Research On Current Loop Control Of LCL Grid-connected Inverter Based On LADRC

With the increasingly serious energy shortages and environmental problems,the distributed renewable energy power generation technology,which is mainly based on green energy such as solar energy and wind energy,has attracted more and more attention.Grid-connected inverter system plays an irreplaceable role as the interface between distributed generation device and power grid,and its control performance directly determines the quality of grid current.In order to solve the cost and volume problems caused by the traditional single-inductance L-type filter,LCL filter with stronger high frequency suppression ability is usually used as the harmonic filter device between the power grid and the inverter.However,the traditional model-dependent control algorithm is difficult to overcome the shortcomings of complex coupling and resonant characteristic of LCL filter in dq coordinate system,which limits the performance improvement of LCL grid-connected inverter.In view of the low model dependence characteristic of the linear active disturbance controller(LADRC),which can solve the coupling and resonance problems without increasing the system hardware cost,this paper studies the current loop control strategy based on LADRC for the LCL grid-connected inverter system.Starting from the mathematical model of LCL three-phase PWM grid-connected inverter,the mathematical model of LCL grid-connected inverter in dq coordinate system is established by mechanism modeling method,and the coupling and resonance characteristics of the model are analyzed,which lays the foundation for the introduction of LADRC control technology.Secondly,by establishing the harmonic model of LCL filter in grid-connected mode,the relationship between the parameters of LCL filter and the harmonic suppression effect is studied.Considering the parameter design constraints of LCL,the parameters of LCL filter prototype are designed and verified by simulation.Then,this paper give a detail introduction to the basic principle of the LADRC technology,on the basis of which the third-order LADRC controller is designed with grid current closed-loop.By calculating the equivalent transfer function of the current loop,the performances of the LADRC controller are analyzed.Combined with analysis of simulation results,the feasibility of the third-order LADRC control strategy is proved.Aimed at avoiding the complex structure of the third-order LADRC controller and the inconvenience of parameter setting and performance analysis,the current loop control strategy is improved and simplified after comparing and analyzing the two control modes of grid side current feedback and inverter side current feedback.Combined with the controlled complex impedance feedforward strategy,the first-order LADRC controller based on inverter side current feedback is designed to solve the aboved discussed problems.The simulation results also prove the superiority of proposed first-order LADRC controllerFinally,to verify the control performance of LADRC in the current loop of LCL grid-connected inverter system,an experimental platform was designed with DSP+CPLD as the control core,by which the practical results prove the effectiveness of the LADRC control strategy adopted in this paper.