Research On Resonance Mechanism And Suppression Technology Of Photovoltaic Clusters

Photovoltaic cluster power generation can improve the power generation efficiency of photovoltaic power plants,but the photovoltaic cluster inverter will produce resonance after the grid-connected,which will affect the stability of the power system and the power quality of the power grid.In order to ensure the power supply reliability of the power grid,this paper analyzes the resonance generation mechanism and resonance characteristics of the photovoltaic cluster system in detail.A lot of researches have been done on the resonance suppression strategy of grid-connected photovoltaic inverters cluster.However,most of them need to change the control structure of each inverter.Based on this,this paper proposes a control strategy of global resonance suppression,which does not need to change the structure of each inverter,and the resonance suppression method is studied in depth.Firstly,according to the output characteristics of photovoltaic cells,the maximum power point of photovoltaic power generation system needs to be tracked.In order to improve the influence of traditional control methods on the harmonic content of photovoltaic cluster system,a control method based on the combination of fuzzy control and adaptive step length is proposed in this paper.Comparing the proposed method with the traditional control method by simulation,the results show that the MPPT control method studied in this paper can make the system reach stability faster than the traditional method,and has less influence on the harmonics of the photovoltaic cluster system.Secondly,according to the structure characteristics of photovoltaic cluster system,LCL filter is selected as the filtering device of photovoltaic grid-connected system.The parameters of each component are calculated through theoretical analysis,and the parameters of the filter are optimized through the simulation and comparison of the influence of the parameters matching relationship on the performance of the system,the harmonic content in the inverter output current is reduced.Thirdly,the resonance mechanism of the single photovoltaic grid-connected inverter is analyzed in detail.Based on the research of the single inverter,the resonance mechanism of multiple photovoltaic inverters cluster systems is analyzed qualitatively and quantitatively by using the small signal analysis method and frequency domain analysis method.The influence of the number of inverters connected in parallel on the resonance frequency of the system is studied and the law of resonance frequency change is found out.The resonance characteristics of the photovoltaic inverters cluster system are compared and analyzed under different system parameters.Finally,according to the previous analysis of the resonance mechanism of the photovoltaic cluster system,the corresponding resonance suppression strategy is studied.The control method of capacitive current feedforward and inverter-side current feedback is used to suppress the resonance of single photovoltaic inverter.The RC-type global resonance suppression strategy is proposed for the grid-connected resonance of multiple photovoltaic inverters cluster,and the system resonance can be suppressed without changing control structure and the original operation mode of each inverter.To improve this method,put forward the control strategy of thyristor switching RC circuit(TSRC),and verified the effectiveness of the proposed method through simulation and experiment.