Introduction and Design Considerations for HEV/EV Battery Management System (II)

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 voltage-reducing resistor. One way to avoid this is to balance the battery, which is the process of managing how each cell is fully charged. There are several techniques for battery balancing; the simplest method is to connect a resistor and a metal-oxide-semiconductor field-effect transistor (MOSFET) in parallel with each cell, and monitor the voltage of each cell by a comparator that monitors the voltage. And use a simple algorithm to turn on the MOSFET for battery shunting. The disadvantage of this method is the waste of bypass energy.

Another technique is called charge transfer, which does not use a resistor, and only one capacitor is connected between the cells. This technology does not waste bypass energy, but it is more complicated because you need to connect the battery over a wider distance instead of bypassing each cell.

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

All of these balances are based on extensive research on cell characteristics and chemistry, represented by spreadsheets and mathematical formulas that run them using tools such as MATLAB. The microprocessor plays an important role in ensuring that all balances are properly performed in the system. To power the microprocessor, the DC/DC converter is directly connected to the battery pack and provides 48V or 12V output depending on the system design to power the system. TI has two devices that power the microprocessor; both are capable of withstanding transient conditions and a wide voltage range under harsh conditions.

The LM5165-Q1 is a 3V to 65V, ultra-low output synchronous buck converter that provides high efficiency over a wide range of input and load currents. The device features integrated high-side and low-side power MOSFETs that deliver up to 150mA of output current at a fixed output voltage of 3.3V or 5V or an adjustable output voltage. The converter is designed to simplify the solution while optimizing application performance such as battery management systems. The device can withstand high operating temperature ranges in electric vehicles at operating temperatures up to 150 ° C junction temperature (Tj).

The LM46000-Q1 SIMPLE SWITCHER® regulator is a synchronous step-down DC/DC converter capable of driving up to 500mA of load current over an input voltage range of 3.5V to 60V. When you need a high input voltage or greater current to the system, the LM46000-Q1 delivers exceptional efficiency, output accuracy and voltage drop voltage in a tiny solution size.

There are many ways to manage the balance of a lithium-ion battery in a battery pack, but the design appearance depends on many factors such as cost, size, thermal characteristics, and accuracy requirements. All of the above factors need to be considered in the design strategy before implementation. Learn more about TI products that meet stringent automotive and system requirements, and see a system block diagram of HEV's high-battery battery packs.