AN2281 datasheet(16/38 Pages) STMICROELECTRONICS

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Library parameters

AN2281

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Library parameters

This paragraph describes the parameters used in the PMAC motor control library supplied

with this application note. All the command lines mentioned in this paragraph are included in

the PMAC_Param.h header file.

5.1

Phase synchronization and phase angle optimization

As discussed in Figure 2, every time an Hall sensor edge occurs, the phase of the sine wave

is refreshed, depending on the transition (high-to-low or low-to-high), with the phase angle

or with

Φ+Π. Moreover, the Hall sensor signal semi-period is stored so that the sine wave

frequency can be computed by averaging the last 4 semi-period measurements.

The tuning of the phase angle

Φ is extremely important and it can enormously effect the

efficiency of the system. Two different solutions for phase angle optimization are possible

using the library supplied with this application note:

5.1.1

Phase angle tuned by Pot2

If the command line:

#define PHASE_READING_FROM_POT2

is not commented, the phase angle is read by the potentiometer Pot2. The minimum and

maximum available phase angles are configurable by definition statements:

#define MIN_PHASE (u16)

xxx //in 360°/65535 unit

(180° <=> 32768)

#define MAX_PHASE

(u16)

xxx //in 360°/65535 unit

(180° <=> 32768)

5.1.2

Phase angle as a function of frequency

If the command line:

#define PHASE_READING_FROM_POT2

is commented out, the phase angle is computed as a linear function of the rotor speed

following the relationship illustrated in Figure 12:

Figure 12. Phase angle vs speed relationship

PH_AT_HIGHSPEED, PH_AT_LOWSPEED (in 360°/65535 unit), PH_LOWSPEED and

PH_HIGHSPEED (in rpm) are configurable in the PMAC_Param.h header file.

Phase angle

PH_AT_HIGHSPEED

PH_AT_LOWSPEED

PH_LOWSPEED

PH_HIGHSPEED

Speed

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