A Voltage Controlled DG Unit Based Active Harmonic Damping for Grid Connected and Islanding Micro grids

Abstract

The use of underground cables and shunt capacitor banks may present power distribution system resonances. Due to different behaviours at harmonic frequencies, specific harmonic mitigation methods shall be developed for current controlled and voltage-controlled DG units.  In thispaper centres on developing a voltage-controlled DG unit-based active harmonic damping method for grid-connected and islanding microgrid systems. An upgraded virtual impedance control method with a virtual damping resistor and a nonlinear virtual capacitor is proposed. The nonlinear virtual capacitor is used to compensate the harmonic voltage drop on the grid-side inductor of a DG unit LCL filter and the virtual resistor is mainly responsible for microgrid resonance damping. The efficiency of the proposed damping method is examined using both a single DG unit and multiple parallel DG units.