“With the development of electric vehicle technology, as well as government policy encouragement and support, electric vehicles (hybrid + pure electric) are growing at a rapid rate of more than 50% every year. As the core components of electric vehicles, the market demand for batteries and battery management systems Also achieved corresponding rapid growth. This article will analyze the battery management system’s demand for memory.
With the development of electric vehicle technology, as well as government policy encouragement and support, electric vehicles (hybrid + pure electric) are growing at a rapid rate of more than 50% every year. As the core components of electric vehicles, the market demand for batteries and battery management systems Also achieved corresponding rapid growth. This article will analyze the battery management system’s demand for memory.
The Battery Management System (BMS) mainly implements three core functions: prediction and calculation of battery charge and discharge status (ie SOC), balance management of single cells, and battery health status log recording 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 (that is, SOC) is its most important function, because the accurate prediction/calculation of the battery charge/discharge state can be effectively balanced and managed. Therefore, the higher the SOC accuracy requirement, the better.
In order to improve the accuracy of the 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, and charging and discharging time. The inherent parameters of the battery will establish a software model through mathematical modeling, while the dynamic parameters will collect data in real time through a data acquisition card, and transmit the data to the MCU unit for storage in real time, and then the MCU will perform algorithmic calculations on the extracted data. Get accurate battery state of charge.
Therefore, the SOC function will store the models of different batteries in the memory. The memory needs to have low power consumption, fast read and write, simple interface, and data retention time of 20 years; the SOC function requires the acquisition card to continuously collect the 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 rate is high and almost A data write operation is performed every second; and the battery life requirement is at least 10 years. If a vehicle runs for 8 hours, then the data write operation of the MCU unit’s memory is written in the battery pack life cycle. 150 million times.
Based on the above analysis, the SOC function in the BMS is very critical, so its performance and reliability of the memory are also very high: it must be a non-volatile memory, the number of erasing and writing must be at least 110 million, and the interface rate is greater than 8MHz, which is low. Power consumption and data can be reliably stored for 20 years. It needs to comply with AECQ-100. In the future, it needs to pass functional safety certification and at least have an ASILB level.
The current mainstream non-volatile memories include EEPROM, Flash and F-RAM. The EEPROM interface has an SPI interface, the rate can be 10Mhz, but each write has a 5ms write wait time, the number of erasing and writing is 1 million times, the power consumption is medium, there are automotive-grade devices, but the functional safety is not currently implemented Certification and data retention capabilities can also be achieved for 20 years.
Flash’s read and write speed is slow, and every write operation must be erased. Therefore, it takes at least a few hundred milliseconds to complete a write operation. The number of erases and writes can only support 100,000 times, which is far less than 110 million times. It is required that the data retention capacity is between 10 and 20 years.
F-RAM uses a special ferroelectric material as the 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 has very low power consumption; due to its special ferroelectric material, the number of erasing and writing of this type of memory can be as high as 10 billion. As shown below:
As shown in the figure above, as a unique non-volatile memory, F-RAM is currently the best memory choice for high-reliability BMS systems in terms of writing speed, durability, power consumption and reliability. .
As the world’s leading F-RAM core supplier, Cypress semiconductor Inc. provides a very complete range of ferroelectric random access memory F-RAM products, with capacities ranging from 4Kb to 8Mb, and the interface is I2C/SPI. With almost unlimited number of reads and writes (10 billion read and write cycles), QSPI interface rate is as high as 108Mhz, no write waiting time, working current is as low as 0.6mA, it is an automotive-grade chip solution that can withstand high temperatures of 125 degrees, and Comply with ASIL-B.