Observer-Based Current Controller for Parallel-Connected Inverters in the Presence of Grid Voltage Harmonics

This article proposes the use of an observer-based current controller within each inverter in a parallel connected multi-inverter system. Suppression of harmonic components by each inverter's current controller contributes to reducing the harmonic emission level of the system at the point of connection (PoC), even while connected to a grid with background voltage harmonics. Furthermore, by including a simple feedforward term in the overall control law, a fast transient response is achieved. In lieu of using a complex model of the whole parallel connected multi-inverter system, the current controller is designed at the individual inverter level; nevertheless, excellent overall system performance is achieved. Simulation and experimental results have been obtained to validate the performance of the proposed parallel connected inverter system.