Transient Behaviour of a Current-Source Inverter-Fed Synchronous Motor with a Solid Rotor

Abstract

This publication presents a solution which enables one to investigate the transient behaviour of a 2 × three-phase current-source inverter-fed synchronous motor with a solid rotor. Based on the block structure of the whole system it was split into components for which mathematical models in state-space were derived. A focal problem was describing the synchronous machine: With inverter-fed operation increased rotating waves of the magnetic air-gap field arise which do not rotate with synchronous speed and thus induce eddy currents in the rotor. As these eddy currents not only flow in the intended paths provided by the damper cage but also in the solid iron it is not possible to formulate coupling inductances in accordance with the classical theory of machines. The set of equations describing the machine is therefore incomplete. Numerical calculation of the magnetic field and system-theoretical expressions yield further sets of equations which can be presented in a complete form. It is also shown how the mutual interactions between the subsystems interconnected in the circuit can be determined mathematically and by programming. Based on the coupling conditions the coupling voltages can be calculated for each time-step in the digital simulation as fictitious control quantities enabling the respective phase-state differential equations to be integrated independently of each other. The presented theory was converted into a simulation program taking the regulation into account. A concluding comparison between test and calculation results shows good correlation.