Compensation of Voltage Harmonics for LCL-filtered Inverters in Islanded Microgrids

In a microgrid (MG), it is possible to have some sensitive loads that require high voltage quality. In this paper, a new technique is proposed for selective compensation of main voltage harmonics in islanded MGs. The proposed technique is capable of adjusting the compensation percentage in proportion with the existing disturbance in the sensitive load bus (SLB) and sharing the compensation workload among DGs in proportion with their nominal power. This compensation, is performed by controlling of the interface inverters of distributed generation (DG) units with LCL filters. Also, to decrease the asymmetry among phase impedances of MG and mitigate the voltage distortion after the output LCL of filters, a novel structure is proposed to generate selective virtual impedance. At fundamental frequency, the proposed structure of the virtual impedance improves the control of the fundamental component. On the ather hand, at main harmonic frequencies, it tries to adaptively improve nonlinear load sharing among DG units and mitigate the voltage distortion after the output LCL filters. Simulation results in MATLAB/SIMULINK environment show the efficiency of the proposed approach in improving load load sharing and decreasing voltage harmonics.