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Secret of the battery pack: What else is there besides the battery?
Whenever I tell people that I am designing a battery pack for an electric car, people always ask me, what is a battery pack? What is the difference between battery and battery? What is the difference between car battery and mobile phone battery?
If we compare an electric car to a team, the operation and advancement of this team requires talents with different backgrounds and different abilities. The battery pack is an indispensable person in this team, and the battery is just an organ of this person. It's his heart.
The ultimate goal of the battery pack is to provide various protection and assistance to the battery, so that the battery has a longer life and can cope with various extreme weather and environmental conditions.
Cover and Tray
The biggest difference between car batteries and mobile phone batteries is that the environment experienced by cars is very different from that of mobile phones. During operation, the car will experience various vibrations, as well as the intrusion of water, soil, and sand from the external environment. Therefore, the casing and base of the battery pack are very important.
The bases of the battery packs of electric vehicles in the world are generally made of aluminum alloy or stainless steel, and the outer shell combined with the car chassis may be made of composite materials with glass fiber.
During the test, the battery pack will undergo three-dimensional vibration and the equivalent of more than 10 years of wind and rain (dust and water spraying from different directions) to ensure that there is no intrusion of any foreign matter inside the battery pack, so that water does not leak.
It is worth noting that the battery pack is connected to other components of the car with wires, and the connection between these wires and the battery pack must be drip-proof.
Temperature Management System (Thermal Management System)
Users also expect their electric cars to perform well in all weather conditions 365 days a year. The car battery pack directly affects the acceleration and endurance of the car, which is very different from how people observe mobile phone batteries.
The temperature management system ensures that the temperature of each cell is constant throughout the year. A large number of batteries are used in extremely hot weather to ensure timely heat dissipation and prevent battery life from diminishing or expanding and exploding. Use a large number of batteries in extremely cold weather to ensure that the inside of the battery is warm enough without affecting performance and life.
The heat dissipation of the battery is the use of liquid coolant flowing through the bottom of the battery pack, and then the cooling plate with excellent thermal conductivity directly contacts the single battery. Or direct air heat dissipation, that is, use a built-in electric fan.
The battery is heated and kept warm by the heater, and the heater's power comes from the battery itself. Therefore, the range of electric vehicles in winter will be slightly reduced.
Another challenge comes from charging in extreme environments. Since the car is turned off when it is charging, the temperature management system needs to be automatically activated when it learns to charge to maintain the internal temperature of the battery pack. This means that the battery pack is still in the sleep state when the entire car is asleep. Is awake.
There are many single cells in the battery pack, either in series or in parallel. The endurance of an electric car directly depends on the single battery with the worst performance, so it is also important to maintain the voltage and remaining power in each single battery.
There is a device called VITM (voltage current temperature module) in the battery pack, which measures the voltage, current and temperature of each cell in real time, guarantees and regulates the usage of a cell through a series of resistors and transistors, and manages the temperature at the same time The system transmits instructions, adjusts the flow and temperature of the coolant, and cools and warms the battery.
Strictly speaking, power electronic devices are not part of a battery pack, but some battery pack manufacturers also classify it as a battery pack.
Power electronic devices include a charging module, an inverter used in regenerative braking, and an accessory power module (APM) that assists in the use of energy in the cabin.
The charger means that the alternating current in the grid is converted into direct current that can be directly used by the battery. However, with technological innovation, more DC charging stations have gradually appeared in the world, and the direct conversion of AC to DC is completed in the charging station, reducing the necessity of this component in the battery pack.
However, in regenerative braking, the AC power from the generator still needs to be converted into DC power that can be used by the battery. During the running of the car, the DC power from the battery must also be converted into AC power that can be used by the power supply. An inverter will be used.
APM reduces the power of a large battery pack to a general 12V battery, which is used for the lighting, radio, CD player, instrument panel, air conditioner, etc. inside the car. Since it is the conversion between the battery and the battery, a converter is required instead of an inverter.
DC power transformation is not as easy as AC power transformation. AC power transformation only requires a transformer, while DC voltage conversion requires an inverter to convert high-voltage direct current to high-voltage alternating current, and a transformer to reduce high-voltage alternating current to low-voltage alternating current , And an inverter to convert low-voltage alternating current into high-voltage direct current.
This process is relatively cumbersome, so the industry will also use a buck converter or a boost converter, which is structured as a transistor or diode, an inductor, and a capacitor.
to sum up
The future of electric vehicles depends on the innovation of car batteries. The new generation of batteries requires longer life, higher energy density, and increases the range and lasting performance of electric vehicles. A single battery cannot be separated from the battery pack, just like the heart cannot be separated from the body, and every organ in it plays a supporting and auxiliary role.
It took us a long time to forget about lead-acid batteries and start using nickel batteries, and it took us a long time to start popularizing lithium batteries. Lithium batteries have a wide range of chemistries and applications.
Before we wait for the arrival of the next new electrochemical technology, the internal innovation and continuous improvement of the battery pack will determine the trend of electric vehicles in the short term, making electric vehicles durable and durable under the challenges of different environments.