Research And Implementation Of SVPWM Over-modulation Algorithm

In order to increase the inverter output voltage or the ac motor maximum outputtorque, over-modulation technology was widely used in electrical transmission.The theory of SVPWM over-modulation technology is represented in the thesis.While the over-modulation method modified the reference voltage vector, which resultsmagnetic field orientation deviation and bring with low order harmonics, the affection tothe control system is also analyzed. Based on the analysis, a kind of modified open-loopover-modulation algorithm and close-loop over-modulation algorithm are proposed. In theopen-loop algorithm, switching method is changed in the over-modulation region Ⅱ, thatcharacterized by real voltage vector “jumping” to keep along with reference voltage vector.The changed switching method reduces the computational effort required forimplementation, while resulting in a marginally higher harmonic distortion. In theclose-loop algorithm, the computation of reference angle in over-modulation region Ⅰisavoided, the computation equation of hold angle in over-modulation region Ⅱ is changedfor smooth operation during transition from region Ⅰ to region Ⅱ. The modifiedclose-loop over-modulation algorithm is simple for digital implementation and bring withlower harmonic distortion, which is suitable for a close control system.The two kinds of modified over-modulation algorithm are simulated and analyzedby MATLAB/Simulink and verified by the results of magnetic field orientation controlledPMSM(Permanent Magnet Synchronous Motor) experiment. The research work of thethesis is some kind of helpful for the application of SVPWM over-modulation technology.