Research On Active Disturbance Rejection Control Of DC-link Voltage Of Photovoltaic Grid-connected Inverter

In the commonly used two-stage photovoltaic grid-connected system,the inverter acts as a bridge between the hardware circuit and the power grid,and its control performance is directly related to the power generation efficiency and stable operation of the system.The inverter is not only responsible for regulating and protecting the current flowing to the grid side,but also must ensure that the bus capacitor voltage connected to the front and rear stages has a certain disturbance rejection performance.Failure to properly control the DC-link voltage will seriously affect the reliability of the system and even trigger related protection equipment.Therefore,the robust control of the DC bus voltage of the inverter has always attracted the attention of a wide range of scholars.Considering the uncertainty of grid connected system operating conditions and a variety of disturbances in power electronic devices,linear active disturbance rejection control(LADRC)is implemented in the outer loop control of inverter to improve the tolerance of DC-link voltage to disturbances.The main work is as follows:(1)By analyzing the circuit structure of the two-stage photovoltaic grid-connected system,the state space mathematical model of the grid-connected inverter is established,and the grid-side power regulation principle is explained through the grid voltageoriented vector control.In addition,according to the power balance relationship on both sides of the DC link,the fluctuation problem of the DC-link voltage is explained,and the traditional double closed-loop voltage and current control and its parameter configuration are introduced in detail.(2)The structural composition and control function of LADRC are analyzed,and the parameter tuning method of LADRC is given by exploring the physical meaning of the "bandwidth" of the control system.Aiming at the mathematical expression of LADRC,the corresponding relationship between LADRC and PID control is discussed from the perspective of equivalent block diagram,and the advantages of LADRC over PID control are proved theoretically,and a simulation model is constructed to verify it.(3)In order to improve the control performance of DC-link voltage,an improved active disturbance rejection control scheme is proposed in the outer voltage loop.The cascaded extended state observer is used to supplement the unestimated residual disturbance dynamics under the traditional method,thus improving the accuracy of disturbance compensation.The disturbance rejection performance of the proposed method is analyzed theoretically,and its stability is tested by Linard-Chipper stability criterion.Finally,the simulation results show that the proposed control method can better stabilize the DC-link voltage under various working conditions and ensure the stable operation of the photovoltaic grid-connected system.