| High Power Medium Voltage Variable Frequency Drive (VFD) has caught the whole word's attention, because it can not only produce a variable AC voltage/frequency output to provide continuous operation over the full speed range but also save energy efficiently. This paper designs a VFD with 24-pulse Rectifier and three-level Inverter based on IGCTs, which can meet the demand of Chinese customers and Power Grid well. To implement this VFD successfully, this paper does some deep research on some problems associated with the VFD. To reach the rated output voltage level of 6kV, series IGCTs was necessary. The paper analyzes the characteristics and behavior of IGCTs deeply both in steady state and dynamic state. Besides, snubber circuit of series IGCTs was designed for its high safety and reliability. To make output waveform more sinusoidal and decrease output du/dt and harmonic current and voltage, LC filter had been designed according to the VFD's characteristic. A method of keeping neutral point potential balanced based on three-level SPWM had been brought forward, which can improve output waveform and decrease the possibility of IGCT's over-voltage. Common-mode voltage problem resulting from the VFD is studied in detail, and corresponding method decreasing it is given. The paper also pay much attention to research on self-excitation of induction motor shunted with LC filter and dead-time compensation based on high voltage three-level Inverter. Most methods proposed in the paper are verified by simulation in MATLAB/SIMULINK and experiments.
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