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To run at a variable speed an AC motor needs some sort of motor driver, also known as an inverter, to create a 3-phase alternating current waveform from the DC Buss Voltage. This is used to excite the motor stator windings in the necessary sequence and frequency to induce or create magnetic fields in the rotor and cause it to run as a motor.
When coasting or braking is desired, this same inverter can extract some of the energy from the spinning magnetic field. In this case, current is induced into the stator windings and the inverter conttrols the phase timing in order to pump it back onto the DC Buss to recharge the batteries. This is called regeneration braking since it will slow the car down depending upon the rate of current extraction.
There is always losses in the switching and conversion process such that you can never recover as much energy as was put in.
When coasting or braking is desired, this same inverter can extract some of the energy from the spinning magnetic field. In this case, current is induced into the stator windings and the inverter conttrols the phase timing in order to pump it back onto the DC Buss to recharge the batteries. This is called regeneration braking since it will slow the car down depending upon the rate of current extraction.
There is always losses in the switching and conversion process such that you can never recover as much energy as was put in.