Research On Asymmetrical Fauit Ride-through Stratege Based On Voltage-controlled Three-phase Grid-connected Inverter

In order to solve the problem of fossil resource depletion and environmental pollution,new energy technology has been developed rapidly.As the penetration rate of distributed generation(DG)continues to increase,its impact on the grid is also increasing.The integration of distributed generation into the power grid can effectively improve the flexibility and safety of the power system,but it also raises related problems.When a short-term fault occurs in the system,large-scale DG off-grid may exacerbate the transient imbalance of the source-load power in the system and weaken the fault self-healing ability of the power grid.In order to improve the stability of the system,the domestic and international grid standards require that the distributed generation connected to the grid have certain fault traversal ability.In this thesis,the operation characteristics and fault crossing control strategy of three-phase grid connected inverter under the condition of asymmetric fault on the grid side are studied.In order to accurately extract the positive and negative sequence components in the system under asymmetric faults,four common separation methods of positive and negative sequence are analyzed and compared,finally,considering the stability and rapidity,the positive and negative sequence extraction scheme based on the structure of the double generalized second-order integrator is adopted.The traditional voltage control strategy will cause current distortion and overcurrent in the process of asymmetric fault ride-through,seriously harming the stability and safety of the system.In view of the above problems,combined with the relevant requirements of fault ride-through,an asymmetric fault ride-through strategy based on positive and negative sequence power control grid-connected inverters is proposed to compensate the dropped positive sequence voltage to improve the current quality and can be flexibly injected into the system Reactive power,at the same time,by limiting the maximum current output during a fault,the overcurrent problem in the process of fault ride-through is solved,and the ability of a voltage-controlled grid-connected inverter to asymmetric fault ride-through is improved.In addition,for the problem of fault type detection and discrimination,this paper compares and analyzes three common discriminant methods,which enables the system to accurately and quickly identify the type of fault when the fault occurs,which has certain guiding significance.In this thesis,the simulation model of three-phase grid-connected inverter based on MATLAB / Simulink is established,and the related control strategies are simulated and analyzed.And built a three-phase grid-connected inverter experimental platform based on DSPTMS320F28335 as the core,by comparing the traditional voltage control strategy with the proposed control scheme under the condition of asymmetric fault,the simulation results show that the asymmetric fault crossing strategy based on positive and negative sequence power control proposed in this paper can effectively improve the current quality and improve the ability of asymmetric fault crossing of grid connected inverters.