Research Of PWM Strategy For High Voltage Multilevel Converter

The stability of a medium-high voltage converter system is the key point forresearch and development in this field. Traditionally, the modulation strategy ofcascaded multilevel converter with separated dc source causes unbalance of the powerdistribution among every invert cells, it would cause some invert cell's powersemiconductor components burden more than others, which makes the wholeconverting system unstable.This paper purposes on balancing power distribution among every invert cells sothat the whole converter system can work more stable. Based on analysis of thestructure and traditional Pulse Width Modulation (PWM) of cascaded multilevelconvert with separated dc sources, here a new modulation strategy is presented. Forverifying the efficiency of this new modulation idea, Fourier analysis and simulationwere executed. And theoretically, this new modulation strategy can make powerdistribution among every invert cell more balance remarkably, so that every powersemiconductor takes almost same burden. This must have been causing a wholeconverter system more stable and working for much time. At last, 3 level SVPWMwas implemented for experimental verification.Every kind of multilevel inverter is synthesizing a quasi sine waveform as anoutput with different level rectangle voltage steps. It would be more close to a sinewaveform if there are more level voltage steps used, but this will cause whole systemstructure and modulation strategy complicated. For N-level inverter, an modulationidea of grouping and cycling among inverting cells is also mentioned here for kickoff.