Most BLDC motors utilize regenerated electricity. For example, an electric car uses this feature for braking and conserving battery capacity . This is a normal function of the BLDC motor.
I do not want this feature. I require the motor to coast as the default condition. If any of the 3 power supplies fail, then relays R2, R3,& R4 carrying the power to the motor will return to the "normally closed" position. All coils are then open circuit, and the motor should coast, or freewheel. The diode D2 at each High Side MOSFET allows current to return to the battery if the MOSFET fuse blows. This bypasses the intrinsic diode. D1 helps to prevent overheating of the HS MOSFET.