Electro-coupling effect on the transient voltage distribution in PWM motor winding

Faster switching with IGBT's is known to enhance the control and efficiency of electrical machines significantly while the same is realized to induce over-voltages at the machine terminal to an extent of 3 to 4pu along with inhomogeneous voltage distribution across the stator winding, which often endanger the insulation reliability. Reliable machine design calls for accurate prediction of voltage distribution under various system variables such as inverter pulse rise time, cable and winding parameters. Significant efforts around the world have been made in the past to predict the over-voltages and volt- distribution across the winding. All the reported models display a linear voltage distribution whilst the experimental results often exhibit non-linear voltage distribution, particularly in 3-phase system. In the present paper, a 3-phase distributed model that constitutes (i) R, L and C of winding and cables, (ii) couplings associated with windings and cables and (iii) independent representation of slot and over hang portion is simulated systematically. The results obtained through the present circuit model are found to match well with the experiments. The nonlinear voltage distribution and negative hump in coil waveform is captured first time and the results are discussed in relation to coupling parameters.