TMC4671 Datasheet • IC Version V1.00 | Document Revision V1.04 • 2018-Dec-11
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statements are correct for the velocity biquad filter. Both filters’ sampling times are fixed to the PWM
period.
The velocity target value biquad is configured as a second order low-pass with a cutoff frequency at 200 Hz
- by default at a sampling frequency of 25 kHz. Biquad filters can be activated separately.
4.9.2 Standard Velocity Filter
By using the standard velocity measurement algorithm, the default velocity filter is enabled and can not be
switched off. The standard velocity filter is a low-pass filter with a cutoff frequency of 20 Hz (slope of -20
dB/Decade). In this configuration, a new velocity is calculated at a sample rate of approx. 4369.067 Hz.
This configuration is intended to be used in low-performance applications with a simple position feedback
system like digital Hall sensors.
4.9.3 Feed-Forward Control Structure
The TMC4671 provides a feed-forward control structure for torque target value and velocity target value.
The structure is intended to support controllers at high dynamic input profiles. It can be switched on when
using the advanced PI controller structure. The feed-forward value is calculated with a DT1 (30) element.
Each DT1 element can be parametrized with two parameters.
Figure 30: DT1 Element Structure
Equations:
e = X − int_val
(36)
(37)
(38)
Z
int_val =
e dt
Y = b_1 · e
The coefficients a_0 and b_1 are represented in Q2.30 format. Registers for parametrization of feed-forward
control structure are feed_forward_velocity_gain, feed_forward_velocity_filter_constant, feed_forward_torque_gain,
and feed_forward_torque_filter_constant.
The input target value to the velocity feed-forward entity is the filtered position target value. For the torque
feed-forward entity the output of the velocity feed-forward entity is used. Sampling time for both entities’
integrators is fixed to the PWM frequency.
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