Analysis And Modelling Of The Conducted Interference Induced By SVC Equipments

Because of the advancement of power electronic technology, the Flexible AC Transmission System (FACTS) are widely used for the utilities and the industrial customers. In addition to improve the reactive power variation by continuous reactive power compensation, it is also used to maintain the bus voltage at a constant level, to release power transmission capacity and to enhance the system stability. Meanwhile, in the FACTS substation, large quantities of electronic units are integrated into the secondary side to realize automatic control, monitoring, diagnosis and communication. It is important to keep these electronic units work normally and orderly. However, very steep transient pulses are generated due to frequent switching of large power electronic devices installed in FACTS equipments, hence resulting in considerable HF conducted and radiated interference through near-field coupling and far-field radiation, which causes electromagnetic contamination to both the power grids and the victim electronic devices positioned nearby. Therefore, it is necessary to propose a comprehensive strategy to address the prominent EMC issues in FACTS substations. The combination of fixed capacitors and thyristor-controlled reactors (FC-TCR) type SVC in the Jinan Steel Corporation in China, solving the voltage fluctuation problem produced by the operation of rolling mills, is selected for electromagnetic interfere measurement, analysis and evaluation.Based on optical fiber, circuit and field transducers, an advanced acquisition system is established to implement on-site measurements of the electromagnetic interference (EMI). Due to the non-flat amplitude-frequency characteristics of the antennas used in EMC measurement, it is desired to establish the equivalent transfer functions of the antennas so as to make digital correction to the measured data, from which the actual electromagnetic interference can be traced back. Based on the previously available fitting method, with introduction of the first-order derivative and right-multiplication to the coefficient matrix by a diagonal matrix, the paper presents an improved vector fitting methodology. Based on the corrected measurement data, the switching bursts of the radiated EMI data within a power cycle are analyzed to give the frequency and amplitude range of the radiated interferences. Further, with utilization of short-time Fourier transform, Wigner-Ville distribution, smoothing pseudo Wigner-Ville distribution and rearranged-smoothing-pseudo Wigner-Ville distribution, a feature extraction methodology for electromagnetic emissions based on time-frequency analysis is established, and more detailed and useful information of the SVC-based electromagnetic environment can be obtained.According to the configuration and parameters of the measured SVC system, models are established to simulate the electromagnetic emissions using Matlab SimPower Systems Blocksets. Three working processes of the rolling mill are simulated using a three-phase dynamic load with active power and reactive power controlled from an external input. Based on the IEEE models and the other references, the control system models are implemented to analyze the EMI pulses through the reactive power compensation. The simulation results are compared with the data measured in the secondary circuit. The simulation can present fundamental reference for characterizing the SVC-based interfering mechanisms and effectively evaluating the electromagnetic environment.Effective immunization measures are investigated, and reasonable suggestions are presented to update the available relative IEC and national standards for EMS tests.