[PIC] Three Phase AC Induction Motor Constant V/F Drive Help Needed

[c_mitra]

In post #5 FvM mentioned that voltage is adjusted based on the motor frequency. Motor frequency depends upon load..

It is not a linear relation- you see the curve in #15 (but use your own curve) and decide the optimum voltage and frequency for maintaining the desired speed.

Best you maintain a table in your software and provide option to update depending on the user performance and the motor type.

 

[FvM]

For a basic VFD inverter V/f characteristic means to set a frequency and a voltage along with it according to a fixed curve. Simply because the actual speed of an induction motor follows the applied field frequency, with a certain slip of 5 to 10 %, depending on the load torque. It makes no sense to correct the voltage for a few percent slip variation.

Speed measurement comes into play if your application wants to reduce load dependent speed variation.