Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 104)

104 Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013
Chapter 1 Detail Drive Configuration and Operation
Process PI Output
At this point of the process PI loop, some conditions must be met to turn on the
PI output (otherwise the PI output is 0).
The PI output can be turned on in one of two ways:
• [Logic Command] bit 12 - “ProcsTrim En” is turned on and the drive is
running. The running state is indicated by [Logic Status] bit 1. When both
of these conditions are true, [Logic Ctrl State] bit 31 “ProcessTrim En” will
be on.
• [PI Command] bit 0 - “Enable” is turned on.
Now the PI output is used to trim speed, torque, or some external loop.
To trim the speed loop, link [Speed Trim 2] or [Speed Trim 3] to [PI Output].
To trim the torque loop, link [Torque Trim] to the [PI Output].
To trim some other loop, link the desired parameter to [PI Output]. For example,
to use analog output 1 as a trim signal to other equipment, link [Anlg Out 1 Real]
to [PI Output].
Pulse Elimination Technique
(PET) See Reflected Wave on page 104 .
Reflected Wave Parameter 510 [FOC Mode Config] bit 9 “ReflWaveComp” enables reflected
wave compensation.
The pulses from a Pulse Width Modulation (PWM) inverter using IGBTs are
very short in duration (50 nanoseconds to 1 millisecond). These short pulse
times combined with the fast rise times (50 to 400 nanoseconds) of the IGBT,
will result in excessive over-voltage transients at the motor.
Voltages in excess of twice the DC bus voltage (650V DC nominal at 480V
input) will occur at the motor and can cause motor winding failure.
The patented reflected wave correction software in the PowerFlex 700S will
reduce these over-voltage transients from a VFD to the motor. The correction
software modifies the PWM modulator to prevent PWM pulses less than a
minimum time from being applied to the motor. The minimum time between
PWM pulses is 10 microseconds. The modifications to the PWM modulator
limit the over-voltage transient to 2.25 per unit volts line-to-line peak at 600 feet
of cable.