Finite element analysis of electrical devices coupled to electric circuits

This report presents the coupling of circuit equations with two dimensional finite element electromagnetic analysis. Time transient and time harmonic analysis are both considered. Conventional finite element analysis uses prescribed currents within domains to represent electrical conductors. Real devices are normally supplied by power supplies and external circuits can be used to represent their voltage sources and impedances. A two dimensional (2d) cross section may be adequate for magnetic analysis, but the electrical connection between components is lost. External circuits can be used to supply this lost information. Coupling has been implemented in this report by combining both the circuit and finite element equations into one system. The 'directly' coupled system is then processed so that it can be analysed using conventional linear algebra methods Two different techniques are presented for entering a circuit into the finite element model. The first requires the user to identify network loops within the circuit. The second uses an extended form of a SPICE circuit definition file. An automatic loop generation algorithm is presented to convert a SPICE format file into network loops. Results are presented for both the time harmonic and time transient cases. Analytical results are discussed which demonstrate the accuracy of the coupling technique and a model of a motor is presented which shows that complex models can be successfully simulated and also demonstrates the commercial importance of this work.