Optimal PWM control of a stacked multicell converter.

摘要

The thesis introduces the basic design and topology of the Stacked Multicell Converter (SMC). This new SMC topology allows increasing input voltage level, while not increasing the switching device stresses by the use of floating capacitors, at the same time, the output current contains less harmonic components. In order to get the converter output ac voltage waveform to be as close to a sine wave as possible, the Optimal Pulse Width Modulation (OPWM) technique is used to determine the switching instants of the power switches in the converter. Since the switching angles are dependent on the magnitude of the fundamental frequency component of the output voltage, these switching angles are pre-calculated and stored in a table. The OPWM is carried out by look-up table. Due to the difference between the mathematical model and the real system, the simulation results are not exactly the same as the analysis results, some harmonics are still in the output current. In order to find the switching angles which reduce the target harmonics, on-line optimization of switching angles is used in this thesis. Both of the OPWM and optimization results are simulated using PSCAD/EMTDC. These results show that on-line optimization simulation can be used to find the switching angles to minimize the target harmonics. (Abstract shortened by UMI.)