Lyapunov-Based Digital Control of a Grid-Connected Inverter With an LCL Filter

Instabilities due to mutual interactions among the converters and inverters are sometimes observed. A system with multiple converters can be controlled stably overall when each converter is controlled according to each energy-based function like the Lyapunov function. This paper proposes a new Lyapunov-based digital control method. First, a principle is derived especially for digital control. A new numerical generator for reference waveforms is then proposed to avoid complex analytical operations. This is applied to a grid-connected inverter with an LCL filter. We also propose a virtual damping method to prevent resonant oscillations in the filter. The proposed methods are investigated and validated through simulation using Saber software and through experiments using a DSP-based digital control system.