Energy conservation and environmental protection have always been a hot topic among people, and electric and hybrid vehicles provide an excellent way to save energy and reduce carbon dioxide emissions. However, an important weakness of electric and hybrid vehicles is their battery capacity and the resulting limitation of driving distance. Optimizing the use of existing battery capacity is becoming increasingly important, as the largest battery size that can fit into a car is often limited by volume and weight.
To provide the hundreds of volts required by modern high-performance batteries used in electric vehicles, several individual cells usually need to be connected in series. Each battery cell in a battery pack is unique in terms of cell capacity, self-discharge rate, temperature characteristics, and battery impedance, and the variance increases as the battery ages. When the cells are being charged, this difference can lead to a situation where some cells are not yet fully charged, but others are already fully charged. Unless additional measures are taken, the charging process must be terminated because if a cell is overcharged, damage and possibly complete destruction can occur.Also read:https://www.aminobattery.com/lithium-battery/190.html
A similar situation also occurs during discharge. On the contrary, the situation is that one battery cell has already been completely discharged, while the other battery cells still have enough energy to continue to provide power for the car (theoretically). However, it is impossible for the car to continue driving at this point, as this would over-discharge the weaker battery cells, resulting in the destruction of the battery cells. To avoid both of these situations above, active balancing between individual cells is necessary.
The currently widely used method is passive balancing technology, which is to use resistors to discharge the battery cells that have already been fully charged so that other battery cells can continue to charge. The disadvantages of this approach are obvious:
*Battery can only be discharged for balancing purposes
*The discharge current of the shunt resistor causes power loss
*Precious energy is converted to heat and cannot power the car
*Reduce the driving distance of the car
Passive balancing only converts the energy stored in the cells into heat loss, while active balancing transfers the charge from one cell to another. There are several ways to achieve charge transfer, such as using switched capacitors or inductors. When using the capacitive method, the capacitor is connected in parallel with the higher voltage cell. Once the cell is fully charged, it is placed in parallel with the lower voltage cell to continue charging it. This process is repeated until all cells reach the same voltage.
The capacitor approach is very cost-effective, but has the disadvantage that the average balancing current is limited to less than 50mA. Using the inductive approach, this limitation does not exist, and in this case a balanced current of 1A or more can be easily achieved.
Fast and virtually lossless charge transfer using active balancing
Active balancing is achieved by connecting an inductor in parallel with the battery that needs to harvest charge. This results in a continuous increase in the current in the coil.Also read:https://www.aimeno.com/lithium-battery/
Once the coil has been decoupled from the battery cell being discharged through the transistor, the energy stored in the inductor can charge an adjacent battery through a diode. Charge can thus be moved back and forth between the two individual cells with very high efficiency and virtually no losses. This method has some decisive advantages:
*Balance current may reach 1A or more
*Balance is lossless in nature
* Balancing extremely fast
* Increased efficiency and battery capacity
*Increased the driving distance of the car
Active balancing using inductors is not considered a low-cost method compared to the other methods mentioned because of the relatively high-cost inductive components used. However, this is not entirely a problem. Modern high-performance batteries currently cost close to $10,000. Using the inductance balancing method, even gaining an additional 10% of capacity represents a value of $1,000—an amount that can be used to purchase large quantities of inductive components.
Lithium-ion batteries have to monitor the individual cells for safety reasons, since overloading can cause combustion and, in extreme cases, explosion. As with overvoltage, undervoltage and temperature monitoring, additional functions such as accurate charging condition determination are required. Components that can perform all these functions with different balancing methods are already available in the semiconductor market. Using advanced active cell balancing solutions (such as the Atmel ATA6870 battery management circuit) each cell has individual electronic monitoring to provide information such as state of charge determination, active/passive balancing or overvoltage, undervoltage and temperature Monitoring and other functions