Research On Low Voltage Ride Through Control Method Of Photovoltaic Grid-connected Inverter

Nowadays,energy shortages and environmental pollution are becoming more and more serious.Therefore,the development and utilization of renewable energy has become the focus of research in various countries.Among them,the use of solar energy has become one of the research hotspots due to its rich resources and cleanliness.In recent years,with the increasing proportion of photovoltaic power generation in power energy,the impact on the safe and stable operation of the power grid after its access to the power grid has become increasingly significant.Therefore,the latest grid-connected standards developed at home and abroad require photovoltaic inverters.It should have low voltage ride through capability when the grid voltage drops.Based on the research of three-phase single-stage photovoltaic grid-connected system,this thesis conducts in-depth research on the low-voltage ride-through control method used in the short-circuit fault of the grid,in order to improve the stability and safety reliability of grid-connected PV inverter operation.The short-circuit faults of the power grid are divided into symmetric and asymmetric drop faults.In this thesis,the mathematical models of photovoltaic grid-connected inverters are established for these two fault conditions,and the grid-connected inverter control strategy of grid voltage vector orientation is analyzed.Based on this,the influence of two fault conditions on the photovoltaic grid-connected power generation system and the simulation verification are analyzed.For the grid side symmetrical drop fault,the conventional control strategy can not provide reactive power support for the grid and limit the overcurrent of the inverter.A low voltage ride through control method is provided to provide reactive power to the grid according to the grid voltage drop depth;Asymmetric drop failure,based on the positive and negative sequence separation method of the second-order generalized integrator frequency-locked loop under the condition of asymmetric grid voltage,the double-frequency fluctuation of the DC side bus voltage of the inverter under the conventional control strategy The problem of distortion and overcurrent in the grid-connected current on the AC side is achieved by using a low-voltage traverse control method that suppresses the voltage fluctuation of the DC side busbar,so that the DC-side voltage of the system remains stable and the grid-connected current does not flow,and the grid-connected current is presented.Low voltage ride through control method with symmetric sinusoidal and providing certain reactive power support to the grid.Based on the theoretical research,the simulation model of photovoltaic grid-connected system is built by MATLAB/Simulink.The simulation results show that when the grid is symmetrically falling,the proposed control method for providing reactive power to the grid according to the voltage drop depth can be proposed.Provide reactive power support for the power grid and limit the overcurrent of the grid-connected current;when the power grid has an asymmetric drop fault,the control method of suppressing the voltage fluctuation of the DC side busbar can effectively suppress the double frequency component of the DC side voltage and reduce its Fluctuation amplitude and limit the overcurrent of the grid-connected current.Thus verifying the effectiveness of the proposed control method.