requirements can be obtained by multiplying the sum of the energy required by each vehicle operation by the number of times of operation. In order to ensure that the power battery pack will not be overdischarged in the application, and considering the compensation required for the battery pack due to battery performance degradation during normal use, the design capacity of the power battery pack is generally larger than the calculated capacity. The existing lead-acid power battery can meet the energy and power requirements of the electric forklift under normal working conditions. In the lifting condition, the large-mass lead-acid battery pack can also play a role in balancing the payload, so it is also an advantage of the lead-acid battery with a large battery mass applied to the electric forklift.

    Due to the difficulty of calculating the performance of the power battery required by the traction vehicle under the complex road conditions with variable traction conditions, the power and energy of the power battery required by the pure electric field vehicle are generally calculated based on the comprehensive common working conditions.

    2.Pure electric road vehicles

    Pure electric road vehicles

    Pure electric road vehicles completely rely on the energy of the power battery pack. The greater the power battery pack energy, the longer the driving range can be achieved, but the volume and weight of the power battery pack are also greater. For pure electric road vehicles, power batteries should be selected according to different design objectives, road conditions and operating conditions. The specific requirements are summarized as follows.

    ① The power battery pack must have enough energy and capacity to ensure that the typical continuous discharge current does not exceed 1C, and the typical peak discharge current generally does not exceed 3C: if a regenerative braking system is installed on the electric vehicle, the power battery pack must be able to Accept pulse current charging above 5C.

    ② The power battery should be able to achieve deep discharge (such as 80% DOD) without affecting its service life, and can achieve full load power and full discharge when necessary.

    ③It is necessary to install a battery management system and a thermal management system to display the remaining capacity of the power battery pack and achieve temperature control.

    ④ Due to the large volume and mass of the power battery pack, the design of the battery box, the spatial arrangement and installation of the power battery need to be specifically designed according to the space of the vehicle and the ratio of front and rear axle loads.

    3.Hybrid Vehicles

    Hybrid Vehicles

    Compared with pure electric vehicles, hybrid electric vehicles have lower energy requirements for power batteries, but they must be able to provide greater instantaneous power when the vehicle needs them, that is, to achieve "small batteries provide large currents".

    Due to the different configurations of HEVs, the battery requirements for series and parallel HEVs are also different.

    ① The series hybrid electric vehicle is completely driven by the electric motor. The internal combustion engine generator and the battery pack together provide the electric energy required by the electric motor. The SOC of the battery is at a high level. The requirements for the battery are similar to those of the pure electric vehicle, but the capacity requirement is less than For pure electric vehicles, the requirements for battery power characteristics are determined according to the needs of the entire vehicle and the battery capacity. In general, the smaller the capacity of the power battery, the higher the requirements for its high-rate discharge capacity.

    ② The internal combustion engine and electric motor of the parallel hybrid vehicle can directly provide driving force for the wheels, and the driving needs of the whole vehicle can be met by different power combinations. The capacity of the power battery can be smaller, but the instantaneous power provided by the battery pack needs to meet the requirements of car acceleration or climbing, and the maximum discharge current of the battery may sometimes be as high as 20C or more.

    Due to the complexity of the working environment, vehicle configuration and working mode of HEVs with different configurations, it is difficult to put forward unified requirements for power batteries for HEVs, but some typical and common requirements can be summarized as follows :

    ① The peak power of the power battery should be large, and it can perform short-term, high-power charging/discharging;

    ②The cycle life should be long, and the battery life should be at least 5 years or more, and the ideal situation is the same life as the electric vehicle;

    ③ The SOC of the battery should be kept at 50%~85% as much as possible;

    ④It needs to be equipped with a battery management system, including a thermal management system.

    Externally rechargeable hybrid electric vehicles (PHEVs) should be able to reach the expected value of more than 40km in pure electric working mode, and have both hybrid driving functions. Therefore, the requirements for power batteries should take into account both pure electric and hybrid power. mode. At the same time, since its application mode is set to start the hybrid driving condition when driving on pure electric power until the power is insufficient, the power battery pack is required to provide high power even at low SOC.

    Due to the low power density of the fuel cell, the existing fuel cell electric vehicle generally adopts the way of co-driving with the power battery to output electric energy to the outside. There are also two forms of parallel connection and series connection in the connection mode of fuel cell and power battery. The performance requirements of power battery on this type of vehicle are similar to that of hybrid electric vehicle.