Resergh On Fractinal Order PI~?D~? Control Of Grid-connected Inverter Based On MPSO Algorithm

Grid-connected inverter is an energy conversion interface device between renewable energy generation system,public power grid and local load.It is responsible for the conversion and control of the energy of distributed generation system(DG),its performance directly determines the quality of grid-connected current,which is very important for the safety,stability and high-quality operation of DG.Therefore,it has great theoretical significance and practical engineering application value to further improve the stability and dynamic performance of the control system of grid connected inverter.In this thesis,for the characteristics of the grid connected inverter system under control of integer order PID,such as a long dynamic response time,a lack of harmonic suppression ability and many uncertainties to reduce stability,a fractional-order PI~?D~?control strategy for grid-connected inverter based on modified particle swarm optimization algorithm(MPSO)is proposed,which extends the stable parameter ranges,improves the self adaptability of the system parameters,effectively improves the control performance of the system,suppresses the disturbance on the grid side,and reduces the harmonic content of the grid-connected current.Firstly,the system damping scheme is determined according to the structure of the single-phase LCL grid-connected inverter,and the modified Oustaloup filter algorithm is used to digital realize the fractional-order PI~?D~?controller(FOPID).On this basis,the influences of the order parameters?and?of the FOPID on the dynamic and steady-state performance of closed-loop system is analyzed.Secondly,the mathematical model of single-phase LCL grid connected inverter control system is derived,on this basis,the decomposition analysis of the control loop is carried out,including the current feedback coefficient and the voltage feed-forward channel transfer function are designed.The control performance of the grid-connected inverter system using integer-order PID controller and FOPID is compared and analyzed.Then,according to the amplitude and phase frequency characteristics of the open-loop system,the influence on the system stability performance when the FOPID parameters changed and the relationship between the controller parameters are studied,and the value ranges of the controller parameters is given.Finally,the inertia weight is improved on the basis of the conventional PSO,and the modified particle swarm algorithm(MPSO)is applied to the parameter optimization of FOPID controller.The MPSO can enhance the global search ability,accelerate the convergence speed,improve the search accuracy,and enhance the parameters self-adaptability of the controller to a greater extent.A simulation model is built on the Matlab/Simulink platform to simulate the dynamic response and anti-interference performance of the grid-connected inverter system.The simulation results show that compared with the integer-order PID controller,undering the control of the FOPID controller based on MPSO,the grid-connected inverter system has greater advantages,which can effectively improve the phase margin of the system,reduce the total harmonic distortion of the output grid current,and make the system have good robustness under the disturbances such as current mutation and grid voltage mutation.