Dynamic average modeling of line-commutated converters for power systems applications

Detailed switch-level models of high-pulse-count converters are relatively straightforward to implement using commonly available simulation packages used for digital time-domain simulations and studying of power systems transients. However, such models are computationally intensive due to switching, and could become the bottle-neck for system-level studies with large number of components and controllers. This paper describes approaches for developing dynamic average-value models, i.e., the analytical derivations and parametric modeling. The resulting approximate models do not represent switching but still capture the transient behavior of the original converter circuit. The paper presents the results for 3- and 6-phase rectifiers implemented in PSCAD/EMTDC and Matlab/Simulink and shows that dynamic average models can be very effective. The paper also shows that as the number of pulses/phases increases, so does the complexity of switching pattern that defines the operating modes.