The Battery Management System (BMS) mainly implements three core functions:
prediction and calculation of battery charge and discharge status (SOC),
balancing management of individual batteries, and battery health status logging
and diagnosis.
With the development of electric vehicle technology and government policy
encouragement and support, electric vehicles (hybrid + pure electric) are
growing at a rate of more than 50% per year. Batteries and battery management
systems are the core components of electric vehicles, and their market demand
Also achieved corresponding rapid growth. This article will analyze the memory
requirements of battery management systems.
The battery management system (Battery Management System, or BMS) mainly
implements three core functions: prediction and calculation of battery charge
and discharge status (i.e., SOC), balancing management of individual batteries,
and battery health status logging and diagnosis. The functional block diagram is
as follows:
In the entire battery management system, the prediction and calculation of
the battery state of charge (i.e. SOC) is its most important function, because
only with accurate prediction/calculation of the battery charge/discharge state
can effective balancing management be carried out. Therefore, the SOC accuracy
requirement is that the higher the better.
In order to improve the accuracy of SOC, in addition to collecting the
voltage and current parameters of the battery, it is also necessary to provide
various parameters such as impedance, temperature, ambient temperature, charge
and discharge time, etc. The inherent parameters of the battery will be built
into a software model through mathematical modeling, while the dynamic
parameters will collect data in real time through the data acquisition card, and
transmit the data to the MCU unit for storage in real time, and then the MCU
will perform algorithm calculations on the extracted data, thereby Get an
accurate battery state of charge.
Therefore, the SOC function will store the models of different batteries
into the memory. The memory must have low power consumption, fast reading and
writing, a simple interface, and a data retention time of 20 years; the SOC
function requires the acquisition card to continuously store the collected data
in real time. The battery voltage/current data is stored in the memory. If an
MCU unit is connected to the collection data of 10 single batteries, the
collection data card will generally use the 1MB isoSPI bus for communication.
That is, for the memory of the MCU unit, the interface speed requirement is high
and almost A data write operation must be performed every second; and the
battery life requirement is at least 10 years. If a car runs for 8 hours, then
the number of data write operations in the MCU unit's memory during the battery
pack life cycle is 105 million times.
In summary, it can be seen from the above analysis that the SOC function in
BMS is very critical, so its performance and reliability for memory are also
very high: it must be non-volatile memory, the number of erases and writes must
be at least more than 110 million times, and the interface rate must be greater
than 8MHz , with low power consumption and the ability to reliably store data
for 20 years, it needs to comply with AECQ-100. In the future, it needs to pass
functional safety certification and have at least the ASILB level.
The current mainstream non-volatile memories include EEPROM, Flash and
F-RAM. The EEPROM interface has an SPI interface, and the rate can reach 10Mhz,
but each write has a 5ms write waiting time, the number of erases and writes is
1 million times, the power consumption is medium, and there are automotive-grade
devices, but there is no functional safety at present. Certification and data
retention capabilities can also be achieved for 20 years.
The read and write speed of Flash is slow. Each write operation must be
erased, so it takes at least a few hundred milliseconds to complete a write
operation. The number of erases and writes can only be supported 100,000 times,
which is far less than 110 million times. According to the requirements, the
data retention capacity is between 10 and 20 years.
F-RAM uses a special ferroelectric material as a storage medium. It has
high reliability, data retention time of 100 years, completely random and high
read and write efficiency without waiting for writing. The SPI interface rate
can support up to 50Mhz or 108MHz QSPI. , and has very low power consumption;
due to its special ferroelectric material, this type of memory can be erased and
written up to 10 billion times.
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