Research On The Speed Control System Of Open-End Winding Induction Motor Based On Dual Three-Level Inverter With A Single DC

Multi-level inverters have became more and more widely applied in the high-voltage,high-power control field due to the features of output power with high quality,less switching losses,power device with low voltage stress and so on.With the development of multi-level inverters,several typical topologies of multi-level converters have been formed.Among these topologies,neutral-point clamped three-level inverter is the most widely used.So the dual three-level inverter with a single DC researched and studied in this thesis is constituted by two neutral-point clamped three-level inverter,and the switch model of dual three-level inverter with a single DC has been established.According to the switch model of dual three-level inverter with a single DC,the space voltage-vector scheme of dual three-level inverter with a single DC is depicted.It explains dual three-level inverter with a single DC belonging to the category of five-level inverter because of the space voltage-vector scheme of dual three-level inverter with a single DC is simliar to the space voltage-vector scheme of neutral-point clamped five-level inverter.The fundamental principle of space voltage-vector 180° decoupled modulation strategy is introduced for dual three-level inverter with a single DC.Then space voltage-vector 120° decoupled modulation strategy was proposed in order to improving space voltage-vector 180° decoupled modulation strategy by parallelogram rule in this paper,and compared two different decoupled modulation strategies from eliminating zero-sequence voltage,balancing inverter DC side capacitor voltage,modulation range and inverter output voltage harmonic content.It founds space voltage vector 120° decoupling modulation method is better than space voltage vector 180° decoupling modulation method both on zero-sequence voltage eliminate and capacitor voltage balance.Finally,a calculation method of total harmonic distortion(THD)of voltage waveform is introduced.Based on the above calculation method,variation curves between dual three-level inverter output phase-voltage THD and fundamental frequency f of above two different decoupled modulation strategies are depicted.Then dual three-level inverter output phase-voltage harmonic content of two different decoupled modulation strategies is compared via FFT,it founds dual three-level inverter output phase-voltage harmonic distribution of two decoupled modulation strategies are different.The mathematical model of open-end winding induction motor is established under the three-phase static coordinate system,the two-phase static coordinate system,and the two-phase rotating coordinate system,respectively.On the basis of mathematical model for open-end winding induction motor,this paper adopts the method of vector control based on oriented rotor field to achieve the vector closed-loop control of open-end winding induction motor,which effectively improving the speed regulation performance of open-end winding induction motor.Simulation platform and experiment platform of speed control system of open-end winding induction motor based on dual three-level inverter with a single DC is built and debugged,where the two different space voltage-vector decoupled modulation strategies and vector control method of open-end winding induction motor based on oriented rotor field are verified.Simulation and experimental results haved verified the correctness and validity of the theoretical content in this thesis.