On The Control System Of Three-phase Off-grid Inverter

With the development of power electronics technology,the performance of inverter is improving and its application is more and more extensive.In addition,environmental problems are increasingly serious,promoting the rapid development of new energy power generation.In the household electricity,it will become the time choice that the zero pollution new energy power supply replaces the traditional power plant power supply.Off-grid inverter will be required to cooperate with the implementation.However,three-phase off-grid inverter with three-phase load can not be balanced distribution.The situation that a phase without load is also very likely to occur,which will not only affect the quality of the inverter output waveform,seriously damage to the electrical equipment.In this thesis,the vector control system of three-phase off-grid inverter is studied.And the output waveform is optimized based on the above research,so as to improve the ability of the inverter with unbalanced load.Firstly,the topology and working principle of the three-phase off-grid inverter are in-depth studied,and the power tube loss is analyzed by using parabolic interpolation,and the working efficiency of the inverter is calculated.Based on the control model of the system,the output voltage and current are decoupled in the d-q coordinate system.Secondly,in view of the problem that the three-phase output voltage balance cannot be achieved by using the traditional two-loop PI control when the load is unbalanced,an optimization is made by the research.The positive sequence,negative sequence and zero sequence components of the unbalanced three-phase output voltage are separated by the symmetric component method,and the components are changed into direct flow control in the rotating coordinate system respectively.The negative sequence component and zero sequence component can track the reference zero voltage without static difference,which effectively improves the ability off-grid inverter with unbalanced load.Finally,the output voltage clipping problem is solved when the bus voltage is unstable by limiting the output voltage in the voltage limit circle.In the MATLAB/Simulink simulation environment,the open-loop and closed-loop control of the off-grid inverter are respectively simulated,and the simulation voltage and current waveforms under different simulation conditions are obtained.In the hardware experiment,DSP chip TMS320F28035 is used,and the off-grid inverter hardware platform is built for the control chip.The validity and feasibility of the improved algorithm are verified by experiments.