The Study And Implementation Of The Single-phase Grid-connected And Grid-off PV Inverter

With the aggravation of environmental pollution,developing green clean energy has gradually become the consensus of the industry development in every country,and power generation based on new energy attracts wide attention of the whole world by its good development prospects and practical value.In view of the difficulties of power generation technology based on new energy,a inverter system is researched,designed and implemented in this thesis based on a single-phase PV inverter,which has grid-connected and grid-off functions,and the main research contents are as follows:(1)According to the different operation modes,mathematical model is respectively established for the inverter system.And the decoupling of the coupling variables are carried out under the rotating reference frame.Based on this,the grid-off control system and grid-connected control system are designed.(2)A novel frequency adaptive multi-SOGI structure is presented to improve SOGI adaptive and anti-disturbance abilities,which solve the poor signal processing capability and tracking performance of the traditional generalized integrator.The principle of operation,dynamic performance,filtering effect and stability of the structure are analyzed in detail,and all of this are verified by simulations.(3)On the foundation of novel frequency adaptive multi-SOGI structure,a novel PLL structure is presented to improve the collapse phenomenon in phase locking of traditional PLL when the grid voltage is distorted,which has the precise phase-locked performance even under distorted voltage and frequency fluctuated conditions.(4)A novel droop control method in DC voltage is proposed for disadvantages in dynamic response of PI controller in external voltage loop in the conventional grid-connected controller.This control method can significantly improve the transient response ability of inverter system for power mutation in preceding stage,effectively avoid introducing the inherent harmonics of DC voltage into the controller,and effectively improve the current quality.(5)An experiment platform of 5KW single-phase inverter is developed by designing the system software and hardware.And the proposed algorithm and control strategy is verified by experiments.