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Article Dans Une Revue IEEE Electrification Magazine Année : 2014

Power Quality Improvement in ac Railway Substations: The concept of chopper-controlled impedance.

Philippe Ladoux
Joseph Fabre

Résumé

With a length of 9,698 km, the 25 kV/50 Hz AC single-phase supply is a widely used railway system in France. Overhead lines are supplied by substations drawing power from two phases of a 3-phase utility. They behave as nonlinear and time-varying loads and represent one of the most important sources of voltage unbalance for the electricity transmission network. In the case of weak networks, railway operators are required to install compensation systems in substations in order to satisfy utility regulations and to avoid penalties regarding voltage unbalance and reactive power consumption. The limits are established by the energy provider with a view to guaranteeing an acceptable power quality to other customers.In three-phase networks, widely used solutions are the classical SVC, based on Thyristor Controlled Reactors (TCRs), and STATCOM based on Voltage Source Inverters. The TCR allows the variation of fundamental lagging current by phase-control, counterbalancing large leading currents from associated fixed capacitors and allowing continuous compensation of the lagging line. However this solution generates a high level of harmonic and requires onerous LC filters. On the other hand, Voltage-sourced inverters (VSI), offer several advantages over thyristor-based solutions in terms of compensation dynamics and reduced harmonic distortion. For the last ten years, although it requires bulky capacitors on the DC bus, the VSI approach has been widely used for avoiding system unbalance. However, in high-power applications, the semiconductor losses bring forth significant costs both in terms of active energy and cooling system maintenance which must be taken into consideration by the railway operator. The concept of the Chopper-Controlled Impedance (CCI), presented in this paper, is based on series or parallel associations of AC Choppers using high-frequency pulse-width modulation to vary reactances at the network frequency. This approach is a low power-loss solution and requires a low volume of reactive elements, a fact which makes this solution very attractive in high-power single-phase systems such as railway networks.
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Dates et versions

hal-02273704 , version 1 (29-08-2019)

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Philippe Ladoux, Joseph Fabre, Herve Caron. Power Quality Improvement in ac Railway Substations: The concept of chopper-controlled impedance.. IEEE Electrification Magazine, 2014, 2 (3), pp.6-15. ⟨10.1109/MELE.2014.2331792⟩. ⟨hal-02273704⟩
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