Research On Decoupling Control Of A Five Level ANPC Converter

Compared with the neutral point clamp three-level converter,active neutral point clamp(ANPC)five-level converter with its advantages of high output voltage level,low harmonic content,high power density,neutral point potential is easy to control and so on.At the same time,there is only a single flying capacitor in single-phase topology,be of high stability.Ensure the voltage amplitude of the neutral point potential of the converter and effectively control the voltage of the flying capacitor are very important to the operation of the converter.At the same time,this converter have an inherent coupling problem between the flying capacitor voltage and the neutral point potential in the control,so decoupling must be implemented.First of all,the topology and working principle of the ANPC five-level converter are analyzed.The switching output function of the converter is given.The switching states of the single-phase inverter are analyzed,which used a five-level modulation strategy based on phase disposition PWM;at the same time,the simulation analysis of phase-shift PWM strategy has been made.Besides,the neutral point current of five-level DC side is deduced.Employing the uniform neutral point balance algorithm,achieve the purpose of neutral point potential controling.Using the influence of five-level redundant switch state on the flying capacitor,a flying capacitor balancing control method is proposed.It reduced the fluctuation of the flying capacitor.Then,the inherent coupling problem of the flying capacitor voltage and the neutral point potential of the five-level ANPC converter is researched.Based on the mathematical model of modulation wave splitting,deduced the coupling mechanism and the specific impact,in order to eliminate the detrimental effect caused by this inherent coupling,the paper proposes the constraints of its decoupling control,and realizes the voltage control process of flying capacitor have no effect to the original neutral point potential status.In order to achieve the output radical waveform voltage controllable in the process of capacitor voltage build-up,the voltage build-up control of the flying capacitor is implemented by the decoupling algorithm based on the modulation wave splitting,which greatly improves the state of the output current waveform quality.A five-level ANPC converter experimental platform is designed.The design of hardware and software is introduced.Based on this experimental platform,experiments of capacitor voltage steady state control,coupling and decoupling comparison experiments,voltage build-up control experiment of flying capacitor based on decoupling were carried out,the validity of the proposed control method is verified.