Global resonance suppression strategy for PV multi-inverter parallel system
JIANG Yunhao
LI Ruoxuan
HOU Tianhao
Abstract：[Objective]With the rapid development of power generation from renewable energy,photovoltaic power generation is widely adopted due to its merits of safety,reliability,flexible adjustment,and clean production.Due to the real demand for large-scale photovoltaic power generation,multiple inverters connected in parallel and grid-connected inverters are often adopted in photovoltaic power stations to enhance the power generation efficiency.However,with the expansion of the grid-connected scale,the inductive impedance under the weak grid poses a threat to the stability and reliability of the grid,leading to poor global resonance suppression as well as a high risk of uncontrollable system stability.The aim of this study is to propose a global resonance suppression strategy for photovoltaic(PV)multi-inverter parallel system to guarantee the stable operation of the system and improve its power quality.[Methods]Firstly,a Norton equivalent model of the PV multi-inverter parallel system was constructed.Based on this model,this paper analyzed in depth the resonance characteristics of the multi-inverter parallel system under a weak grid,and it was found that the coupling resonance frequency was negatively correlated with the number of inverters.Secondly,based on the control theory,the optimal control strategy combining capacitor current feedback and grid voltage feed-forward was applied to solve the global coupling resonance problem in the multi-inverter system.At the same time,the global resonance suppression strategy of paralleling virtual admittance at the point of common coupling(PCC)was designed to realize the effective suppression of global resonance from the system level.Finally,comparative simulation experiments before and after adopting the strategy proposed in this paper were conducted under two-inverter parallel system and four-inverter parallel system.In addition,simulation experiments were also carried out to compare the suppression effect under the same system by using other methods reported previously and the strategy proposed in this paper.The correctness and effectiveness of the proposed strategy were verified through simulation.[Results]Theoretical analysis and simulation results show that the proposed global resonance suppression strategy can significantly improve the stability of the system.The rationality of the control strategy and its parameters are validated and optimized by the Nyquist criterion.Simulation test results show that after the application of the proposed strategy,the harmonic content in the system is reduced from 17.32％to 1.71％.This indicates that the proposed strategy can effectively suppress the global resonance of the system and enhance the stability of the system operation.[Conclusion]In this paper,a Norton equivalent model of PV multi-inverter parallel system was constructed.Innovatively,the resonance characteristics of the multi-inverter parallel system under a weak grid were analyzed,and a global resonance suppression strategy of paralleling virtual admittance at the PCC was proposed on the basis of the optimal control of capacitor current feedback and grid voltage feed-forward.The strategy effectively improves the stability of the system operation in the presence of a large number of parallel inverters and high inductive reactance of the grid.The comparative simulation verification further demonstrates that the proposed strategy can suppress the global resonance of the system effectively,providing important reference for the efficient operation of PV power generation grid-connected system.
Keywords：weak gridparallel inverterresonance characteristicfeed-forward optimizationvirtual admittanceglobal suppressioninductive impedance
Publication Date：2025-07-25
Online Publishing Date：2025-09-18(First online date of this platform, not the publication date of the document)
Pages：8( 493-500 )