6KV Cell Series Multi-level High Voltage Frequency Inverter And The Research On Its Control Strategy Based On Stator Flux Orientation

This thesis studied a 6KV/1000KVA cell series multi-level high voltage frequency inverter, including its main circuit topology, function and composition of the main controller, the structure of power cell, the carrier phase-shifted SPWM. Various kinds of circuits with digital input and output have been designed and accomplished, its function have also been realized.Sorts of experimental waveform of the 6KV cell series multi-level high voltage frequency inverter in VF control, including the no load experiment, low voltage and big current experiment, and experiment loaded with high voltage motor have been tested and analyzed. The static characteristics, the asymmetry of the output voltage, the static frequency precison of the output, the frequency resolution of the output, and the harmonic of the output have been evaluated.The mathematic model of the induction motor and the coordinate transform have been analyzed. Two kinds of model of induction motor based on stator flux oriented and its entire control scheme have been studied. The adjust regulator and the disturbance observer have also been designed. The comparison of the stator flux orientation control stratedy and rotor flux orientation control stratedy have been studied.Current model, voltage model, modified voltage model of the flux estimation and the state observer have been researched. The merit and shortcoming, the application fields, the stability of the voltage model and current model have been analyzed. The emphsis has been mainly focused on the analysis on the error aroused by the initial value and DC offset, including convergence speed and static error. The cause of the quiver of voltage model and modified voltage model have been discussed.Two commonly used speed identification method, the dynamic speed estimator and model reference adaptive system, have been investigated and simulated. The key point of the design of the two different speed estimator have been discussed. The actual reason of the poor performance, even instability of the sensorless vector control system, have been pointed out and the improvement have been put forword...