Research On Fuzzy String-level Active Disturbance Rejection Control Strategy For LCL-type Grid-connected Photovoltaic Inverters

The photovoltaic power generation system will cause the harmonic resonance phenomenon of the system during the transmission of energy,and the resonance phenomenon will amplify the disturbance,and the harmonic will affect the success rate of grid connection.Aiming at the problems caused by the harmonic resonance phenomenon,this paper designs Linear Active Disturbance Rejection Control(LADRC)as the core control algorithm and Fuzzy Logic Control(FLC)as the auxiliary control algorithm based on LCL-type grid-connected PV inverter,Theoretical analysis and numerical simulation verification are carried out from the establishment of the equivalent circuit model of the LCL-type grid-connected photovoltaic inverter,the harmonic resonance generation mechanism,the design of the self-anti-turbulence and fuzzy controllers,the influence of the controller parameters on the system performance,and the performance of the system under simulated working conditions.In this athesis,a fuzzy cascade linear active disturbance control algorithm Fuzzy Cascade Linear Active Disturbance Rejection Control(FCLADRC)combining with the 2nd order linear active disturbance control algorithm and the 1st order fuzzy improved linear active disturbance control algorithm is proposed.Firstly,the mathematical model of LCL-type grid-connected photovoltaic inverter is established and the resonance generation mechanism is analyzed.Then,the 3rd-order LADRC controller is designed and the closed-loop control block diagram of the system under the 3rd-order LADRC is designed,and the system transfer function is written.Furthermore,in order to reduce the amount of engineering calculations,the 3rd-order system is processed by the equivalent decomposition,which is equivalent to the superposition of the 2nd-order system and the 1st-order system,in which the2nd-order system uses the 2nd-order LADRC,and the 1st-order system uses the1st-order LADRC,and in order to improve the 1st-order LADRC’s In order to improve the disturbance observation capability of the 1st order LADRC,a new observer is introduced to form a tandem observer with the original observer to form the Improve Linear Active Disturbance Rejection Control(ILADRC),This constitutes the Cascade Linear Active Disturbance Rejection Control(CLADRC)double closed-loop control strategy based on linear self-resistance.Further,FLC is introduced into the 1st order ILADRC to form the 1st order Fuzzy Improve Linear Active Disturbance Rejection Control(FILADRC),so that the system obtains the real-time parameter optimization capability,and the 1st order FILADRC and the 2nd order LADRC form the fuzzy serial self-resisting double closed-loop control strategy,i.e.,the FCLADRC.and finally,the numerical simulation model of the LCL-type photovoltaic grid-connected inverter is constructed,and the comparative simulation is carried out for verification.After simulation verification,the FCLADRC double closed-loop control strategy designed in this paper not only effectively suppresses the harmonic resonance phenomenon of the system,but also improves the observation accuracy of the system on the perturbation and realizes the function of real-time optimization of the controller parameters,which ensures the system’s steady-state operation capability and transient fault transition capability,and it has an excellent value for engineering applications.