Improved Sliding Mode Active Disturbance Rejection Control Strategy for PV-Storage Integrated Converter
In order to reduce the use of fossil fuels and carbon dioxide emissions,renewable energy sources such as photovoltaic(PV)power generation systems have developed rapidly.However,the output power of photovoltaic arrays has great volatility.Direct integration into the grid may cause fluctuations in grid voltage and frequency,which have a negative impact on the stable operation of the grid.The establishment of a PV-storage integrated converter to connect the photovoltaic module and the power grid is an effective way.However,the PV-storage integrated converter is a multi-input system with nonlinear and strong coupling characteristics.The traditional control cannot achieve the ideal control effect,which decreases the energy utilization rate.Therefore,an improved sliding mode active disturbance rejection control(SM-ADRC)strategy is proposed to reduce the transient DC bus voltage fluctuation and accelerate the power response speed by improving the extended state observer(ESO)and the state error feedback law.The specific design method of SM-ADRC strategy for second-order systems is as follows.Firstly,aiming at the problem of insufficient accuracy of ESO for state variables and disturbance observation,a new error is introduced as the adjustment basis of ESO to improve tracking ability.The improved ESO has a faster estimation speed and higher estimation accuracy of x2 and x3 than the traditional ESO simulation under unit step and unit slope,which effectively improves the performance of active disturbance rejection control.Secondly,aiming at the problem of insufficient robustness of the traditional state error feedback law,the state error feedback law is changed to the back stepping complementary sliding mode control(BCSMC)based on the improved exponential reaching law.It is found that the introduction of the back stepping method effectively improves the convergence accuracy of the system,and the introduction of the improved exponential reaching law effectively reduces the sliding mode chattering phenomenon.Finally,the error range of the improved ESO is obtained,and the stability of BCSMC and improved ESO based on the improved exponential reaching law is proved according to the eigen value criterion and the Lyapunov method.Through the state space averaging method,the mathematical models of the converter part and the bidirectional DC-DC converter part in the PV-storage integrated converter are established.The current inner loop control of the converter part and the voltage outer loop control of the bidirectional DC-DC converter part are changed to the improved SM-ADRC.The DC bus fluctuation and power response speed under three working conditions of photovoltaic power mutation,power command mutation and grid drop fault are compared by simulation and experiment.The superiority of the improved SM-ADRC strategy compared with the traditional SM-ADRC strategy and PI control strategy is verified.
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