Research On SVPWM Control Strategy And Midpoint Potential Balance Of Three-level NPC Inverter

With the rapid development of industrialization,high-voltage high-power conversion technology has become a major trend in the development of modern power electronics technology.Among them,multi-level inverters have low voltage requirements for switching devices,low common mode voltage,and low harmonic content of output voltage And other advantages,it has been widely used in medium and high voltage frequency conversion speed regulation technology,power active filtering and other aspects.Comparing the topology and control strategies of various inverters,this paper takes diode-clamped(NPC)three-level as the research object,and conducts in-depth research on its control strategy and the inherent problems of midpoint potential imbalance.First of all,this paper gives a detailed introduction to the topology and working principle of the NPC three-level inverter,and establishes a mathematical model.For the traditional SVPWM,there are complex sector judgments and the calculation of their basic vectors.Time needs to go through a lot of trigonometric function calculations and other issues.The SVPWM modulation algorithm based on the 60° coordinate system is proposed.The steps of coordinate transformation,sector judgment,and basic vector action time calculation are introduced in detail,which shortens the calculation time and improved the system operation speed.Aiming at the neutral point potential imbalance problem inherent in NPC three-level inverters,the cause and harm of the imbalance problem are first studied,the common control strategies are analyzed,and the most common use is to change the role of redundant small vectors.On the basis of time to achieve the goal of midpoint potential balance,a hybrid control strategy based on the combination of hysteresis control and active control is proposed to maintain the midpoint potential balance.In view of the shortcomings of the virtual space vector algorithm in software control,a variable parameter virtual space vector algorithm that can change the parameters required to synthesize the virtual vector is proposed.Based on the above theoretical analysis and research,the simulation model is built in MATLAB/Simulink simulation software,and the traditional SVPWM algorithm mentioned in the article,the SVPWM modulation algorithm based on the 60°coordinate system and several midpoint potential control strategies are simulated.The results show that the output waveform of the SVPWM modulation algorithm based on the 60°coordinate system is more stable and the harmonic distortion rate is smaller.The simulation model of the NPC three-level inverter system is established to verify the correctness of the algorithm and the effectiveness of the midpoint potential balance control scheme.