Improvement of low-frequency railway power system stability using an advanced multivariable control concept

Low-frequency stability is a major concern in 16.7 Hz railway grids. Using state-of-the-art railway control concepts low-frequency oscillations in the range of 2-5 Hz are experienced, well documented but not finally solved in several publications. In this paper an advanced multivariable control concept is demonstrated. Besides achieving very good dynamic behavior, the approach improves the introduced stability problem. The proper operation of the control is verified using measurement results. Furthermore the paper includes a time constant analysis of railway grids and elementary assumptions for stability investigations. A state-of-the-art control is compared to the advanced multivariable control. The comparison leads to the essential difference partly causing the low frequency stability problem. Finally a time domain simulation verifies the stability problem caused by the state-of-the-art control and shows the improved performance of the multivariable control.