Research On Gain Adaptive Control Strategy Of LCL Grid-Connected Inverter

With the growth of distributed generation systems in renewable energy,microgrids play an important role in meeting future power needs.In order to meet the power demand of dispersed users in remote areas,most of the transmission lines are long,which undoubtedly increases the equivalent grid impedance.The microgrid is a weak grid,and its grid impedance can not be ignored.The traditional controller can't meet the performance index of the system when the grid impedance changes,which makes the control of the grid-connected inverter becomes the present research hotspots.In this paper,the PR proportional resonance controller is used to compensate,and the active damper is used to eliminate the resonance peak caused by the LCL filter,which constitutes the double closed-loop control loop of the grid current outer loop and capacitor current inner loop.It can ensure the grid-connected inverter operates stably and has certain robustness while ignoring the impedance of the grid.Premising on stability of grid-connected inverter,the ratio of the microgrid impedance and the output impedance of the grid-connected inverter satisfy the nyquist criterion to analyse the stability of the system.When the grid impedance changes greatly,the fixed PR controller can't meet the optimal operating conditions of the system.In this paper,guaranteeing optimal phase margin,taking into account other performance indicators,the gain adaptive control strategy based on the tunable PR controller is adopted.Through the simulation,the impedance of the microgrid is divided into sections,and the gain coefficient corresponding to the impedance interval is obtained by repeated experiments and a gain schedule is generated.Finally,the experimental platform of a 2kW single-phase grid-connected inverter is built,and the feasibility of the control algorithm and the stability of the system is verified by the experimental platform.The control algorithm is implemented in the DSP,which mainly includes the conversion of the actual detected value and the sampled digital quantity,the phase-locked loop based on the second-order generalized integrator,the gain adaptive control algorithm and the generation of the digital SPWM waveform.