Research On High Power Photovoltaic Grid-connected Inverting System

Photovoltaic grid-connected power generation is considered to be the most important source of energy in21st century due to its superiorities in containing abundant solar energy resource, being clean, easy to install and maintain, with building-integrated ability for solar energy utilization, etc. However, the system design and core control technologies of high power photovoltaic grid-connected system still contain some problems, which significantly restrict further development of photovoltaic industry. Therefore, this dissertation gives theoretical study on topology design and control technologies of three phase photovoltaic grid-connected inverting system. Simulations and experiments demonstrate the correctness of the research results.Influence to grid-connected inverter caused by grid unbalance has been discussed, the unbalance control strategies based on the unified inverter model has been researched. Second order harmonic filtering method has been discussed, PSF and NSF method for extracting unbalance electromotive force is proposed. Simulation and experiment proved its correctness.Model of LCL filter has been set up, stability analysis in four cases has been discussed, engineering design principle and the step of LCL filter is proposed, and100kW LCL filter design has proved its correctness. Filtering damping method virtual damping resistor control strategy is proposed, its design and validation has been given out.Influence to photovoltaic grid-connected system caused by low voltage fault has been discussed, dual loop control and reactive power generation low voltage ride through strategies have been given out. Nonlinear low voltage ride through control strategies is proposed, its DC capicatance design adopting the strategy has been validated.Design principles of large scale photovoltaic grid-connected system is proposed, five system operation modes have been researched, based on the common DC bus topology, N+1method, infinite enumerative method, dynamic equational method group control strategies aimed at efficiency optimization have been proposed, their advantages have been validated.630kVA reciprocal power-fed full automatic high power grid-connected inverter test system is proposed,630kVA rectifier and modularized4U control system design have been given out. In3kW-500kW series single stage photovoltaic grid-connected inverters designed by the dissertation,500kW inverter has been used to validate performance of the test system, and it has been also used to performe "Golden Sun" electric performance test on the test system.