Research On Low Voltage Ride Through Of Photovoltaic Grid Connected Inverter Based On Linear Active Disturbance Rejection

With the continuous development of photovoltaic power generation technology,the installed capacity of photovoltaic power stations is also increasing,making its impact on the grid more and more significant.When a voltage drop occurs due to a fault or disturbance in the power grid,the photovoltaic grid-connected system will suddenly run off the grid due to overvoltage or overcurrent,which will have a certain impact on the stability of the grid.In order to ensure that the photovoltaic grid-connected system does not run off-grid and smoothly surpass the voltage drop period,low-voltage ride-through technology has become a key link in the vigorous development of photovoltaic grid-connected power generation.The traditional low-voltage ride-through mostly adopts a double closed-loop control strategy,and the control method is mainly based on the PI controller.However,the PI controller is unsatisfactory for the suppression of disturbances such as system DC bus voltage fluctuations caused by voltage sag,especially when the voltage reaches zero;Linear auto disturbance rejection controller is a new type of controller that is researched and developed based on the PID controller.With its feedback compensation effect on the total disturbance,the control system can eliminate the influence of errors from the root cause.Therefore,this paper uses a linear auto-rejection controller to replace the PI controller in the double closed-loop control strategy of the photovoltaic grid-connected inverter,effectively enhancing the system's ability to achieve low voltage ride through.First,analyze the two-stage structure of the photovoltaic grid-connected system;then establish a mathematical model of the grid-connected inverter part,and propose to adopt the grid-connected inverter by analyzing the operating characteristics of the photovoltaic grid-connected system when the power grid has a low voltage fault Double closed-loop control strategy to control,in order to achieve low-voltage ride-through function of the system.Secondly,by analyzing the limitations of the PID controller,a linear auto-disturbance rejection controller that can observe and compensate disturbances in real time is proposed,and the structure and principle of the linear auto-disturbance rejection controller are analyzed.The control system uses a linear auto-disturbance control to not only simplify the system structure,but also reduce the difficulty of theoretical analysis and reduce the workload of parameter setting.Finally,the type of grid voltage drop fault is analyzed,and the corresponding simulation model is built according to the change of the control method of the grid-connected inverter.The double closed-loop control strategy based on grid voltage orientation is used for symmetrical drop faults,and the positive and negative rotation is used for asymmetrical drop faults.The dual closed-loop control strategy for coordinate axis control uses a linear auto-disturbance rejection controller to replace the PI controller of the outer voltage loop.Simulation experiments show that the grid-connected inverter adopts linear auto-disturbance rejection when a voltage drop occurs at the grid connection point.The low-voltage ride-through control strategy can not only effectively suppress the DC-side bus voltage fluctuations,maintain the grid-connected system without off-grid operation,but also provide certain reactive power to support the rapid recovery of grid voltage,which greatly enhances the grid-connected system's low-voltage ride-through capability.