Research On Repetitive Control Strategy Of The Photovoltaic Grid-connected Inverter With LCL Filter

Energy is the lifeblood of the national economy.With the depletion of traditional energy sources,solar photovoltaic power generation has become a major hot spot in the global new energy field,and it has shown a trend of rapid development.Photovoltaic power generation is currently the most widely used method for solar energy development and utilization.In the photovoltaic power generation system,if the grid-connected inverters of the grid-connected inverter are not well controlled,it will cause serious damage to the grid.In order to improve the quality of grid-connected current,this paper proposes an improved repetitive control strategy based on active damping and composite compensator.First,the active damping method based on grid current feedback is used to suppress the resonance peak of the LCL filter while slowing down the phase change speed at the resonance peak.Secondly,for the defects that only the system phase lag can be compensated for in the case of repetitive control advance compensation,a compensation method combining the first-order compensation with the advance compensation is proposed.The first-order compensation makes the repetitive control system have unity gain and zero phase shift characteristic in the middle and low frequency range.Advance compensation is used to improve the accuracy of the phase compensation in the middle and high frequency range,and to slow the phase change rate in the high frequency band,so that the slower amplitude attenuation can also meet the requirements of repetitive control stability and have a larger stability margin.At the same time,the method avoids the use of low-pass filters and traps,and greatly simplifies the structure of the repetitive control compensators.In order to further improve the dynamic performance of the system,this paper adopts compound control strategy combining PI control and the repetitive control to control the grid-connected current.The simulation results verify the correctness and effectiveness of the method.High-precision phase-locked loop is the premise to achieve accurate control of grid-connected current.In order to solve the problem of large phase-locked error of the traditional phase-locked loop in the case of non-ideal grid voltage,a phase-locked loop that can quickly extract the fundamental voltage component of the grid and accurately calculate the phase angle of the grid voltage is proposed.The PLL filters the higher harmonics of the grid voltage through the second-order generalized integral,and delays the phase angle of the voltage signal π/4 in the two phase stationary coordinate system,and then transforms it into the rotating coordinate system,and the positive sequence component is extracted by adding and subtraction of the non delayed dq axis voltage signal.It avoids the DC offset problem of the phase-locked loop based on double second order generalized integrator in positive and negative sequence voltage extraction,and solves the defect that the phase-locked loop of the delayed signal cancellation can eliminate only partial harmonics.The simulation results show that the method still has accurate phase-locking characteristics under unbalanced voltage,harmonic voltage and frequency fluctuation.