| Abstract |
In this paper, a hierarchical control scheme consisting of primary and secondary levels is proposed forachieving accurate reactive power and harmonic currents sharing among interface inverters ofdistributed generators (DGs) in islanded microgrids. Firstly, fundamental and main harmoniccomponents of each inverter output current are extracted at primary level and transmitted to thesecondary controller. Then, instantaneous circulating currents at different frequencies are calculatedand applied by the secondary level to generate proper control signals for accurate reactive power andharmonic current sharing among the inverters. Consequently, these signals are sent to the primarylevel and inserted as voltage references after passing the control blocks. In contrast to the conventionalvirtual impedance schemes, where reactive power and harmonic current sharing are realized at theexpense of introducing additional voltage drop and distortion, the proposed control strategy effect onthe amplitude and waveform quality of DGs' voltage is negligible. Meanwhile, it is able to provideaccurate harmonic current sharing even if nonlinear loads are directly connected at the terminal of DGunits. Control system design is described in detail and simulation results are provided to demonstratethe effectiveness of the proposed control method. |
