Research On Grid Fault Ride-through Stability Control Of Grid-connected Photovoltaic Power System

With the increasing penetration rate of photovoltaic power systems, theestablishment of grid-friendly photovoltaic power plant will be one of the importantissues for sustainable development of photovoltaic industry. Grid-friendly requirementsof grid-connected photovoltaic system can not only ensure that the output power qualityin the grid during normal operation, and to ensure that no inverter is not off-grid as wellas not damaged during the period of power grid failure, taking full advantage of the PVinverter output capacity to participate in the rapid reactive power grid the active andreactive power regulation, and support for fault ride-through and the voltage of PCC.This paper analyzes the stability of the PV grid system in the grid failure, especiallythe three-phase unbalanced fault, including the DC bus voltage stability, active andreactive power output stability and harmonic stability.Secondly, this paper proposes three-phase and single-phase photovoltaicgrid-connected inverter control systems. According to the response of three-phasetwo-stage grid-connected PV system under unbalanced grid conditions，the PWMcurrent control strategy on the last stage should aim to stabilize the active power output,which coordinates with the DC-DC converter on the pre-stage during unbalanced voltagedips. This paper develops two method of grid-connected current reference calculationfulfilling this control requirement. One is An Improved Algorithm based on the doublesynchronization reference frame, the other is the direct generation algorithm based on thevector relationship of three-phase current and active power.Then, the paper completed DC bus capacitor selection and AC side inductor designbased on10kW three-phase grid-connected photovoltaic system and used MATLAB/Simulink to build simulation system, complete simulation verification of the proposedcontrol system and schemes under different fault types and depth.Finally, relying on the experimental platform of State Key Laboratory of AlternateElectrical Power System with Renewable Energy Sources North China Electric PowerUniversity, this paper completed experimental verification of the proposed faultride-through control system based on10kW monocrystalline photovoltaic invertergrid-connected system.