Thyristor(diode) on-state voltage, the ABCD modeling parameters revisited including isothermal overload and surge current modeling

Circuit modeling is an essential tool in the design of power electronic applications. The widespread use of these models, however, depends upon the availability of parametric data for devices and the proper trade-off of the accuracy and simplicity of the model. This paper addresses these two areas with regard to the forward on-state voltage of thyristors and diodes. As has been described in previous papers, forward on-state forward voltage drop can be modeled by the now classical ABCD parameters. This paper discusses the problems and strengths of the ABCD model and describes how the ABCD parameters can be quickly and efficiently calculated by a 3rd order, multiple, nonlinear regression in a new STARS Visual module. This paper proposes an alternate mathematical model to the ABCD model, labeled the MNOP model, and describes the advantages of this model. This paper also describes one of the main limitations of the ABCD model, which is the fact that it is typically used to describe the maximum forward voltage drop on the data sheet, which is NOT an isothermal curve. This, in turn, does not permit the change in the on-state forward voltage drop as a function of junction temperature to be modeled. Isothermal models of diodes and thyristors will be discussed and a new simplified model proposed for surge and overload conditions.