Research And Implementation Of Multi-function Grid-connected Inverter In Distributed Photovoltaic Power Generation System

With the consumption of traditional fossil energy,the development and utilization of solar energy with clean,environmental protection and renewable characteristics has become a current research hotspot.At the same time,with the development of power electronic technology,more and more nonlinear loads are connected,which generates a lot of harmonics,the multi-function grid-connected inverter in the distributed photovoltaic power generation system will provide certain harmonic compensation to the grid while providing photovoltaic grid-connected power,improve the power quality of the grid,and help promote the development and improvement of the photovoltaic industry power grid environment.This paper compares and analyzes the structure and working principle of photovoltaic grid-connected inverter and active power filter,studies the feasibility of the unified control of the two for unified control,and gives a photovoltaic grid-connected inverter with active filtering the unified control system.For the harmonic detection part,this paper analyzes the single-phase harmonic detection method based on instantaneous reactive power,improves it,and simplifies the application of i_p-i_qmethod in single-phase system.The phase-locked loop technology of the multi-function grid-connected inverter is studied.In order to solve the problem that the traditional SOGI phase-locked loop cannot accurately output when there is high-order harmonic,DC component and frequency interfere to the power grid,a composite SOGI phase-locked loop is proposed.Using the cascaded SOGI module eliminates DC components and higher harmonics in the power grid,and uses frequency feedforward to enable the phase-locked loop to track the frequency change of the grid voltage in real time to improve the anti-interference performance of the phase-locked loop.By studying the grid-connected current control technology of the multi-function grid-connected inverter,it is proposed to add a cut-off frequency based on the PCI control algorithm to form a quasi-PCI controller and increase the ability to eliminate errors at a given AC frequency.According to the definition of complex number,a simplified form of single-phase quasi-PCI controller is designed.On this basis,a quasi-PCI and PI joint grid-connected current controller is further proposed,and the use of PI controller to control the DC component without static error is further eliminated the DC component of the grid-connected current.It can provide higher quality grid-connected power.Finally,the overall structure of the multi-function grid-connected inverter is designed.The hardware and software design process of the multi-function grid-connected inverter with DSP TMS320F28335,which is produced by TI company,as the control core.The functions of the upper and lower arm drive circuits of the Heric inverter circuit are divided.Adopt the method of designing the upper and lower bridge arm drive circuits separately to realize the complementary and cooperative protection function,and successfully developed the multifunctional grid-connected inverter experimental prototype.