Improved Coherency-Based Wide-Band Equivalents for Real-Time Digital Simulators

This paper introduces an approach which enables very large power systems to be modeled on real-time electro-magnetic transients (EMT) digital simulators. This is achieved using an improved wide-band multi-port equivalent, which reduces a large power network into a small manageable equivalent model that preserves wide-band behaviors. The low-frequency or electromechanical transients are captured with a transient stability analysis (TSA) type electromechanical equivalent derived using coherency-based reduction techniques. The high-frequency behavior is accurately captured by placing in parallel with the TSA equivalent, a passive frequency dependant network equivalent (FDNE). The validity of the proposed technique is demonstrated by comparing the approach with detailed electromagnetic simulations of a modified version of the New England 39-bus test system that includes an HVDC infeed. The power of the method is demonstrated by the real-time electromagnetic transient simulation of a large 2300-bus 139-generator system.