Research On Three-level Converter Control Method And Neutral-Point Voltage Balance

Recently, three-level inverters have been becoming increasingly popular in medium-high voltage ac drive systems and FACTS equipments, mainly because of their high voltage-capability, high output quality, low switching losses and low EMC concerns. The thesis primarily makes an in-depth research on the multilevel inverter topological structure and control methord and analyzed the balance problem of Diode-clamped converter's neutral-point voltage, and finds the modulation algorithm of neutral-point electronic charge and its modify methods.The thesis makes rather detailed summarize for the research signification and actuality development of multilevel inverter firstly. Then the thesis investigates the three basic topological structures for multilevel inverter including the principle of working and each advantage and disadvantage. On the basis, the thesis investigates the two control methods of inverters, which is SPWM and SVPWM. It mainly discusses the SVPWM method and analyzes the keystone of three-level SVPWM. And it puts forward the algorithm of SVPWM, which uses the little triangle vertex vector synthesized reference vector, and comes out the little triangle regional judgment rules, exports every synthesize voltage vector's effect time and vector optimized method. And then it uses basic topological structure of diode-clamped three-level inverter as basic, analyses the reason of lopsided neutral-point voltage, and gives the modulated algorithm of neutral-point electronic charge. It labors the reasons of invalidation in the simulation, and puts forward the correction method of improving invalidation instances.At the end of the thesis, it builds the simulation models which uses SPWM and SVPWM as controlled method, and the simulation model which uses SVPWM controlled method with neutral-point voltage balance function. It describes the putting up ideas and the effect of main function module in detail, and validates the exactitude and possibility of every project referred before used the result of simulation.