Research On LVRT Of Photovoltaic Grid-connected System

With the development of new energy technology,solar energy has become the most widely used new energy,and solar photovoltaic power generation is currently the safest,most clean,the most potential way of emerging power.The penetration rate of photovoltaic power generation is increasing year by year,and its grid-connection is an inevitable trend.At present,the photovoltaic(pv)grid system has become research hot topic,its Low Voltage Ride Through(LVRT)technology is the core of the photovoltaic system,safe and stable operation of grid system plays a decisive role.With the increase of the permeability of photovoltaic power station,it is very important to study the low voltage crossing ability of photovoltaic system.In this paper,the control strategy of inverter is designed with LVRT,and the reactive compensation device is introduced to realize further LVRT.The control strategy of the inverter adopts the double closed-loop structure of voltage and current,and the outer ring adopts the classical PI control to realize the stable DC voltage without static difference tracking.The sliding mode variable structure control strategy is used to track the transient changes of reference current in real time to obtain the high-precision steady-state output.Failure analysis of the control logic,more active current and the rated current,when active current is greater than 1.1 times the rated current,The output power of the pv array is reduced by cutting off the outer ring,and the inverter is provided with a certain reactive power to support the grid voltage.Then the sliding mode control strategy of inner ring is introduced in detail,the hysteresis of adaptive sliding mode control function to control the switching frequency and alleviate the buffeting effect in order to ensure the stable operation of the photovoltaic system.But because of the limitation of the inverter switching device capacity and incorporated into the power grid voltage grade is higher and higher,only by the inverter control has been unable to realize to the and node voltage compensation,so compensation of reactive power is in the low voltage side of transformer device(STATCOM),introduced the STATCOM model of PI direct voltage control strategy of targeting and node voltage drop depth is divided into five different models,using parallel fireworks algorithm based on different blast radius is targeted to solve the model of PI parameters.The improved parallel fireworks algorithm can improve the convergence speed and avoid getting into local optimum.At the same time,the PI parameters obtained by the improved algorithm are applied to the system itself with better compensation capability,and the LVRT the photovoltaic system is realized.At last MATLAB is used as the experimental platform to build a simulation model,and the effectiveness and superiority of LVRT strategy are verified by comparison.