Nonlinear Modal Decoupling of Multi-Oscillator Systems With Applications to Power Systems

Many natural and manmade dynamical systems that are modeled as large nonlinear multioscillator systems like power systems are hard to analyze. For such systems, we propose a nonlinear modal decoupling (NMD) approach inversely constructing as many decoupled nonlinear oscillators as the system's oscillation modes so that individual decoupled oscillators can be easily analyzed to infer dynamics and stability of the original system. The NMD follows a similar idea to the normal form except that we eliminate inter-modal terms but allow intra-modal terms of desired nonlinearities in decoupled systems, so decoupled systems can flexibly be shaped into desired forms of nonlinear oscillators. The NMD is then applied to power systems toward two types of nonlinear oscillators, i.e. the single-machine-infinite-bus (SMIB) systems and a proposed non-SMIB oscillator. Numerical studies on a 3-machine 9-bus system and New England 10-machine 39-bus system show that: 1) decoupled oscillators keep a majority of the original system's modal nonlinearities and the NMD can provide a bigger validity region than the normal form and 2) decoupled nonSMIB oscillators may keep more authentic dynamics of the original system than decoupled SMIB systems.