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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

dXdT = P · e +

· I · e(t) dt

(22)

with

e = X_TARGET − X

(23)

where X_TARGET represents target

ux, target torque, target velocity, or target position with control error e,

which is the diﬀerence between target value and actual values. The time constant dt is set according to the

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

Info

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

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 su

cient.

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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