An internal model for tracking a sinusoidal reference with unknown frequency and uncertain plant^*

We propose a novel internal model-based controller to solve the reference tracking problem for an uncertain plant and a sinusoidal reference of unknown frequency. A third order self-synchronizing synchronverter model is used as an internal model, leading to remarkable results. We only require that the plant P is stable and linear, and that an "initial guess"ωn on the reference frequency ωr is available. Under these assumptions, we ensure tracking for ωr ∈ [0.25ωn,4ωn]. Moreover, among other features, our controller is able to withstand (at steady-state) large step jumps in ωr (≈ 300% frequency jumps) and in the dynamics of P (e.g., P is allowed to change sign during operation). Extensive numerical experiments are provided to illustrate these impressive features.