Design Of Three Phase Off Grid Inverter For Photovoltaic Power Generation System

In the double pressure of energy crisis and environmental pollution,people pay more and more attention to the development and utilization of new energy,all the countries in the world have invested a lot of human resources,material and financial resources to research new methods of power generation.And solar energy is very popular duo to its inexhaustible,no noise,no pollution and other advantages,is one of the research hotspots of new energy power generation.Photovoltaic power generation technology is the main way of solar energy development and utilization,known as the main energy in twenty-first century.According to the fact that our country is vast in territory and rich in solar energy resources,off grid photovoltaic power generation can effectively solve or alleviate the problem of the production and consumption of electricity in some areas without electricity,which is an important measure of PV poverty alleviation project in China.Therefore,the study object of this paper is identified as three phase off grid inverter of photovoltaic power generation system.This paper summarized the status of development and utilization of solar energy and the research status of photovoltaic off grid inverter topology at home and abroad,the principle and output characteristics of photovoltaic cells and the Maximum Power Point Tracking(MPPT)technology were studied and analyzed,the capacity of the PV system was designed in detail according to the actual load.This design was a two-level cascaded photovoltaic off grid inverter,which included the pre-stage Boost converter and the post-stage three phase inverter,and its modeling and control system design were made.The pre-stage Boost converter was modeled by the state space averaging method.On the basis of obtaining the state space expression and transfer function of the system,the design of voltage closed-loop feedback was carried out,and the simulation circuit was built in the PSIM software.By analyzing the Bode diagram and the dynamic step response diagram,the stability and rapidity of the model design were verified.Based on the analysis of principle and algorithm implementation,the post-stage three phase inverter used the Space Vector Pulse Width Modulation technology to produce the driving waveforms.The mathematical model of the inverter was built,then the mathematical equations of the three phase off grid inverter in synchronous rotating coordinate system were obtained by coordinate transformation,which simplified the design of the control system.Double loop feedback PI control algorithm based on the instantaneous voltage and current was adopted,and the control parameters of current inner loop and voltage outer loop were designed.Then the Simulink simulation of three phase off grid inverter was constructed.The inverter output phase voltage harmonic analysis showed that the control strategy made the output waveform sine good,harmonic volume small,power quality higher.Based on theoretical analysis and simulation,the hardware design and software design of the pre-stage Boost converter and the post-stage inverter were carried out,then experimental prototype of Boost converter and inverter were made,which power were 300W and 2kW respectively.And the inverter took Lab VIEW as the control core,the experimental output voltage waveform was good sinusoidal,the Total Harmonic Distortion(THD)was 2.08%,which met the relevant requirements of power quality.The experimental results confirmed the correctness of circuit design and control strategy of Boost converter and inverter,reduced the harmonic components of the inverter output voltage and improved the stability and rapidity of the PV system.