The Control Strategy Research Of PV Grid-connected Inverter Based On LCL Filter

Photovoltaic generation has been gradually given attention to the development of renewable energy;the grid-connected inverter with LCL is a hot spot as a key part in photovoltaic generation system.However,the LCL-filter without taking damping resistance into consideration is a three-order system,and there is a large resonance peak in system,so the difficulty for control is increased.Advantages and disadvantages of several traditional control methods on the basis of three-phase photovoltaic grid-connected inverter with LCL are analyzed,and a inverter control strategy based on two-degree of freedom control is proposed,the performance of the system is improved by the method proposed in this paper,so it has practical significance.Firstly,topological structures of grid-connected inverters with L and LCL are analyzed,establish its mathematical model,and performances are analyzed by bode diagram of systems.As for the complexity of the design of the LCL-filter,the basic standard for the parameters design of the LCL-filter is given according to performance indexes of system,and parameters of the LCL-filter selected in this paper are designed.Secondly,as for the problem of resonance peak for LCL-filter,two common control strategies are analyzed:Active damping control and reactive damping control.Resonance peak of system can be validly restrained and the stability of system can be attained according to the analysis of logarithmic frequency characteristic curves and root locus of system.But the reactive damping control has power loss problem,the active damping control need to add additional hardware.In order to solve this problem,active damping control strategy based on two-degree of freedom is proposed in this paper,and two-degree of freedom controller that can be applied for the grid-connected inverter is also be designed.The mathematical model of the system is established and its performance is analyzed,and the two-degree of freedom controller is applied to grid-connected system and great performance can be attained by observing logarithmic frequency characteristic curves of the system.Finally,the grid-connected current is analyzed by Simulink simulation.The results show that better stability precision and dynamic performances of the system can be attained and the harmonic contents of the system can meet the grid-connected requirements by using the two-degree of freedom controller.