Low-order harmonic analysis and suppression strategy optimization of cascaded converters for train traction
Power electronic transformers(PET)incorporating cascaded H-bridge(CHB)converters as the front-stage topology rep-resent an important development trend for future train traction.Minimizing low-order harmonics in CHB converters holds immense im-portance in enhancing the control performance of PETs.However,the factors affecting low-order harmonics in CHB converters differ from those in conventional four-quadrant converters.There is still a lack of detailed research on the underlying mechanisms and suppres-sion strategies.This paper delved into the generation mechanisms of low-order harmonics in CHB converters on the traction network side,highlighting that low-order harmonics were related to the module count and topology of H-bridge cascades,in addition to DC volt-age fluctuations,device dead-zones and switching voltage drops.According to the findings,a low-order harmonic suppression algorithm was designed,taking into account DC voltage fluctuations and circuit topology characteristics.Furthermore,a comprehensive optimiza-tion strategy for suppressing low-order current harmonics in CHB converters was suggested,integrating the dead zone effects and volt-age drop impacts.In the final section,an experiment using a low-power experimental platform was detailed.The experimental results veri-fy the accuracy of the theoretical analysis and the effectiveness of the optimized suppression solution.
cascaded H-bridge(CHB)of traction converterlow-order harmonic analysisharmonic suppression strategyDC voltage fluctuationdevice dead-zoneswitching voltage drop