Research And Design Of T-type Three-level Photovoltaic Grid-connected Inverter

Nowadays,many countries are facing the problem that the traditional fossil fuels are gradually depleted and their ecological environment worsens.In order to improve this status quo,in response to sustainable development,we must speed up the adjustment of the traditional energy consumption structure,looking for alternative clean energy is imminent.Solar energy is favored by all countries as a clean energy source.It is considered as the most promising renewable energy.The related technology has been rapidly developed and has become a trend of becoming a widely used new energy source.And photovoltaic power generation technology has drawn the attention of all countries.With the development of photovoltaic grid-connected technology,the technical requirements of the inverter have become more demanding.High-power,small size,high efficiency,low harmonic ratio has become the main direction of converter development,three-level topology can well meet these requirements.Taking into account the T-type three-level topology compared to the diode embedded topology,more obvious advantages.Therefore,the paper focuses on the research and design of T-topology three-level photovoltaic grid-connected inverter.In this thesis,a two-stage topology is adopted:the front stage adopts Boost circuit to complete the DC side boost and maximum power tracking,and the post-stage inverter section realizes DC bus voltage regulation and grid-connected current control.First of all,based on the derivation and establishment of the mathematical model of photovoltaic cell,the influence of light intensity and temperature on the photovoltaic output characteristics is discussed.Simulink simulation is used to verify the effect.The advantages and disadvantages of three kinds of MPPT control strategies including constant voltage method,conductance incremental method and disturbance observation method are compared and analyzed.Secondly,the mathematical model of T-inverter under different coordinate systems is analyzed.The topology of isolated and non-isolated T-grid inverter and the three-level topology commutation method are briefly described.Subsequently,the traditional three-level SVPWM modulation strategy is described.A simplified SVPWM algorithm based on two-level reference vectors is proposed.Based on this,the effect of each type of voltage vector on the neutral point potentials is analyzed.The neutral point potential control strategy.Then introduced the grid control strategy,made a detailed analysis of the voltage loop,current loop and PLL design.Simulink system simulation software verifies the rationality and effectiveness of SVPWM modulation strategy,mid-point control method and grid-connected strategy.Finally,the TMS320F28335DSP is selected as the core controller to set up the system overall experimental platform,and the related hardware circuit design and software implementation are carried out.The correctness of the control strategy is verified through experiments,and the experimental results are good.