A Positive- and Negative-Sequence Equivalent Circuit Model for Linear Induction Machine Adapted to Urban Rail Transit

The equivalent circuit model is a crucial tool for estimating the performance of linear induction machines (LIMs), and it is widely used in design, optimization, etc. However, the conventional model which does not account for the asymmetrical current is not as precise in certain scenarios. Such asymmetrical current is caused by the inherent end effect in LIMs, which persists even when the machine is powered by a symmetrical voltage source. In this article, a novel equivalent circuit model is proposed to enhance the precision of analyzing LIMs performance under asymmetrical current. First, the relationship between current, back electro-motive force (EMF) and voltage is established by analyzing the positive- and negative-sequence airgap magnetic field. Second, the excitation source is converted from symmetrical phase voltage to positive- and negative-sequence current by solving the circuit constraint equation. Finally, a positive- and negative-sequence equivalent circuit model is constructed and the LIM performance is further analyzed. The proposed model is thoroughly validated through comparison with other methods and experimental data.