Research Of Parallel On T-type Three-level Photovoltaic Inverter

Photovoltaic power generation has been more favored by domestic and foreign researchers in recent years,with the depletion of fossil energy.The power of photovoltaic tends to be large.There are two main ways to increase inverter power.One is to increase the capacity of single inverter and the other approach is to use multiple inverters parallel system.This paper mainly studies the system of T-type three-phase three-level inverter parallel.T-type three-level inverter,the improvement of diode NPC three-level inverter topology,which has the advantages of saving six diodes and reducing internal losses,so it is a promising topology.This paper analyzes the T-type inverter principle and commutation process and studies the SVPWM space vector modulation method.Not only can it reduce switching loss but also reduce the switching frequency by using seven symmetrical.In addition,this paper makes the inverter output voltage and current waveform close to a sine wave by designing the filter inductor and capacitor size parameters.The structure of the main circuit and the circulation vector was analyzed and the mathematical model of a single-phase inverter based on the harmonic disturbances was established Through the detailed study of the parallel mathematical model of two T-type.The influence factor of the quality of the output voltage waveform and the correction action of instantaneous value feedback regulation for the waveform was studied according to the mathematical model of harmonic disturbances.The mechanism of harmonic circulation was researched based on this model and a method of increasing Be(s)gain was proposed to suppress the generation of harmonics circulation.The mechanism of production of common-mode voltage and current was studied in inverter parallel system.The paper put forward three methods to inhibition the common current.The output characteristics of active power and reactive power was researched in inverter parallel system.Distributed logic control scheme based on the power error was adopted in inverter parallel system.The distributed logic controller and DPLL was designed to make the output voltage amplitude and phase track the synchronization reference signal completely.The effect of current of the output power was realized according to the study of logic controller.To adjust the power in inverter parallel system can inhibition of produce of the ac circulation in paralleling system.Finally,the model of two inverters in parallel was set up in Matlab/Simulink.The output waveform of the single inverter is well and the circulation can be effectively suppressed when two inverters are in parallel through the simulation verification.It shows the effective feasibility of two inverters design in parallel and the control strategies.