Due to its high durability, fast writing, low power consumption, instant storage and simple design, ferroelectric memory is widely used in automotive event data recorder (EDR) and ECU design to complete data acquisition and diagnostic information. At the time of hybrid and electric vehicles, Ramtron also used ferroelectrics in battery management systems. For hybrid technology, battery management records have become necessary. Therefore, memory plays a role in hybrid/electric vehicles. Extremely important role.
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The following is an interview with EEWORLD, Rammon Global Marketing Director Xu Mengyu, through the memory solution, to explain the positive role of semiconductor companies in hybrid and electric vehicles.
EEWORLD: How should we understand the application of memory in hybrid technology? What is the significance of the memory technology revolution for the promotion of hybrid (electric) technology? After all, in automotive electronics, memory is not a decisive factor but at the same time a necessary condition.
Xu Mengyu: F-RAM is used in the Battery Management System (BMS) of electric vehicles to store battery model lookup tables (LUTs) for predicting and calculating battery state of charge (SOC), as well as for health status (SOH) logs and diagnostics. EHV's battery life requirements are at least 8 years.
In terms of write speed, durability, low power consumption, and reliability, no other non-volatile memory can better meet the storage requirements of the BMS than the F-RAM.
The SOC is calculated primarily by the integration of current versus time and is corrected based on various factors affecting battery performance, and then subtracted from the known fully charged battery capacity is the remaining charge.
Measurements of voltage or current can only provide a rough estimate of the battery's SOC, and other factors must be considered for more accurate results. At this time, it is usually to establish a software model that reflects the characteristics of the battery, and develop a corresponding algorithm to introduce the correction factor into the measurement result, and finally get a more accurate SOC. Thus, the characteristics of the battery model are embodied by software algorithms and respond to different external and internal conditions. This method requires sensors to provide measurement data, F-RAM to store model data, and a microprocessor to calculate the relevant results.
The battery is non-linear. The voltage characteristics are a function of the discharge rate, temperature, and age of the battery. Each cell model can be constructed from a set of "look up tables" that give stepwise approximations of the performance response curve that represent how the battery discharge performance is a function of temperature, discharge rate, or other parameters. This required lookup table was developed based on laboratory measurements under controlled conditions and differs by the chemistry and structure of each cell.
In order to obtain an accurate description of the battery's charge/discharge characteristics, a similar look-up table containing all known factors that significantly affect battery capacity (Ah) and impedance must be developed, including battery temperature, ambient temperature, charge and discharge speed, and heat dissipation. Speed, battery self-discharge speed or coulomb efficiency, and battery capacity decay with battery life.
Then, based on this set of related lookup tables, a mathematical model or algorithm describing the behavior of the battery in response to all relevant parameters can be built and then integrated into the memory of the microprocessor module and used to predict battery performance.
Sensors in the battery provide analog inputs to the model that characterize temperature, cell voltage and current, and accurate analog-to-digital converters convert these inputs into digital form. Additional information about the ambient temperature and various alarm conditions can also be provided to the model if needed. These inputs can be continuously monitored and updated under the microprocessor request to control the model.
At any time, the model can use these inputs to estimate the state of the battery.
The BMS can also provide an input for estimating the SOH of the battery, but since SOH only gradually changes with battery life, it does not require too frequent sampling. The sampling interval depends on the SOH determination method used, which may be as low as once a day. For example, impedance measurements may only be made when the car is not in use. When the car is running, only the number of cycles is counted.
SOH can help determine if there is abuse. The number of charge and discharge cycles, maximum and minimum voltages and temperatures, and maximum charge and discharge currents can be recorded for subsequent estimation. This is a very important tool when evaluating warranty claims.
EEWORLD: What is the difference between the memory required for hybrid or electric vehicles compared to traditional automotive electronics? Why are there differences? How Ramtron meets these special needs.
Xu Mengwei: Ramtron is actively developing safety functions in memory for the certification and identification of anti-theft and anti-counterfeit batteries. We also plan to integrate more intelligence into our products to expand our market share in such applications.
EEWORLD: Can you tell us about the technologies or products that Ramtron applications currently use in hybrid or electric vehicles?
Xu Mengwei: Ramtron offers a range of products that have passed AEC-Q100 Grade 1 certification, so our F-RAM products can be used in many key system applications under the hood, such as battery management system systems in hybrid/electric vehicles, etc. .
Ramtron also supports the Production Part Approval Process (PPAP). PPAP is a control program used by the automotive industry to ensure that all components used in the automotive supply chain have detailed documentation.
EEWORLD: I believe that you also see in the Chinese market that the development momentum of hybrid power is very strong. What do you think are the advantages and disadvantages of China's automotive electronics, especially hybrid systems? Can you give some advice to Chinese automotive electronics manufacturers from the perspective of a storage company?
Xu Mengyu: At present, hybrid vehicles are not particularly popular in China for several reasons. The price of conventional cars is already very expensive. If electric motors, batteries and many other necessary accessories are added, the price will naturally be higher. Moreover, although the price of gasoline is already high, it is still enough to push the market to turn to a more fuel-efficient hybrid car. However, in China, with the imminent introduction of fuel taxes and the public's great concern for air quality, this situation will change very quickly. In addition, China is also considering implementing subsidies and tax cuts for hybrid vehicles.
China is one of the countries that lead the development of battery technology. Companies such as Lishen and BYD are able to use their technology to get involved in the electric vehicle sector, and the Chinese government has made electric vehicles a strategic option. In addition, China's lithium-ion battery production is the highest in the world, and this high-energy density technology is the key to new electric vehicles.
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