Whenever the load causes the motor to spin faster than the applied frequency, then the
motor becomes a generator. That is, if the applied frequency is decreased to, say, 30 Hz while
the motor is still running nearly at 60 Hz, the motor will generate energy back to the drive. Then,
the drive must do something with that energy. One way is to shunt it through a dynamic braking
(DB) resistor, which dissipates the energy as heat