AN2281 datasheet(24/38 Pages) STMICROELECTRONICS

24 / 38 page

Getting started with the ST7FLITE35-based PMAC motor control system

AN2281

24/38

6.4.1

Determining the phase angle and optimizing the start-up parameters

After device programming, once the ICC cable has been removed, microcontroller begins to

execute the firmware and motor should start moving. As earlier discussed, the value of

phase angle

Φ can greatly influence the efficiency of the system so that a wrong value of

could even prevent the motor from starting. For this reason, Pot2 should be slowly turned

(starting from 0% position) until motor start running and, then, the phase angle should be

finely tuned in order to increase the motor efficiency (that is reducing the current at fixed

speed). This can be easily achieved by changing the MIN_PHASE and MAX_PHASE

parameters with the purpose of progressively incrementing the resolution of potentiometer

Pot2.

It could happen that, even if you slowly turn the Pot2 potentiometer from the 0% position to

the 100% position, the motor does not start spinning. In this case, the voltage fed to the

motor may not be sufficient and you should increase it slightly by turning the Pot1

potentiometer towards the 100% position. While doing this, you should monitor one of the

three phase currents to be sure it does not exceed the absolute maximum ratings of the

motor. Then repeat the procedure for optimum phase identification.

Once the motor has started running, you should then try to determine the optimum phase

angle versus frequency characteristic in order to find out the best PH_AT_HIGHSPEED,

PH_AT_LOWSPEED, PH_LOWSPEED and PH_HIGHSPEED parameters.

You should then disable “phase angle read by Pot2”.

AN2281 Datasheet(PDF) 24 Page - STMicroelectronics