Robust Control For Photovoltaic Plants Connected To The Power Grid Based On State Observer

In all applications of renewable energy,solar and wind power are considered as the mature and commercial technologies.As one of the most advocated green energy,photovoltaic generation industry has a broad development prospects,because traditional energy resource is depleting.Grid-connected photovoltaic power generation technology is the main application of solar power generation,which mainly includes parts of solar cell array,grid inverter,and the corresponding central control system.The inverter is especially the key technology.Based on state observer,by introducing a periodic external excitation signal generation model in the closed-loop of control process,repetitive control is capable of tracking or suppressing periodic signal with zero stable-state error.Through theoretical analysis,the traditional control strategies of grid-connected photovoltaic inverter system perform unsatisfied.Therefore,a novel control strategy of grid-connected photovoltaic inverter system based on robust controller is proposed.A kind of photovoltaic?PV?plant power generation system with grid-connected application is proposed in this paper.The study in this paper involves the system topology,maximum power point tracking?MPPT?methods of PV power,the control strategy of inverter,the system prototype design testing technologies.The primary work of this dissertation is summarized as follows:?1?According to the characteristics of PV power systems,a kind of topology for PV power generation system is built,and the system has grid-connected operation modes.The components of the system are analyzed and modeled respectively.With an analysis of several grid-connected and off-grid photovoltaic inverter system topologies,repetitive controller structures of grid-connected photovoltaic inverter,such as double-loop control,output feedback and state observer are established,and their physical model are built.In this process,a mathematical phenomenon that periodic signals could not be tracked perfectly was discovered from the perspective of coordinate transformation,also the Matlab/Simulink simulation models are established.?2?Based on the topology of the PV system,the MPPT technologies for the PV system and the inverter control technology of the system are investigated.The output power characteristics of PV power are analyzed.For MPPT of PV power,a fuzzy sliding mode control tracking technology is suggested,and the MPPT methods are simulated.Aiming at the failure of the traditional MPPT method under local shadow conditions,the optimal control method of the MPP of the PV branch is studied.The control principle of the series compensation voltage is analyzed,and the maximum power point prediction is used to realize the MPPT of the PV array under local shadow conditions with simulation verification.With a concern of the physical model of double-loop grid-connected photovoltaic inverter repetitive controller,from aspect of frequency domain,the open/closed loop transfer functions are derived.With the H_?model,the undetermined parameters could be possibly worked out by toolbox Hinfsyn in Matlab.The feasibility of proposed method was validated.?3?Aiming at grid-connected photovoltaic inverter repetitive controller based on state observer,a new reconstructed state space equation was obtained through a series of theoretical deduction,and was transformed into discrete-time two-dimensional model.Then the appropriate Lyapunov function was given out;besides,.Linear matrix inequality?LMI?sovling method of state observer parameters is given.Based on this,a mathematic simulation model of Matlab is employed.The practicality of the method is verified by a microprocessor based photovoltaic grid-connected experimental platform.?4?For the grid-connected inverter based on output feedback,the mixed H₂/H_?multiobjective robust stability condition of the PV grid-connected inverter is obtained from aspect of LMI.In the process of numerical solution,combined with the Lyapunov method and robust control theory in modern control theory,a variety of software toolboxes of Matlab are used to simplify the calculation process.The simulation results show that the control method has an excellent performance of good stability,low harmonics distortion and fast convergence.?5?The design verification of the grid-connected PV power generation system is carried out.The feasibility of the designed method is verified by several physical experiments,including the maximum power tracking and grid-connected control experiments.Based on the grid current control,the grid-connected mode take into account synchronization with the grid voltage,and the inverter input power fluctuations caused by environmental condition changes and corresponding grid current changes.The prototype of machine experiment is carried out,and the robustness of the control strategies mentioned above is compared.