Research On Grid-connected Inverter System Based On Active Disturbance Rejection Control

As a representative of new energy,electric energy is very clean and economical,and has been widely used in many fields.The electric energy undergoes at least one power conversion before it is used,and the inverter plays an important role in the power conversion process,which can reduce losses and ensure safety.However,the output waveform of the inverter will be affected by other factors,such as non-ideal characteristics such as the no-load time of switching devices,nonlinear loads,and harmonic interference at all levels of the actual power grid system,which will cause the total harmonic distortion of the output waveform to increase and track errors increase,resulting in degraded waveform quality.Taking Active Disturbance Rejection（ADRC）control as the core,this paper designs active disturbance rejection controllers for single-phase and three-phase grid-connected inverters respectively.The state variables are estimated by the observer,the control rate compensates the system model,and the feedforward control is used to suppress the harmonic effects of grid voltage;analyze controller performance,and perform Simulink simulation and hardware-in-the-loop simulation.The main research contents of this paper are as follows:Firstly,a mathematical model is built for the topology of the single-phase grid-connected inverter system,and the first-order discretized transfer function of the inverter is obtained by padé approximation.Based on this,the ADRC controller is designed and verified by digital simulation.The ADRC controller proposed in this paper includes a tracking differentiator,a linear expansion state observer,and a linear control rate.The three will have functions such as smoothing signal mutation,real-time estimation of system state,and control signals.The grid voltage feedforward control is used to eliminate the harmonic influence of the grid voltage and improve the phase lag phenomenon of the grid current.Referring to the design of the linear controller,a nonlinear extended state observer and control rate are further proposed.Finally,a digital simulation is built to analyze the grid-connected current.Secondly,the capacitor current of the three-phase grid-connected inverter system is controlled,the discrete mathematical model of the system is built,and the linear ADRC controller is designed and verified by digital simulation.The mathematical model of the threephase grid-connected system is simplified and its dq-axis current is obtained by coordinate transformation.Due to the symmetry of the dq-axis current,the same linear ADRC controller is designed to control the controlled object.The linear expansion state observer is used to observe the state variables of the system in real time,and the linear control rate realizes the compensation of the system model and the control signal,and the grid voltage feedforward correction is used to further improve the quality of the incoming current.Finally,a digital simulation model is built,and the controller performance is analyzed according to the Simulink simulation waveform to verify the effectiveness of the controller.Finally,a hardware-in-the-loop simulation platform for grid-connected inverter is built in the laboratory to verify the control strategy of the above-mentioned grid-connected inverter system.Two softwares,Star Sim HIL and Star Sim RCP from Modeling-Tech,are selected.First,the single-phase and three-phase grid-connected system built by Simulink is divided into two parts: control and model.And download the two parts to the corresponding PXI hardware device to run,so as to simulate and simulate a real grid-connected inverter system,and further verify the validity and rationality of this control strategy in the application of grid-connected inverter system.