PROJECT TITLE :
Analysis and Mitigation of Resonance Propagation in Grid-Connected and Islanding Microgrids
The appliance of underground cables and shunt capacitor banks could introduce power distribution system resonances. During this paper, the impacts of voltage-controlled and current-controlled distributed generation (DG) units to microgrid resonance propagation are compared. It can be seen that a standard voltage-controlled DG unit with an LC filter features a short-circuit feature at the chosen harmonic frequencies, whereas a current-controlled DG unit presents an open-circuit characteristic. Due to completely different behaviors at harmonic frequencies, specific harmonic mitigation methods shall be developed for current-controlled and voltage-controlled DG units, respectively. This paper also focuses on developing a voltage-controlled DG unit-based active harmonic damping technique for grid-connected and islanding microgrid systems. An improved virtual impedance control technique with a virtual damping resistor and a nonlinear virtual capacitor is proposed. The nonlinear virtual capacitor is employed to compensate the harmonic voltage drop on the grid-facet inductor of a DG unit LCL filter. The virtual resistor is especially responsible for microgrid resonance damping. The effectiveness of the proposed damping method is examined using both one DG unit and multiple parallel DG units.
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