1.School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China;2.State Grid Liaoning Electric Power Company Limited Economic Research Institute, Shenyang 110015, China

Neighboring microgrids are usually interconnected by long transmission lines. For the system where both sending and receiving ends of transmission lines have independent harmonic sources, the harmonic interaction characteristic and the harmonic amplification mechanism are more complicated, and the conventional resonance suppression method of resistive active power filter is not suitable. Based on the transmission line theory, this paper analyzes the harmonic propagation mechanism of interconnected lines, and proposes a resonance suppression method based on harmonic impedance matching. To overcome the uncertainty of line parameters and phase angle information of harmonic sources, this paper proposes a coordinated control method for harmonic impedances of active power filters based on the line middle-point harmonic voltage detection. According to the harmonic voltage content, the phase angles of harmonic impedance at both ends of the line are adjusted online to realize resonance suppression. Meanwhile, an improved control strategy of active power filters is proposed to ensure that the harmonic impedance phase angle can be adjusted arbitrarily. Simulation results verify the effectiveness of the proposed scheme.