Research On Control Strategy Of Grid-connected Inverter Based On Improved Adaptive Delay Bank Filter

Since the beginning of the 21 st century,the rapid economic development of various countries has brought about the problem of the increasing use of traditional energy resources,which has directly led to the deterioration of the ecological environment.Renewable energy has been recognized all over the world for its unique advantages.Solar energy as one of which can be directly developed and utilized.It attracts wide attention for the advantages of clean,harmless and huge reserves.The inverter plays an important role in the process of grid-connected as the output power of photovoltaic unit needs to be converted to the grid.Therefore,the stable operation of the system has higher requirements for the performance of the inverter.Although the use of large industrial electrical equipment and non-linear load has promoted the development of society,the harmonic pollution of grid has also increased.Therefore,it is of great practical significance to study the operation stability of grid-connected photovoltaic inverters when the grid contains harmonics.Aiming at the harmonic problem of grid current caused by grid background harmonics,the control strategy of grid current harmonic compensation is deeply studied in this paper.The research contents are divided into the following parts:Firstly,the existing harmonic detection methods and harmonic suppression methods of grid-connected current are reviewed.The single-phase grid-connected inverters with photovoltaic generation unit are determined to adopt single-stage structure and the relevant parameters are designed.The basic principle of droop control and phase-locked technology are introduced in detail.The influence of distorted grid voltage on grid current is analyzed,which lays the foundation for harmonic suppression.This paper combines harmonic detection device with phase-locked loop to reduce the control unit for extracting grid voltage harmonics accurately.A frequency-locked loop based on improved adaptive delay bank filter is proposed to extract the fundamental voltage of grid,so that the harmonic voltage of grid can be obtained.After being adjusted by quasi-PR controller,the output of the fundamental controller is superimposed to make the output voltage of grid-connected inverter equal to grid voltage,so that the grid current harmonic can be suppressed.Aiming at the problems of poor robustness and difficult tuning of control parameters of traditional linear control methods,an energy shaping grid-connected control strategy based on passive control theory is proposed.The port-controlled Hamilton model of single-phase PV inverter is established.The desired equilibrium point,the control parameters are determined and the control equation is obtained.The stability of the energy shaping controller is analyzed and the model is built to verify the simulation.Finally,a single-phase PV grid-connected inverter platform is built to verify the proposed grid current harmonic suppression strategy.The experimental results verify that the proposed control strategy can extract voltage harmonics accurately,and the energy shaping control algorithm has strong robustness.