Coordinated virtual resistance and capacitance control scheme for accurate reactive power sharing and selective harmonic compensation in islanded microgrid

Abstract

Line impedance mismatch and unregulated harmonic currents cause serious problems for an islanded microgrid,such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To overcome theseissues, a coordinated virtual resistance and capacitance are introduced together with its control scheme for parallel distributedgeneration (DG) in an islanded microgrid. The proposed coordinated virtual impedance control scheme directly modifies the DGoutput impedance at the fundamental frequency to realise accurate current sharing among DG units. In addition, a variableharmonic impedance control loop is proposed for each DG to absorb the non-linear load harmonic current. Thanks to theproposed control scheme, the PCC harmonic voltage distortion is successfully compensated and power-sharing among DGunits is accurately achieved. The stability of the microgrid system was analysed in detail to verify the feasibility of thecoordinated virtual impedance control scheme. Experiments on a laboratory prototype microgrid are performed to validate theperformance of the proposed control scheme.