Line current harmonics of three-level neutral-point-clamped electric multiple unit rectifiers: analysis, simulation and testing

The harmonic spectra of the AC supply currents of electric multiple units (EMUs) employing three-level neutral-point-clamped converters are discussed in this study. The analytical expressions of high-order harmonics because of high-frequency three-level phase-opposition disposition pulse-width modulation are derived by using double Fourier series and a contour plot in a two-dimensional plane. The carrier phase-shift control to cancel some of the high-order harmonics when two or more converters are interlaced is validated. The impact of converter´s DC voltage controller on low-order harmonics is formulated. The harmonic spectra are verified by computer simulations and through actual measured data taken at lower train speed and rated power from an EMU of the CRH380AL and tested on a 9 km long testing railway line in a purpose built rolling stocks plant.