Analytical investigation of nonlinear interactions between Voltage Source Converters interconnected to a transmission grid

The increase of renewable energy sources and HVDC links lead to power systems composed of a large number of interconnected Voltage Source Converters, involving predominant nonlinear oscillations. The strong coupling effect in the severely stressed system obscures the characteristics of the nonlinear dynamics. To tackle this problem, a proposed Nonlinear Mode method based on Normal Form theory makes possible to decompose the system modeled by N coupled nonlinear damped oscillators into a sum of decoupled nonlinear damped oscillators, keeping the physical meaning along with reducing the complexity of the problem. Mode decomposition and amplitude-dependent frequency-shift are then extracted, rendering a deeper insight of the system dynamics possible. The efficiency of the method is illustrated by a simple but didactic case-study.