Research On Control Strategy Of Photovoltaic System Off-grid Operation Based On Double Integral Sliding Mode Control

The problem of climate warming caused by the over-exploitation of fossil energy is a huge challenge facing by the human society today.“Zero Carbon” is being transformed from a global consensus into a national policy goal,and the inclusion of “Carbon Peak”and “Carbon Neutral” in the government work report marks that China will bring profound changes in the energy field.It is critical to use clean and pollution-free solar energy to replace traditional energy for achieving “Carbon Emission Reduction” from climate governance to energy transition.Under this background,this paper carried out the research on the bus voltage transient disturbance caused by the change of system working mode based on the off-grid photovoltaic power generation system as the research object,and proposed an improved control strategy to realize smooth transition between the working pattern,and maintain the stability of bus voltage by adopting the sliding mode control strategy to ensure system dynamic performance and control precision at the same time.Specific work is as follows:Firstly,a PI controller is designed to realize the closed-loop regulation of Boost converter based on the analysis of modeling of photovoltaic cell and Boost converter.Then for the PI controller cannot better adapt to the requirements of Boost converter regulation ability when the parameters change greatly,a double integral sliding mode controller(DISMC)for off-grid photovoltaic power generation system is designed based on the theory of sliding mode control to ensure the system with fast dynamic response and high steady-state accuracy.Meanwhile,in the MPPT control strategy of off-grid photovoltaic power generation system,the expected effect of DISMC in improving the dynamic response and steady-state accuracy of the system is verified,and the problems of slow dynamic response and large steady-state error under the traditional control strategy are solved.On this basis,the analysis of the bus voltage transient disturbance caused by the change of system working mode has been carried out and reveals the causes of voltage sags of DC bus.Besides,the closed-loop control strategy of voltage offset compensation has been designed by using bus voltage information,which solves the problem of bus voltage instability caused by the change of working mode,and realizes the smooth transition between MPPT mode and CVC mode in off-grid photovoltaic power generation system.Finally,the overall model of off-grid photovoltaic power generation system has been established by simulation,and the parameters of each part of the system are calculated and selected.By changing the load and light intensity,it simulates the real engineering environment of the system as well.The simulation results verify the correctness and effectiveness of the closed-loop control strategy under DISMC,and realize the smooth transition between system working patterns,as well as ensuring the stability of the bus voltage.Meanwhile,the simulation results verify that DISMC has a great effect in improving the dynamic response and steady-state accuracy of the system.