Research And Design On Three Phase Photovoltaic Grid-connected Inverters Based On LCL-filter

As an important energy conversion device in PV power generation systems, PV inverter plays a critical role in the system’s efficiency and stability, so the study of photovoltaic grid inverter design is of great significance and it’s also one of the PV research hotspots and focus. This thesis is composed of the following four aspects.The first part introduces the working principles of sine pulse width modulation(SPWM) and space vector pulse width modulation(SVPWM)primarily, and then the focus is on analyzing implementation steps of SVPWM modulation technology. At the same time, studies advantages of SVPWM compared with the SPWM and relevance and consistency between them. Lastly, in order to test and verify the validity and advantage, the simulation is done by Matlab software.The second part compares and analyses mathematical model of three-phase grid inverter according to the filter type including L, LC and LCL. Then we mainly focused on the LCL filter by analysing its working characteristics and damping control based on Matlab.The third part studies the theoretical basis of LCL filter parameter selection in the system and also presents parametric coordinate formulas.In this part,we also introduce the design principle and steps of system controller by applying voltage and current double closed-loop control.The selection of parameters and control algorithm are emulated and validated on Matlab. The system can run steadily and reliably, whichproves that the validity of parameters and the algorithm.The fourth part takes 500 k W three-phase PV inverter as object, and gives the design methods of main circuit realization and parameters calculation based on the above theories and algorithms studies. Lastly,we have set up the hardware test platform and done grid-connected test.The result shows that the design of the system and the algorithm in the application of the system is feasible with large power practical guiding significance to the design and performance improvement of PV grid inverter.