Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 260)

5-6 Functional Description
7000-UM150I-EN-P – June 2013 7000 “B” Frame
Speed Control
The function of the speed control block is to determine the torque-
producing component (I
sq
) of the stator current (I
s
). The inputs to the
block are the Speed Reference (278) from the speed ramp and the
Stator Freq (448) and Slip Frequency (343) from the motor model. If
drive is installed with an optional tachometer, then the motor speed
is determined by counting the tach pulses.
In Sensorless operation, the Slip Frequency is subtracted from the
Stator Freq and filtered to determine the Speed Feedback (289). In
Pulse Tach mode, the speed is determined directly by using Tach
Feedback (348). The Speed Feedback is subtracted from the Speed
Reference to determine the Speed Error (472) which is processed by
the speed PI regulator. The gains of the regulator are based on the
Total Inertia (82) of the system and the desired Spdreg Bandwidth
(81). The output of the speed regulator is the Torque Reference (291)
whose rate of change is limited by Trq Rate Limit (83). The
calculated Torque Reference is divided by the Flux Reference (305)
to determine the torque component of the stator current Isq
Command (292). To calculate the torque producing current supplied
by the inverter Iy Command (294), the current supplied by the motor
filter capacitor in torque production (orthogonal to motor flux) is
calculated and subtracted from Isq Command.
In Sensorless mode, the drive uses Trq Command 0 (86) and Trq
Command 1 (87) for an open loop start up. At frequencies greater
than 3Hz, the drive closes the speed loop and disables the open loop
start mode. In Pulse Tach mode, the drive is always in closed loop.
The maximum torque a drive can deliver in motoring mode is
determined by Trq Lmt Motoring (84). In regenerative mode the
torque is limited to Trq Lmt Braking (85). It should be noted that at
speeds above the Base Speed (98), the motor torque capability is de-
rated and varies in inverse proportion to the speed.
Depending open the application, a drive can be configured in
different torque control modes by setting the parameter Trq Control
Mode (90). E.g. in stand-alone drives the parameter is set as Speed
Reg allowing the drive to be in speed control mode. In Master-Slave
or torque follower applications, the master drive is set in Speed Reg
mode which enables the speed regulator. The torque reference
produced by the Master drive is then passed on to the slave drive
which is operating in Ext Torq Cmd mode. The slave drive then
“follows” the torque command. Figure 5.4 shows other various
modes of operation.