Electromagnetic compatibility of variable speed drives

This paper presents a methodology far the prediction of conducted and radiated emissions from variable speed drives. The conducted emissions have been predicted in the frequency range 150 kHz to 16 MHz, i.e. radio frequency interference, and this corresponds to the frequency ranges required by the current electromagnetic compatibility (EMC) legislations, set at 150 kHz to 30 MHz. The circuit model consisted of the drive, a simple induction motor model, the shielded cable between the drive and the motor and the line impedance stabilising network (LISN) which was used during the measurement of the conducted emissions. Also highlighted is the importance of identifying any parasitic capacitances within the drive as these tend to have a distinct effect on the conducted emissions at higher frequencies. The conducted emissions were measured using a LISN, so the results obtained were in line with the current EMC legislations. The simulation results are confirmed with measured results on the drive and motor in question. It is also shown how the results from the SABER model can be used to predict the radiated emissions from variable speed motor drives using a simple finite element model.