Empirical study of simulation fidelity in geographically distributed real-time simulations

Interconnection of digital real-time simulators over wide-area communication networks is an innovative approach to extend local real-time simulation capabilities to enable large-scale simulations. Furthermore, it allows the integration of geographically distributed assets as Power Hardware-in-the-Loop and Controller Hardware-in-the-Loop, thus providing a flexible framework for performing unique research experiments. In most cases, it is not possible to perform large scale real-time simulations and comprehensive experiments locally due to lack of simulation capacity and unavailability of unique assets. Main challenge associated with geographically distributed real-time simulation is to ensure simulation fidelity of the same degree as in the case when the entire simulation is performed at the same location. Simulation fidelity in geographically distributed real-time simulation is investigated and an empirical characterization is provided in this paper. Fidelity degradation caused by different values of time delay and sending rate of data exchange between two digital real-time simulators is presented. Two methods for representation of interface quantities in co-simulation interface algorithms are considered for performing simulations. The first method is based on representation of interface quantities as root mean square of magnitude, frequency, and phase angle of the current and voltage waveforms. The second method utilizes representation of interface quantities in form of time-varying Fourier coefficients, known as dynamic phasors. The empirical study is performed for transmission-distribution co-simulation using two racks of Real-Time Digital Simulator (RTDS®).