ParametersM-Max Series Adjustable Frequency Drive MN04020003E—October 2013 www.eaton.com 115Regenerative BrakingIf the rotor of an asynchronous motor is drivenoversynchronously in the direction of the rotating field, itgenerates electric power via its stator windings. The motorbecomes a generator. In the frequency inverter, thisgenerative energy causes an increase in the DC link voltage.Oversynchronous speeds occur, for example, when theoutput frequency in frequency inverter operation is reducedwith short deceleration times, the connected machine has alarge flywheel mass, or when the flowing medium in pumpsand fans works against the speed reduction.The rise in the DC link voltage is monitored by the M-Maxfrequency inverter and always enables a braking torque ofaround 30% of the motor rated torque. A higher brakingtorque can be achieved by selecting a more powerfulfrequency inverter. From the 1.1 kW (3.3A at 400V =MMX34AA3D3_) rating, the internal brake chopper with anexternal power resistor enables up to 100% of the ratedmotor torque.Regenerative Braking with External Braking ResistorThe brake chopper can be activated at parameter P12.5. Thisfunction is only activated with the three-phase frequencyinverters MMX34…3D3_ (3.3A) to MMX34…014_ (14A).These ratings have an internal brake transistor that candissipate excess brake energy via an external power resistor(connection terminals R+ and R–) when large flywheelmasses or short deceleration times are involved.This parameter is not visible with frequency inverters withouta braking transistor.ItemNumber Description1 Machine flywheel mass2 Inverter with brake chopper (brake transistor)3 Brake resistor (RB)See Energy Flow (brake torque)MRB3 ~R+R–123
