UM0324 datasheet(32/105 Pages) STMICROELECTRONICS

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Running the demo program

UM0324

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You must select two contiguous channels (for example, ADC_CHANNEL8 and

ADC_CHANNEL9

) and the one with the highest number must be associated with

PHASE_A_CHANNEL (for example, PHASE_A_CHANNEL -> ADC_CHANNEL9,

PHASE_B_CHANNEL->ADC_CHANNEL8) .

3.4

How to build the system when using an incremental encoder

Quadrature incremental encoders are widely used to read the rotor position of electric

machines.

As the name implies, incremental encoders actually read angular displacements with

respect to an initial position: if that position is known, then rotor absolute angle is known too.

Quadrature encoders have two output signals (represented in Figure 17 as TI1 and TI2).

With these, and with the STR750 standard timer in encoder interface mode, it is possible to

get information about rolling direction.

Figure 17.

Encoder output signals: counter operation

In addition, rotor angular velocity can be easily calculated as a time derivative of angular

position.

To set up the AC IM IFOC software library for use with an incremental encoder, simply

modify the 75x_MCconf.h and MC_encoder_param.h header files according to the

indications given in Section 2.2.1 on page 18 and Section 2.2.3 on page 21 respectively.

However, some extra care should be taken, concerning what is considered to be the positive

rolling direction: this software library assumes that the positive rolling direction is the rolling

direction of a machine that is fed with a three-phase system of positive sequence.

Because of this, and because of how the encoder output signals are wired to the

microcontroller input pins, it is possible to have a sign discrepancy between the real rolling

direction and the direction that is read. To avoid this kind of reading error, you can apply the

following procedure:

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