Introduction of the hottest Texas Instruments HEV

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Ti: introduction to hev/ev battery management system

the battery pack is an array of multiple batteries (usually lithium-ion batteries in pure electric vehicles), which can generate voltages up to hundreds of volts. The voltage of the battery pack depends on the system requirements of the electric vehicle

The second component of the system is the inverter. The AC traction motor used in electric vehicles can provide acceleration when the vehicle is completely stopped, and it is very reliable. The voltage of the battery pack is direct current (DC), which is converted into alternating current (AC) by the inverter (usually three-phase). As with voltage, the number of phases depends on the system requirements and the type of motor used, but is usually three-phase

the motor used is usually induction motor, which requires AC voltage. Such motors are commonly used in electric vehicles because they are easy to drive, reliable and cost-effective. The outer component of the motor is the stator, which is wound with three coils. The inner layer is usually a rotor made of copper or aluminum bars

as shown in the figure, the basic transmission system of electric vehicle (EV) is composed of three system modules

simple process of electric vehicle drive chain – battery management system (BMS) to inverter, and then to three-phase AC motor

precautions related to electric shock free pool group and charge state management: since the battery pack is composed of multiple batteries in series, its effective use performance is based on the weakest single battery. The difference in battery capacity is due to the chemical imbalance in the manufacturing process, the location in the battery pack (heat change) and the change related to service or life

the difference between battery voltages indicates the imbalance of batteries at the system level. The reasons for this difference are still under study. It is very important to fully understand this, because it affects the duration of the battery pack in terms of power output, as well as the useful life of each single battery and the service life of the battery pack

one of the most important parameters to be considered is the state of charge. Because the power of each single battery is different, we use percentage to reflect the power imbalance between batteries. If the charge state of one battery is 94% and that of the other battery is 88%, there is a 6% imbalance between the two. In addition, each battery also has a different voltage, called open circuit voltage (OCV), which is the state of chemical charge

The challenge of the battery pack is that not every battery loses power at the same rate when drawing current. Therefore, even if the battery is connected in series, the discharge rate will occur at different speeds. Since some batteries absorb less electricity than others, their ability to recover and absorb electricity will change over time. Other conditions, including temperature, accelerate the cycle. As mentioned earlier, some battery cells may become hotter due to their positioning or location close to the heat sink

the main cause of battery failure is the complete collapse of the battery, which will affect the battery voltage, because the battery is basically just a resistance to reduce the voltage. One way to avoid this is through battery balancing, which is the process of managing how to fully charge each single battery. There are several technologies to achieve battery balance; The simplest method is to connect a resistor and a metal oxide semiconductor field effect transistor (MOSFET) in parallel on each single cell, monitor the voltage of each single cell through the voltage comparator, and use a simple algorithm to turn on the MOSFET to divide the current of the transmission ratio battery. The disadvantage of this method is the waste of bypass energy

another technology is called charge transfer, which does not use the number of experiments and frequency. According to the requirements, the program resistor can be input, and only one capacitor is connected between the single cells. This technology will not waste bypass energy, but it is more complex because you need to connect batteries over a wider distance rather than bypassing each single battery

the technology used in electric vehicles is usually inductive charging, in which the transformer is connected to the unbalanced single battery, because it is a higher power system. Circuit design tends to be large, which requires the design to include a larger area to adapt to the number of circuits required to implement the solution

all these equilibria are based on extensive research on the characteristics and chemistry of single cells, represented by spreadsheets and mathematical formulas that run them using tools such as MATLAB. The microprocessor plays an important role in the system to ensure that all balances are performed correctly. In order to power the microprocessor, the dc/dc converter is directly connected to the battery pack and provides 48V or 12V output according to the system design to power the system. Ti has two devices that can power microprocessors; Both can withstand the transient characteristics and wide voltage range under harsh conditions

lm5165-q1 is a 3V to 65V, ultra-low output synchronous step-down converter, which can provide high efficiency in a wide range of input voltage and load current. The device has integrated high-end and low-end power MOSFET, which can provide an output current of up to 150mA with a fixed output voltage of 3.3V or 5V or an adjustable output voltage. The converter is designed to simplify the scheme and optimize the performance of applications such as battery management system. When the operating temperature is up to 150 ° C junction temperature (TJ), the device can withstand the high operating temperature range in electric vehicles

lm46000-q1 simple switch regulator is a synchronous buck dc/dc converter, which can drive up to 500mA load current in the input voltage range of 3.5V to 60V. When you need a high input voltage or more current of the system, the lm4600 hot innovative Yongqi smells business opportunities. 0-q1 provides excellent efficiency, output accuracy and voltage drop with a very small solution size

there are many ways to manage the balance of lithium-ion batteries in a battery pack, but the design appearance depends on many factors, such as cost, size, thermal characteristics and accuracy requirements. Before implementation, all the above factors need to be taken into account in the design strategy. Learn more about TI products that meet strict automotive and system requirements, and check the system block diagram of HEV high cell count battery packs

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