In forensic sciences, verification of digital media recordings is an important aspect. Electrical network frequency (ENF) criterion is a promising technique for media recording authentication. The ENF reference database is recorded from a single point on the power grid based on the fact that the ENF variation is the same across all points on the grid. This fact is not valid in case of system disturbances, whereas the ENF as a reference database varies in time and space. Post-disturbance ENF recorded from a single point is mismatched with the ENF extracted from media recorded at any other point on the grid. This will lead to judicial errors in the forensic examination of recordings. A new method for establishing a robust ENF reference database using geographical information system (GIS) and wide area frequency measurements is proposed. The method is based on building the ENF reference database from a number of frequency sensors deployed over multipoint on the grid rather than single point. The minimum number of sensors required is determined according to the frequency sensitivity of the ENF extraction algorithm and the estimation accuracy of the frequency sensor. The sensors locations are decided based on partitioning the power grid to a set of geographical frequency coherent areas. A novel harmony search algorithm using GIS data and wide area frequency measurements is proposed to identify the geographical frequency coherent areas for different disturbance scenarios. Results showed that the proposed method can be used to enhance the accuracy of the ENF database matching process.

The multilevel inverter is a promising technology compared to two-level inverters in the applications of ac-drives and smart-grid applications. In this paper, a dual-T-type three-level inverters is used to drive an open-end winding induction machine. The Space-Vector Pulse-Width Modulation is selected as a good-performing control strategy to control the dual-inverter. Furthermore, an optimized method is used to select the proper switching state for the new configuration to decrease the converter losses. A comparison between the proposed configuration and the conventional diode clamped converter is made. The proposed drive system is designed and modelled by using Matlab/Simulink. It is shown that the converter can give the same hexagon, wave forms and harmonic spectrum of the five level converter. An optimized switching state selection is used to reduce the converter losses. The advantages and drawbacks of the dual-T-type configuration are discussed. In addition, the harmonic analysis and the loss calculations of the dual-T-type converter are provided and compared to the T-type three-level converter and the conventional five-level diode-clamped-converter.