FeRAM application in BMS
As the development of electric vehicle technology and the government’s policy encouraging and supporting, electric vehicles (hybrid + pure electric) are rising greatly by more than 50% per year. As the key components of electric vehicles, batteries and battery management systems have great market demand. Also have a relative rapid growing. This article will analyze the memory requirements of the battery management system.
The battery management system (Battery Management System, or BMS) mainly implements three key functions: prediction and calculation of battery charge and discharge status (ie SOC), balance management of single batteries, and battery health status log recording and diagnosis.
In the entire battery management system, the prediction and calculation of the battery state of charge (ie SOC) is its most important function, because only with accurate prediction/calculation of the battery charge/discharge state, can effective balance management be carried out. Therefore, the higher the SOC accuracy requirement, the better.
In order to improve the accuracy of SOC, in addition to collecting the voltage and current parameters of the battery, various parameters such as impedance, temperature, ambient temperature, charging and discharging time, etc. must also be supplied. 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 the 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, thereby Get an accurate battery state of charge.
Therefore, the SOC function will store the models of different batteries into the memory, which must have the requirements of low power consumption, fast reading and writing, simple interface, and data retention time of 20 years; 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 data collection card will generally use the 1MB isoSPI bus for communication, that is, the memory of the MCU unit requires a high interface rate and almost A data write operation must be performed every second; and the life of the battery is required to be at least 10 years. If the running time of a car is 8 hours, the number of data write operations in the memory of the MCU unit within the life cycle of the battery pack is 105 million times.
From the above analysis, it can be known that the SOC function in the BMS is very important, so its performance and reliability for the memory are also very high. It must be a non-volatile memory, the number of erases and writes must exceed at least 110 million times, the interface rate is greater than 8MHz, low Power consumption and data can be reliably stored for 20 years. It must comply with AECQ-100. In the future, it must pass functional safety certification and have at least an ASILB level.
The current mainstream non-volatile memories include EEPROM, Flash and Fe-RAM. The interface of EEPROM has SPI interface, the rate can reach 10Mhz, but there is a 5ms write waiting time for each write, the number of erasing and writing is 1 million times, the power consumption is medium, there are automotive-grade devices, but there is no functional safety at present Certification and data retention can also be achieved for 20 years.
The read and write speed of Flash is relatively slow, and each write operation must be erased, so it takes at least several hundred milliseconds to complete a write operation, and the number of erases and writes can only support 100,000 times, which is far lower than 110 million times. Requirements, the data retention capability is between 10 and 20 years.
Ferroelectric RAM (FeRAM, F-RAM or FRAM) is a random-access memory similar in construction to DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile random-access memory technologies that offer the same functionality as flash memory. An FeRAM chip contains a thin film of ferroelectric material, often lead zirconate titanate, commonly referred to as PZT. The atoms in the PZT layer change polarity in an electric field, thereby producing a power-efficient binary switch. However, the most important aspect of the PZT is that it is not affected by power disruption or magnetic interference, making FeRAM a reliable nonvolatile memory.
FeRAM’s advantages over Flash include: lower power usage, faster write performance and a much greater maximum read/write endurance (about 1010 to 1015 cycles). FeRAMs have data retention times of more than 10 years at +85 °C (up to many decades at lower temperatures). Marked disadvantages of FeRAM are much lower storage densities than flash devices, storage capacity limitations and higher cost. Like DRAM, FeRAM’s read process is destructive, necessitating a write-after-read architecture.
As a unique non-volatile memory, Fe-RAM is currently the best memory choice for high-reliability BMS systems in terms of writing speed, durability, power consumption and reliability .(FeRAM application in BMS. )
As the world’s leading Fe-RAM leading supplier, Fujitsu Semiconductor supplies a full complete range of ferroelectric random access memory Fe-RAM products, with a capacity from 4Kb to 12Mb and an I2C/SPI interface with almost Unlimited read and write times (10 billion read and write cycles). QSPI interface rate up to 108Mhz, no write waiting time, working current as low as 0.6mA, it is an automotive-grade chip solution that can endure high temperatures of 125 ℃ degrees, and meets ASIL- b.