Abstract
The use of power electronic switching controllers for all types of traction drives can lead to harmonic currents on the supply side. These currents, by conductive or mutual coupling, can cause interference in signalling and telecommunications circuits. After reviewing these basic considerations, this paper outlines the harmonic spectra of d.c.-supplied chopper and inverter drives. In the case of chopper controllers, choosing a frequency unrelated to any signalling frequency combined with the attenuation provided by the input filter is usually sufficient to avoid dangerous interference.
For inverter drives, the situation is more complex due to the intrinsic sweep frequency nature of the drive. However, special modulation strategies can be used for the inverter which eliminates, or at least reduces to a safe level, any particular frequency which may interfere with signalling equipment. A method for generating these optimized pulse-width modulation schemes using fast on-board microprocessors is briefly described.
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