Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 228)

228 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 4 Motor Control
Volts/Hertz
Volts/Hertz operation creates a fixed relationship between output voltage and
output frequency. Volts/Hertz works the same for Permanent Magnet and
SyncRel VHz as it does for induction VHz. The relationship can be defined in
two ways by setting P65 [VHz Curve] to 0 “Custom V/Hz” or 1 “Fan/Pump.”
0 = “Custom V/Hz”
Custom Volts/Hertz enables a wide variety of patterns using linear segments. The
default configuration is a straight line from zero to rated voltage and frequency.
This is the same volts/hertz ratio that the motor sees if started across the line. As
seen in the diagram below, the volts/hertz ratio can be changed to provide
increased torque performance when required by programming five distinct
points on the curve.
• P60 [Start Acc Boost] - Used to create additional torque for breakaway
from zero speed and acceleration of heavy loads at lower speeds.
• P61 [Run Boost] - Used to create additional running torque at low speeds.
The value is typically less than the required acceleration torque. The drive
will lower the boost voltage to this level when running at low speeds (not
accelerating). This reduces excess motor heating that could be caused if the
higher start / accel boost level were used.
• P62 [Break Voltage] and P63 [Break Frequency] - Used to increase the
slope of the lower portion of the Volts/Hertz curve, providing additional
torque.
• P25 [Motor NP Volts] and P27 [Motor NP Hertz] - Set the upper portion
of the curve to match the motor design. Marks the beginning of the
constant power region.
• P36 [Maximum Voltage] and P37 [Maximum Frequency] - Slope the
portion of the curve used above base speed.
Frequency Ref. V Ref.
Gate
Signals
V/Hz Control
V/Hz
Voltage
Control
Inverter Motor
Maximum Voltage
Break Voltage
Start/Accel Boost
Run Boost
Break
Frequency
Break Frequency
(Nameplate)
Maximum
Frequency
Base Voltage
(Nameplate)