Research On Sliding Mode Control Strategy Of Inverter

In recent years, with the rapid development of communications technology, information technology and power system, the voltage source inverter is getting more and more widely used in all kinds of field as a clean, stable power supply and the requirements of inverter output power quality are also increasing. Thus, under the same main circuit topology, the control methods become so important. In order to improve the quality of the inverter output voltage and current waveforms, numbers of scholars are eager to proposing more advanced control methods. Sliding mode control is a nonlinear control method. It can ensure the system’s stability and robustness with uncertain parameters. Compared to other nonlinear control methods, it is easier to be implemented. Because of the characteristics of the power switching devices, the inverter belongs to variable structure system essentially. Therefore sliding mode control is very suitable for the control of the inverter.Paper summarized the basic principles of traditional inverter control methods and the advantages and disadvantages, development status of sliding mode control and its applications in the field of power electronics conversion. The sliding mode control technique of inverter was analyzed deeply. The sliding mode controller of three-phase voltage source inverter was designed. Improved strategy was proposed to improve the sliding mode control for the control system, which has better effects. At last, the latest inverter fractional sliding mode control theory was studied.Firstly, the basic topology of the three-phase full-bridge inverter was showed. The mathematical model of the inverter output side was analyzed and the mathematical model of two-phase rotating coordinate system was derived based on the coordinate transformation which simplified the controller design. For strong coupling of the inverter system, the original system was decoupled using inverse system method. Sliding mode controller was designed for the decoupled system, further simplifying the design process of sliding mode controller.Secondly, the paper analyzed sliding mode controller design of the three-phase full-bridge inverter. The terminal sliding mode control theory was described and nonsingular terminal sliding controller of the decoupled inverter system was designed. In order to eliminate the effects of external disturbance to system chattering, the state observer was added into the system to offset the adverse effects. Based on the theory of auto disturbance rejection, the choice of observer was the extended state observer, which is adaptive to external disturbance, more convenient to design. The paper analyzed the design method of ESO in inverter system, and the validity of the method was verified combined with sliding mode control.Finally, with the latest development of modern control theory, the application of fractional sliding mode control in the inverter control was researched and analyzed. For fractional sliding mode controller of inverter, fractional sliding surface and fractional reaching law were designed and the stability was proved. Compared to the general sliding mode control, fractional sliding mode control has more adjustable parameters, more accurate output, which make the output of sliding mode control smoother and has a better dynamic response. Simulation results showed the effectiveness of the method.