Real time interface for interconnecting fully digital and analog simulators using short line or transformer

Recently, thanks to the rapid progress of computer technology, fully digital real-time simulators are in the market and used by many utilities. They have several advantages over the conventional analog simulators, for example, the flexibility of network configuration, low cost, compactness and reproducibility of results. If we can connect the digital simulator with the existing analog one, many features of the digital simulator as outlined above could be extended to the existing analog simulator, which has other merits. There are some studies, which utilize the propagation delay time of transmission lines in interconnecting these two types of simulators. But such a technique requires a transmission line long enough to compensate for the delay time which is introduced by the interconnection of these simulators. In other words, if there is no suitable long transmission line available in the power system, it cannot be adopted as an interfacing technique. In this paper, two real-time interface methods not relying on the propagation delay of transmission lines are developed and verified. These methods can be applied whenever there exists a transmission line of any length or a transformer in a power system.