Capacitive harmonic analysis and DSTATCOM-based comprehensive power quality management in metro substations

Urban Railway Transit Power Supply System (URTPSS) involves power quality problems related to reactive power and harmonics. In addition to this, it is susceptible to multi-system resonance at specific frequencies. Negative impedance caused by capacitive characteristics carries the risk of harmonic amplification, which may lead to equipment damage and instability within the metro substation system. This paper analyzes the monitored profile of the real-world “SHL” metro substation and identifies the capacitive harmonics of the 35kV AC bus. A theoretical analysis is performed and a dynamic model of a Metro Traction Step-Down Substation (MTSDS) is developed to study capacitive harmonics and their potential causes, and to analyze the network impedance across multiple frequencies. Following that, a Distribution Static Synchronous Compensation (DSTATCOM) solution is proposed, featuring a 35kV-10MVar power stage configuration and its associated controller design. The improved instantaneous power controller utilizes the inner α-coordinate current loop to suppress harmonic magnitudes and reconstruct the capacitive impedance. The β-coordinate current is utilized to regulate reactive power demand and correct the system power factor. Simulation results performed in the PSCAD/EMTDC and RSCAD/RTDS environments validate the effectiveness of the DSTATCOM solution with the improved controller under steady-state and load-changing operating conditions.