System for controlling braking energy regeneration step variable and method thereof

A method for variably controlling braking energy regeneration in a vehicle, the method comprising:

• measuring, by a longitudinal acceleration sensor, a road gradient of a road on which the vehicle is traveling;
• determining, by an operation condition controller, whether the vehicle is coasting;
• receiving, by the operation condition controller, the measured road gradient from the longitudinal acceleration sensor, comparing the measured road gradient with a predetermined specific grade to determine whether the measured road gradient is greater than or equal to the specific grade, wherein when the measured road gradient is greater than or equal to the specific grade, the operation condition controller outputs gradient information based on the measured road gradient to a grade resistance feed forward (FF) controller;
• receiving, by the FF controller, the gradient information from the operation condition controller and calculating a grade resistance torque as a FF control value;
• outputting, by a deceleration based feedback (FB) controller, a FB control value based on a difference between deceleration manually set by a driver of the vehicle using a paddle shift and an actual vehicle deceleration;
• and
• applying, by a coasting torque controller, a coasting torque to a regenerative torque depending on a regeneration step set manually by the driver, the coasting torque including a compensation torque calculated as a sum of the FF control value and the FB control value.