The Research On PWM Control Strategies In The Three Level Inverter

Three-level inverter is applied widely in the many industry fields for its excellent performance. Through referring lots of national and native conference documents, the understanding to the current researches of three level inverter are obtained , the profound comprehend to the features of the different PWM control strategies and control methods are acquiredThe paper deeply analyzes fundamental principle, performance and development of three level inverter, and compares the advantages and disadvantages of three kinds of typical multilevel circuit. Based on analyzing inverter circuits based on the hybrid cells improved by H cascade inverter circuits using the independent power and bring forward a new control pattern for Hybrid multilevel inverter which uses different voltage ratio in the hybrid cells for getting more multilevel voltages.The paper deeply analyzes the circuit equations of three levels inverter , And establishes the mathematical model of three-level inverter based on the switch function, discusses the application of various current PWM control techniques and compares the advantage and disadvantage of them , and the hysteretic band current control strategy of three level inverter is studied in detail in the paper based on close loop PWM controller.Then this paper deeply analyses PWM control strategies of three-level inverter .The paper discusses and proposes SPWM strategy and the voltage SVPWM algorithm improved, and provides the results that they are simple and effective through simulation.which indicate that they are accurate and feasible.The paper introduces SVPWM modulations of three-level inverter including optimal space vector PWM controller and simple SVPWM control arithmetic.Finally,this paper discusses the problems of neutral point control that exists in the three-level inverter, and adopts two methods to control neutral voltage balance namely judging power direction and detecting instantaneous current value.