Design Of CdTe Thin Film Photovoltaic Grid Connected Inverter Based On Generalized Prediction

As the contradiction between the ever-growing energy needs of the society and energy and environmental crisis deepens,the proportion of renewable energies in energy consumption is increasing year by year.Among the renewable energies,photovoltaics is the significant one with great potentials because it is environment-friendly,pollution-free and almost inexhaustible.Therefore,the development and application of photovoltaics becomes a hot topic in the world.Accordingly,the key technologies of photovoltaics are researched in this thesis.Firstly,analyze the structure of the grid-connected inverter.Choose the two-stage nonisolated inverter as the research object,which includes the front DC-DC and latter DC-AC.For the wave filter of DC-AC inverter,use branch capacity to connect with resistance in series to avoid resonance of LCL wave filter.Meanwhile,expound the design process of this passive LCL wave filter parameters,setting theoretical basis for subsequent research.Then,simply contrast feedback control strategies.Choose the inverter-side current feedback strategy to deduce the discrete transfer function between the inverter-side current and the inverter-side output voltage,providing a more precise prediction model for subsequent generalized predictive control strategy.Secondly,give a brief introduction to Cd Te thin-film photovoltaic battery.Establish a mathematical model of photovoltaic battery.Analyze why multiple peaks occur to the output power curve of the photovoltaic battery series connection under the shaded circumstance.To avoid such problems,photovoltaic battery parallel circuit structure boosted by the converter shall be adopted.Then,give a brief introduction to three traditional MPPT control algorithms.As for the problem that the optimal speed and accuracy of traditional incremental conductance method are mutually exclusive,in this thesis,an improved incremental conductance method with variable step size is raised.The MPPT control algorithm improved by stimulation test in the shaded circumstance can solve the problem that the optimal speed and accuracy of traditional incremental conductance method are mutually exclusiveThirdly,raise the generalized predictive control strategy to solve problems like gridconnected circuit current harmonic component,wave filter model mismatch,dynamic stability and dynamic response speed.Explain the basic theory of predictive control and expound the deduction process of the generalized predictive control algorithm and performance function parameters configuration.Meanwhile,conduct stimulation tests under the circumstance of power abrupt change,wave filter parameter abrupt change and weak grid.According to the stimulation test result,the control strategy can effectively reduce the harmonic component in the grid-connected circuit current,improve the grid-connected current quality and has strong robust stability under the circumstance of model mismatch,good dynamic stability and dynamic response speed.Finally,establish an inverter experimental platform using DSP28035 as control center to verify the validity of the control strategies raised in this thesis.