Harmonic Analysis Model based on PSCAD/EMTDC

초록

The modern AC electric train has thyristor or PWM (Pulse Width Modulation)-controlled converters, which give rise to higher harmonics. The harmonic current injected from the AC electric train is propagated through a power feeding circuit. As the feeding circuit is a distributed constant circuit composed of RLC, the capacitance and the inductance of the feeding circuit on the side of the power system cause a parallel resonance and amplification of harmonic current at a specific frequency. The amplified harmonic current usually brings about various problems. That is, the harmonic current causes interference in the adjacent lines of communications and the railway signaling system. Furthermore, in case it flows on the side of the power system, not only overheating and vibration at the power capacitors but also erroneous operation at the protective devices can occur. Therefore, an exact assessment of the harmonic current flow must be undertaken during the designing and planning stage for the AC electric railway systems. From this point of view, this study presents an approach to model and to analyze a traction power feeding system focused on the amplification of the harmonic current. The system model is made using the PSCAD/EMTDC program [1]. Representation for each component of this system has many advantages: 1) Overhead catenary lines, which have impedances and shunt admittances, can be easily represented by the PSCAD/EMTDC. 2) Distributed circuit parameters for the line model can be effortlessly defined. 3) The entire system can be easily modeled by the combination of each component in parallel and/or series. 4) Harmonic calculation can be performed straightforwardly. The proposed model is applied to a real AT (Auto-transformer)-fed system in which the electric train with thyristor-controlled converters is running. In order to verify the proposed model, we modeled the actual AC electric railway system using the PSCAD/EMTDC. We have analyzed and tested this system, which is focused on the amplification of the harmonic current. The simulation results from the proposed model and the measurement data from the test are described."

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