CHAPTER 5.0 Functional Overview
5-35
CDS7324 (FORMERLY LSF-0819)
Rev. A
INSTALLATION & USER’S MANUAL
5.11.1 Position Loop Compensator
5.11.1.1
PI Compensator
The outer most loop is the position loop. Two options exist for the position compensator. These are a PI
compensator; or a Time-optimal compensator.
The PI compensator has a structure as shown in the diagram below: -
Ki
1
s
pos
demand
+
-
motvelliminc
-motvelliminc
vcmd
Anti-Windup
Kp
Figure 5.5 : Position Loop PI Compensator Structure
The output of the compensator is limited to
motvelliminc
, a term derived from the motor_max_velocity (1085)
parameter. The compensator also implements anti-windup for the compensator’s integrator. The PI compensator
has the gains as listed below.
Field
Number
Name Type
Units
1326
position_PI_loop_p-gain
f32
1/s
1327
position_PI_ loop_i-gain
f32
1/s
2
Table 5.22 List of Position Loop PI Compensator Gains
Field
Number
Name Type
Units
1328
position_PI_loop_error
f32
increments
1034
internal_loop_demand
f32
increments.
1157
velocity_command_acceleration_limited
f32
incs/Tsamp
Table 5.23 Position Loop PI Compensator Read-only Parameters
5.11.1.2
Time-Optimal Compensator
The time-optimal compensator is a non-linear compensator that uses a square root function of the position error,
to give optimal deceleration performance.
The position error is scaled by parameter thermal_limit_factor (1397) to give a scaled position error (i.e.
thermal_limit_factor is 1 when no limiting, <1 when limiting),. Dependent on the size (i.e. absolute) of this scaled
position error, the output of the compensator will have a linear relationship to the scaled position error, for small
position errors, OR will have a square root relationship for larger errors. The cut-off point between the linear and
square root relationship depends on
Ka / (Kp
2
).
