Research On Multi-objective Hybrid Modulation Strategy Of Three-level Converter

In recent years,with the rapid development of power electronics technology,threelevel converter has been widely used in electric energy conversion.This paper analyzes various modulation strategies for the neutral point clamped three-level converter,aiming to study the problems of neutral point voltage balance,switching loss and common mode voltage,and achieve multi-objective hybrid modulation.First of all,this paper introduces the development history and application of the threelevel converter,as well as the typical circuit topology and modulation strategy,and derives the problems that three-level converter needs to solve.Aiming at the neutral point clamp three-level converter studied in this paper,the working process of the three-level converter is analyzed in detail from the main circuit topology,operating principle and mathematical model.Then,this paper introduces the basic working principle and duty cycle calculation method of four typical three-level pulse width modulation strategies,and analyzes their performance in terms of neutral point voltage balance,switching loss and common mode voltage,and points out the advantages and disadvantages of typical pulse width modulation strategies in these aspects are described.Finally,for the control objectives of neutral-point voltage balance,switching loss,and common mode voltage,this paper adopts two multi-objective hybrid control modulation strategies,namely closest clamping mode PWM(CCMDPWM)strategy and reduced common mode voltage virtual space vector PWM(RCMV＿VSVPWM)strategy.CCMDPWM is based on the planning zero sequence voltage injection PWM(PZIPWM)strategy,which forms discontinuous pulse width modulation by injecting a specific zero sequence voltage,which sacrifices the control ability of neutral-point voltage to a certain extent.But the multi-objective hybrid control of neutral point voltage balance and reduction of switching loss is realized.RCMV＿VSVPWM selects the vector of low common mode voltage by discarding the high common mode voltage,a new set of virtual voltage vectors is obtained.This method has the characteristics of the average value of the internal neutral point current is zero and the common mode voltage is low in a switching cycle,and the multi-objective hybrid control of reduces the common-mode voltage and maintains the balance of the neutral point voltage is achieved.Finally,through experiments on these two methods,and their effectiveness is verified.