Harmonic analysis and modelling of transformerless electric railway traction drives
Shahnia, F. and Sharifian, M.B.B. (2005) Harmonic analysis and modelling of transformerless electric railway traction drives. In: 13th International Conference on Electrical Drives and Power Electronics (EDPE) 2005, 26 - 28 September 2005, Dubrovnik, Croatia
The design of the electrical distribution system of electrified railways includes single- phase 1x25 or two-phase 2x25 kV AC systems. Most of the electric railways use AC induction motors as their electric drives for their better characteristics and costs in comparison with other kinds of motors. Previously, a transformer was utilized in the electric train for reducing the catenary voltage to the rated voltage of the induction motor. A transformerless connection for feeding the induction motor is presented in this paper. This structure is used for converting single phase AC voltage of the catenary to DC and converting the DC voltage to three phase AC voltage with a PWM controlled inverter. In such a structure, harmonic currents injected into the power system during the PWM switching process are low. Through the whole paper, current harmonics are measured analytically and also modelled with PSCAD/EMTDC software. The results of the simulation include the waveforms of the system current and the magnitude of THD. Using such a structure can reduce the necessity of using a transformer for feeding the induction motor and also reduce the amounts of harmonics injected to the power system greatly.
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