1  The Brief introduction As below :

Recently I always mention the KEKE  changing . it is from fuel to Electric one .and some storage energy project for the lifepo4 Battery . i know it is very very important for them  work together ,but many guys is not very clear for them.  therefore  let me introduce soemthere as below 

2  DC-DC Converter working principle and Type

     2.1 DC-DC converter, achieving high-efficiency voltage regulation through inductor resonance and MOS FET PWM switching; sinusoidal LDO with minimal heat generation and enhanced low-frequency response; available in unidirectional 
DC-DC (discharge power only) and bidirectional DC-DC (charge and discharge only, for energy storage/electric vehicles).
as below  : 
It is DC-DC to work with the storage energy system
https://youtube.com/shorts/n5R6Baq7ArE?si=fsmmkwnMNO0VIEfq

          2 .2   Unidirectional DC-DC:

Battery supplies power (consumer electronics)
Battery → DC-DC → Load, discharging only, not charging
Single-cell lithium battery handheld devices (earphones, remote controls, detectors): Buck-Boost stabilizes 3.3V/1.8V to the MCU
Power bank output: Boost 3.0~4.2V to 5V USB
Electric vehicle 24V/48V lithium battery: Buck step-down 5V/12V to the instrument panel, lights

    2.3  Bidirectional DC-DC:

Energy Storage/Power Battery System (Rechargeable and Dischargeable) Bidirectional energy exchange between the battery and the BMS .working in conjunction with the BMS, has two core applications: Firstly Charging/Discharging Power Regulation Secondly when it is on the Charging Mode, High-voltage bus voltage reduction adapts to battery charging voltage, current limiting prevents overcharging. when it is on Discharging Mode:, the Battery voltage boost stabilizes the bus voltage, suppressing voltage drop under large loads. also it will be the Active Balancing for Multi-Series Battery Packs When there is a large voltage difference between individual cells, the DC-DC converter transfers energy from the high-voltage cell to the low-voltage cell, eliminating resistance heating and significantly improving battery pack capacity and cycle life (passive balancing relies on resistance power consumption, which is extremely inefficient).

3 DC-DC Converter work with Smart BMS 

 3.1   About the BMS. I have introduced it as below
https://ztekbri.com/blog/bms-type-application/

 3 .2      the working process for the DC-DC Converter and BMS

Firstly BMS detects excessive differential voltage between battery cells → issues balancing command

Secondly Bidirectional DC-DC converter starts, transferring energy between cells

Thirdly During charging, BMS limits maximum charging current, DC-DC converter dynamically adjusts output voltage to match battery

 Finally In case of fault, BMS disconnects the main circuit, DC-DC converter stops switching to protect the battery.