Research On Control Strategy And Application For Grid-connected/Islanding Of Two-stage Photovoltaic Inverter System

Fossil energy shortage and environmental pollution have become more and more serious.Therefore,the technology of new energy generation has gradually become a hot research in various countries,especially within the field of distributed generation has become a global trend,and represented by photovoltaic power generation system,distributed generation has been widely applied in micro grid component.However,the problem of low output efficiency and slow response speed restricts the development of photovoltaic technology.Therefore,the Maximum Power Point Tracking(MPPT)can be used to make photovoltaic array work at the Maximum Power Point in any environment and improve the output efficiency of photovoltaic array.At the same time,in order to improve the reliability of important load power supply system,photovoltaic systems need to work on the grid and off-grid.However,the impact of current and voltage is created when the work mode is switched.Through the study of hybrid control,the impact of current and voltage can be weakened,and realizing the smooth transition of operating mode.This paper focus on the related technology research of two-stage photovoltaic inverter system grid-connected/islanding seamless transfer,from system model,topology analysis,control strategy and so on,analyzing detailed the maximum power point tracking technologies and seamless transfer of inverter.Specific work is as follows:(1)In view of the problem that the efficiency of constant voltage method is low and disturbance observation method is easily affected.This paper comes up with the MPPT first-order sliding mode control.The MPPT first-order sliding mode control solves the problem of bad robustness and low response speed.However,first-order sliding mode has the problem of chatting.On this basis,this paper puts forward the second-sliding mode control technology,and designing MPPT second-sliding mode control based on the advantage of no-chatting to reduce the chatting problem of first-sliding mode control.At the same time,the second-sliding mode control has the the advantage of good robustness and fast response speed.(2)Discussing the switching mode of seamless transfer and analyzing the problem of seamless transfer based on the droop control,such as the overshoot of active power,impact of current and voltage.Due to the problem,this paper adds second-order sliding mode voltage compensation in the voltage ring of droop control.The method adds compensation signal created by compensation control to voltage ring,The overshoot of active power is weakened when the system is switched,the impact of current and voltage are suppressed,and realizing the smooth switching of running mode.(3)Based on the theoretical analysis,through the design of the hardware and software of the two-stage photovoltaic inverter system,the experimental platform has been built.After that,under the different working mode,through the experiment verification of preamp MPPT control and second stage inverter seamless transfer,guarantees the validity of control theory in this paper.