Study On Stability Control Of Grid-connected System With Different Grid Impedance

With the vigorous development of the new energy power generation technology,power electronic converter plays an important role in distributed generation based on renewable energy sources which is connected to the grid through the inverter.When current control method inverter operates in grid-connected mode,usually,the effects of the grid impedance need to be considered,which might affect the system stability.Therefore,based on the impedance-based criterion,the necessity of searching power grid impedance and approaches of eliminating harmonics instability phenomena are elaborated.Whether the parasitic capacitance is considered in the grid impedance which effects the system stability is also researched.When power grid impedance is considered in the grid-connected system,start by analyzing harmonic distortion issues and out of voltage limit instability to the distribution power system.The reasons for instability phenomena are classified and power grid impedance is becoming a focus in research.What's more,problem-solving approaches of instability phenomena are researched in detail.Then parasitic capacitance is considered or not in grid impedance,whose effects of the system stability are analyzed.When the parasitic capacitance of power grid impedance is neglected in the grid-connected inverter system,in the high grid impedance,the distribution system harmonic suppression strategy is proposed aiming at harmonic distortion issues and reactive power control is researched in detail aiming at voltage overrun.In order to enhance system stability and ensure the amplitude of PCC voltage within allowable range,a dual control strategy achieved by combination of the distribution system harmonic suppression and reactive power control is proposed in this paper.Considering the parasitic capacitance of power grid impedance in the inverter system and using Lumped-parameter model,the grid impedance model is complex hyperbolic tangent transfer function,therefore,the Pade linear fitting method as the main method is researched which can linearized complex transfer function and reduce workload.Simultaneously,selection method of the suitable fitting order is analyzed and a simple linearized model is obtained.Finally,the stability problem in the grid-connected system caused by power grid impedance is analyzed based on impedance criterion.The Matlab/Simulink simulations and actual tests are carried out to verify the correctness of theoretical analysis.Finally,an experiment platform of parallel-connected inverters is built based on TMS320F2812 DSP and the software and hardware of system is designed,respectively.Then the experimental results prove the correction of theoretical analysis.