TMC4671 Datasheet • IC Version V1.00 | Document Revision V1.04 • 2018-Dec-11
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4.8.3 PI Controller Calculations - Advanced Structure
The PI controllers in the advanced controller structure perform the calculation
Z
t
dXdT = P · e +
P · I · e(t) dt
(22)
(23)
0
with
e = X_TARGET − X
where X_TARGET represents target flux, target torque, target velocity, or target position with control error e,
which is the difference between target value and actual values. The time constant d is set according to the
t
PWM period but can be downsampled for the velocity and position controller by register MODE_PID_SMPL.
Velocity and position controller evaluation can be down-sampled by a constant factor when needed.
Figure 24: Advanced PI Controller
The PI velocity controller will be given a derivative part (so it will be a PID controller)
in a future version of the chip. Also, the normalization of the PI parameters might
be changed due to low performance at high PWM frequencies. This will need
changes in the user’s application controller software.
Info
Info
The P Factor in the advanced position controller is not properly scaled. Due
to the high gain in velocity control loop, the position controller gain should be
respectively low. The P Factor normalization of Q8.8 does not match these needs.
This will be changed in a future version of the chip to a different Q format.
This change will need changes in the user’s application controller software. We
recommend to use the classical PI control structure if performance is not sufficient.
4.8.4 PI Controller - Clipping
The limiting of target values for PI controllers and output values of PI controllers is programmable. Per
power on default these limits are set to maximum values. During initialization, these limits should be set
properly for correct operation and clipping.
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