Capacitive Regenerative Braking in Single-Phase Motors

Capacitive regenerative braking may occur in capacitor start motors when power is removed. A series resonant circuit is formed with the main winding and start winding connected in series through a relay or centrifugal switch to the start capacitor. The circuit will resonate over a range of speeds. Slip (which is negative) and saturation are determined by the conditions that the sum of the real impedances in the circuit must be zero and the sum of the imaginary impedances must also be zero. The rotational energy of the motor is converted into stator and rotor heating losses. Formulas are derived for the range of speed over which regeneration may take place, and a method of predicting braking torques is given. Braking torques several times larger than the rated maximum motor torque can be developed.