Research On High Frequency Isolated Grid-connected PV Inverter

In recent years, solar photovoltaic power generation has became one of the most promising renewable energy with its advantages of clean, safe, convenient and efficient. As the part of power control and transformation, grid-connected PV inverter has been a research hotspot in the field of photovoltaic. A novel high frequency isolated grid-connected PV inverter was studied in this thesis. The novel topology has the feature of high efficiency, small size and light weight, which is suitable for low power single phase photovoltaic systems.Firstly, the grid-connected PV inverters were studied by classification to analyse the anvantages and disadvantages, and led to the superiority of high frequency isolated grid-connected PV inverter in residential PV systems. For the shortage of the traditional DC/DC high frequency isolated grid-connected PV inverter, this thesis studied a novel high frequency isolated grid-connected PV inverter based on sinusoidal pulse width position modulation (SPWPM) and analyzed the working principle in steady state. The SPWPM was validated by mathematical derivation.Secondly, the closed-loop control strategy contains overturn link and grid voltage feedforward was designed according to the high frequency isolated grid-connected PV inverter’s work characteristics and mathematical model. In order to eliminate the grid-connected current distortion caused by the static phase error in the noevel topology, the phase compensation control strategy and proportional-resonant control strategy were employed in the current control loop, and the control stategy was validated by building the inverter simulation model. Afterwards the specific discretization implementation method of the contol strategy was given.Based on the above theoretical analysis, the high frequency isolated grid-connected PV inverter hardware circuit was designed in this thesis. Combining with the high frequency operation and SPWPM principle characteristic, the key components parameters were designed including high frequency transformer, inductor and capacitor, and the power switching devices were type selected. The control circuit based on digital signal prosessor was built and the analog signal regulation circuit was designed. The grid-connected system was established by drawing the printed circuit board.Finally, the high frequency isolated grid-connected PV inverter system was debugged. The grid-connected current achieved close loop digital control in SPWPM mode, and the logical start and halt process was presented. The phase cpmpensation control was used to improve the current close loop controller algorithm, based on the analysis of experimental results about output current zero crossing distortion. The control strategy was validatd by experimental results.