Low-Frequency Oscillation Suppression of Train-Grid Coupling Systems by H∞ Loop Shaping

A more generalized method is presented for the suppression of low-frequency oscillation (LFO) in train-grid coupling systems. LFO frequently occurs under special circumstance, while multiple trains are accessing the traction line and may cause severe consequences for operation safety. It is well known that impedance mismatch is the major cause of this phenomenon. Yet, how to handle it has been a long-standing issue. In this article, we redesign the dc-link voltage controller (DVC) of the vehicular single-phase pulsewidth modulation (PWM) rectifier while maintaining the conventional control structure. The controller is obtained with an H-infinity loop-shaping (H-infinity -LS) process, which is essentially an optimization of the frequency response of the train-grid coupling system. This is approached with an optimally selected weighting function. In this way, the robust stability margin (RSM) can be improved, too. Furthermore, variations of the operation conditions, such as position and amount of trains, are regarded as parameter perturbations. The v -gap metric is adopted to quantify the influence of these perturbations. With our method, the controller is obtained by an analytical process instead of trial-and-error that relies on the experience of engineers. We also avoid the additional costs of replacing the traction transformers to change the grid-side impedance.