Magnetic Saturation and Steady-State Analysis of Electrical Motors

A method is presented for the steady-state analysis of universal motors operating under direct or alternating voltage sources, and in the presence of saturation of the iron in the magnetic circuit. The saturation is modelled through a completely general functional dependence of the air-gap flux on the current, thus resulting in a unified treatment for various saturation models. It is shown that the calculation of the steady-state response can be reduced to the solution of a single algebraic equation. The presence of saturation is shown to increase both the amplitude and the phase lag of the current. For a particular saturation model having the form of a rational function, analytical formulas are derived which allow for the calculation of the current from its unsaturated or fully-saturated values. The changes in the input power, output power, and mechanical efficiency of the motor due to saturation are investigated.