Design And Research Based On Wind Power Grid-connected Inverter Control Technology

As the global demand for green and pollution-free energy is increasing,new energy sources,mainly wind and light energy,are receiving more and more attention from governments and society.In the application of new energy sources,gridconnected inverters assume a great role as an important connecting device between the output power and the grid.In order to reduce the output current harmonic content of the grid-connected current,this paper takes the single-phase LCL grid-connected inverter on the wind grid side as the research object,and analyzes the resonance problem and current control strategy of the LCL filter itself.The specific research contents are as follows:(1)The output voltage of the grid-connected inverter contains a great number of switching harmonics.The suppression characteristics of different types of filters for harmonics are analyzed,and the LCL-type filter with large gain for low-frequency amplitude and good suppression for high-frequency harmonic signals is selected.However,the resonant spikes of LCL-type filter will lead to system instability.To address this problem,passive damping scheme and active damping scheme are considered,and the capacitor-current proportional feedback in active damping is selected by comparing and analyzing the damping effect,conversion efficiency,cost and volume of several damping schemes.(2)The operating principle of the LCL filter circuit is introduced.When the LCL grid-connected inverter is digitally controlled,the system generates a half-beat delay,and the delay seriously affects the stability of the system.A mathematical model of the LCL grid-connected inverter containing grid impedance is constructed,and the effect of the control delay on the active damping effect of the capacitor current state variable is analyzed.In order to eliminate the effect of control delay on active damping,the capacitor current instant sampling method is proposed.Finally,the proposed method is verified by simulation to enhance the system stability.(3)The incoming current harmonics can contribute to the deterioration of the power quality after grid connection.In order to improve the quality of the gridconnected current waveform,the grid-connected current control strategy has been studied.The quasi-PR controller can track the fundamental frequency without static difference,but it is less effective in suppressing the odd harmonics such as the 3rd,5th and 7th harmonics present in the grid-connected current.To address this problem,the multiresonant PR control can effectively suppress the odd harmonic content,but it is easy to cause system instability when the number of harmonic compensation is high,so this paper proposes an improved multiresonant PR control strategy,i.e.,multiresonant controller with phase compensator combined control strategy.Finally,the effectiveness of the designed current controller is verified by simulation.(4)An experimental prototype of a 3k W wind grid-side inverter was completed in the laboratory,and the main power control circuit,core control circuit,currentvoltage sampling and regulation circuit,etc.were designed and the software-related design was completed.The experimental results show the feasibility and good dynamic characteristics of the improved multi-resonant PR controller.