Rockwell Automation Publication 750-AT006D-EN-P - January 2022 89
Chapter 6 Active Front End Tuning
The Bus observer and feed forward power are both enabled by default, which gives you the advantage of seamless adjustment of the power
flow to the system, regardless of whether you are using an integrated drive or a separate DC bus supply.
Figure 74 - Power Flow in Integrated Drive with External Load connected at the DC Bus Terminals
Resonance Mitigation and Feed Forward Components of Grid Voltages
The measured input line voltages on the grid side are instrumental to compensate for fluctuations in the AC line and to guarantee adequate
disturbance rejection under voltage sag conditions. The corresponding d-axis and q-axis voltage components in the synchronous reference
frame are calculated and processed through Low Pass Filters (LPFs) to render a better current quality and to prevent any high-switching
devices on the line from affecting the power converter and causing noise and aliasing issues. Under these conditions, a relatively large time
constant (1…2 ms) can seem adequate. The time constant of the low pass filter can be set using 13:360 [FFVltgLPFTime]. See Table 32
.
In applications where large nonlinear loads, such as diode/thyristor rectifiers, are connected at the same point of common coupling (PCC)
with PowerFlex 755T drives, it is desirable to significantly reduce the time constant to zero. The reduction of the time constant of the feed
forward voltages low pass filters helps to alleviate the effects of the nonlinear loads and achieve proper resonance rejection under distorted
lines with a relatively lower frequencies: 5th, 7th,11th, 13th, etc. Notice that the disturbance rejection is affected by size of the nonlinear load,
the inductance connecting the nonlinear load to the PCC, the inductance connecting the AFE power converter to the PCC as well as the firing
angle in case of controlled rectifiers. In applications where full load regenerative operation is expected, it is recommended to set
13:45 [DC Bus Ref Sel] to Manual and set 13:48 [DC BusRef Preset] to a value that exceeds the value of 13:46 [Auto DC Bus ref] by 10…15V to
avoid saturation.
In addition, it is highly recommended to set 13:75 [Curr Reg BW] to 150 Hz and 13:55 [Voltage Reg BW] to 15 Hz. To minimize the interactions
between the current and voltage control loops and these harmonics, it is recommended to set the active damping 13:81 [Actv Damping Gn] to 0.
Table 32
summarizes the parameters that are discussed in this section
13:323 [c BusObs Ki]
Bus Observer Integral
Gain - Calc
Displays the calculated value of the Bus Observer integral gain.
• Used when 13:305 [BusObs C/U Sel] is set to Calculated (0).
• Calculated based on the settings in 13:306 [BusObs Sys BW] and 13:307 [BusObsSysDamping].
13:324 [u BusObs Ki]
Bus Observer Integral
Gain - User
Enter the Bus Observer integral gain in units of Hz.
• Used when 13:305 [BusObs C/U Sel] is set to User Entered (1).
13:325 [BusObs Curr Est]
Bus Observer Current
Estimate
Displays the DC bus current estimate from the Bus Observer.
Table 31 - Bus Observer Tuning Parameter Settings (Continued)
Parameter No. Parameter Name Description
Motor
Esmated External DC Loads
(DC Bus Observer)
DC Power Flow
AFE Power Flow
Calculated Inverter Power (FF Power Control)
DC Bus
To Next Page
Loading...
Need help?
General
