A modular controllable topology of high-voltage and large-capacity lithium battery packs

Abstract

The invention provides a controllable topological structure for a modularized high-voltage and high-capacity lithium battery pack. According to the used lithium battery pack, the matching requirements are reduced, the yield of battery production is improved and the cost is reduced. The battery pack is modularized, so that design, production and maintenance are facilitated. Parallel battery modules are balanced by using current as a criterion, mutual charging and discharging in parallel batteries are suppressed, the life of the battery pack is greatly prolonged, meanwhile, the effective use capacity of the battery pack is increased after being balanced and is closer to a theoretical value; and furthermore, compared with balancing of series batteries by using voltage as the criterion, parallel current balancing is more accurate and the balancing loss is zero.

Description

technical field [0001] The invention designs a modularized high-voltage and large-capacity lithium battery group controllable topology structure, and specifically relates to a series-parallel controllable topology suitable for high-voltage and large-capacity lithium battery group applications and a control strategy using the topology structure. Background technique [0002] In recent years, lithium batteries have become a hot spot of competition and development direction in the field of modern energy storage due to their outstanding advantages such as high specific energy, long life, environmental protection and pollution-free. In order to obtain a high-voltage, large-capacity battery pack, the single lithium batteries are generally connected in parallel first to form a parallel battery unit with a target capacity, which is equivalent to a single battery, and then a certain number of parallel single battery pack units are connected in series to achieve The target voltage val...

AI Technical Summary

Problems solved by technology

[0003] When lithium batteries are directly connected in parallel, due to the poor consistency of internal parameters, there are unavoidable differences in capacity, internal resistance, voltage, and charging constant current ratio. The parallel batteries will charge and discharge each other at different stages of charging and discharging. The expansion of the internal mutual charge and discharge will also be worse, especially in the initial and stop stages of the charge and discharge process, the open circuit voltage of the battery changes drastically, and the internal mutual charge and discharge current even exceeds the maximum allowed by the lithium battery when the batteries with a large open circuit voltage difference are connected in parallel. The charging and discharging current at multiple rates will cause aging and even spontaneous combustion and explosion accidents. Long-term internal self-charging and discharging will lead to a sharp decline in battery life. Compared with the nearly 1,000 cycle life of a single lithium battery, the life of a lithium battery after parallel connection may be reduced to 300~ 400 cycles

Therefore, the consistency of lithium batteries is very critical when the batteries are connected in parallel. The screening requirements for battery groups are more stringent. Due to the characteristics of existing materials and production accuracy, there are certain differences between the single batteries produced in the same batch. The rate is low, and a large number of single cells are screened out

However, even if the parameters of the lithium battery are completely consistent in the initial state, the inconsistency of the lithium battery will become more and more obvious as the battery continues to age during use, and the internal mutual charge and discharge of parallel batteries cannot be avoided.

[0004] When the parallel monomer battery units are connected in series, the capacity consistency of the battery units is highly required. If the capacity of the battery parallel units is inconsistent, the unit with the lower capacity will be discharged first during the charging and discharging process, and the unit with the higher capacity will be discharged first. It will be fully charged first. If the protection measures are not perfect, there will be overcharge or overdischarge, which will seriously affect the battery life, and even cause spontaneous combustion and self-explosion accidents.

In addition, in the charge-discharge cycle of the lithium battery pack, the highest value of the cell voltage in the battery pack is used as the charge cut-off voltage, and the lowest value of the cell voltage is used as the discharge cut-off voltage. As the usage imbalance becomes worse, the effective capacity of the battery pack will continue to decline

For a high-voltage lithium battery pack, hundreds of battery cells need to be connected in series, and the above situation will be even worse. At the same time, it is difficult to realize functions such as information collection and energy balance of more than a hundred batteries.

[0005] Therefore, the current topological structure of high-voltage and large-capacity lithium battery packs faces various problems such as high selection and elimination rate of matching groups, low life after grouping, complex battery management, attenuation of effective use capacity, and energy imbalance, which have not yet been resolved.

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