Research On Active Disturbance Rejection Control Strategy Based On LCL Grid-connected Inverter

With the accelerated development of the world’s industrialization as a whole,the traditional energy sources it relies on are facing the problem of being exhausted.Distributed power generation is an important part of the development of renewable energy.As the key interface of distributed power generation,microgrid inverters have received more and more research and development.LCL type inverter is widely used because of its many advantages,but the requirements for control are also higher.Since the active disturbance rejection control can not only make the system run stably,but also can suppress the disturbance caused by the non-ideal condition of the grid voltage to the inverter,so its research has more important application value.In this paper,an improved active disturbance rejection control strategy is used to control the gridconnected current of the LCL grid-connected inverter.The main tasks are as follows:(1)From the perspective of matrix transformation,the expressions of inverter system in αβ and d-q coordinates are derived,and the adverse effects of grid voltage on LCL grid connected inverter are analyzed.(2)A cascade ADRC strategy with model compensation term is proposed.Firstly,the basic principle of ADRC is introduced,and the use of the model information is analyzed.Then,by analyzing the steady-state error of linear state observer,it is pointed out that the traditional third-order ADRC strategy will make the total disturbance of the system have a large disturbance amplification coefficient.Based on the above,a cascade structure of ADRC is proposed,which can effectively reduce the amplification coefficient of the total disturbance observed and enhance the anti-disturbance capability.In order to further improve the estimation accuracy of the disturbance,the ADRC adopts the model to compensate the auto disturbance rejection.Finally,the stability of the controller is guaranteed by reverse step method.The simulation and experiment are compared with the existing ADRC in the control of grid connected current.The results show that the proposed strategy has stronger disturbance suppression capability.(3)The strategy of immersion and invariant ADRC is proposed.In order to control the cascaded ADRC,this strategy uses linear error feedback,replacing it with a nonlinear error feedback method can further improve the overall accuracy of external disturbance estimation,but it is difficult to ensure its stability.First,the basic principles of immersion and invariant are briefly introduced,and then the control method of immersion and invariant stability is applied to the design of advanced state observers.The mapping relationship between the class of the non-linear target system and the observation error system is determined,which makes the extended state observer have nonlinear error feedback mode,and ensures the stability by using high gain method,so that all States in the system are bounded and the observation error can reach any small.Finally,the stability of the overall controller is ensured by backstepping method.In the grid-connected current control,simulation and experiment are compared with the traditional ADRC.The results show that the proposed strategy has stronger disturbance suppression ability.