Cooperative Operation of DG Inverters and a RIHAF for Power Quality Improvement in an Integrated Transformer-Structured Grid-Connected Microgrid

Harmonics in microgrids have attracted intensive power quality concern. It is analyzed in this paper that both currents in the voltage-controlled DG inverter side and the main grid side are easily involved in harmonic distortion due to nonlinear loads and background harmonics. To deal with this issue, a cooperative operation strategy for the DG inverters and a reactor-integrated hybrid active power filter (RIHAF) are proposed based on an integrated transformer-structured grid-connected microgrid. First, for the purpose of cost reduction and covering space saving, an integrated transformer based on a reactor integration technique (RIT) is conceived and the principle of the RIT is illustrated. To improve the current quality in the DG inverter side, a harmonic impedance reinforcement control method is employed to enhance the harmonic rejection performance of the voltage-controlled DG inverter. Besides, taking advantage of the integrated transformer, a RIHAF is proposed to suppress the current harmonics in the main grid side. Detailed simulation results show that current harmonics in both the DG inverter side and the main grid side can be simultaneously suppressed with the proposed cooperative operation strategy. Finally, experimental results from a scaled-down integrated transformer-structured microgrid platform are presented to verify the effectiveness of the RIT and the proposed cooperative operation strategy.