4-191
Example:
Press Application
In this application there are two conditions causing regenerative energy back to the inverter and therefore
recharging the DC bus.
(1) When the brake is not set, the motor will accelerate and rotate the flywheel. When motor decelerates, the
rotation speed will exceed the motor speed due to the large flywheel
’s inertia feeding back regenerative
energy to the inverter resulting in an increased DC bus.
(2) When the brake is set, the motor will rotate the flywheel and compress the spring. At the highest point when
the press moves beyond its center, the spring will release its stored energy back to the flywheel and therefore
feeding back regenerative energy to the inverter resulting in an increased DC bus.
Brake
FLYWHEEL
Motor
Inverter
f
out
f
motor
Gear
box
Motoring : f
out
> f
motor
Overhauling : f
out
< f
motor
Figure 4.3.90 Press Operation
Over-voltage prevention (OVP) function monitors the DC-bus voltage and adjusts the speed reference,
acceleration and deceleration rate, to prevent the inverter from tripping on an overvoltage condition.
When the speed reference is reduced, the motor will start to decelerate. When the inverter is operating at a fixed
output frequency and excessive regenerative energy back to the inverter is detected the inverter will accelerate
the motor in order to reduce the DC-bus voltage. Refer to Figure 4.3.91.
