Interharmonic source model for Variable Frequency Drivers

Calculation of the interharmonic current produced by VFD (variable frequency driver) is equivalent to calculate the corresponding DC side ripple current component. This paper models the DC side ripple current calculation problem with the assumption that motor can be equivalent to its short circuit impedance and a pure voltage source in series. With the well-known modulation theory, explicit formulas to calculate the equivalent DC side electromotive force and impedance are developed. Thus the corresponding DC side ripple component can be solved without iteration, and then the interharmonic current can be calculated with the modulation theory. The proposed model has been verified with time domain simulation using Matlab/simulink.