PECTRUM of the input current drawn by the electric

drive from the network is affected by the used type of the

input rectifier. In the case of the diode rectifier, the number of

its pulses is decisive. Standard AC adjustable speed drives

utilize the input three phase six-pulse diode rectifier for the

AC-DC conversion. These drives generate harmonics into the

network, so the drawn current is not harmonic, but nonharmonic

with a high level of distortion if no harmonic filter

is used. The input current total harmonic distortion is

calculated from the formula