Research On SVPWM Simplification Algorithm And Capacitor Voltage Control Strategy Of Five-level NPC Converter On New Coordinate System

Large-capacity three-level converter is gradually replacing the traditional two-level converter,which is widely used in the field below 3kV.However,in the field of medium and high voltage above 6kV,the three-level converter still cannot meet the demand of industrial technology progress.Therefore,this paper takes Neutral Point Clamped(NPC)converter at five levels as the research object,and adopts Space Vector Pulse Width Modulation(SVPWM)to study the complexity of traditional SVPWM Modulation strategy,common mode voltage and dc side capacitance voltage,etc.mainly including the following parts:Firstly,studies the five level NPC converter topology and its five kinds of working mode,The traditional SVPWM algorithm applied to five level NPC converter,analyzes the working principle of the traditional five level SVPWM modulation strategies,at the same time,analyzes the mechanism of common-mode voltage,to reduce the common mode voltage amplitude,on the basis of traditional SVPWM algorithm uses the five-stage switch sequence,respectively based on MATLAB and the hardware-in-the-loop simulation platform RT-Box for the simulation and experimental validation.Secondly,aiming at the complexity of the traditional five-level SVPWM modulation strategy and the problem of high common mode voltage,a new five level SVPWM simplification algorithm based on the new coordinate system of X,Y and Z is proposed,which can greatly reduce the amount of calculation and reduce the difficulty of calculation.During the design of the switch sequence,a reasonable redundancy state is selected to eliminate Common Mode Voltage(CMV).The simulation and experimental results show that the new five-level SVPWM simplified algorithm in the new coordinate system can eliminate the Common Mode Voltage while realizing the modulation purposeFinally,in view of the five level NPC converter DC side capacitor voltage imbalance,flat space vector diagram according to the five distribution characteristics of redundant state,it can be divided into high and low modulation,a hybrid SVPWM strategy is proposed to realize the capacitor voltage balance,at low modulation,according to the capacitor voltage deviation and the load current direction dynamically selected redundant state,the dc side capacitor voltage balance,compared to the virtual space vector capacitor voltage balance algorithm,the balancing algorithm less amount of calculation;In high modulation,through active current and redundant state judge each capacitor charging and discharging state,select the default switch capacitor voltage balance sequence implementation,compared with the model prediction balance algorithm,and can reduce switching loss,hybrid SVPWM capacitor voltage balance control strategy is validated by computer simulation under different conditions can realize the balance of the dc side capacitor voltage.