# Parameter design of power battery for pure electric vehicle

The power battery is the energy source of the whole vehicle, and all the energy consumption of the whole vehicle comes from the power battery. Therefore, the type, quality and various technical parameters of the selected power battery will affect the performance of the pure electric vehicle, and it is one of the key components of the pure electric vehicle. Power battery parameter matching includes the matching of battery capacity, battery number, battery voltage and other parameters.

**1.Power battery matching principle**The choice of power battery type should meet the operating requirements of pure electric vehicles. Pure electric vehicles require power batteries to have high specific energy and specific power to meet the requirements of pure electric vehicles’ driving range and power performance. At the same time, it is also hoped that power batteries have a charge-discharge cycle life equivalent to the service life of a car and have high efficiency. , Good cost performance and maintenance-free features. The power batteries currently available for pure electric vehicles mainly include lead-acid batteries, metal nickel hydride batteries and lithium-ion batteries. Among them, the superior performance of lithium-ion battery, such as high energy and fast charge and discharge speed, has attracted more and more attention, and it is a product with the best market prospects.

The voltage level of the power battery must be consistent with the voltage level of the drive motor and meet the requirements of motor voltage changes. At the same time, because accessories such as electric air conditioners, electric vacuum pumps, and electric power steering pumps also consume a certain amount of electric energy, the total voltage of the battery pack is larger than the rated voltage of the driving motor.

Power batteries generally have two types: energy type and power type. In order to meet the driving requirements of pure electric vehicles, energy-type batteries are used. When matching, the energy of the battery is mainly investigated, that is, the battery should have a larger capacity to increase the driving range of the vehicle . The battery capacity is proportional to its power. The larger the capacity, the greater its output power. Therefore, its output power can meet the requirements of the entire vehicle power system. Therefore, the battery capacity is mainly determined according to its driving range, and the determined battery capacity is also Must meet the standards of existing products in the market, and design through repeated verification of existing products.

**2.Power battery parameter matching design**A power battery pack is a single mechanical assembly composed of one or more battery modules; a battery module is a combination of a group of connected single batteries; a single battery is the smallest unit that constitutes a battery, generally composed of a positive electrode, a negative electrode, and an electrolyte. .

(1) The capacity of the power battery pack.

The capacity of the battery pack depends on the driving range of the pure electric vehicle. The larger the capacity of the battery pack, the longer the driving range of the pure electric vehicle, but the quality and cost of the vehicle also increase. Therefore, reasonable matching of the capacity of the power battery pack can greatly improve the performance of the entire vehicle.

The power consumed by a pure electric vehicle cruising on a level road is

In the formula, P_{md} (kW) is the power consumed when the pure electric vehicle is cruising; ν_{d} (m/s) is the cruising speed of the pure electric vehicle.

Battery pack energy should meet

In the formula, E_{z} (kW·h) is the battery pack energy; ζ_{soc} is the depth of discharge of the battery; η_{e} is the overall efficiency of the motor and the controller, which refers to the motor shaft output power divided by the controller input power multiplied by 100%; n, η_{d} is Battery discharge efficiency; η_{a} is the proportional coefficient of energy consumption of car accessories; S(m) is the driving range of pure electric vehicles.

The relationship between battery pack energy and capacity is

In the formula, U_{z} (V) is the battery pack voltage: C_{z} (A·h) is the battery pack capacity.

The battery capacity should meet

(2) The number of power battery modules.

The number of battery modules must meet the requirements of peak power and driving range required by the driving motor for power supply, pure electric vehicle driving.

The minimum operating voltage of the battery pack should be able to meet the minimum operating voltage of the drive motor system, so the number of battery modules required is

In the formula, N_{1} is the number of battery modules required to meet the minimum operating voltage of the motor system; Uemin (V) is the minimum operating voltage of the drive motor: U_{zd} (V) is the voltage of the battery cell unit module.

The number of battery modules that meet the peak power requirements of pure electric vehicles is

In the formula, N_{2} is the number of battery modules that meet the peak power requirements of the motor: Pbmax (kW) is the maximum output power of the single battery; N_{0} is the number of single batteries contained in the battery module.

The maximum output power of a single battery is

In the formula, U_{b} (V) is the open circuit voltage of the single battery; R_{b0} (Ω) is the equivalent internal resistance of the single battery.

The number of battery modules that meet the driving range requirements of pure electric vehicles is

In the formula, N_{3} is the number of battery modules that meet the driving range requirements of pure electric vehicles.

The actual number of battery pack modules is

In the formula, N_{z} is the actual number of battery modules.