This paper presents a method to model three-phase saturable transformers for real-time simulation, using the example of a wye-delta configuration. The magnetizing path of the transformer is modelled with parallel connected linear inductors to simulate a piecewise linear saturation characteristic. Depending on the saturation state, the inductors are switched on and off via ideal switches, which are modelled via parametrized curves. An efficient implementation is proposed for real-time simulation. The simulation offline on the PC, online on the realtime target with a step size of 50us and the application on a wind turbine converter system validate the method. The achieved results demonstrate the performance of the method.

A novel model order reduction (MOR) method, SparseRC, for multiterminal RC circuits is proposed. Specifically tailored to systems with many terminals, SparseRC employs graph-partitioning and fill-in reducing orderings to improve sparsity during model reduction, while maintaining accuracy via moment matching. The reduced models are easily converted to their circuit representation. These contain much fewer nodes and circuit elements than otherwise obtained with conventional MOR techniques, allowing faster simulations at little accuracy loss.

In this paper, the dominant spectral-zero method (dominant SZM) is presented, a new passivity-preserving model-reduction method for circuit simulation. Passivity is guaranteed via spectral-zero interpolation, and a dominance criterion is proposed for selecting spectral zeros. Dominant SZM is implemented as an iterative eigenvalue-approximation problem using the subspace-accelerated dominant-pole algorithm. Passive circuits are reduced automatically irrespective of how the original system equations are formulated (e.g., circuit models containing controlled sources or susceptance elements). Dominant SZM gives comparable and often more accurate reduced models than known techniques such as PRIMA, modal approximation, or positive real balanced truncation.