Battery management system functions

Accurately estimate the State of Charge (SOC) of the power lifepo4 battery pack, that is, the remaining battery capacity, to ensure that the SOC is maintained within a reasonable range, and to guard against damage to the battery due to overcharging or discharging, so as to predict the remaining energy or state of charge of the hybrid vehicle energy storage battery at any time.

Dynamic monitoring of the working status of the power lithium-ion battery pack: During the battery charging and discharging process, collect the terminal voltage and temperature, charging and discharging current, and total voltage of each battery in the electric vehicle battery pack in real-time to prevent overcharging or discharging of the battery. At the same time, it can provide timely information on battery conditions, select problematic batteries, maintain the reliability and efficiency of the entire battery operation, and make the implementation of the remaining power estimation model possible. In addition, it is necessary to establish a usage history file for each battery, in order to further optimize and develop new types of electricity, chargers, motors, and other supply materials, and to provide a basis for offline decomposition of system faults.

Balancing between individual batteries and battery compartments:

Balancing is carried out between individual batteries and battery packs to ensure that all batteries in the battery pack are in a balanced and consistent state. Battery balancing is generally divided into active balancing and passive balancing. Currently, most of the bMS that have been put into the market adopt passive equilibrium. Balancing technology is a key technology in battery energy management systems that the world is currently committed to researching and developing.

Current Development Status of Battery Management Systems

In the future, electric vehicles will use lithium-ion batteries as a crucial power source, mainly due to their high energy density and stable performance. However, the quality of lithium-ion batteries is not easy to grasp when they are processed in large quantities. There are slight differences in battery capacity when the battery cells leave the factory, and with factors such as operating environment and aging, the inconsistency between batteries will become more apparent. Battery efficiency and lifespan will also deteriorate. In addition, overcharging or discharging may lead to safety issues such as fire and combustion in severe cases. Therefore, through the Battery Management System (bMS), it is possible to accurately measure the usage status of the battery pack, protect the battery from overcharging and discharging, balance the power of each battery in the battery pack, and decompose and calculate the power of the battery pack into understandable driving range information, ensuring the safe operation of the power lithium-ion battery.

In 2012, the global battery management system (BMS) market grew by over 10%, and from 2013 to 2015, the growth rate will significantly increase to 25-35%. At present, both vehicle manufacturers, battery manufacturers, and related automotive component manufacturers are investing in the research and development of battery management systems (BMS) in order to master key technologies in the electric vehicle industry. As car manufacturers are users of battery management systems, they often prefer to use their own software to solve problems and use specialized factory regulations to maintain operational flexibility. The development of the Battery Management System (BMS) industry may be similar to that of lithium-ion batteries. In order to master key technologies, car manufacturers will closely cooperate with long-term cooperative suppliers in product development, making it difficult for new manufacturers to enter. Therefore, in the future, if new manufacturers want to enter the supply chain of car factories, in addition to strengthening cooperation with relevant supply chains, they will have the opportunity to seize the opportunity by creating customized methods tailored to their needs.

Tesla's Battery System

The battery system is the power source of electric vehicles and the most core system component in the entire industry chain. Taking Tesla ModelS as an example, its battery system (lithium-ion battery+battery management system) accounts for 56% of the cost, while traditional sedan engines account for only about 15% -25%. By 2016, the cost share of battery systems had decreased, and the cost structure had also changed. The cost of individual batteries accounted for 83%, the cost share of battery management systems was about 13%, and the remaining 4% was for battery cooling systems. By conducting a detailed review of the composition of Tesla's battery system and its supporting charging facilities, we can gain an intuitive and in-depth understanding of Tesla's battery industry chain. Other new energy vehicles can also serve similar purposes. At present, the cost of battery systems is one of the most crucial factors restricting the development of Tesla and other new energy vehicles. Understanding battery systems is equivalent to having the key to understanding the new energy vehicle industry.

By conducting a detailed review of the composition of Tesla's battery system and its supporting charging facilities, we can gain an intuitive and in-depth understanding of Tesla's battery industry chain. Other new energy vehicles can also serve similar purposes. At present, the cost of battery systems is one of the most crucial factors restricting the development of Tesla and other new energy vehicles. Understanding battery systems is equivalent to having the key to understanding the new energy vehicle industry.

In order for electric vehicles to be practical, they must consider their range after a single charge and the convenience of charging. To understand these two points, one must pay attention to the battery structure, charging speed of charging equipment, and device distribution. ModelS has previously launched models with battery power of 40, 60, 70, 75, 85, 90, and 100kWh. For models with 85kWh and above, there are also performance versions that offer better power performance to choose from, such as the perf version and the Ludichous version. The maximum distance and maximum horsepower that can be driven each time the battery overflows vary depending on the model. With the advancement of technology and in order to better meet people's needs, Tesla has gradually cancelled some Model S battery models, and the power models that can still be ordered today are 75, 90, and 100kWh.

Model X has launched models of 60, 70, 75, 90, and 100kWh, and currently only models of 70 and 100kWh can be ordered. According to information from Zhongguancun Online, the battery pack power of the basic version of Tesla designed Model 3 electric vehicle is approximately 60kWh. According to Musk's Twitter and related information, Genleifeng has speculated that the highest possible version is only 75kWh. This is crucial because the Model 3 has a smaller wheelbase compared to the Model S and Model X, and the positioning of the Model 3 is also an entry-level model. According to ElonMusk's Twitter message on July 9th, the first Model 3 was taken offline on the same day, and Tesla will hold a delivery ceremony for the first 30 consumers who ordered Model 3 on July 28th. In addition, Model3 uses batteries differently from ModelS and ModelX. At a media briefing held by Tesla Motors Japan on July 15, 2015, Kurt Kelty, the battery technology director of the US headquarters, announced that the Model 3 will use the new 21700 lithium-ion battery, which will have an energy density 30% higher than the 18650 lithium-ion battery used for the Model S and Model X.

Construction of Tesla batteries and battery panels

Unlike other electric vehicles, the batteries used by Tesla are not specialized large batteries, but rather are packaged with thousands of cylindrical small batteries. Both ModelS and ModelX currently use 18650NCA special batteries supplied by Panasonic, which have a cross-sectional diameter of 18 millimeters and a height of 65 millimeters. The conventional 18650 lithium-ion battery is widely used in the battery cells of laptops, and its chemical formula is LiNiCoAlO2.

The advantage of using a single battery is that a single 18650 battery has limited explosive power. Even if a parallel battery cell fails, it can shorten the driving distance provided by at most one battery cell. Moreover, this battery has mature technology and is suitable for large-scale processing. At the same time, the battery has good consistency and low cost.

Due to the excellent thermal management system of Tesla electric vehicles, Panasonic's specially designed 18650 battery for Tesla has been able to remove some unnecessary safety facilities compared to conventional models, making it lighter and cheaper. At the same time, Tesla has installed fuses on each battery cell instead of the usual safety device installed throughout the entire battery pack.

Due to the use of small single cell batteries in the power system, Tesla's battery system structure appears exceptionally complex and exquisite. Taking the ModelS85kWh model as an example, the battery panel is divided into 16 battery packs. As shown in the figure below, each rectangular block is a battery pack, with two groups stacked on the far right.

The battery packs are connected in series with a total voltage of 402 volts. Each battery pack of Tesla is composed of 6 individual battery packs connected in series, with each battery pack consisting of 74 18650 batteries connected in parallel. In order to facilitate the placement of the heat dissipation pipeline inside the battery pack, the individual battery pack is arranged irregularly.

Therefore, the Model S 85kWh model uses up to 7104 batteries, and calculated based on a working voltage of 3.6V and a capacitance of 3.2Ah, the total battery capacity is approximately 82kWh, slightly lower than the battery capacity specified by the model. The weight of these 7000+battery packs is nearly 700 kilograms, accounting for nearly half of the weight of the entire vehicle. Similarly, the 100kWh model battery panel uses a total of 8256 individual batteries, which are also divided into 16 battery packs.

In order to protect the battery pack, Tesla has designed a waterproof and breathable valve on the top surface of the front of the battery pack, which utilizes the order of magnitude difference in volume between gas molecules, liquid, and dust particles to allow gas molecules to pass through, while liquid and dust cannot pass through, achieving the goal of waterproof and breathable, and preventing water vapor from condensing inside the battery pack.

The placement of the ModelS battery panel precisely makes it the base plate between the axles, which brings many benefits. Due to the fact that the battery panel is the largest part of the vehicle's weight (the ModelS85kWh battery pack weighs 544 kilograms), the center of gravity of the Model S is only 18 inches high, resulting in a large lateral acceleration (0.9g) and good anti roll performance.

At the same time, in order to protect the battery panel located at the bottom, Tesla has added a protective structure composed of aluminum alloy (or steel, fiberglass, carbon fiber, plastic, etc.) material at the bottom of the battery panel. Currently, ModelS uses aluminum alloy material to wrap the battery module and maintain a certain buffer distance, and named it BallisTicShield.

Truss battery cooling system

In addition to the battery pack, the most common part inside the battery panel is the "coolant" pipeline. Each Tesla has a special liquid circulation temperature management system around each single battery.

The "coolant" appears green and is composed of a mixture of 50% water and 50% ethylene glycol. The 'coolant' continuously flows in the pipeline and eventually dissipates through the heat exchanger at the head of the vehicle, thereby maintaining a balanced battery temperature and guarding against local overheating that may lead to a decrease in battery performance. Tesla's battery thermal management system can control the temperature between battery packs to ± 2 ℃, and controlling the temperature of the battery panels can effectively extend the battery's service life.

Truss supporting charging facilities

Tesla's charging methods are divided into three types: home charging, destination charging, and super charging stations.

Home charging is Tesla's most critical charging method. Tesla cars can be charged directly through a 220V10A/16A household socket. Most households in China use 220V40A meters for electricity, but sockets are usually 10A or 16A. By using the charging cable and corresponding plug connection provided with TESLA and selecting a charging current of 10A or 16A, charging can be done without the need for a separate meter or any equipment modification. However, the charging speed is slow, and the battery life is only about 8 kilometers per hour.

Due to the fact that most residential areas in China use 220V single-phase power supply, the maximum current can reach 40A. By installing the household charging stations included with each ModelS and ModelX in their own parking space, they can be charged with a 40A charging current. In this way, the charging speed can be much faster than the charging current of 16A supplied by most domestic electric vehicles.

In addition, you can also choose to install a Tesla specific charging wall (HighpowerWallConnector). Apply for a separate 80A meter or increase the capacity of an existing meter, and achieve fast charging by installing a TESLA dedicated charging wall and installing a second charger (in the car, optional when purchasing). Charging can reach 17.6kWh per hour, and it can travel 80-100 kilometers. It takes 5-6 hours from no charge to full charge.

Destination charging is a charging method set up for the convenience of travel. Tesla cooperates to install targeted charging stations in some places, including restaurants, restaurants, shopping centers, and resorts, where car owners can also charge upon arrival. The charging station at the destination charging station is identical to the charging station or charging wall installed in home charging. The fee standard is also determined by the installation company. According to Tesla's official website, there are currently 654 charging stations in 30 provinces (including municipalities and autonomous regions) in China.

In addition to the above two charging methods, Tesla also has a DC fast charging method - super charging. Tesla claims that its supercharging station is currently the world's fastest charging station, with charging typically taking only a few minutes. The location of charging stations is usually located near restaurants, shopping centers, WiFi hotspots, etc., and can be charged during parking breaks. This is the first choice for long-distance travel by car.

According to Tesla's official website data, 861 supercharging stations have been established worldwide, totaling 5655 supercharging stations. According to Tesla's official Weibo account released in June, 117 super charging stations and 554 super charging stations have been built in China to date. In 2017, Tesla's global charging network will double in size; The expansion of charging networks in China will also closely follow the global expansion speed.

Some Tesla supercharging stations also use solar panels to supply some of the charged electricity, while also providing a sunshade effect. The cost of each charging station is approximately between $100000 and $175000, with most of the funds being spent on reshaping the foundation.

Previously, ElonMusk revealed on Twitter that Tesla will upgrade the Super with an output power likely exceeding 350kW, which will undoubtedly greatly accelerate charging speed and reduce charging time.

The charging gun used in the super charging station is also an extremely technologically intensive component. When Tesla is charging at the super charging station, the sensor in the charging gun will constantly test the temperature changes of the battery inside the car. Once the battery temperature is too high, the charging gun immediately sends a signal to reduce the charging intensity and lower the battery temperature; At the same time, the cooling system inside the battery panel also responds synchronously, enhancing the cooling force synchronously. The process of automatically adjusting the charging intensity involves highly collaborative work among the current of the electric gun, battery cooling system, and charging station.

In addition to Tesla, there are other brands of electric vehicles on the market that also have their own charging stations, and power companies such as State Grid and China Southern Power Grid have also built some public charging stations. Tesla officially announced the new national standard charging adapter at the Guangzhou Auto Show in November 2016. From then on, Tesla electric vehicles can not only charge in Tesla's charging network, but also use charging facilities that comply with China's new national standards for charging.

Plug one end of the adapter into a non Tesla charging station plug that meets the new national standard, and then plug the other end into the Tesla vehicle to charge. However, at present, some charging stations still need to obtain corresponding charging cards to charge, and the charging speed is also uneven.

Tesla Battery Charging Management Technology

The fast charging of Tesla electric vehicles benefits from its fast charging technology. By using variable current and three-stage charging methods, the charging current is reasonably distributed to achieve the highest charging efficiency and fast charging. The technology used for fast charging of mobile phones today is similar to this.

Regarding lithium-ion batteries, the smaller the deep discharge motor, the longer its lifespan. Conversely, frequent deep discharge (using less than 20% of the battery capacity) will lead to a decrease in battery lifespan. Tesla batteries have a unique process that doubles the total battery life in a 50% to 0% cycle mode (using no more than 50% battery charge). In deep cycle mode, after 900 cycles, the capacity decays to 50%. So from the perspective of protecting the battery life, it is possible to control each stroke within 80% of the maximum range as much as possible, and be prepared to charge after exceeding 80% of the power consumption. However, regular deep discharge can be used to activate the battery.