Rockwell Automation 20M LPM15 Liquid-Cooled Adjustable Frequency AC Drive FRN 2.xxx - Manual (Page 114)

D-4 Application Notes
Overspeed Overspeed Limit is a user-programmable value that allows operation at
maximum speed, but also provides an “overspeed band” that will allow a
speed regulator such as slip compensation to increase the output frequency
above maximum speed in order to maintain maximum motor speed.
The figure below illustrates a typical Custom V/Hz profile. Minimum Speed
is entered in Hertz and determines the lower speed reference limit during
normal operation. Maximum Speed is entered in Hertz and determines the
upper speed reference limit. The two “Speed” parameters only limit the
speed reference and not the output frequency.
The actual output frequency at maximum speed reference is the sum of the
speed reference plus “speed adder” components from functions such as slip
compensation.
The Overspeed Limit is entered in Hertz and added to Maximum Speed and
the sum of the two (Speed Limit) limit the output frequency. This sum
(Speed Limit) is compared to Maximum Frequency and an alarm is initiated
which prevents operation if the Speed Limit exceeds Maximum Frequency.
Power Loss Ride Through When AC input power is lost, energy is being supplied to the motor from the
DC bus capacitors. The energy from the capacitors is not being replaced
(via the AC line), thus, the DC bus voltage will fall rapidly. The drive must
detect this fall and react according to the way it is programmed. Two
parameters display DC bus voltage:
• [DC Bus Voltage] - displays the instantaneous value
• [DC Bus Memory] - displays a 6 minute running average of the voltage.
All drive reactions to power loss are based on [DC Bus Memory]. This
averages low and high line conditions and sets the drive to react to the
Frequency
Output V
olta
g
e
Note 1: The lower limit on this range can be 0 depending on the value of Speed Adder
Overspeed
Limit
Frequency Trim
due to Speed
Control Mode
Maximum Voltage
Motor NP Voltage
Run Boost
Break Voltage
Start Boost
Allowable Output Frequency
Range - Normal Operation 1
Allowable Speed Reference Range
Allowable Output Frequency Range -
Bus Regulation or Current Limit
Maximum
Frequency Motor NP Hz 0 Break
Frequency
Maximum
Speed
Minimum
Speed
Output
Frequency
Limit