Stability analysis of an Ideal-Transformer-Model interface algorithm

The subject addressed in the proposed paper is to define stability conditions of an Ideal Transformer Model interface algorithm used for coupling two real-time simulators. The Ideal Transformer Model algorithm is one of the most straightforward methods for hardware-in-the-loop simulations. Integration of the Ideal Transformer Model into the system does not affect systems impedance characteristics and this is its most prominent advantage. However, specific change of system and load impedance ratio may result into system instability. Furthermore, it is shown that the transition of the system into an unstable state is the consequence of the time-delay between simulators. Time-delay turns out as a disturbance that amplifies an error due to transmission of the voltage signal between the simulators. Taking into account Nyquist stability criterion, three cases with different system and load impedance ratio are presented, first with the simulations in Matlab Simulink and later on with simulations on RT simulators.