Analysis And Suppression Of Harmonic Resonances For The Grid-connected Photovoltaic System Considering The Distributed Capacitance Of Cable

When the photovoltaic(PV)inverter connects to the end of a transmission cable parasitized by non-negligible distributed capacitance and distributed inductance,not only the interaction between the transmission cable with grid-connected PV inverters leads to complex resonance issues,but also the grid background harmonic voltage propagation along the cable might result in serious harmonic amplification problem due to the resonance between distributed capacitance and distributed inductance of the cable,which will aggravates the power quality of point of the common coupling(PCC)voltage and threaten the safety of the equipment.The model of the grid-connected PV system with a transmission cable is established in this paper.A control block diagram of grid-connected inverter with capacitive current active damping current control is build,and the equivalent Norton model of the grid-connected inverter is obtained by the equivalent transformation.Futhermore,the model of the cable impedance is analyzed,based on which a series of resonant points are found in the bode plot of cable impedance considerating the influence of the distributed capacitance.The resonance characteristic of the grid-connected inverter was analyzed,and it is found that the system exhibits multiple resonances due to the influence of cable impedance.The mechanism of multi-resonances is studied from the perspective of impedances interaction.An active damping strategy based on capacitor voltage feedback is proposed to eliminate the considerble multi-resonances,which increases the phase margins of the system.According to the transmission line theory,the background harmonic voltages oscillating propagation characteristics are analysised in this paper.The output impedance of the grid-connected inverter with capacitive current active damping current control has great influence on harmonic voltages oscillating propagation characteristic,resulting in serious harmonics propagation amplification.An universal background harmonic propagation amplification suppression method based on extreme inverter-harmonic impedance remodeling(EHIR)control is proposed in this paper.The effectiveness of the two proposed strategies are verified by both theoretical analysis and simulation results.Finally,a single-phase lumped network with several ?-section cells is established,and the feasibility of the cable model for experimental verification is analyzed in this paper.A digital signal processor TMS320F28335 is used to contorl the single-phase inverter.The experimental results prove the correction of the theoretical analysis and the effectiveness of the proposed strategies in this paper.