Research On Control Technology Of Photovoltaic Grid-Connected Inverter

To solve the two problems of energy shortage and environmental pollution, solar photovoltaic power generation had received extensively attention all over the world in recent years, grid-connected inverter as the key part of the photovoltaic power generation system, which had become the focus of current research. In this paper, three-phase bridge grid-connected inverter with LCL filter was selected as an research subject, the principles of LCL filter’s resonance peak and the restraining measures had been analyzed, focused on the control technology for grid-connected inverter, this paper studies the three control methods from two aspects of the grid-connected current and the input power, and verified the control performance of the three methods by simulation analysis.First, introduced the topological structure about the grid-connected inverter of the grid-connected photovoltaic system and chosen the three-phase bridge type as the research focus in this paper, designed the parameters of the LCL filter and analyzed the grid-connected control technology which is used wildly in the current.Secondly, adopted the grid-connected control technology which based on the quasi proportion resonant (QPR) controller of current double closed-loop, the use of capacitive current inner loop feedback control as the active damping to suppress LCL filter resonance peaks; on the base of the QPR current dual closed-loop control technology, take advantage of the resonator infinitely large part of the specific frequency gain characteristics to analyse the ability for inhibiting specific sub-harmonic of the harmonic compensator.Thirdly, analyzed a grid-connected control technology which based on the hysteresis loop power control, as adopting the hysteresis control method that leaded to no fixed switching frequency and increased the difficulty of filtering for the system, a method of fixed-frequency direct power control method of the filter inductor online estimate, whicn could solve the shortcomings of the no fixed switching frequency of the hysteresis control, this method had both the advantages of fast response and good robustness of the hysteresis control, finally, had a comparative analysis of the two direct power control methods.Finally, analyzed the working characteristics of photovoltaic grid inverters and active filter to identify the combining site of the unified control, which could achieve multi-usage, decrease the cost of application and improve the utilization efficiency of the system, adopted the control technology which based on the quasi proportion resonant (QPR) controller of current double closed-loop, focused on analysis of three modes which under the conditions of the unified control.