Control System B-3MN1902
B.1.2 Velocity (S peed) control
Setting the control mode to Velocity Control configures the FlexDrive
II
or Flex+Drive
II
as a
speed amplifier, as shown in Figure 44. Here, a speed reference is obtained from a specified
source.
H Mint / host command (profiled)
H High speed analog input (not profiled)
H Analog input (profiled)
H Fieldbus (profiled).
The source provides a signal that can either be fed directly into the Speed controller (only
when using the high speed analog input source), or through a profiler. The high speed
reference source is ideal for connecting to a motion controller (e.g. NextMove PCI) that will
have already profiled the signal and will provide optimum loop closure.
The profiler generates a speed demand signal that smoothly changes between successive
speed targets (reference values). This is achieved by specifying acceleration and
deceleration times (see the WorkBench v5 Parameters tool). The speed demand signal is fed
into the speed controller and used, together with the speed measured from the feedback
device, to generate a torque demand signal. If the speed controller is tuned correctly, the
measured speed will accurately track the speed demand.
Finally , the torque demand signal is fed into a torque controller, which determines the
appropriate amount of current to apply to the windings of the motor. This demand current is
compared with the actual winding current measured from sensors, and a suitable pulse width
modulation (PWM) signal is generated. This PWM signal is fed to the power electronics in the
drive.
Speed
controller
Torque
controller
Power stage
+ motor
Torque
demand
PWM
Speed
demand
Speed
profiler
Speed
reference
Measured current
Measured speed
High speed
speed reference
Figure 44 - Control structure in Velocity control mode
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