Research On Hybrid Control Strategy Based On LLCL Type Single-Phase Grid-Connected Inverter

Renewable energy is now widely used.In order to make renewable energy better utilized,grid-connected inverters are widely used as a device to convert primary clean energy into usable energy and connect to the grid.Distributed power generation system.The inverters currently in use generally adopt a pulse width modulation method,which causes harmonics generated by high-frequency operation of the switching device to enter the power grid,thereby polluting the power grid and possibly interfering with the normal operation of other devices in the power grid,and therefore must pass A suitable way to filter the current entering the grid.The traditional single L filter is easy to control,but because of the large volume of the single L filter,the system response speed is slow,and has been replaced by the LCL filter.The LCL filter has a small volume and good dynamic response characteristics.The LLCL filter has a smaller size and lower loss by improving the LCL filter.Since higher order filters may cause resonance between the inverter and the grid,a suitable damping scheme must be used to suppress the occurrence of resonance.The currently used methods are classified into a passive damping scheme and an active damping scheme.The passive damping scheme attenuates the inherent resonant peak of the high-order filter by adding suitable passive components on the main circuit,which is convenient to implement,but generates additional power loss due to the access of the resistor;the active damping strategy is adopted.Increasing the sensor can achieve the same suppression effect as passive damping,and suppressing the generation of the resonance peak by a digital algorithm.After summarizing and analyzing various active and passive damping schemes and control methods for high-order output filters,this paper discusses an active damping scheme that can be applied to LLCL filters.The PR control has a large gain at the fundamental frequency,which can greatly reduce the steady-state error,but the repeated errors in the period cannot be completely eliminated,and the repeated control can well suppress the repeated errors in the period.Signal,but it also has the disadvantage of poor dynamic response,which can not effectively eliminate non-periodic errors.Therefore,this paper mainly analyzes the two control methods and combines the advantages of the two into the LLCL grid-connected inverter.The effectiveness of the algorithm is verified by Matlab simulation.The main work of this paper is as follows:1.The filtering characteristics and principle of LCL and LLCL type grid-connected filters in grid-connected inverters are analyzed.The LCL and LLCL filters are modeled.Based on this,theinverter side is analyzed.The effect of different values ??of inductance,capacitance and grid side inductance on filter performance.According to the requirements of IEEE specifications,the LLCL filter parameters were designed and the design results were verified by simulation.2.Taking the LLCL filter as an example,the common passive damping method is introduced.The problem of passive damping is analyzed.The active damping method is introduced to suppress the resonance generated by the filter.The theoretical verification is verified by simulation.feasibility.3.The principle and design method of proportional resonance control and repetitive control are analyzed.Combining the proportional resonance control and the repetitive control,a hybrid control method is formed and applied to the LLCL-based single-phase grid-connected inverter.The feasibility of the method is verified by simulation.