An analysis method to model and culculate the line side harmonic currents produced by variable speed induction motor drives is proposed. An accurate analytical investigation of the line currents in presence of a power conversion system with a load represented by a PWM inverter feeding an induction motor is carried out. With the obtained mathematical results it is possible to reproduce the distorted current waveforms injected by the whole drive system in the grid. Finally the simulation results are compared with the real harmonic distortion generated by a variable speed drive.