Research And Implementation Of PI Repetitive Control For Three-phase Grid-tied Inverters

To build a sustainable development system,renewable energy distributed generation systems,such as photovoltaics,wind power,and fuel cells,have become the focus and research targets of various countries.Grid-tied inverters which used to transfer the power into the grid,are important power electronic implements.,and the control strategy has been extensively studied.Repetitive control technology based on the internal model principle,has the ability of suppressing the periodic harmonic disturbance which occur in grid-tied inverters frequently.However,in practical applications,repetitive control technology has poor dynamic response due to the delay time.This thesis research on PI repetitive control for three-phase grid-tied inverters.The main contents are as below.A grid-connected inverter overall plan was designed.The topology of the inverter is determined,the key parameters of the power circuit are calculated,and the device is designed based on the demand analysis.The small signal model of the DC/DC converter and the model of the DC/AC converter in the rotating coordinate system are established respectively.The model of the DC/AC converter decouple the dq phase coordinate in order to control it independently.PI control and deadbeat control combined with repetitive control are designed based on the internal model principle.Repetitive control technology can't be applied alone due to the poor dynamic response.To overcome the shortcoming,the paper analyzes two conventional control methods: PI control and dead-beating control and then combining it with the repetitive control.Compared the output waveform quality under several control schemes through the simulation,it's concluded that PI repetitive control is the final choice.The PI parameters are designed by counteracting the dominant pole of object's transfer function the by zero offset.Using zero phase shift error tracking theory to design the repetitive compensation link.The method can improve the problem of poor dynamic response of the repetitive control itself and can effectively suppress the harmonics in the inverter.A multi-mode repeater controller with 6 frequency multiplication signals as the internal model is proposed.Then a multi-mode repetitive control method is proposed to suppress the harmonics at specific frequencies by overlaying the control of the internal modes in parallel.But,the improved controller introduces the problem due to the internal model division precision.Lagrange interpolation is adopted to approach the decimal beat.The notch Filter and the second-order filter in series to optimize the traditional phase compensation function.The simulation verified that the proposed repetitive control has better performance than direct repetitive control.A two-phase three-phase grid-connected inverter experimental platform was set up to verify the control method of this paper.Experimental result shows that the combination of PI control and repetitive control is better than single PI control.After the above-mentioned improvement of repetitive control,the THD of the incoming current decreases from 2.62% to 2.04%,and the dominant harmonics of 3,5,and 7 times are effectively suppressed,when a given current step changes,it has a faster response speed,the output can quickly follow the given.