Use of Series Negative Impedance to Cancel the Effect of Equivalent Grid Impedance on the Grid-Connected Inverter Stability in the DPGS

An active grid impedance cancellator is proposed to suppress the effect of the grid disturbance and stabilize the distributed power generation (DPG) grid-connected inverters operating under the weak grid. Harmonic interaction between the DPG inverter and the grid is thereby avoided owing to the cancellation of equivalent grid impedance. The impedance cancellator composed of a full-bridge dc-ac converter without passive filtering elements is connected in series at the inverter output to simulate a negative virtual grid impedance. In addition, an active damping function is integrated to suppress the filter resonance of the inverter. In the paper, the system configuration and the control strategy of the impedance cancellator are introduced. The power consumption of the cancellator is also evaluated. A single-phase grid-connected inverter prototype has been built to verify the effectiveness of the proposed method. The experimental results show a good agreement with the theoretical knowledge.