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10
Lead/Lag - Fixed Lag
Control Mode for multiple drives where the Main drive is PI controlled and all Lag (Aux) drives/motors operate at a
fixed frequency, AP1-60 (Lag Freq). During staging/de-staging, a shift of the Main PI controlled drive occurs. With
actual feedback wired to Drive 1 only, Drives 2 and 3 receive the feedback signal through Modbus communications.
Note that the Lead (+) drive (controlling communications) does not change, only the Main PI controlled drive
changes.
The following figure shows the basic operating sequence for Fixed Lag operation with Drives 1, 2 and 3. In this case
the alternating sequence AP1-49 (ALT Sequence) is set to FILO (First In Last Out) and the run priority AP1-45 (Curr.
Prty 1) is 0321. Run priority means that Drive 1 is the first priority and the Drives 2 and 3 are 2
nd
and 3
rd
priority.
With FILO, the motor starting order is Motor 1 (M1) -> Motor 2 (M2) -> Motor 3 (M3). Motor stopping order is Motor
3 (M3) -> Motor 2 (M2) -> Motor 1 (M1).
10.1
Fixed Lag - Conditions for Staging Lag Drives
1.
Feedback is below the setpoint PID-11 (PID Ref 1 Set) and below the deviation amount AP1-50 (Stage
Pres. Dv).
2.
Output Frequency of the Main Drive reached the stage frequency AP1-61 (Stage Freq 1) of the Lag drive.
3.
The stage delay time AP1-53 (Stage DT) has expired.
Fixed Lag - FILO
10.2
Fixed Lag - Staging Details
With the start of Drive 1 which is the Lead (+) and the Main drive, the speed ramps up. If the three staging conditions
are met, (feedback below setpoint, operating frequency reaches staging frequency and the delay time has expired),
Drive 2 (M2) starts
and now becomes the Main PI controlled drive. Drive 1 (M1) becomes a Lag (Aux) drive
and runs at the Fixed Lag frequency. There is a shift of the Main PI controlled drive from Drive 1 to 2.
If
feedback still remains below the setpoint, Drive 3 (M3) will start and
now Drive 3 becomes the Main PI controlled
drive.
There is a shift of the Main drive from Drive 2 to 3. Drive 2 becomes another Lag (Aux) drive,
the 2
nd
Lag drive in operation. Drives 1 and 2 run at the Fixed Lag frequency. Drive 3 is operating with PI control as the
Main drive.
Summary of Contents for RSi H2P Series
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