Back Electromotive Force (Back-EMF)
Back electromotive force (back-EMF or BEMF) is the voltage generated in a motor winding by the motor's changing magnetic flux; during motoring it opposes the applied voltage.
Why it matters in an EV drive
Back-EMF generally rises with motor speed and magnetic flux. At high speed it consumes more of the inverter's available voltage margin, which is why field weakening or another flux-control strategy may be needed above base speed.
A spinning permanent-magnet motor can produce back-EMF even when the inverter gates are off. Controllers can also use the waveform to estimate rotor position and speed, but back-EMF information becomes weak near zero speed. Back-EMF is a generated voltage, not the same thing as regenerative power: useful regeneration also requires current and a controlled path back to the DC bus.
For the wider control and safe-state context, see Motor Control and Efficiency Maps.