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Control System B-3MN1919
B.1.2 Velocity (Speed) control
Setting the control mode to Velocity Control configures the MicroFlex as a speed amplifier, as
shown in Figure 52. Here, a speed reference is obtained from a specified source:
H Mint WorkBench
H A host using the ActiveX control
H Analog input
The source provides a signal that is fed into the S peed controller.
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 W orkBench 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 c ur r ent
Measured s peed
Host
Analog input
Figure 52 - Control structure in Velocity control mode
The speed controller is a PI (Proportional Integral) controller. Gains are set using the Mint
keywords KVPROP, and KVINT. The speed is compared with the measured speed and the
error is fed into the PI control calculation. The speed control calculation is performed every
250μs, and the result forms the torque demand for the torque controller . As with the position
controller, the gain values KVPROP and KVINT must be tuned for each application.
This can either be performed automatically within the Commissioning Wizard, or manually
using the Fine-tuning tool of Mint WorkBench.
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