JL/X130 - 1680
5
2.1.4 Hyper-synchronous
regeneration
The shaded areas in the braking quadrants are where regeneration can occur. Outside the shaded areas any
braking that occurs is achieved through a process known as plugging in which the absorbed energy is
dissipated in the rotor and the rotor resistors.
Hence for regeneration to occur the load must be forcing the speed to exceed synchronous speed. The
JLX must arrange for the correct loop conditions and thyristor combination to be selected to regenerate the
current back into the supply. As the motor approaches the synchronous speed in either of the motoring
quadrants, the opposing stator phase rotation is selected to activate the braking quadrant. Simultaneously
the speed demand is set above synchronous speed to ensure that the motor speed exceeds the synchronous
speed allowing slip to create regenerative current.
Dotted line is
Speed / Torque curve
for shorted Rotor
Motoring
Forward
Quadrant
Braking in
Reverse
Quadrant
Motoring
Reverse
Quadrant
Braking in
Forward
Quadrant
Zero slip hence zero torque
at synchronous speed point.
Dotted line is
Speed / Torque
curve for
shorted Rotor
Motor speed is higher than synchronous speed hence regenerative current is created by
slip and returned to the supply by the JLX. The braking torque is optimised for the lowest
slip by using a shorted rotor. The maximum torque depends primarily on the overload limit
of the JLX and also the motor / installation rating. The speed will rise above synchronous
speed until the torque reaches a level that satisfies the load.
This action is mirrored in the Braking Forward quadrant under similar conditions.
The shaded area
is the zone where
regeneration to
the supply occurs
The shaded area is the zone where
regeneration to the supply occurs
Dotted line is
Speed / Torque
curve for
shorted Rotor
Dotted line is
Speed / Torque
curve for
shorted Rotor
Speed Axis
Torque Axis
Forward motor speed
when regenerating
Reverse motor speed
when regenerating
Synchronous
speed point.