Investigation of stabilities of Lyapunov-Based digital control for grid-connected inverter

Instabilities due to mutual interactions among converters and inverters are sometimes observed. The Lyapunov-based, or an energy-based control is useful to assure stability of parallel-connected power converters. This paper investigates why the Lyapunov-based method can stabilize the system even when linear methods fail in stabilization due to a large line impedance. The analysis is based on the impedance method. Some examples including a pure inductive and a resonant-type line cases are analyzed. It is made clear how their stability are ensured from their frequency characteristics.