The Research On Control Strategy Of Grid-connected Inverter Under Unbalanced Grid Voltage

Traditional energy consumption leads to environmental pollution become serious,while fossil fuel reserves and the development face to crisis,the use of renewable energy sources become a trend.Distributed generation technology is already quite mature,so the Grid-connection control strategy determines the quality of the power,especially when the grid voltage in an unbalanced state brings the grid system with strict test.The main content of this thesis is Grid-connection control strategy on under the condition of grid voltage unbalance.Paper firstly investigated the power grid which under ideal state and grid voltage unbalance,introduced the working principle of three-phase grid-connected inverter,and the impact of unbalanced voltage control.The mathematical model of grid inverter is established for ideal and the grid voltage unbalance state.Using symmetrical component method is put forward to solve control under the circumstance of asymmetric in other words to use the control strategy of the positive and negative sequence separation.After the completion of the system based on the analysis and modeling,specific control scheme is put forward.The main injection control structures and asymmetric currents start from the PLL.Take the DDSRF-PLL to lock grid voltage to control positive and negative sequence current separation of dual current.The merits of the two kinds of modulation technology are analyzed,and ultimately selected SVPWM to achieve inverter modulation.Finally,based on the above theory to design hardware circuit,including the design of DC-link filter capacitor and grid filter,selection of the sensor,buffer circuit,protection circuit and control circuit.To use the simulation and experimental on control strategy to make validation and analysis.Under the condition of power grid voltage asymmetry,respectively,to make system simulation for the traditional control strategy and control strategy of separation of positive and negative.Design software and according to the experiment of phase lock loop and the current controller for debugging.Obtain the experimental results and analysis.