Research On Low Voltage Ride Through Control Strategy Of Photovoltaic Power Generation System

With the continuous reduction of energy sources such as coal and petroleum,and the increase in environmental pollution and other related issues,the research and development of new energy has received more extensive attention.In particular,the research of solar energy-based power generation technology occupies an important position in the research of new energy sources.The research focus of photovoltaic power generation system is the inverter.The choice of control strategy and the design of the entire control system directly affect the performance of the system.With the increase in the installed capacity and capacity of photovoltaic power stations in recent years,more photovoltaic energy has been incorporated into the power grid.Therefore,once a voltage drop due to a power grid failure occurs,the inverter may be damaged or even cause a net loss.At that time,the photovoltaic grid-connected system needs low voltage ride-through capability.The research of this dissertation focuses on the single-level three-level grid-connected inverters,and studies the low-voltage ride-through strategy in the state of power grid fault dips.The article first introduced the photovoltaic cell and mathematical modeling,briefly described the MPPT control method,and established a mathematical model of photovoltaic grid-connected inverter.Then the low-voltage ride-through strategy of the system under symmetrical drop situation is deeply analyzed,and the types of common dropout voltages are introduced.When the grid voltage drops,the active power and reactive power values are recalculated.At the same time,the current output from the grid-connected inverter is limited to avoid the impact on the power grid.Finally,after the fault is removed,the system is removed.Make the power grid quickly reach the pre-failure operating state.Then the low voltage ride-through strategy under unbalanced voltage drop of the grid is studied.The mathematical model of the inverter under this condition is analyzed.Because there is a negative sequence component under the asymmetric fault,the positive sequence sum of the grid-connected current is needed.Negative-sequence components are controlled,and then by providing reactive power to support the power system,the grid eventually returns to normal.In this paper,a photovoltaic power generation system model is also built on the Matlab/Simulink platform,and the balance voltage drop and unbalanced voltage of the power grid voltage are separately studied.The simulation results prove that the photovoltaic inverter is in the condition of dropping different forms and different depths.The converter has good low-voltage ride-through capability and can even complete zero voltage ride through to ensure that the grid after the fault is removed can quickly return to normal operation.