Passive battery balancing mechanism
Passive battery balancing is a relatively simple and low-cost balancing method that primarily dissipates excess energy through external resistors or discharge devices. When the voltage difference between individual battery cells exceeds a certain threshold, the passive balancing system is activated, converting the excess energy into heat through resistors or loads, thereby adjusting the voltage levels of the individual battery cells to a similar state.
Working principle
Passive balancing mechanisms typically employ switches and bleed resistors connected in parallel with each cell. During a charging cycle, when the voltage of one cell is higher than that of the others, the BMS activates the switch, releasing excess energy as heat through the bleed resistor. This process continues until the voltages of all cells are nearly equal. Passive balancing primarily relies on resistor discharge to release the charge in the higher-voltage battery as heat, thus creating more charging time for the other batteries.
Advantages and disadvantages
advantage:
Low cost: Passive balancing systems are relatively simple to design and implement, and have low cost.
The circuit design is simple: no complex control system is required, and it is easy to implement and maintain.
Correction of self-discharge mismatch: It can correct the self-discharge current mismatch between different battery cells over a long period of time.
shortcoming:
Energy waste: The presence of the discharge resistor causes energy to be released as heat, which is a complete waste.
Heat generation: The heat released during the equalization process increases the system's heat dissipation burden and may affect battery life.
System power limitation: The power of the entire system is limited by the smallest capacity battery, resulting in power loss.
Active battery balancing mechanism
Active battery balancing is a more complex balancing technology that achieves equilibrium by controlling the charging and discharging of individual battery cells. This requires an intelligent battery management system (BMS) capable of monitoring and controlling the charging and discharging process of each battery cell to ensure that their state of charge (SOC) and voltage remain within appropriate ranges.
Working principle
Active balancing mechanisms achieve balancing through power transfer. During charge and discharge cycles, the BMS monitors the SOC and voltage of each battery cell. When a difference exceeds a set threshold, it activates a balancing strategy. This typically involves redistributing power from battery cells with more remaining power (stronger cells) to those with less remaining power (weaker cells), thereby ensuring full utilization of energy within the battery pack.
There are several ways to implement active load balancing, including but not limited to:
Capacitive equalization: uses capacitors as an intermediate medium for energy transfer, and transfers electricity from a strong battery to a weak battery through switch control.
Transformer-type equalization: Utilizing the principle of a transformer, electricity is transferred from a high-voltage battery to a low-voltage battery.
Battery-to-battery direct balancing: Through intelligent BMS control, direct charging and discharging between individual battery cells is achieved.
Advantages and disadvantages
advantage:
High energy efficiency: Active balancing does not waste energy, but redistributes energy to other battery cells in the battery pack.
Extending system uptime: Active balancing can extend the battery pack's uptime by optimizing energy distribution.
Improved charging efficiency: Active balancing can shorten charging time and improve charging efficiency.
shortcoming:
The system is complex: it requires more complex control systems and hardware support, making it more difficult to design and implement.
Higher cost: The cost is relatively high due to the need for a smart BMS and additional equalization hardware.
Equalization time: Although active equalization is more efficient, the equalization process may take some time, especially when the battery pack capacity is large.
Comparative analysis
Application scenarios: Passive balancing is more suitable for small-capacity, low-cell-count lithium battery packs, while active balancing is more suitable for high-cell-count, large-capacity power lithium battery packs.
Energy efficiency: Active balancing is significantly better than passive balancing in terms of energy utilization, which can reduce energy waste and improve the overall performance of the battery pack.
System complexity and cost: Active balancing requires more complex control systems and hardware support, thus incurring higher costs and greater design and implementation difficulties. Passive balancing, on the other hand, is relatively simpler and less expensive.
Balancing effect: Active balancing can more precisely control the SOC and voltage differences between individual battery cells, achieving a more efficient balancing effect. Passive balancing, on the other hand, may have limited balancing effect due to energy waste and heat generation.
in conclusion
Battery balancing, as a crucial component of the battery management system for new energy vehicles, plays a vital role in improving battery pack performance, extending lifespan, and ensuring safety. Active and passive battery balancing mechanisms each have their advantages and disadvantages, and the choice should be made based on specific application scenarios and needs. With the continuous development of new energy vehicle technology, more efficient and intelligent battery balancing technologies may emerge in the future, providing strong support for the development of new energy vehicles.
