Finite Element Analysis Modeling and Experimental Verification of Reflected Wave Phenomena in Variable Speed Machine Drive Cables

Graduation date: 2016Modern variable speed machine drive (VSMD) systems are used for a variety of purposes including generation, propulsion, pumps and compressors. They employ high switching frequency power electronics to drive the electric machine. The machine is subject to large voltage overshoot if long power cables, are used, called Reflected Wave Phenomena (RWP), that can result in high electrical stress on the VSMD insulation system. \ud \ud The adoption of higher switching speed wide bandgap (WBG) power semiconductor devices for increased VSMD system efficiencies will result in RWP, up to twice the DC bus voltage, occurring in shorter power cable lengths with likely occurrences of even larger over-voltage at previously acceptable cable lengths. \ud \ud This work investigates the effects that VSMD inverter switching frequency, pulse rise time and cable length have on RWP. A 2D finite element analysis (FEA) cable model is proposed to account for the frequency dependent cable such as skin effect. The FEA model is then compiled into a circuit simulation component and simulated against varying VSMD system parameters. The accuracy of the modeling technique is experimentally verified by testing varying power cable lengths. Simulations and experimental testing show that PWM rise time, switching frequency and cable length all heavily impact the over-voltages seen at the output of the power cables. The simulation results were found to similarly match the experimental findings