Harmonic modeling of the motor side of an inverter locomotive

An AC-voltage source feeding an electric network results in a periodic excitation of the network. In steady state, all currents and voltages will be periodic with cycle time corresponding to the frequency of the voltage source. If the network is linear, all signals are sinusoidal and the network is solved using traditional methods. If the network contains components with nonlinear or switching dynamics, iterative methods based on harmonic balance are often required to obtain the periodic steady state solution. By linearization of the system around the periodic solution, a linear time periodic model is obtained. This can be used as a local description of the system in the neighborhood of the periodic solution. If only periodic signals are considered, a linearized model can be represented by a matrix, called the harmonic transfer matrix (HTM). The method is applied to the motor side of a modern inverter train. Via the HTM, the steady state response to constant or periodic disturbances or changes in reference values can be obtained.