Research On The Balance Of Neutral-Point Potential And Loss Distribution For Three-Level Active Neutral Point Clamped Inverter

Large capacity and high frequency inverter technology is very important to power electronics.Multilevel inverters are widely used in large capacity and high frequency applications due to high output efficiency,good output waveforms,low output harmonic,low voltage stress of single tube and so on.Based on the study of SVPWM method for three-level Active Neutral-Point-Clamped(ANPC)inverter,the neutral-point potential(NP)and loss distribution balancing for three-level ANPC inverter are researched in this paper.The main works are listed as follows:1.The expression of NP for three level ANPC inverter is derived.The effect of different space vectors on NP is analyzed.And the factors influencing the unbalance of NP are analyzed.2.On the basis of the above research,an improved virtual SVPWM(VSVPWM)method is proposed.In this method,the balance of NP can be effectively controlled by dynamically recalculating the partition coefficients of the positive and negative small vectors which are used to synthesize the virtual small vectors or reselecting the improved virtual medium vectors.3.Further on the basis of the above study,to avoid the increase of switching losses and the complexity of control algorithm,an improved SVPWM strategy is proposed based on the original SVPWM pulse sequences.In this method,the chargin,g and discharging of the DC side capacitors and the balance of NP can be effectively controlled by adjusting the duty cycle of the three phase switching sequences in each fundamental switching period.4.The calculation method of power switching device losses for three level inverter is introduced.The eight kinds of commutation modes and the corresponding loss distribution of the SVPWM strategy are studied,and two optimal control strategies of the loss distribution balancing are proposed for different load power factors.In this method,the loss distribution balancing of switching devices under different load conditions can be effectively controlled.5.The Matlab/Simulink simulation model and experimental platform based on DSP+CPLD for three-level ANPC inverter are set up.The validity of above proposed control strategies is verified.