Design Of Sliding Mode Control Method For Three-level Grid-connected Inverter

With the rapid development of modern control theory and inverter control technology,in recent years,the research of grid-connected inverter systems has changed from classic inverter topology to multi-level topology,while Neutral Point Clamp(NPC)Topology is one of the most well-known multi-level topological structures.It can not only meet low-cost and efficient conversion schemes,but also be widely used in various production practices.This paper takes the three-level neutral point clamp grid-connected inverter topology as the research object,and focuses on the inverter control strategy to provide strong support for improving the grid-connected power quality.This article mainly studies from the following aspects:First,the circuit topology and basic principles of system operation of the NPC three-level grid-connected inverter are expounded;the relationship between the inverter output voltage and the switching action combination is obtained according to the topology and the relevant mathematical model is established;the SVPWM strategy is deeply studied the modulation technique of the paper gives four steps to realize the strategy and design simulation to verify its feasibility;Second,in-depth analysis of the causes of the midpoint potential imbalance on the DC side of the inverter,the midpoint potential balance is controlled by introducing a modulation factor k;and considering the two factors of the midpoint potential difference and the direction of current flow,the PI link is designed to adjust the value of k in real time To solve the problem of midpoint potential balance;Third,the control strategy of the inverter is mainly studied.According to the dq model of the three-level inverter,the PI(Proportional Integral,PI)algorithm is designed for the current loop of the controller.The decoupling theory study of the current loop is used to derive Adjust the coefficient and analyze its performance;but due to PI control problems such as difficulty in selecting appropriate parameters and poor control accuracy,the Model Predictive Control(MPC)algorithm is introduced,and the optimal switch is obtained by establishing a discrete-time model and value function State,so as to optimize the control algorithm of the inverter;however,the MPC strategy makes the switching state change irregular and the switching frequency is not fixed,so the sliding mode control(Sliding Mode Control)algorithm is designed.Strong robustness and anti-jamming,finally make the system well controlled;Fourth,the design of each module and control algorithm of the system is simulated in MATLAB/Simulink.According to the selected system parameters,output current to the inverter by changing the reference current,adding power grid disturbances,midpoint potential balance control effect,and the system's ability to complete the follow-up,etc.The impact of the simulation test and research.Through the comparative analysis of simulation experiment waveforms and data,when the grid-connected inverter adopts the SMC-based strategy,the output waveform is smoother,the output current harmonic rate is lower,the midpoint potential balance control effect is better,and the system completion tracking time is faster,etc.Advantages,so the SMC strategy has advantages and practical feasibility in the NPC three-level inverter grid-connected control.