Coupled Electromechanical Analysis for Torsional Design of Electric Powertrains

Calculation procedures are well-established for torsional analyses of industrial powertrains. Usually, the mechanical drivetrain is described by a one-dimensional model, the electromechanical (EME) interaction is neglected, and the electromagnetic loads are included in the solution as external loads. This enables the calculation of electromagnetic loads before the actual torsional analyses. While practical and simplistic, it has been observed that EME interaction may change critical speeds and damping significantly in some applications. The authors main aim is to introduce a coupled EME approach for torsional analyses of industrial powertrains. A fully coupled approach that is systematically compared to the traditional, purely mechanical, analyses and to some intermediate forms of torsional analyses. A calculation example is used to demonstrate the pros and cons of these different approaches based on steady-state, critical speed, harmonic response, short circuit and reclosure analyses. The obtained results will show that the EME interaction is significant when large inertia load is applied, and the first natural elastic frequency is low. A typical industrial application requiring careful torsional analysis is a reciprocating compressor driven by an electric motor with a soft coupling. The largest difference between the un-coupled and coupled analyses was observed in reclosure analyses.