A Composite Exponential and Linear MOA Model for Switching Transient Simulation

The multi-exponential MOA model currently used to simulate switching transients (current model) approximates the V-I characteristic of a MOA with several exponential segments. A test case illustrates a numerical oscillation caused by this model. The source of the oscillation is identified as the value jump of the derivative of the approximating function at the boundary point of adjacent exponential segments. The problem can be solved by using the Quasi-Newton method, but at the expense of computing time. A modified model is presented in this paper. This new model (proposed model) features a composite exponential and linear approximation to the V-I characteristic, and a monotonic derivative of the approximating function. The combination of the Newton method of iteration and the proposed model not only avoids numerical oscillation, but also has a better performance on computing time than the combination of the Quasi-Newton method and the current model.