94 Rockwell Automation Publication 750-AT006D-EN-P - January 2022
Chapter 6 Active Front End Tuning
High-frequency Variation
The operation of the AFE relies on a stable input frequency. The Power Disturbance Module monitors the rate of change of frequency with
respect to time (DFDT). It detects a high-frequency variation condition when the frequency change with respect to time exceeds 100 Hz/s.
You can choose the actions Ignore, Alarm, Ride Through, or Fault by configuring 13:179 [DFDT Det Actn]. When Ride Through is selected, the
drive activates the Ride Through function when it detects a high-frequency variation for a period of time that is configured using 13:172
[RideThrough Time]; see Ride Through Mode
on page 94. If a DFDT condition is cleared before this time expires, the converter resumes
normal operation. However, if the DFDT is condition still active when the Ride Through time expires, the converter will perform as configured
in 13:180 [DFDTRdThrExpActn].
Phase Loss
Operation of the AFE relies on a balanced supply. While the AFE power converter can successfully operate under phase loss condition at light
loading conditions, operation under phase loss and higher loading conditions imposes several stresses on the power structure and affects
the control performance. The Disturbance Module monitors the current of each incoming phase. It detects a phase loss condition when the
current on any given phase drops below the factory-set level for the factory-set time such that the sum of the instantaneous value of the
other two phases is equal to zero. A phase loss condition can be detected at relatively high load conditions (≥30%). You can choose Ignore,
Alarm, Ride Through, or Fault by configuring 13:176 [LSCPhLossDetActn]. When Ride Through is selected, the drive activates the Ride Through
function when it detects a phase loss condition for a period of time that is configured using 13:172 [RideThrough Time]; see Ride Through
Mode on page 94. If a phase loss condition is cleared before this time expires, the converter resumes normal operation. If the phase loss
condition is still active when the Ride Through time expires, the converter will perform as configured in 13:177 [PhsLossRTExpActn].
Power Loss
The Power Disturbance Module monitors the root mean square (RMS) values of the input line voltages. It detects a power loss condition when
the RMS voltage of the three input phases drops to less than 15% of the nominal value. You can choose Ignore, Alarm, Ride Through, or Fault
by configuring parameter P13:170 [PwrLoss Det Actn]. When the Ride Through is selected, the drive activates the Ride Through function when
it detects a phase loss condition for a period of time that is configured using 13:172 [RideThrough Time]; see Ride Through Mode
on page 94.
If a power loss condition is cleared before this time expires, the converter resumes normal operation. If the power loss condition is still
active when the Ride Through time expires, the converter will perform as configured in 13:171 [PwrLossRTExpActn].
Ride Through Mode
Ride Through mode is one of the selectable actions available when the Power Disturbance Module detects abnormal conditions. Ride Through
mode temporarily disables PWM gating of the insulated-gate bipolar transistors (IGBTs) in the line-side converter. This avoids instability and
reduces the probability of fault. It also preserves the energy in the DC bus capacitors. It can support the load for a short time. Because the fly
back diodes remain in circuit, the line-side converter behaves like a passive diode bridge. Ride Through disables the voltage and current
loops. It also resets the voltage and current integrators.
The flow diagram in Figure 77
illustrates the operation of Ride Through mode. The Power Disturbance module continuously monitors the
incoming voltage, current, and frequency. When it detects an abnormal condition, it follows the disturbance action. If the selected
disturbance action is Ride Through, it disables PWM gating and the control loops. When the abnormal condition clears (voltages, currents,
and frequency return to normal), the control loops and PWM gating resume. If the abnormal condition lasts longer than the time in
13:172 [RideThrough Time], the product follows the selection in 13:171 [PwrLossRTExpActn].
Ride Through Mode in PowerFlex 755TL And TR Drives
PowerFlex 755TL and TR drives are integrated. This means they have a line-side converter and a motor-side inverter. These drives utilize
Rockwell Automation’s Adaptive Bus Reference Ride Through technology. The line-side converter is disabled when the abnormal condition is
detected. If the Ride Through option is selected, an additional signal passes from the line-side converter to the motor-side inverter. When
the signal is high, the motor-side inverter takes control of the DC bus. The DC bus regulator in the motor-side inverter can take energy from
the load, if necessary, to keep the DC bus voltage high enough. When the abnormal condition ceases, control passes back to the line-side
converter.
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