A comparative study on approaches to curve fitting of magnetization characteristics for induction generators

The curve fitting of magnetizing characteristics of self excited induction generators (SEIG) resulting airgap voltage (V_g) with magnetising current (I_m) is crucial for performance analysis of such machines using design tools. The magnetisation characteristic may be obtained using the B - H curve of the core material. An appropriate curve fitting technique/regression analysis is employed to represent V_g - I_m curve from which V_g - X_m curve can be derived. There is wide literature on approximation of magnetization curves of variety of materials. Accurate analysis of a magnetization curve, or the B - H characteristic, has always posed problems for electrical engineers dealing with machine design. The problem has been to find a single function to represent the wide range from the origin to saturation with a minimum error over the whole range. Moreover, such a function should be mathematically simple for easy application. In this paper, different techniques are critically compared to guide the designers on a right approach with special reference to SEIG.