With the rapid development of automatic guided vehicle (AGV) technology, lithium battery, as its main power source, is widely used due to its high energy density, long service life and low self-discharge rate. However, the problem of voltage imbalance between single batteries may occur during the use of lithium batteries, which not only affects the endurance and operation efficiency of the AGV, but also may shorten the service life of the battery. In order to solve this problem, active and passive Battery balancing technology in battery management system (BMS) came into being. This article will analyze the active and passive battery balance of the lithium battery of AGV, and discuss its working principle, advantages and disadvantages and application scenarios.

I. Reasons for lithium battery imbalance

in AGV lithium battery due to various factors such as manufacturing process, capacity difference, charging and discharging state and temperature of different single batteries, the voltage of each single battery in the battery pack may be inconsistent. This imbalance will affect the overall performance of the battery pack, resulting in the following problems:

1. capacity loss: The total capacity of the battery pack is often determined by the single battery with the lowest capacity, so imbalance will lead to the reduction of available capacity.
2. Potential safety hazard: overcharging or overdischarging of some single batteries may lead to battery expansion, liquid leakage and even fire, seriously affecting safety.
3. Cycle Life reduction: long-term unbalanced state will accelerate the aging process of the battery and shorten its service life.

therefore, battery balance management is the key to ensure the safe and efficient operation of the lithium battery of AGV.

II. Passive battery balance

1. Working principle

passive Battery balancing is a relatively simple and common battery balancing method. The basic principle is to convert the excess energy of the single cell with higher voltage into heat energy through resistance during the charging or discharging process, so as to reduce its voltage and achieve the goal of balance. This method is usually controlled by the battery management system (BMS) and has the following characteristics:

• simple and easy to implement: the passive balancing circuit has relatively simple structure and low cost, and is easy to integrate into the existing battery management system.
• Suitable for small battery pack: for small battery packs or applications with low balance requirements, passive balance can meet basic requirements.

2. Advantages and disadvantages

advantages:

• low cost: the circuits and components required for passive balance are relatively simple, reducing the overall cost of the system.
• <span style = "font-size: 14px;"> easy to implement: the passive balancing technology is relatively mature and easy to integrate with existing BMS.

Disadvantages:

• low efficiency: passive balance generates heat in the process of energy transfer, resulting in energy loss, thus reducing the overall efficiency.
• Slow balancing speed: due to excessive power consumption by relying on resistance, the balancing speed is relatively slow, which may not meet the requirements of high frequency charging and discharging scenarios.

3. Active battery balance

1. Working principle

active Battery balancing is a more complex but more efficient battery balancing method. The basic principle is to transfer the electric quantity from the single battery with higher voltage to the single battery with lower voltage through the battery management system. This process is usually realized by using the battery balance module (BPM), which can dynamically adjust the state of each single battery during charging and discharging.

• Energy transfer: active balance avoids energy loss and improves overall efficiency by directly transferring electric energy.
• Rapid response: active balance can quickly respond to the state changes of the single battery and adjust the overall performance of the battery pack in time.

2. Advantages and disadvantages

advantages:

• high efficiency: active balance avoids energy loss through electric energy transfer, and the overall efficiency is significantly improved.
• Fast balancing speed: it can quickly realize the balance of each single battery in the battery pack, and is suitable for high frequency charging and discharging scenarios.
• Extend battery life: through effective balance management, reduce the imbalance of single battery and prolong the service life of battery pack.

Disadvantages:

• high cost: the circuit design of the active balancing system is complex, requiring more components and higher technical requirements, resulting in increased cost.
• Large volume: Active balancing systems usually require more space and are not suitable for some applications with high volume requirements.

IV. Application scenario comparison

1. Application scenarios of passive Battery balancing

passive Battery balancing is suitable for applications that are cost-sensitive and do not require high Battery balancing, such:

• small AGV system: for small or simple AGV Systems, passive balance can meet basic battery management requirements.
• Low frequency charge and discharge applications: in applications with low charging and discharging frequency, passive balance technology can effectively control battery of the working state.

2. Application scenarios of active Battery balancing

active Battery balancing is suitable for applications with high performance requirements, such:

• high frequency charge and discharge AGV system: In the AGV system that requires frequent charging and discharging, active balance can provide faster response speed and higher efficiency.
• Large capacity battery pack: for lithium battery pack of large capacity, active balance can effectively manage the imbalance between batteries and ensure the safe and stable operation of the system.

The active and passive Battery balancing technologies of AGV lithium battery have their own advantages and disadvantages. Enterprises should consider comprehensively according to their own application scenarios and requirements when choosing. Passive battery balance is suitable for some occasions with low performance requirements due to its low cost and simple implementation. However, active battery balance is famous for its high efficiency and fast response, it is suitable for high-end applications with high frequency charge and discharge.