Third harmonic appearance in six pulse thyristor controlled rectifier supplying DC motor 1

[rafael055]

HI

I am performing simulink simpower simulations of harmonic analysis of 5KW 440V 1000rpm dc motor fed by 6 pulse thyristor bridge.
for alpha of 75 degrees and different torque inputs the fft analysis of the ac current showing me third harmonics.
what is the reason for this ?

 

[unclebob]

There's a problem with your model. Both pulsations should be identical, same period, same Vpeak.