TMC4671 Datasheet • IC Version V1.00 | Document Revision V1.04 • 2018-Dec-11
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3.5.6 Knowledge of Relevant Motor Parameters and Position Sensor (Encoder) Parameters
3.5.6.1 Number of Pole Pairs of a Motor
The number of pole pairs is an essential motor parameter. It defines the ratio between electrical revolutions
and mechanical revolutions. For a motor with one pole pair, one mechanical revolution is equivalent to
one electrical revolution. For a motor with npp pole pairs, one mechanical revolution is equivalent to npp
electrical revolutions, with n = 1, 2, 3, 4, . . . .
Some define the number of poles NP instead of number of pole pairs NPP for a motor, which results in a
factor of two that might cause confusion. For the TMC4671, we use NPP number of pole pairs.
3.5.6.2 Number of Encoder Positions per Revolution
For the encoder, the number of positions per revolution (PPR) is an essential parameter. The number of
positions per revolution is essential for the FOC.
Some encoder vendors give the number of lines per revolution (LPR) or just named line count (LC) as
encoder parameter. Line count and positions per revolution might differ by a factor of four. This is because
of the quadrature encoding - A signal and B signal with phase shift - that give four positions per line,
enabling the determination of the direction of revolution. Some encoder vendors associate counts per
revolution (CPR) or pulses per revolution associated to PPR acronym.
The TMC4671 uses Positions Per Revolution (PPR) as encoder parameter.
3.5.7 Proportional Integral (PI) Controllers for Closed Loop Current Control
Last but not least, two PI controllers are required for the FOC. The TMC4671 is equipped with two PI
controllers - one for control of torque generating current I_Q and one to control current I_D to zero.
3.5.8 Pulse Width Modulation (PWM) and Space Vector Pulse Width Modulation (SVPWM)
The PWM power stage is a must-have for energy efficient motor control. The PWM engine of the TMC4671
just needs a couple of parameters to set PWM frequency fPWM and switching pauses for both high side
switches tBBM_H and low side switches tBBM_L. Some control bits are for the programming of power
switch polarities for maximum flexibility in the selection in gate drivers for the power MOS-FETs. An
additional control bit selects SVPWM on or off. The TMC4671 allows for change of PWM frequency by a
single parameter during operation.
With this, the TMC4671 is advanced compared to software solutions where PWM and SVPM configuration
of CPU internal peripherals normally needs settings of many parameters.
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