Dedicated IC method or will become a battery management system innovation stumbling block

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

Borrowing a term in the economy, electric car BMS products are currently in the state of "lack". Although the product function is constantly improving, the market application is expanding, but the key technical level of the product is still stagnant, the original pain point still exists. One of the important reasons for this situation is our product design method, which is the battery management special IC supplied by foreign semiconductor IC manufacturers, and design with its application.

BMS products can be divided into two relatively independent parts of software algorithm and hardware architecture because software algorithms are more professional and associated with hardware parts. This article only conducts part of the connection between hardware architecture and product function. Analysis discussion.

First start from battery management dedicated chip. The emergence and development of battery management dedicated IC is closely related to various problems encountered in the process of lithium ion battery. First, in order to solve the overcharge of the lithium-ion battery, the charge and discharge protection chip of the single battery was designed.

Later, it was developed in a multi-segment of the lithium-ion battery to develop a multi-string chip. At this time, it became Battery management chip, it is important to collect each battery voltage data in the battery pack. Further, in order to cope with the problem of inconsistencies, the driving function of the power switch is further integrated, which is a battery management IC with equalization.

Objective speaking, battery management dedicated IC has achieved early BMS industry and led the development of BMS products. It is because there is a special chip, BMS design can be greatly simplified, and the miniaturization and reliability of the product have greatly improved, but at the same time, we must also see the limitations of special chips. As mentioned earlier, the battery management dedicated chip is also developed with the application of lithium ion batteries, and early lithium-ion batteries are used in small electronic equipment, and later they are widely used in laptops, and the battery management dedicated chip has always been Low strings, small equipment services.

When the lithium-ion battery pack is applied to electric cars, the situation has changed. Electric vehicle lithium ion battery pack is a high string, large-capacity battery is used in series, and the number of tens of strings or even hundreds of strings are no longer a laptop, and the series of serialized lines can be used in series. The dedicated IC has not been idle, and the product of more strings applications is quickly launched, but considering the voltage and application complexity generally no more than 20 strings.

Typical architecture of BMS using these ICs is a centralized architecture. There is only one connection between the BMS and the battery pack, depending on the number of battery packs, the number of specific chips on the BMS board is also depends on the number of battery packs. As can be seen from the schematic, the advantages of centralized BMS products are simple and low cost.

When the number of strings in the battery pack, for example, 10 are string, the connection is not quite complicated, and in the case where the battery pack capacity is small, the BMS mounting position can be close to the entire battery pack, shorten the wiring distance, battery pack - --- BMS, the entire energy system is more compact, more suitable on electric bicycles and electric motorcycles. However, when applied on the lithium ion battery pack of the electric vehicle, because the battery capacity is large, the physical dimension is relatively large after the group, the connection will be longer, and the length is not very, plus the number of strings, there are many , Dozens of or even the arrangement of hundreds of lines is very troublesome. Another important detail is that the order of these connectors is to be fixed, because the pin of the special chip has already implicitted the sequence of the battery in advance, so the connection on each string should be accessed to the Pin foot bit specified by the BMS.

Although there is no difficulty in the BMS design work, it is a small trouble in the actual connection between BMS and battery packs. General lines are connected to the battery together, and the other end is connected to the BMS through the plugin, and the work is connected to the battery. It is also difficult to complete, and it is difficult to complete by the machine, connected to each electrode of each cell.

Can't make any mistakes, this whole workload is ideally. Through the analysis of the centralized architecture, we see that the dedicated IC is suitable for small capacity, low strings, and there will be connected lines in large capacity and high strings. Look at a balanced problem, the centralized architecture is more suitable for the completion of passive balance, and the circuit design does not have new complexity, and the current mainstream dedicated IC has this function.

However, the current capacity is limited, the level of the half-hour, and the problem is not large if the initial consistency of the battery pack is not large, and there will be a risk of unbalance correction in the middle and later consistency. If you want to join an active balance function, the existing architecture basically does not help, and additional harness and switch matrix, the complexity of the circuit has risen sharply. The switch matrix should have a large number of electronic switches, but because of the number, the control circuit is quite complicated, and the company is replaced by the relay, simplifies the design, but bringing the relay as a mechanical switch to life problems and misunderstand risk.

Of course, it is also possible to extend its life by lowering the switching frequency of the relay, avoiding risks through malfunction inspection, but this is always unable to ensure the average failure of the device, and more, the number of relays is also quite, more than one. This is a compromise method that is not allowed, rather than solving the positive solution of the active balanced switch matrix. In order to solve the complex challenge of the connection, BMS of the distributed architecture appears.

This BMS is separated from other functions to other functions, and the entire system is divided into CSC (single management unit), BMU (battery management controller), and CSC is installed on a single battery, responsible for this string battery information collection And transfer, each string of battery is incorporated into BMU through the bus. This architecture solves the complicated challenge of harness through the bus, and is relatively simple installation, high efficiency, good flexibility, suitable for different battery packages. Distributed BMS can not use battery management dedicated IC, which is a relatively successful idea for the purpose of innovation design.

Insufficient, the distributed architecture has not solved the corresponding relationship and active balanced challenge. The CSC also sets the address (although it can be set after installation, it is necessary to make it easier to implement before installation, error probability Small), active balance still requires additional harness and switch matrix. Moreover, because each CSC is to be MCU and the isolated communication bus, the price is higher than the centralized architecture BMS, especially in low strings.

Distributed ideas gave a well tip of centralized style, which is through the bus to solve the harbor problem, and the dedicated IC has also seen the benefits, and quickly launched a communication bus with no isolation, further improved themselves. Semi-distributed architecture, actually the secondary centralized architecture has become one of the mainstream design of BMS. This is to divide the entire battery component into several modules.

Each module uses a small BMS designed with a dedicated chip, and then connects to a final controller through the bus. The semi-distributed architecture focuses on the advantages of the distributed harness and the advantages of a centralized design, but unfortunately, the problem that the previous architecture has not been solved and followed, the one-one correspondence and the active balanced problem exist. Chasing the source, one-to-one correspondence, the problem of switch matrix in the active balance, from the conventional limitations of the battery management special chip, although the battery management special chip is also evolving.

Because it is a multi-brace application, on the dedicated IC, each battery detection channel must be determined in advance, and afterwards, the order of each channel cannot be imagined, and now see any ICs can not design such a function. Similarly, the switch matrix is ​​also from multi-string applications, but also because of the power part, this is the natural and weakness of IC, and the existing architecture is the reason for the active balance. Therefore, if it is a low string, there is no need to actively balanced the function, which is feasible, such as electric tools, electric bicycles and electric motorcycles; in the use of electric vehicle levels, especially the active balance function, Design BMS in a dedicated IC is still more.

From the production of 2015, the electric car has successfully completed the introduction period of the industry, followed by the development period. BMS urgently needs to solve the disease, the market calls new products, only jump out of the special IC method, BMS innovation party can look forward to. .

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