Research On Control Of Three-phase Grid-connected Inverter Under Distorted Voltage Conditions

In recent years, wind power, solar and other renewable energy has been rapidly developed in scale and in the installed capacity. Based on this situation, the distributed energy system(DG) constructed in the grid connected system is in the large-scale application. More and more DG systems are access to the grid, which is bound to have an impact on the power grid. The performance of the grid will have an enormous impact on the output of the DG system. The grid itself contains the background harmonic and power electronic converters as the nonlinear devices make a further deterioration to the performance of the grid. Thus a series of factors leading to the worse output of the DG system and the performance of grid connected system is reduced. Therefore, research on inverter control methods of grid connected system, the distortion of grid voltage and the output performance of inverter, guarantying highly efficient and stable operation of the grid connected system has the important practical significance.The main purpose of this paper is to study on control technology of the three-phase grid connected inverter in distorted and unbalanced grid voltage condition. Firstly the development status and research background of the DG system is introduced in this paper, Simultaneously, research status of control technology of grid connected inverter in recent years at home and abroad is discussed. Secondly, the model of the three-phase grid connected inverter is analyzed and the parameter design of LCL filter is discussed. Through analyzing the reason of instability in direct grid current feedback control, the active damping control based on the feedback of capacity current is adopted to suppress the resonate of system. The method of zero compensation is proposed in this paper, which makes zero compensation at the corner frequency to improve system stability and achieves the efficiency and stability of the system. Finally, combined with the PR control technology to follow the fundamental current at the specific frequency, a grid connected performance is better with PI control technology. Through adding harmonic compensator(HC) into PR control technology to suppress high order harmonic in the grid voltage, the PR+HC method basing on direct grid current control is achieved. The simulation results show that the direct grid current control technology proposed in this article has the advantages of simple structure and stable performance, which can achieve better grid connected.Constructing a three-phase three leg grid inverter experimental platform which use the TMS320F2812 as main control chip, the experimental results show that the direct feedback control of grid current proposed in this paper has stable control performance and realize better grid connected performance.