Abstract
This paper proposes a new approach on the novel current control strategy for grid-tied
voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard
grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy
system to enhance the penetration of total utility power. However, restrictive grid codes require
that renewable sources connected to the grid must support stability of the grid under grid faults.
Conventional synchronously rotating frame dq current controllers are insufficient under grid faults
due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a
proportional current controller with a first-order low-pass filter disturbance observer (DOb). The
proposed controller establishes independent control on positive, as well as negative, sequence current
components under asymmetrical grid voltage conditions. The approach is independent of parametric
component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb.
A numerical simulation model of the overall power system was implemented in aMATLAB/Simulink
(2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active
power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover,
a set of simulation results provided in the article matches the developed theoretical background for
its feasibility.