For the article on the leveling, let's talk about the inconsistency of the battery and the parallel connection of the modules.
Due to the energy demand, it is disassembled into total energy=voltage* capacity. If a fixed-size battery cell is to be used in the integration process, serial-parallel operation is required to achieve the target demand total capacity. Our configuration of the battery system can be divided into several ways:
1) The cells are connected in parallel and then connected in series: this is a typical series-parallel application mode. Since the minimum cell is in the range of 3.2~3.7V, the equilibrium voltage difference of the whole current branch is also small.
benefit:
Battery fuse design is relatively easy
The number of battery sampling channels is small, and the cost and complexity of BMS are low.
Battery self-balancing at the single-level current branch
Design difficulties:
Battery consistency
Reliable uniformity design of busbar fuses
Uniformity of current density, as well as consistency of fuse characteristics
2) Parallel connection of modules in series after assembly: This method is typically used for large energy storage units, especially energy storage stations and buses. The effect is better, especially in the process of parallel connection. Mode, multiplex pre-charge and distribution box, making the entire connection more controllable
Direct parallel connection after grouping is difficult and requires pre-charging
And now the design is often extended at the module level.
Modules connected in parallel and then connected in series
Modules are connected in series and then in parallel
The latter was previously used in parallel with two branches in a commercial vehicle.
The concept of this standard cabinet is also widely used in commercial vehicles, buses and logistics vehicles. In terms of versatility, the development of configuration based on standardized cabinets is more reliable, development cycle and development efficiency than custom development. Has a significant advantage. The further innovation is the concept of removing the module inside the box, and returning to the previous mode of direct cell implantation.
The former is really rare, and now I saw one, the ES8 battery box
The design here is also caused by the capacity of Ah. In the short term, the Ah specification of PHEV2 is 50+Ah, and it takes 1 year to 1.5 years to go to 60+Ah.
This involves the circulation between the modules, and there will be problems of SOC, temperature rise, and unsynchronized life caused by inconsistent distribution currents of the two branches.
According to the configuration of this Busbar
The Busbar in the entire battery pack may look like this.
The parallel battery system of this module puts higher requirements on the consistency of the battery.
Remarks: The series battery generally emphasizes the consistency of capacity. Since there is only one large loop, the total current is only one, and the similar nuclear power states are maintained between the batteries.
Parallel battery system
Since the battery system must work on the entire discharge or charging SOC curve, if the internal resistance of the battery is very different, a large module circulation will occur during the entire discharge process, and this current and the entire loop current are different. CMU cannot consistently match voltage and current
In the later stage of life, the dispersion of the entire battery module is further amplified. The initial resistance of the module is smaller, the more current is distributed, and the SOC drops rapidly. The additional voltage fluctuations are formed here, resulting in two modules. There is always a current flowing back and forth
There are a lot of disturbance factors here. It is the difference of voltage, internal resistance and temperature when one module and another module are accumulated. When the external working condition load is heavy, the battery heating will additionally cause the battery temperature to rise differently. The difference between the two modules is also growing, forming a vicious circle
This CMU design also has some difficulties. The voltage of the two modules 6S is not high enough. How to take power is a problem. I will think about it and think about how it is done.
Summary: I think there seems to be a big design limitation in doing so. Although this 1500 data may be possible in laboratories, endurance cars and large-scale road tests, in terms of mass production, consider the actual consumer. Use, the difference in running load, it is difficult to guarantee that 1500 times really happen, and the final result may be discounted.
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