Stability and Accuracy Analysis of Digital Real-Time Simulators Interconnection for Co-simulation Infrastructure Design

The aim of this thesis work is to analyze the main co-simulation techniques and standards to evaluate the feasibility of data transmission between different Digital Real-Time Simulators [DRTS] exploiting high-bandwidth and low-latency protocols (e.g. Xilinx Aurora 8B/10B) to allow Hardware In-the-Loop (HIL) testing in co-simulation infrastructure. The communication latency is a very important parameter to be determined before interconnecting different DRTS, to run complex power system simulations because it is considered one of the main numerical stability issues. In fact, latency could influence on time-domain accuracy and frequency-domain stability of the solution in fast time-stepped simulation. In this work, the time delay of communication protocols that enable DRTS interconnection is measured to ensure that latencies will not affect power system co-simulation results. As part of the analysis, this calculation has been compared with other variables to determine if their values affect the time delay behavior of DRTS interconnection, such as the amount of data transmitted, and the imposed time step. Retards are present on PHIL systems due to the delay time from when the electrical signal is transmitted from the real-time simulator (RTS) and passes through the power amplifiers (coupled in the real-time simulator) until the hardware under test (HUT) actually receives the signal. The retard phenomenon happens also in co-simulation, but the retard is due to delays in the communication from one point to another. Based on the previous statements, the purpose of the thesis second step is to create a simple electrical circuit to be implemented and split it into two parts running on two DRTS. In this stage, a theoretical analysis was performed to establish the parameters that ensured stability of the system. To state those parameters, the theoretical analysis was approached by an Interface Algorithm method, which through a set of non-differential equations analyzed the stability of delayed systems. Once stablished the parameters that assured the system stability, the simulation was performed using a single DRTS (RTDS Technology Novacor2 chassis) exploiting an echo link to experimentally test the behavior of the system. The performed tests on the DRTS showed the limitations of the real-time simulator when comparing it with respect to the theoretical simulations. As a conclusion, it is stated the appropriate parameters regarding the time step and circuit specifications that must be followed to set-up a composed co-simulation infrastructure in DRTS.