On Effective Electromagnetic Shielding of Modern Pulse Width Modulating Adjustable Speed Drives

This paper presents a practical approach toward efficient shielding of adjustable speed drives (ASD). The electromagnetic interference problem affects a complex roller rig testing facility that is developed at the Railway Technologies Laboratory of Virginia Tech. The rig uses a slew of sensitive instruments to study the wheel-rail contact mechanics in the railway applications. Eight ASDs run the rig in close vicinity of the sensors, which heavily affects their measurements. System requirements such as heat management, structural rigidity, size, and cost, restrict additional shielding for these drives. In this paper, a two-dimensional finite element analysis is used to find the proper shielding material, optimum thickness, and aperture size that maximize the shielding effectiveness. Based on the simulation results, an enclosure is fabricated for the VT Roller Rig control tower. Simulation results show that steel exhibits the least sensitivity to perforation, especially at frequencies above 10 kHz. Results also reveal 23.4% difference between 0.5 and 3 mm thicknesses at 1 kHz, while the difference is 3.5% at 5 MHz. Moreover, experimental results demonstrate agreement between the simulated and actual performances. Measurements confirm that using 16 GA off-the-shelf carbon steel sheets with 80% perforation, an average shielding effectiveness of 40 dB is achieved.