Research On Three-level Inverter Based AC Drive

Variable Frequency Speed Regulating is widely used because of its excellent in starting, speed reguration,and braking, as well as energy conservation, the technique of low voltage Variable Frequency Speed Regulating is fairly well, but when applying it's technology to high voltage, large power field, the performance is not very good and should be improved, because of the lack of power device and limited of insulation rate, the structure and control methods are very complex, furthermore, the cost is very high, another disadvantage is the power factor of system is very low, and it resultes in the distortion of power grid. During these several years, more and more research has been done in multilevel inverter and proposed several topologies of multilevel inverter. Lots of them have been put into practice.There are several advantages when compared with traditional two-level power inverter. The smaller voltage steps lead to the production of higher power quality waveforms and lower the dv/dt stresses on the load, also reducing the electromagnetic compatibility (EMC) concerns.So, in this paper; firstly, we give a summary knowledge of variety topologies of multilevel inverters, and then do some deep research with Diode-Clamped three level inverter and its application in AC driving.In order to improve the utility of DC link voltage and enhance current drive capability, the paper have done a deep study of space vector over-modulation for three-level inverter and its control strategy, then we put forward a new algorithm of voltage vector duration, the algorithm is simple compared with that in other literature.In three level inverter, there are lots of redundancy voltage space vector, so when choose voltage space vector, we should consider not only the harmonic distortion but also consider the balance of DC link voltage, In this paper, firstly, the neutral point potential variation is analyzed by setting up the neutral point potential model, and the relationship between the vector selecting and eliminating of harmonic is analysed then a novel neutral point potential technique, using fuzzy logic control strategy, was proposed.Because of the difference between three level inverter and normal (two level) inverter, this paper present the model of three level inverter power supplied Variable Frequency Speed Regulating system, and realized three level inverter based variable voltage variable frequency (VVVF) control and rotor field oriented control (FOC) of induction machine, Lastly, the feasibility of the proposed method has been proven by simulation and laboratory experiments.