Generalized High-frequency Small-signal Modeling of Electric Machines using Electromagnetic FEA

With the increased application of variable speed drives for efficient speed and torque control of electric machines, there has been a growing number of practical machine drive-related process failures. Typical variable speed drives have a pulse width modulated inverter switching at tens of kilohertz, with dv/dt of thousands volt per millisecond. The high switching frequency introduces additional electromagnetic losses in electric machine cores, permanent magnets (PMs), and windings. The high dv/dt introduces damaging bearing currents and leakage currents, adversely affects the machine insulation due to terminal overvoltages, and contributes to the electromagnetic interference (EMI). To address these high-frequency issues in a systematic manner, this paper proposes a new framework by including parasitic capacitive effects into the widely-used coupled-circuit model of electric machines. To study the influence of high-frequency voltage harmonics introduced by pulse width modulation (PWM) voltage source inverters, the high-frequency small-signal model is further deduced and its numerical implementation in electromagnetic finite element analysis (FEA) tools is presented. Typical applications of the proposed modeling approach are discussed.