Analysis of Two Common Balancing Technologies for EV Electric Vehicle Battery Balancing

The electric vehicle battery pack is composed of multiple single cells. Due to differences in manufacturing processes, usage environments, and charging and discharging processes, the performance of each single cell may vary.

Battery consistency refers to the state where the performance parameters of each single cell in the battery pack are as close to consistent as possible. Battery inconsistencies can cause the following problems:

Reduced battery pack capacity and service life: Poorly performing batteries can become a bottleneck, limiting the capacity and service life of the entire battery pack.

Reduced battery safety: Batteries with poor performance may be the first to experience problems such as overcharge, over-discharge, and overheating, causing safety accidents.

Reduced battery pack performance: Battery inconsistency will lead to problems such as reduced battery pack efficiency, increased internal resistance, and reduced power.

In order to solve the problem of battery inconsistency, the battery pack needs to be balanced so that the performance of each single cell is as close to consistent as possible.

Electric vehicle battery balancing technology classification

Currently, there are two main types of battery balancing technologies for electric vehicles:

Passive balancing technology: Using components such as resistors to balance the battery during charging or discharging. Passive equalization technology has a simple structure and low cost, but the equalization speed is slow and the efficiency is low.

Active balancing technology: Electronic switches and power devices are used to actively charge and discharge the battery to achieve rapid balancing. Active balancing technology has fast balancing speed and high efficiency, but has complex structure and high cost.

How battery balancing works

Passive equalization technology

The principle of passive equalization technology is to use resistors to equalize the battery during charging or discharging.

During the charging process, a battery with poor performance is connected in parallel with a resistor to discharge the battery; during the discharge process, a battery with better performance is connected in parallel with a resistor to charge the battery.

In this way, the voltages of the individual cells are gradually brought to a consistent level.

Active balancing technology

The principle of active balancing technology is to use electronic switches and power devices to actively charge and discharge the battery.

During the charging process, a battery with poor performance is connected in parallel with a buck circuit to transfer excess charging energy to a battery with better performance; during the discharge process, a battery with better performance is connected in parallel with a boost circuit. Transfer the energy from that battery to a less capable battery.

In this way, the voltages of each battery are quickly brought into line.

Recommended when battery balancing is invalid

If the internal cell balancing of the battery pack fails to balance the individual cells, it is recommended to take the following measures:

Replace the battery: If the battery performance is severely degraded, it is recommended to replace the battery.

Use an equalizer alone to equalize: If the battery performance degradation is not serious, you can take out the battery separately and use a special equalizer for equalization.

Data reference

Battery balancing accuracy: Generally speaking, battery balancing accuracy should be controlled within ±5mV.

Battery balancing time: Passive balancing time is generally several hours, and active balancing time is generally tens of minutes.

Battery balancing is an important function of the electric vehicle battery management system, which can effectively improve the performance, safety and service life of the battery pack.