A variable frequency internal model controller inspired by synchronverter theory

We investigate a new class of controllers to solve the regulator problem for single-input single-output stable uncertain linear plants, when the signals are a finite superposition of sinusoids with uncertain frequencies (including constants). For this purpose, we formulate a novel type of nonlinear internal model: including a third order synchronverter model in the controller algorithm, we are able to exploit the well-known self-synchronizing feature of the synchronverters, making it possible to solve the regulator problem with little information on the signals (uncertain frequencies), and almost no information on the plant, which is only required to be stable. For instance, the same controller works both for the plant P and for the plant-P, and also after a step change in the signals' frequencies (within reasonable bounds), a surprising feature that is not true for traditional internal model-based controllers. The performance of the proposed controller is validated through three numerical examples of different nature.