The Method for Assessing the Magnitude of Air Gap Torque Ripple of an Induction Motor Powered by an Autonomous Voltage Source Inverter or Current Source Inverter

The magnitude of the air gap torque (electromagnetic torque) ripple is an important characteristic of the operating mode of an induction motor powered by a voltage source inverter or a current source inverter. Its empirical determination is quite difficult (the torque sensor is expensive and requires precise installation). The air gap torque of the IM can be calculated using the harmonic analysis method. This method involves decomposing the supply voltage or current of the converter into a truncated Fourier series into time harmonics and calculating the parameters of the T-shaped equivalent circuit of the induction motor for each harmonic. After that it is possible to calculate in this way power, efficiency, the average value of the air gap torque, and the magnitudes of currents or voltages. So, the ripple factor of the air gap torque, which the magnitude of torque pulsations in relative units. The disadvantage is the large amount of initial data on the machine parameters and operating mode characteristics required for the calculation. A simple method is proposed by the author for approximately calculating (assessing) the magnitude of air gap torque ripple in a quasi-steady state using two oscillograms: phase current and phase voltage of an induction motor. The relationship between the harmonic composition of the voltage and the magnitude of the air gap torque ripple has been revealed.