Research On The Integration Control Strategy And Low Voltage Ride-Through Technology Of Grid-Connected PV System

With the decrease of traditional fossil energy reserves and increase of environmental pollution problems, the grid-connected PV generation technology based on solar power generation has developed rapidly in the world. The inverter is an important component in grid-connected PV system, and the selection of control strategy and design of control system directly affect the performance of the entire system. It is one of the main problems for the grid-connected PV generation technology research. Meanwhile, with the number and capacity of installed grid-connected PV systems increasing, the low voltage ride-through ability is required.This paper mainly focus on control strategies of the grid-connected PV inverter under normal grid and grid fault conditions. Firstly, according to the mathematical model of the grid-connected P V inverter in synchronous rotating coordinate system, the voltage and current double closed loop control system are designed. A general PI controller parameter optimization design method is presented based on the relationship between natural frequency and four parameters including the system pole distribution, bandwidth, gain margin and phase margin. Then, the performance characteristics of the grid-connected PV inverter under unbalanced grid conditions are researched. Aimed at the problem with the separation of positive and negative sequence components, a method based DSOGI-FLL phase-locked loop techniques is proposed to extract positive and negative sequence components of grid voltage and current. A grid positive sequence voltage oriented vector control strategy is designed, and then an energy consumption crowbar is used to ensure stable operation of the grid-connected PV inverter under asymmetrical grid fault conditions. Finally, according to the national standard for low-voltage ride through capability of the medium and large grid-connected solar power plants, control strategy of using energy consumption crowbar to realize LVRT is analyzed in detail. The consumption resistor value and crowbar circuit control strategies which affect low voltage ride through capability are researched in depth.