Research On SVPWM Control Strategies And Over-modulation Schemes In The Five-level Inverter

Multilevel inverters have been widely used in medium-voltage high powerapplications such as high power drive, active filter and ships propulsion. Comparedwith the traditional two level inverters, the multilevel ones have many advantages:low output voltage harmonic content, low switching frequency, small switch loss andelectromagnetic interference. The research object of this thesis is diode-clampedfive-level inverter, main research contents about the key technology in multilevelinverter are as follows:Firstly, the thesis introduced the circuit topology of NPC and H-bridge inveter,deeply analyzed the working principle of diode clamped five-level inverter. The basicprinciple of SVPWM and seven-segment switching sequence design were presentedin this thesis, the space vector pulse width modulation strategies of five-level based onfour kinds of algorithms were analyzed. Compared with the traditional SVPWMmodulation methods, new algorithms simplify vectors selecting and function timecalculation and save the resources of processor. No trigonometric functioncalculations are needed compared to traditional SVPWM algorithm. Simulation andexperiments prove the correctness and validity of the modulation strategy.Secondly, in order to improve the performance of the inverter output, get themaxium electromagnetic torque and fully use DC voltage, this thesis deeply studiedthe control strategies in over-modulation range. Three strategies were discussed: twolevel decomposition, classification, principle of superposition, the output voltage andthe harmonic spectrum illustrated that reference voltage vector can smoothly transitfrom the linear region to the over-modulation region and expand the scope of theoperation of the inverter. Simulation and experimental results validated the accuracyof the over-modulation strategy.Furthermore, five level vector control system was studied based on the load ofpermanent magnet synchronous motor. The mathematical model of permanent magnetsynchronous motor was analyzed and the rotor flux oriented control was discussed inthis thesis. Five level vector control system has such advantages: good dynamic andstatic performance, realizing fast track of speed and position, small error. All theadvantages above could achieve the maximum torque control of the motor.Finally, the design of the main circuit of the NPC five level inverter and thesoftware and hardware of the control system were completed, five level inverterexperimental platforms was built based on TMS320F28335DSP and XC3S400FPGA. The related experimental researches of five-level inverter had been completedbased on the experiment platform.