Research On Modulation Strategy And Power Loss Of A Five Level ANPC Converter

Compared with the three-level,the five-level active neutral-point-clamed five-level inverter(ANPC-5L)has a large number of output levels,less current harmonics,and five electric The flat has a variety of switch redundancy states,each of which corresponds to a different current path,which facilitates the control of the midpoint potential and the flying capacitor voltage,and thus has attracted extensive attention from scholars at home and abr oad.In five-level practical engineering applications,common mode voltage and flying capacitor decoupling control have always been the focus and difficulty of ANPC-5L research.The AC side and DC side of the inverter pass through the ground due to the common mode voltage.The capacitor forms a high-frequency common-mode current,which seriously threatens the safety of the system.For a flying capacitor,during its control,the current will flow through the midpoint,affecting the midpoint potential,and the flying capacitor voltage is the ANPC-5L output phase voltage.As an important part,there is a coupling between the flying capacitor and the midpoint potential and the phase voltage,which is not conducive to the performance optimization of the flying ca pacitor and the inverter.In addition,as the capacity continues to increase,the loss will also increase,which has a great impact on the operation efficiency of ANPC-5L,and will also affect the heat dissipation problem.Therefore,the loss of ANPC-5L needs to be analyzed and the study.This paper first analyzes and explains the topology and working principle of ANPC-5L.Secondly,based on the common-mode voltage problem,a five-level low-common-mode voltage modulation strategy is proposed based on the three-level intermittent modulation strategy to achieve common-mode voltage suppression in the full-linear region.Then,based on the problem of flying-capacitor voltage coupling,this paper proposes a split-modulated wave based on the carrier phase-shifting modulation strategy.Based on this,a mathematical model of the split-modulated wave is established to quantify the split-modulated wave for the flying capacitor current and phase.Based on the influence of voltage and midpoint current,a flying capacitor decoupling control algorithm based on split modulated wave is proposed.Finally,based on the loss of ANPC-5L,this paper studies the power loss of the ANPC-5L SPWM modulation strategy by continuous modeling method,and obtains the loss and modulation degree.The specific relationship between parameters such as power factor,but the modulation strategy of this method is poor.To solve this defect,this paper proposes the idea of discrete modeling,which is to discretize a fundamental period and calculate each power loss by sub-region.The loss of the discrete period is calculated,and then mathematically processed to finally obtain the power loss in a fundamental wave.This method can realize the power calculation of different modulation strategies.The ANPC-5L prototype was built and the hardware and software design of the platform was introduced.Furthermore,experiments such as common mode voltage suppression and flying capacitor decoupling control are carried out to verify the correctness and effectiveness of the proposed modulation strategy.