Research On Sliding Mode Control Strategy Based On Three-level Solar Inverter

In recent years,with the increasing demand for energy and increasing environmental pollution,solar energy has attracted much attention as a clean energy source.With the development of microgrids,photovoltaic power generation has become an important way to use solar energy and has been applied in various industries.More and more extensive.With the upgrading of photovoltaic applications,people have higher requirements for the output power quality of grid-connected inverters.In order to obtain higher quality output voltage and current,researchers have improved the photovoltaic grid-connected inverter from two aspects:improving the main circuit topology of grid-connected inverters and adopting advanced control methods.The T-type three-level inverter is an improved product of the clamped three-level inverter.Not only the structure is relatively simple,but the efficiency is also improved.Therefore,the T-type three-level inverter is applied to the photovoltaic grid-connected system.It can reduce the cost of the system and improve the efficiency of the system,especially in medium and high power grid-connected systems.Sliding mode control is essentially a non-linear control method.It can still obtain better stability and robustness under uncertain system parameters,and it is easier to implement than other non-linear control methods.Because of the characteristics of power switching devices such as IGBT and MOSFET,the inverter is actually a variable structure system.Therefore,sliding mode control is very suitable for inverter control.In order to improve the quality of photovoltaic grid-connected power,a sliding mode control strategy is studied and simulated in the main circuit topology of the three-level inverter,and a good control effect is obtained.First,the paper introduces the characteristics of several typical multilevel inverters,compares their respective advantages and disadvantages,and finally decides to use a T-type three-level inverter as the main topology.The working principle and implementation method are explained.The modulation principle and implementation of the T-type three-level inverter space vector modulation method are studied.According to the effect of different vectors on the midpoint voltage in the SVPWM modulation algorithm,a distribution factor method based on PI adjustment is used to balance the key voltages.The simulation experiments verify the reliability and effectiveness of the SVPWM modulation strategy.Then,the basic topology of the grid-connected circuit of the T-type three-level inverter and the LCL filter is given.The mathematical system model of the output side of the grid-connected inverter is analyzed and established.The mathematical model under the dq coordinate axis of the inverter is obtained by transformation,and the controller design difficulty is reduced by simplifying the mathematical model.Next,the thesis expounds the sliding mode control theory.Aiming at the problem of the unsatisfactory dynamic response characteristics and robustness in traditional control,a double closed-loop sliding mode control strategy based on the super-spiral algorithm is proposed.Finally,according to the inverter grid-connected mathematical model and control strategy,the structure and parameters of the sliding mode controller are designed,the specific design process is given,and the system stability is analyzed theoretically.The PSIM platform was used for simulation experiments to study the robustness,dynamic response characteristics,and harmonic content of the grid-connected current of the designed photovoltaic grid-connected system.The feasibility of the proposed control strategy was verified.The comparison of PI control results proves that the new control strategy proposed in this paper can achieve the purpose of improving the grid-connected power quality and robustness of the system.Figure[31]table[8]reference[62]...