Study On The Simple SVPWM Algorithm Of Multi-level Convert

Because of its advantages of reducing output current and voltage distortion andlower switching devices stress, the applications of multi-level converter become moreand more wide. One of the key factors which determine the output characteristics ofconverters is Pulse Width Modulation algorithm. Taking three-phase three-line diodeneutral-point clamped(NPC) multi-level converter and cascade multi-level converteras research object, their modulation strategies and simplification were analyzed indetail and researched respectively and a simplified modulation strategy easy to realizewas presented in this paper..Aimed at the modulation of three-phase three-line diode NPC multi-levelconverter, the sector judgment and duration calculation were complicated intraditional Space Vector Pulse-Width Modulation (SVPWM).This paper summarizedthe simplified SVPWM algorithm for diode neutral-point clamped three-levelconverters, whose thinking was: derive the switching moments of devices in each legbased on classification algorithm, summarize its characteristic and present thesimplified method to implement the algorithm. The calculation of intermediate stepssuch as sector judgment wasn’t involved any more during the algorithm implementingand the switching moments of each leg were obtained directly depending on thereference voltage. The simulation and experimental results demonstrated that thesimplified strategy proposed can obtain reference voltage equivalently. Extended intofive-level converter, this simplified algorithm was compared with the SVPWMalgorithm based on60°g-h coordinate system. The speed and effectiveness ofsimplified algorithm are better than the latter.Neutral point potential balancing control is a difficult problem to restrain theextension and application of three-level neutral-point clamped topology. Based on theanalyzing the effects of each vector on the neutral-point potential, the scheme ofcontrolling neutral-point charge quantity was adopted to adjust neutral-point potentialin dc-side. Through theoretical analysis, the neutral-point charge can be eliminatedand the dynamic balance can be obtained by controlling the durations of positive andnegative small vectors. Combined with simplified modulation strategy for three-level,the simplified neutral-point potential strategy was derived. The simulation resultsshow that the neutral-point potential can be controlled beyond the range permittedusing the modulation strategy proposed. Considering the dead-time effect, the relationship between the output voltages of converters and switching states indifferent current polarities, the optimal dead-time compensation strategy waspresented based on former analysis and the validity of the strategy proposed wasverified by simulation.Compared with the potential clamped multi-level converters, five-level NPC/Hbridge converters have less potential clamped diodes and no voltage balance problem.The commutation method was studied and the mathematical model of multi-levelconverters was built, after which, the modulation strategy was analyzed. Comparedwith the potential clamped five-level NPC topology, the modulating was realizedusing five-level simplified SVPWM after analyzing and determining the switchingsequences of devices in each leg based on the relationship between the outputvoltages of converters and switching states. Combined with carrier phase shiftingSPWM and three-level simplified SVPWM algorithm,the modulation of five-levelNPC/H bridge with two π/2phase-difference triangular carriers was turned into themodulation of three-level converters. The implementation of five-level NPC/Hbridgemodulation using two modulation strategies was verified by simulation and thesimulation speed and effectiveness of carrier phase shiftingmodulation strategy arebetter than five-level simplified SVPWM. The modulation strategy validity ofthree-level simplified SVPWM combining carrier phase shifting was verified byexperiment.