An adaptive controller for inverter-interfaced DGs connected to grids with a wide range of unknown impedances

Significantly degraded dynamic performance, or even instability, can occur when connecting a distributed generator interfaced through an inverter to a grid whose impedance is significantly different than the one that the inverter is designed for. Previous solutions in the literature require measurement of the grid impedance and re-engineering of the inverter controller. In this paper, a novel, adaptive current control is proposed. It employs an embedded Model Reference Adaptive Control that turns the plant model with uncertainties into a known, desired model. Consequently, the controller can self-adapt to a wide range of grid impedances without problems of instability and degradation of dynamic performance. This allows mass manufactured inverters of a single design to be connected to grids of different stiffness. The design of the proposed controller and simulation verification results are presented.