Advanced Applications | International English |
8.2.2Braking and Stopping with an Inverter
Ramping Down and Braking
As stated above, if the inverter reduces the output frequency (i.e. Ramps down) the motor and load will slow down. If the load and motor inertia is high, regeneration will occur. In many cases there is insufficient regeneration to cause excessive voltage; in fact very fast ramp down rates can often be used in certain processes without problems. In many cases the energy is absorbed by other losses, such as gearbox or rolling friction. The ramp down time, controlled by the inverter allows predictable deceleration and stopping times.
Where regeneration does cause trips, several solutions are possible. An external brake, DC braking or Compound braking may be used. These are described in section 8.2.2.
However, a simple solution is to connect a resistor across the DC link of the inverter to dissipate the regenerated energy.
Some inverters incorporate a controller which switches the resistor on and off to maintain the DC link voltage at a constant level.
The MICROMASTER MM420 has no controller and the use of an external controller or resistor is not possible.
External Optional Resistor
+ 
Motor
- 
Resistive Brake Controller (built in on some Controllers)
Figure
DC Braking.
If a controlled DC voltage is applied to the motor, a braking and holding torque is produced in the rotor. During DC braking the stored energy of the motor and load is dissipated in the rotor itself, so there is no regeneration back to the inverter.
However, because no frequency is applied, there is no control over motor speed, and it is not possible to predict the stopping time of the motor and load. The torque on the rotor is maintained even at standstill, so DC braking can be used to hold the rotor and load for short periods if required.
Parameter P1232 sets the level of DC Braking current, and braking will be applied for the time set in P1233 irrespective of the motor speed. The parameter value
50 | MICROMASTER Applications Handbook |