Inclusion of frequency dependences into prediction model of conducted electromagnetic emissions for a VFD motor system

This paper presents a quantitative prediction model of conducted electromagnetic emissions (EME) for a variable frequency drive (VFD) motor system based on the macro-modeling approach. This model relies on the effective representations of the frequency dependent characteristics of the parasitic behaviors between converter arms and heatsink, of shielded power cable, and of motor windings. The frequency dependent performances between converter arms and heatsink, and of the motor windings are obtained by processing measurement data. Then the vector fitting method (VFM) with passivity enforcement and circuit synthesis method are adopted to obtain the corresponding equivalent circuits. The equivalent circuit implementation of shielded power cable is achieved by applying a node-to-node admittance functions (NAFs) model, which considers the propagation phenomenon and frequency dependent losses accurately. The conducted EME model is compatible with commonly used transient circuit solvers since it only includes constant circuit elements. The conducted emissions of the VFD system are then evaluated by analyzing the common mode (CM) and differential mode (DM) voltages and currents.