Coordinated control for harmonic mitigation of parallel voltage-source inverters

The increasing use of power electronic devices can deteriorate the power quality by introducing voltage and current harmonics. In islanded microgrids, the presence of nonlinear loads can distort the point of common coupling (PCC) voltage, while the dead-time effect can also bring additional circulating current harmonics among parallel inverters. To simultaneously attenuate the PCC voltage harmonics and suppress the dead-time induced circulating current harmonics, this paper proposes a coordinated control strategy for harmonic mitigation of parallel inverters. The proposed control strategy allows inverter impedances to be properly reshaped at selective harmonic frequencies. As a consequence, the PCC voltage harmonics are filtered by the inverter operating in the harmonic compensation mode (HCM), whereas the dead-time induced circulating current harmonics are suppressed by the inverter operating in the harmonic rejection mode (HRM). Experimental results from an islanded microgrid prototype with two parallel inverters are provided to validate the effectiveness of the proposed control strategy.