Time Efficient Calculation of Current Harmonics in Inverter-Fed Electrically Excited Synchronous Machines

The prediction of the time slope of the stator and rotor currents in an inverter-fed electrically excited synchronous machine (ESM) is mainly carried out using models of transient co-simulation with time stepping finite element method (FEM). In the case of calculating a large number of operating points, this method is very time consuming and computationally expensive. This paper presents a fast and efficient methodology that allows the calculation of these currents in a fraction of the usual time. Steady state operating points can be calculated directly with less computational expense and using open-source software.A comparison with one of the already frequently validated transient co-simulation models for an ESM proves the applicability of the methodology and at the same time shows which potential it has for extension.

I. Introduction

In the simulative investigation of electrically excited synchronous machines (ESM) fed from an inverter, it is of key interest to determine the current vs. time curves in the stator and the rotor winding. In the case of ESMs, it is useful to determine these in rotor-fixed dq coordinates [1]. In this way, the additional losses due to the current harmonics can be determined. Until now, there have been two ways to implement this: first, a finite-element-method (FEM) model of an ESM including voltage sources and an inverter model can form the basis for a simulation. However, this is very time consuming and computationally expensive. Another option is a transient co-simulation. This requires significantly less computing time but suitable software for the time-stepping solution of the machine’s differential equation system must be found. However, neither method is fast enough, especially not for the calculation of many operating points across a torque-speed map of an inverter-fed ESM [2].