Optimized design coordination of a single phase static VAr compensator for AC railway traction

Static VAr Compensators are widely used in single-phase railway-traction for variable reactive-power compensation and voltage support. This paper proposes an offline-optimized design of a single-phase static VAr compensator for traction applications. The proposed design is constituted optimally using a thyristor controlled reactor (TCR), fixed-capacitor (FC), a 3rd harmonic series-tuned filter and a coupling-reactor. The LC filter bypasses TCR 3rd harmonic current. The FC also offers low-impedance path to higher-order harmonics whereas the coupling-reactor damps residual harmonics. The proposed design has lesser number of passive components (five components), reduced size (44 % lesser passive components) compared to classical-schemes and yet limits the current harmonic-distortion below maximum permissible limit (5 %THD, IEEE Std.-519–2022) at all load conditions. The overall volt-ampere consumed by filter circuit elements is also reduced by 75 % compared to classical-scheme which in turn reduces the overall rated-VA of SVC components. The proposed design has least chances of resonance with source-inductance, and performs irrespective of source short-circuit ratio. An offline-optimized iterative design method including a particle swarm optimization is described for minimal component count and size of SVC with minimum line-current THD which is a challenge in 1-phase SVC. The simulation and experimental results are presented to support the proposed scheme.