Can anybody help me understand the logic behind bldc motor regenerative braking.how it works and how can it implement??

 

Sure, the basic idea in driving a BLDC motor is to apply torque to the rotor at exactly the right time to accelerate and maintain the rotor speed. To do this accurately you need to know the current rotor position. There are other sub-optimal control sequences which will not accelerate or maintain the rotor speed and these exhibit a "braking" effect.

The idea is the same for an internal combustion engine. You can set the spark for any time before or after the cylinder reaches "top dead center". There is a particular range of settings that allow the engine to do useful work; all the other sub-optimal settings are equivalent to engine "braking". Some of those settings may actually damage the engine.