Reveal the brain battery BMS battery management system

As we all known, pure electric vehicle power is output by battery. The battery management system (BMS) is one of the cores, and is responsible for the control of the battery charging and discharging, battery state estimation and other functions. If compare an electric vehicles with human body, the battery system is the heart, and BMS battery management system is the brain that control the body.

Why do you want to have a BMS?

Now that is called a battery management system, BMS's main job is to handle and on-board battery related tasks. Despite the battery manufacturing technology has made various differentiation between the batteries, but single section lithium battery still exist between the internal resistance, capacity, voltage and other differences, so in practice, the battery pack inside each monomer battery is easy to appear the phenomenon such as uneven heat or excessive charge and discharge. Over time, these poor working conditions of the battery is likely to damage in advance, the whole life of the battery pack is greatly reduced.

Not only that, the battery under severe charging status also has the danger of explosion, causing damage to the battery pack is also a threat to the user's life safety. Therefore, must be for electric cars Power battery set equipped with a set of targeted battery management system (Battery Management System, BMS), to the battery pack for effective monitoring, protection, and energy balance and fault alarm, and improve the work efficiency and service life of power battery.

What is the main purpose of BMS?

There were hundreds of pieces of batteries in an electric car, BMS is how to manage? If we met, the battery pack the profile of internal has hundreds of pieces of batteries, we will see how to manage the intensity of the batteries system? BMS system's main work is divided into two big tasks - for detection of the battery and ensure the safety of the battery.

Some battery test implementation is relatively simple, mainly through sensors to collect the battery in the use of the parameters in the process of information such as: temperature, voltage and current of each battery monomer, battery voltage, current, etc. These data later in the battery management plays a vital role, may say that if it were not for the battery status data as support, battery management system is impossible.

If we consider testing process of battery, the battery "check-up", then the "physical" is online, continuous, uninterrupted. Process when found abnormal data, corresponding battery can timely query condition, and sort out the defective battery, so as to keep the battery for the whole operation of the reliability and efficiency. When the battery "check-up" is done, will enter the phase analysis, diagnosis, calculation, then generate "medical report", this process can be understood as state evaluation of the battery.

What is SOC?

If you drive electric vehicle, then will see SOC logo on the dashboard, what is the meaning of this? Namely Stateof Charge, SOC is charged state of the battery pack, we are more used to call it the battery remaining power. SOC is judge the battery charge and discharge and a series of failures, the basis of accurate estimate SOC, can prevent the battery charge and discharge, prolong the service life of the battery, so as to improve the utilization of the battery.

In fact, in addition to the SOC estimation and SOH (State of Health), SOP (State of Power), the user can through the car instrument, according to see these data, thus confirming work, functional state of the battery. Accordingly, on the basis of the protection battery, the potential maximum, greatly improving driving experience.

For life, it is very important to the accuracy of SOC

SOC algorithm has been the battery management system (BMS) one of the key technologies in the development and application, it is accurate or not directly affects the calculation, table show the difference of life and real life, if not enough accurate calculations, even lead to the battery run out car broke down.

Estimates about the state of the battery, the need to pass a series of complicated calculations. Accurate estimates that the battery remaining power, ensure the SOC to maintain in a reasonable scope, prevent the charge or discharge the battery damage, at any time to forecast a hybrid car energy storage battery. How much is remaining energy or energy storage battery charged condition. The SOC estimation precision is high, for the same amount of cells, can have a higher range. So, the high accuracy of SOC estimation need battery costs can be reduced effectively.

Nowadays, domestic battery manufacturers have mastered the core algorithm of precise, through the estimation method based on battery parameters, effectively eliminate the influence of the cumulative error, estimation is more accurate. Sliding estimation (sliding is the abbreviation of lithium battery cathode material, the nickel cobalt manganese ternary material) accuracy in 3%, LFP (another lithium ion batteries anode material, called lithium iron phosphate) is about 5%.In terms of data, domestic battery enterprise technical standards have reached the international leading level.

The patron saint of the battery and personnel safety

BMS has another big core functions, is to provide security for the battery and personnel.

Battery overcharge, discharge have been known to bring local overheating, affect battery life, seriously threatens the safety of the battery pack, causing personal safety hidden trouble. At this time, the charging and discharging management module of BMS will open the protection function, on the one hand and the whole car, charging machine to realize communication, real-time to provide battery status on the other hand, facilitate timely issued a command control, effectively prevent the occurrence of high charge, low discharge.

In protecting the battery module, equilibrium is also an important part of the necessary means is to protect and enhance battery life. In addition, the protection of the battery also includes overvoltage, undervoltage, over temperature, over current protection, etc. In simple terms, when the actual parameters above or below a prescribed value, the system will automatically make judgments, and take off, prefilled way to protect the security of the battery.

In terms of personal safety, BMS by high pressure control means to protect. Battery voltage is 300-500 - v, far above the human safety voltage 36 v, risk is great, high pressure control must be done well, the most common is the relay, high pressure interlock, insulation protection. Comprehensive high pressure protection control, which can effectively protect drivers, passengers and the personal safety of maintenance personnel.

How to understand the security level of the battery

Many domestic battery enterprise USES is the international general ISO26262 evaluation standard. And ISO26262 standard according to the degree of security risks, divided by A to D level of security requirements (Automotive safety integrity level, ASIL), where D level as the highest level, to the most stringent security requirements. The higher the grade, the higher requirements for the safety of the system, in order to achieve the security price is higher, the means of hardware diagnostic coverage rate is higher, more rigorous development process, the corresponding development costs increase, the development cycle, more rigorous technical requirements.

ASILD level, the failure rate of 10 ^ - 8 / h, assume that means 1 car run 4 hours a day, need to run 7 years appear once the functional failure caused by BMS. And such a low probability of failure rate, comparable with the runtime requirements. Generally speaking, the car industry demand for parts is B or C grade.

Many of the current domestic battery industry is already abroad, for more international brands to provide products and technical support. This shows that domestic battery with BMS technology isn't behind Japan and Europe and the United States, even in some areas has reached the international advanced level.

The page contains the contents of the machine translation.