Harmonic Instability analysis using state-space modeling in Grid-Connected Inverter System with long transmission cable

The distributed parasitic capacitance along the long transmission cable (LTC) may cause harmonic instability issues in grid-connected inverter system, this paper proposes a harmonic instability analysis method using state-space modeling and participation analysis for investigating the mechanism of harmonic instability and its key influencing factors. Firstly, the vector matching method is proposed to equivalent the AC system with frequency-dependent LTC, and the high-frequency state space model of the grid-connected inverter system in dq-frame system is established considering inner and outer control loop, phase-locked loop and control delay etc.; Secondly, the key influencing factors contributing to the harmonic oscillation are identified by the participation factor analysis method, moreover, the root locus method is used to study how the delay time, inner loop controller parameters, cable length and grid impedance affect the harmonic instability of the system. Finally, Based on RT-LAB hardware-in-loop experiment platform, the experimental results can verify the correctness of the theoretical analysis in this paper.