  Unbalanced and nonlinear loads connected to microgrids (MG) with local
distributed energy resources (DERs) are two of the leading causes of power
quality problems. Nonlinearloads introduce voltage and current harmonics, and
single-phase loads can cause voltage and current imbalances in a three-phase
network. This paper presents a hierarchical control scheme for
voltage-controlled photovoltaic (PV) inverters with unbalanced and nonlinear
loads in micro-grids. The hierarchical control consists of primary control and
voltage compensation control(VCC) and a DC voltage regulator (VR). The primary
control scheme controls active and reactive power-sharing and the VCCregulates
the unbalanced voltage and harmonics distortion. The effectiveness of the
scheme is verified using Opal-RT real-time simulation and experimentally using
control hardware-in-the-loop. The voltage distortion at the point of common
coupling (PCC)decreased from 6.38 percent to 1.91 percent after compensation,
while the unbalanced and harmonic loads are shared proportionally among the DG
units.
