A harmonic current suppression control strategy for droop-controlled inverter connected to the distorted grid

The grid-feeding voltage controlled inverter (GF-VCI) based on droop control is vulnerable to the harmonic voltages of the utility grid. Because of the equivalent impedance of system is small, the slight distorted grid voltage will result in the harmonic component increasing of GF-VCI output currents. Therefore, the reason of generation of distorted grid-feeding current of GF-VCI under the distorted grid voltage is investigated firstly in this paper. Then, a harmonic grid-feeding current suppression control strategy for GF-VCI is proposed. Two different filters are compared and analysed before being adopted for abstracting the fundamental components of grid voltage. The injected fundamental power is controlled through droop controller, and a hybrid voltage controller of GF-VCI with PI and R regulators in rotary frame is adopted for improving of the tracking capability of the grid harmonic voltage component at the point of common coupling. As a result, the difference of harmonic voltage between PCC and GF-VCI is reduced and the THD_i of grid feeding-currents is decreased. Finally, the proposed control strategy is verified through simulations and experimental results.