Harmonic compensator for 50-Hz fed AC railway vehicles

AC railway vehicles controlled by PWM line-side power converters inject harmonic current into the feeding overhead line. This causes problems such as resonance expansions which produce malfunctions or overcurrents at substations and electromagnetic interference with signalling systems. Normal active filters only shift the harmonic frequencies to a higher range. A novel harmonic compensator produces an exact counter-MMF of which in the main transformer main flux is then sinusoidal. Experimental results from a small model of a Japanese AC railway vehicle are described. Especially the 3-4 kHz frequency range that coincides with the signalling band harmonic currents are quite well suppressed. From the result, this novel compensating method appears promising for any 50 Hz-fed PWM controlled AC railway traction system