The Control Of Three-level Photovoltaic Grid-connected Inverter

This paper discusses a SVPWM-based grid-connected photovoltaic power generation control strategy,and aims at researching three-level inverter structure.Considering of the obvious advantages of multi-level control of inverter,the development and application of the inverter will be inevitable for grid-connected power generation.Since three-level is the basis to build multi-level control,analyzing and researching three-level inverter have perspectiveness and reality for this reason.The reason of selecting SVPWM is also because of its wider modulation range,higher DC utilization factor,relatively mature technology and easy algorithm implementation.The most common structure in three-level topology structure is NPC structure(i.e.neutral point clamped structure).Through comparison and research,it is found that diode clamped NPC structure is the most common in the three NPC structures,and the structure has mature technology and low cost.This paper takes this structure as the research object,and analyzes its topology structure and discusses its inverter working mechanism.On the basis of researching traditional control algorithm with SVPWM,this paper further puts forwards a simplified algorithm of re-partitioning appropriate vector composition in large sector for the purpose of improving the disadvantages of complexity and low precision of control algorithm,i.e.large sector will be re-partitioned into two right triangle areas;reference vectors are composited basic vectors that correspond to two right triangles.This improved algorithm can omit neutral-point voltage control,greatly simplifies algorithm,and correspondingly lowers control difficulty.This paper systematically researches three-phase phase-locked loop technology changed on the basis of dq coordinates.In order to inhibit the influence of negative sequence component on phase position calculation,T/4(T refers to three-phase voltage cycle)delay calculation method is used to separate positive and negative sequence components.This algorithm improves corresponding dynamic speed of phase-locked loop capable of accelerating,further improves stability,and can effectively inhibit signal distortion.Establishment and research of MATLAB simulation model based on grid-connected control strategy of diode-clamped NPC three-level inverter further prove that coordinate transformation-based phase-locked loop technology and large-sector partitioning&composition algorithm can get better grid-connected current waveform,and the harmonic content of current is less than 1%.Test platform of 10 kw NPC three-level photovoltaic(PV)grid inverter was Established with DSP2808 and CPLD as the control core.Grid-connection control strategy based on SVPWM simplified algorithm was verified.The test results show that grid current harmonic is less than 3%,the power factor is above 0.99,the machine efficiency is up to 98%,and it has perfect protection function under the rated output power.Figure[55]Table[7]References[52]...